Fourteenth CW and High Average Power RF Workshop

14 Sept 2026, 07:30 → 17 Sept 2026, 19:15 Europe/Zurich

Amfi (Stadshallen)

Welcome to the 14th Continuous Wave and High Average Power RF Workshop, 2026! Join your colleagues from around the world to discuss the application of RF power and its inherent challenges. Share your experiences with high-power vacuum electronics, combiners, circulators, phase-shifters, solid-state sources, and other RF equipment. CWRF 2026 will be held September 14 - 17, 2026 in Lund, Sweden, near the European Spallation Source laboratory. 

Goal of the Continuous Wave and High Average Power RF Workshop is to share the experience and ideas on applications which utilize high-power klystrons, gridded tubes, solid-state architectures, high-voltage modulators, high-power combiners, circulators, transmission lines, cavities, power couplers or tuners. New ideas on upgrading the high-power RF system and novel ways of the RF power generation and distribution will also be discussed.

CERN Indico system is used to manage the abstracts, presentations and archive the workshop contributions from 2024, 2022, 2020, 2018, 2016 2014, 2012, 2010 and 2008. You will need to log in, using either your already existing CERN Indico account, or by creating a new light-weight account. Please follow the instructions under Call for Abstracts if you need an assistance.

Scientific program and International organisation committees

• Alessandro Fabris (ELETTRA)
• Doug Horan (ANL)
• Takahiro Inagaki (SPring8)
• Morten Jensen - European Spallation Source ERIC (ESS)
• Ming-Chyuan Lin (NSRRC)
• John Moss (ORNL)
• Alireza Nassiri - Argonne National Laboratory (ANL)
• Francis Perez (ALBA - CELLS)
• Jim Rose - Brookhaven National Laboratory (BNL)
• Markus Schneider (PSI)
• Daniel Valuch (CERN)

 

Contacts:

Daniel Valuch (Indico, abstracts, program)

Local Organising Committee

Morten Jensen (Workshop chair, organiser)

Caroline Prabert (Administration)

Zeinab Afshari (Administration)

 

 

Directions to ESS from airports (from ESS external homepage).pdf

How to create your own indico account (for external users) _ Department of Theoretical Physics.pdf

Map Lund city railway, tramway and hotels in the city centre and on the tramway to ESS, 19 June 2024.pdf

Map with lunch restaurants in Lund city centre, Sept 2026.pdf

Venue Interior Map Stadshallen Lund.pdf

Monday 14 September

Registration

Welcome

1 Welcome

Speaker: Camille Ginsburg (European Spallation Source ERIC)

2 Introduction and practical information

Speaker: morten jensen (European Spallation Source ERIC)

Session 1

Convener: Cristina Pasotti (Sincrotrone Triest S.C.p.A.)

3 Transition to 352MHz Solid State RF Power at the Advanced Photon Source

The Advanced Photon Source (APS) has utilized 352MHz/1MW cw klystrons as rf power sources for its booster and storage ring since the start of operations nearly thirty years ago. Klystron obsolescence and high-volage power system issues due to decades of operation made the switch to solid state rf power the best option to maintain APS operation for the next thirty years. For the storage ring, four klystrons and a waveguide-based power splitting scheme will be replaced by twelve 160kW solid state rf amplifiers, with each amplifier driving one single-cell accelerating cavity. Managing the phased transition from klystrons to solid state amplifiers while maintaining operational reliability will be discussed.

Speaker: Douglas Horan (Argonne National Laboratory)

Horan_CWRF2026.pdf

4 Status and plans for the upgrade of the PETRA IV RF system

In the framework of the planned upgrade of PETRA III to the fourth-generation light source PETRA IV at DESY, it is necessary to replace the more than forty-year-old RF system with state-of-the-art components to suppress coupled-bunch instabilities caused by parasitic higher-order modes (HOM). The plan is to install single-cell normal-conducting HOM-damped cavities, each driven by a high-power solid-state amplifier (SSA) at the fundamental frequency of 500 MHz. In 2023, a prototype of the fundamental RF system was installed in PETRA III, which consists of a HOM-damped cavity driven by a 120 kW SSA that can be operated in addition to the existing RF system. In order to suppress the negative effects of Touschek and intrabeam scattering, a third harmonic system is foreseen which lengthens the bunches and reduces their charge density. One option for this cavity based on The Choke Mode Cavity by T. Shintake has been built. This presentation shows the planned design of the PETRA IV RF system, the status of the 3rd harmonic prototype Shintake cavity and reports on the performance of the fundamental prototype system in PETRA III with beam.

Speaker: Nils-Oliver Froehlich (DESY)

2026-09-14-CWRF_2026_.Status and plans for the upgrade of the PETRA IV RF system.pdf

10:00 Break

Session 2

Convener: Pei Zhang (Institute of High Energy Physics)

5 Design and preparation of the RF system for SPring-8-II upgrade

The synchrotron radiation facility SPring-8 plans to begin the upgrade to SPring-8-II next year, which will increase the brightness of the X-ray radiation by two orders of magnitude compared to current levels. In SPring-8-II, the emittance will be reduced from 2.4 nmrad to 50 pmrad by reducing the electron beam energy from 8 GeV to 6 GeV, introducing a multi-bend achromatic optics and damping wigglers. The power reduction of hard X-ray region due to the reduction of the beam energy is compensated by shortening the period of the undulator and increasing the beam current to 200 mA. By lowering the electron beam energy and converting the bending magnets from electromagnet with permanent magnet, the project also aims to reduce the electricity consumption to half of the current level. Because of the reduced beam energy, the required RF accelerating voltage will be half of the current value. So, the number of cavities will be reduced from 32 to 16. Numerical simulation and beam test of higher-order-modes (HOMs) of the current 509 MHz normal conducting cavities reveals that it is safe to reuse the cavity at the new ring. The RF source will continue to use the existing 1.2 MW klystrons. Each of the klystron will supply 500 kW of power to the 4 cavities. Since the circulators and dummy loads have recently been experiencing aged problems, we plan to replace them with new units. The low-level RF system was replaced with a Micro-TCA.4-based digital control system. The beam position monitor (BPM) measurement circuit for the storage ring was similarly replaced with a Micro-TCA.4-based system, and a new synchrotron oscillation suppression system utilizing these new systems was introduced. For SPring-8-II, to compensate for the reduction in beam lifetime resulting from lower emittance, we are investigating harmonic cavities and its RF sources to extend the bunch length. In this presentation, we report on the preparation status of the RF system for SPring-8-II.

Speaker: Dr Takahiro Inagaki (RIKEN SPring-8 Center)

CWRF26-Inagaki_talk.pdf

CWRF26-Inagaki_talk.pptx

6 Design and Characterization of an 80-Way TM₀₁₀ Cavity Combiner/Splitter for High-Power Solid-State RF Systems

High-power solid-state power amplifiers (SSPA) require efficient combination of large numbers of transistor modules while preserving modularity and serviceability. This contribution presents the design and tuning strategy of an 80-way resonant cavity network operating in the TM010 mode at 352.21 MHz. Almost the same hardware is used as an 80:1 combiner under coherent peripheral excitation and as a 1:80 splitter for passive power splitting, with low power loss at medium power level, as to coherently feed the 80 SSPAs, without the need of drivers. Eighty magnetic loop couplers are arranged at equivalent H-field locations, while the common port is adjusted for the total cavity loading and critical coupling. Frequency tuning exploits the spatial separation of electric and magnetic energy in the EM fields. A metallic post inserted near the cavity center, where the electric field is maximum produces a negative resonance shift. A post located near an edge in a magnetic-field-dominant region produces a positive shift. The design workflow combines analytical mode tuning evaluation in accordance with cavity perturbation theory. In addition, full wave 81-port driven simulations were realized with Ansys HFSS, and measurements confirm the expected results. The characterization reports resonant frequency, unloaded and loaded Q, common-port return loss, port isolation, insertion loss, combining efficiency and thermal drift.

Speaker: Dr Dragos Dancila

CWRF_26_ Combiner_talk_260914.pdf

7 First results from the solid-state power amplifiers designed to drive the 4-port RFQ of the NEWGAIN project without circulators.

As presented at this workshop in 2022, we want to try driving the 4-port, 88 MHz, vane RFQ of the NEWGAIN project without circulators. Four 40 kW amplifiers, intended to operate in mismatched conditions, withstanding up to 15% power reflected by the detuned cavity are being built and the first one was recently tested. The talk discusses the first results, the issues encountered and the choice of the combining architecture.

Speaker: Marco Di Giacomo (CEA-GANIL)

First results from the SSPA designed to drive the NEWGAIN 4-port RFQ without circulators.pdf

First results from the SSPA designed to drive the NEWGAIN 4-port RFQ without circulators.pptx

12:00 Lunch

Session 3

Convener: morten jensen (European Spallation Source ERIC)

8 The ongoing R&D for the ITER ICRF antenna arc and impairment detection and localization

The ITER Ion Cyclotron Range of Frequencies (ICRF) system is a high power (10-20 MW) continuous-wave (CW) RF (40-55 MHz) system. It will be used for plasma heating as well as wall-cleaning on the ITER tokamak. The ITER ICRF system consists of a 24-element phased array antenna fed by 4 tube-based RF sources through a specific transmission line & matching network.
The system, including its antenna, is designed such as not to arc (i.e. compliant with specified maximum voltages and electric fields). However, as with any high-power RF system, arcs can still occur, in particular during the commissioning phase, or for example in case of any particular event that can, for example, temporarily alter the vacuum conditions.
The ITER ICRF antenna shall be protected by several arc detection systems. This requirement is specified not only for complementarity (i.e. for protection coverage of the full system), but also for redundancy.
A RAdar Arc and impairments Detection and localization (RAAD) system for the protection of the ITER ICRF antenna is presented in this contribution. It offers several benefits over existing techniques. It can perform fast detection, localization, and classification of arcs and impairments/degradations along the full path of the RF power (in less than 5 μs as required for the protection of ITER ICRF antenna). It also operates completely independently of ICRF power operations. The detection and monitoring of impairments/degradations enable the prevention of faults, while the localization and classification of faults permit pinpoint maintenance operations.
The digitally phase-modulated radar signal is coupled into the transmission lines through a specifically designed coupling unit. A solution based on signal synchronization has been implemented to cope with high-power interference from RF frequency harmonics in the radar operating bandwidth. Other events such as antenna load variations and matching element modifications can be easily discriminated against arc events, being much slower than the radar pulse repetition period.
RAAD was installed and successfully tested during vacuum conditioning and during plasma operation (with and without RF power) on the AUG tokamak Ion Cyclotron RF system. Dedicated discharges were performed which showed that: a) RAAD can successfully detect all arcs, but localization of arcing was still not possible; b) RAAD can successfully detect and localize impairments.
After this first experimental campaign, the radar signal has been modified into an orthogonal frequency division multiplexing signal to allow an accurate equalization and permit localization of arcs. A second experimental campaign with dedicated discharges has been carried out on the EAST tokamak demonstrating the capability to localize arcs.
A further radar signal optimization and equalization technique is underway that will permit localization of all arcs in the next planned AUG experiment campaign (November 2026).
Finally, a so-called SSHAD system (Sub & Sub Harmonic Arc Detection) system (a kind of “passive” RADAR) was also developed and tested. It will also be covered in this contribution.

S. PORPORATO1, R. MAGGIORA1, M. PEROTTI1, M. SACCANI1, S. SALVADOR1, D. MILANESIO1
W. HELOU2, E. LERCHE2, P. BARGES2, P. RAUL2, F. CALARCO2, N FERRIGNO2, K. SAITO2, A. CADINOT2, C. BARBIER2, K. ROUX2, A. BUSTOS2
V BOBKOV3, H. FAUGEL3, R OCHOUKOV3
L. LIU4, W. ZHANG4, X. ZHANG4
1 Department of Electronics, Politecnico di Torino, Torino, Italy
2 ITER Organization, Route de Vinon-sur-Verdon, CS 90 046, 13067 St. Paul Lez Durance Cedex, France
3 Max Planck Institute for Plasma Physics, Boltzmannstr. 2, 85748 Garching, Germany
4 Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031, China

Speaker: Simone Porporato (Politecnico di Torino)

CWRF2026_ITER-ICRF-Arc-Detection_Porporato.pdf

CWRF2026_ITER-ICRF-Arc-Detection_Porporato.pptx

9 Operation Status and Experience of the TPS High-Power RF System

TPS is a 3 GeV third-generation synchrotron light source operating at a stored beam current of 500 mA. It is currently equipped with two 500 MHz RF stations, each capable of delivering up to 300 kW of RF power. One RF station is driven by a 300 kW klystron-based RF transmitter, while the other can be configured to operate with either a 300 kW klystron or a 300 kW solid-state power amplifier (SSPA), depending on operational requirements. To meet future demands for higher RF power, a power-combining system has also been developed and implemented. This report presents the operational status and experience of the TPS high-power RF system over the past several years, including operational fault events encountered during routine operation and the corresponding solutions adopted.

Speaker: Fu-Tsai Chung

Talk_CWRF2026上V4.pdf

10 Status and Operational Integration of the High Power RF Systems for the HiCANS Platform at ESS Bilbao

ESS Bilbao is actively developing the HiCANS Platform project, a medium-power neutron source demonstrator based on the High-Current Accelerator-Driven Neutron Source concept. This platform serves as a validation facility, integrating a 3 MeV proton linear accelerator that features an already operational injector and a Radio Frequency Quadrupole (RFQ) which is currently under commissioning.
This contribution focuses on the status, upgrades, and operating experience of the High-Power Radio Frequency (HPRF) systems for HiCANS Platform. We present a comprehensive facility status report detailing the performance, experiences and issues of the RF power sources, conditioning procedures, and high-power distribution networks.
Furthermore, we discuss the integration challenges, conditioning strategies, and initial operation results of the RFQ power station.

Speaker: Pedro González

CWRF2026- HiCANS Status - ESSB_pjg.pdf

CWRF2026- HiCANS Status - ESSB_pjg.pptx

11 Megawatt-Class Multi-Staged Depressed Collector Gyrotron Pulse Modulator

In 2025, Diversified Technologies, Inc. (DTI) delivered a short pulse megawatt-class gyrotron Multi-Staged-depressed collector test set. The system integrates low power cathode and body power supplies, two independent cathode capacitor banks, cathode high voltage solid state opening switch, and isolated mod-anode and filament heater supplies on a high voltage hot deck, with manual controls and flying leads to the gyrotron cathode. Configured for flexible experimental operation, the test set provides the cathode with pulses over 75 kV and 30 A. The pulsewidth of the system ranges from a microsecond to several hundred milliseconds, but was intentionally built to leave space for additional capacitors, allowing the pulse length to be increased up to 5 seconds.
The architecture provides cathode current, fast fault interruption of the cathode voltage and compatibility with external interlock and protection signals. Front-panel diagnostics provide direct access to the cathode, body, and all three-collector voltage and current monitor outputs, enabling characterization of tube performance during operation. A controls dishpan houses the main system controls and indicators including a Kirk Key interface, safety interlocks, system indicators, analog instrumentation, and trigger interfaces.
A single stack of solid-state switch modules receives high voltage from a capacitor bank. The switch stack is driven with a single inductively coupled loop from the sustaining switch driver board located in the controls dishpan, minimizing isolation complexity while maintaining synchronized switching. A snubber circuit limits the rate of change in voltage and any overshoot during switch stack turn-on and turn-off. This circuit protects the IGBT devices in the switch stack, reducing device stress and improving performance.
Filament power is supplied by a regulated high voltage power supply (HVPS) with a continuously adjustable output through a front panel variable transformer (Variac). An isolation transformer provides isolation between the HVPS and Variac. The resulting platform provides a flexible environment for the development and characterization of high power gyrotrons.

Speaker: Shannon Hunter (Diversified Technologies, Inc.)

Gyro Poster_Final.pdf

12 Development of Solid-state Power Amplifier for Accelerator Based on the New Concept and Technologies in IMP

The Institute of Modern Physics (IMP) of the Chinese Academy of Sciences is the first scientific research unit in China to fully apply solid-state power source (SSPA) to linear accelerator engineering projects since the launch of the ADS project in 2011. This design has since been adopted for two large-scale scientific facilities in Guangdong Province: China initiative Accelerator Driven System (CiADS) and High Intensity Heavy-ion Accelerator Facility (HIAF). In a recent decade of accelerators project construction, IMP has accumulated valuable experience in SSPA design build and operation during the operation and upgrade of several projects which meet the stringent system requirements: high performance, low cost, high scalability, high reliability, and ease of maintenance need. New designs and technologies have been developed for this accelerator solution, such as high-performance power amplifier materials, the "hot swap" concept, special combiners, and new methods for long-term stable operation and on-site maintenance, especially for processing failures without interrupting RF power.

Speaker: Liepeng SUN

POSTER CWRF26.pdf

POSTER CWRF26.pptx

13 Operational Experience with the Second 500 MHz Solid-State Amplifier Transmitter at NSLS-II

The National Synchrotron Light Source II (NSLS-II) at Brookhaven National Laboratory commissioned its second 500 MHz solid-state amplifier (SSA) transmitter, supplied by Ampegon, in May 2025 to support operation of the storage ring superconducting RF cavities. The compact transmitter architecture provides a high-power, modular solution that demonstrates reliable performance during routine operation while significantly reducing the overall system footprint. During the first several months of operation following commissioning, a few design-related issues were identified that required engineering modifications. The first involved intermittent arcing within the ten-way RF combiner. The second issue involved the distribution of 24 VDC power to the RF modules. The original design routed the supply through a single RJ45 cable daisy-chained across all 50 amplifier modules, resulting in current levels that exceeded the intended carrying capability of the conductors. There are a few other small issues that needed to be overcome, which will be discussed as well. This presentation summarizes the operational experience with the transmitter and the way that they were resolved.

Speaker: Roger Borger

CWRF_Workshop_2026_BNL_NSLS-II_SSA2_One_Year_Operations_Poster_Final.pdf

CWRF_Workshop_2026_BNL_NSLS-II_SSA2_One_Year_Operations_Poster_Final.pptx

14 Development of a 4 kW SSPA and Full-Reflection Circulator for SCL3 Superconducting Cavities

The SCL3 superconducting accelerator at RAON consists of 81.25 MHz QWR and 162.5 MHz HWR cavities. It operates under severe full-reflection conditions where over 90% of the incident power is reflected due to deliberate overcoupling. To deliver continuous RF power without interlock trips, we developed a 4 kW CW Class-AB LDMOS SSPA. We also designed a full-reflection circulator that compensates for thermal resonant-pole shifts. Using a movable short, performance was verified across all reflection phases from 0 to 360 degrees. The system successfully maintained its rated output power and achieved an input reflection S11 of -15 dB or lower. All 128 SSPA sets passed acceptance testing, were installed in the SCL3 gallery, and are now in operation for beam commissioning.

Speaker: Ki taek Son (Institute for Rare Isotope Science)

Development and Operation of 4 kW CW Solid-State Power Amplifiers for the SC.pdf

Development and Operation of 4 kW CW Solid-State Power Amplifiers for the S.pdf

Development and Operation of 4 kW CW Solid-State Power Amplifiers for the S.pptx

15:20 Break

Session 4

Convener: Sam Pitman (CERN)

15 From High Failure Rates to Improved Reliability: Operational Experience with the CERN 200 MHz Solid-State Amplifier System

Following the talk presented at CWRF2024, which highlighted an exceptionally high transistor failure rate with limited understanding of the underlying causes, this talk will present the progress made in understanding the behaviour and reliability of the system since then. We will discuss the system-level effects that have been identified as contributing to reliability issues and early-life degradation of the transistors, with particular emphasis on the interaction between these different mechanisms. Failure analyses carried out on damaged devices will be presented, together with the measurements and investigations that helped establish a clearer picture of the dominant failure modes. The talk will also describe the corrective actions and system improvements implemented as a result of this work, which have reduced the transistor failure rate by approximately 40% and significantly improved overall system reliability. Finally, we will present the remaining challenges and the future upgrade plans aimed at further improving the robustness, maintainability and long-term performance of the system.

Speaker: Sam Pitman (CERN)

CWRF2026_SSPA_CERN.pdf

CWRF2026_SSPA_CERN.pptx

16 SSA Upgrade of the APS Storage Ring RF systems

Recently four of the twelve cavities for APS storage ring were upgraded to Solid state systems. The presentation describes the upgrade process, challenges and future efforts.

Speaker: Aditya Goel (Argonne National Lab)

CWRF 2026.pdf

CWRF 2026.pptx

17 Operational Status and LS3 Upgrades for HL-LHC Klystron-Based RF Systems

This presentation will provide an operational status of CERN klystron-based RF systems and the planned upgrades during Long Shutdown 3 (LS3) for the High Luminosity (HL) LHC era. It will provide an overview of the key changes to be implemented, including the deployment of high-efficiency klystrons, the introduction of new circulators and loads, and the transition to an updated control system architecture.
In addition, the presentation will discuss the strategies for testing, validation, and installation of these components, highlighting the challenges and solutions associated with large-scale system integration.

Speaker: Dario Soriano Guillen

cwrf26_dsoriano_PDF.pdf

cwrf26_dsoriano.pptx

18 S-Band Solid-State Power Amplifier Driver System for AWAKE

This work presents the design, development, and integration of a prototype 400 W S-band solid-state power amplifier (SSPA) based on LDMOS technology as a reliable RF driver for S-band klystrons. The prototype operates at 2.998 GHz with a pulse width of 6 μs and a duty cycle of 0.006%. It integrates the SSPA, DC power supply, cooling system, control system, and a custom Pulse Measurement Unit (PMU). The PMU provides pulse-width monitoring, missing-pulse detection, forward and reflected RF pulse power measurements, voltage and current monitoring, and hardware interlocks for system protection and real-time diagnostics. The complete RF driver system has been integrated and experimentally characterized. Initial measurements demonstrate stable pulsed operation and successful performance of the RF, power measurement, and control subsystems, providing a compact and scalable RF driver solution for future accelerator applications. This work was supported by the AWAKE-VR project.

Speaker: Yasin Alekajbaf (Uppsala University)

Yasin_CWRF2026_V.pdf

19:00 Reception

Tuesday 15 September

Welcome

Session 5

Convener: Prof. Daniel Valuch (CERN)

19 Lots of Little Problems or One Big Problem – Our Experiences Running a Hybrid Mix of Klystron Tube Transmitters and Solid-State Transmitters at NSLS-II.

Since 2021 NSLS-II at Brookhaven Laboratory has been operating with at least one Solid-State Amplifier (SSA) and one Klystron Control Unit(s)(KSU). In the spring of 2025, we decommissioned one of the KSU units and installed our second SSA in its place. After running with this hybrid mix for a few years, patterns start to emerge in the behavior of the two different technologies. This presentation will go thru the constant little (sometimes not so little) issues that occur with the SSA(s) vs the steady KSU operation. The KSU always has the potential for a tube failure, which is a potential big problem. This presentation details the numerous issues that we battle every day to keep the SSA’s running, while the KSU just steadily hums along with each hour going by brings it closer to its inevitable failure. I will explain how the SSA(s) by design can tolerate multiple failures and keep running where the KSU only has redundancy in its PSM modules. I will compare the faults on the SSA(s) and the KSU over the past years and explore the question: Which do you prefer? Lots of little problems or one big problem.

Speaker: Brian Holub (Brookhaven National Laboratory)

CWRF2026_ Large or small Problems_Final.pdf

CWRF2026_ Large or small Problems_Final.pptx

20 High-Efficiency RF Power for FCC-ee: Development Status of the Tristron

This presentation will address RF powering schemes for the Future Circular Collider electron–positron machine (FCC-ee), with a particular focus on the development of a new high-efficiency RF power source: the tristron.
Designed and manufactured at CERN, the tristron represents a promising alternative to conventional technologies, aiming to significantly improve overall system efficiency and performance.
The talk will provide an overview of the tristron concept, followed by a summary of recent progress in its development. Emphasis will be placed on key achievements and challenges in the design and manufacturing, as well as ongoing advancements in testing and validation of components.

Speaker: Chiara Marrelli (CERN)

Marrelli_CWRF26.pdf

Marrelli_CWRF26.pptx

21 Operational experience and developments of the European XFEL RF System

The European XFEL started beam operation in 2017. In order to reduce downtime and optimize general performance of the HPRF system some changes and developments for the RF stations have been implemented.
The presentation gives an overview about the operation experience and the mayor failures of the RF stations. A brief description of operational measures to save energy of the RF stations is given. The “plug and play” based klystron spare part concept was improved by the development of so called “Connection Module” together with Canon.
Finally, a small outcast/ overview on the idea of a HDC (High Duty Cycle) upgrade for the XFEL will be presented.

Speaker: Sebastian Goeller (DESY)

XFEL RF station operation experience and developments---15-09-26.pdf

22 Generating 200 kW of CW in 1920's. The Grimeton Radio Station electromechanical transmitter

The 200 kW VLF transmitter at the Historical Grimeton Radio Station was built in the 1920’s. It could be described as an electromechanical transmitter using a motorgenerator setup to achieve a 200 kW CW "RF" power output at 17.2 kHz. The radio station is a World Heritage since 2004.

Details of the high frequency generator will be presented together with the high frequency transformers and the magnetic modulator. Also the antenna system (a multiple resonant antenna 2.3 km long) will be discussed. Measurements and some network models will be presented as well.

CV

Robert Petersson was born 1956 in Karlskoga. He graduated from Chalmers University of Technology with a M.Sc. in Electrical Engineering in 1981. He has a long professional experience in the field of antennas and microwave engineering. He is also a licensed radio amateur (SM6GHS) since 1974.

He started his career at LM Ericsson in Mölndal 1981, working mostly in the area of spaceborn antennas. From 1999 the technical area was spaceborn microwave electronics. From 2018 Robert is employed at Qamcom Research and Technology.

Robert is a member of the Alexander Friendship Association since many years and have more recently participated in the associations courses in operation, maintainance and understanding of the Grimeton VLF transmitter.

Speaker: Robert Petersson (Alexander Friendship Association)

SAQ CWRF26_Grimeton.pdf

23 Group Picture

2026-09-16 14.35.15.jpg

10:20 Break

Session 6

Convener: Mr Patrick Kramer

24 Design of the LANSCE Klystron Modulator Test Stand

The Los Alamos Neutron Science Center (LANSCE) linac has been providing proton beams to users for 53 years. Each of the 44 modules in the Coupled Cavity Linac portion of LANSCE uses a 1.25 MW peak power klystron capable of producing 1000 µs pulses at 120 Hz. When the accelerator was designed, the most practical way to pulse the klystron current was to connect the klystron cathode to a High Voltage DC capacitor bank and build a Modulating Anode into the klystron electron gun to pulse the current on and off. This specific klystron design has been largely unchanged for over 50 years, but LANSCE has become the last user of Mod-Anode klystrons at this power level. Recently, Cathode Pulse modulators developed for the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory and the European Spallation Source (ESS) have approached the peak and average power levels required by LANSCE. We describe a new High Power RF test stand at LANL that will be used to demonstrate that a Cathode Pulse modulator can meet the requirements of both the present 1.25 MW klystrons and future 1.6 MW klystrons. Upgrading the LANSCE RF powerplant to 1.6 MW klystrons will compensate for possible decreases in CCL structure shunt impedance and provide the accelerator operators more flexibility in tuning the linac. In the long term, it will enable higher H- beam current delivery to the Proton Storage Ring after the an upgrade of the H- ion source is completed.

Speaker: Joseph Bradley III (Los Alamos National Laboratory)

2026 CW and HPRF wkshp Kly Mod Tst Std v 11.pdf

2026 CW and HPRF wkshp Kly Mod Tst Std v 11.pptx

25 Report on the 400 kW SSPA development at ESS.

The presentation provides an update on the development of the 400 kW Solid-State Power Amplifier operating at 352 MHz for the European Spallation Source (ESS), developed by ESS in collaboration with Uppsala University. It details the initial measurements of critical components, including the Solid-State Power Amplifier (SSPA) modules, which has a nominal output power of 1.6 kW, cavity splitter and cavity combiners, Local Protection System (LPS), and monitoring solution. Achieving 400kW power level requires the architecture to integrate 320 SSPA modules. In the first combining stage, 80 modules are connected through a cavity combiner to form a 100 kW unit. Four such units are subsequently combined using a progressive combiner to produce the required 400 kW output power. The design emphasizes efficiency and compatibility, maintaining a footprint identical to the existing tetrode station at ESS, approximately 4 square meters. Its expected wall-plug efficiency is competitive with that of power stations based on alternative RF amplification technologies.

Speaker: Bruno Lagoguez

400kW SSPA ESS for CWRF.pdf

400kW SSPA ESS for CWRF.pptx

26 High-power RF SSPA for RFQ in the RAON heavy-ion accelerator

The Rare Isotope Accelerator complex for On-line Experiments (RAON) is a large-scale research facility designed to produce and accelerate a wide variety of heavy-ion beams for advanced studies in nuclear physics, materials science, and other interdisciplinary fields. Beam commissioning of the low-energy superconducting linac (SCL3), which includes an injector section, quarter-wave resonators (QWRs), and half-wave resonators (HWRs), has been conducted and beam is also being provided to domestic users. There are an radio-frequency quadrapole (RFQ) in the injector, which is a normal conducting cavity of 81.25 MHz. 150 kW high power solid-state power amplifier (SSPA) for the RFQ has been operated for the beam operation. The system consists of 5 kW high power amplifiers (HPA), 5 kW high power circulators, high-power combiners, power distribution units, an EPICS controller, and cooling water manifolds. Each 5 kW amplifier is constructed from 1 kW power amplifier modules utilizing LDMOS FETs. The SSPA was originally produced as a prototype; however, as it has aged over the past decade, a new high-power SSPA is currently being designed and built. This paper presents the details of the high power SSPA system for the RFQ.

Speaker: Kyungtae Seol

CWRF2026 Oral_poster (KTSeol).pdf

CWRF2026 poster (KTSeol).pdf

27 Robustness of the 3rd Generation of High-Power Solid-State RF Amplifiers for 500 MHz

With its third generation of 500 MHz solid-state RF amplifiers, Cryoelectra has achieved a level of reliability such that virtually no RF units have failed over more than 14 million transistor operating hours.
This was made possible by the patented design of the RF power modules, as well as by sophisticated manufacturing technology and the quality assurance measures implemented.
The RF power module contains 16 RF units, each with a single transistor. Their output signals are combined at the center of the module by a coaxial combiner. The outer part of the combiner also serves as a water-cooled heat sink for the power dissipated by the RF units and the terminating load of the circulators. The RF outputs of up to 15 RF modules are connected directly to a waveguide combiner to reduce power losses and eliminate sources of error. This poster presents current MTTF values as well as measures which improved them.

Speakers: Mirco Nedos (Cryoelectra GmbH), Nico Pupeter (Cryoelectra GmbH)

Poster_A0_Robustness_500 MHz_SSA_3rd_Generation.pdf

Poster_Presentation.pdf

12:00 Committee working lunch

12:00 Lunch

Session 7

Convener: Chiara Marrelli (CERN)

28 MW-Class RF Power Sources at ESS: Present and Future

The ESS Linac currently operates 62 MW-class klystrons amongst numerous other RF sources to provide the RF power required for operation at 2MW beam power. The talk reviews the present operational situation of these klystrons, the experience with past klystron deliveries by industry and the near-term procurement plans. The recent optimization of klystron operating parameters to improve wall-plug efficiency will be presented, together with its impact on facility power consumption. The talk will also discuss the present upgrade for 3MW beam operation and the selection of RF source technology for the eventual 5MW beam power upgrade in the future, comparing the klystrons with high-power multi-beam gridded tubes.

Speaker: Mr Patrick Krämer (European Spallation Source ERIC)

CWRF2026_MWclassRFpowerSourcesAtESS_Kramer.pdf

CWRF2026_MWclassRFpowerSourcesAtESS_Kramer.pptx

29 Inside the ESS RF Systems: From Design to Beam.

This talk will introduce the ESS accelerator facility through the lens of its RF systems. It will give a high-level overview of the RF architecture, highlighting selected key subsystems and the main challenges encountered during the installation and commissioning of the accelerator.

The talk will provide useful background ahead of the site tour, introducing some of the key RF features that participants will see during the visit. It will also give a brief update on relevant developments since the previous workshop, focusing on topics not covered in other ESS presentations.

Speaker: Morten Jensen (European Spallation Source ERIC)

Inside the ESS RF Systems- From Design to Beam sm. .pdf

Inside the ESS RF Systems- From Design to Beam sm. .pptx

30 Site Visit Safety Training

Site safety induction Video

Information to visitors_Dec2025.docx

Information to visitors_Dec2025.pdf

14:40 Break

15:05 Red and Green groups departure to the tram, and the rest according to plan

lajödlskfj

Site Visit

Wednesday 16 September

Welcome

Session 8

Convener: Marco Di Giacomo (CEA-GANIL)

31 GaN Amplifier Progress for 805 MHz Coupled Cavity Linac at LANSCE

The Los Alamos Neutron Science Center uses a room temperature coupled-cavity linac to accelerate H- ions from 100 to 800 MeV. It is powered by forty-four 1.25 MW peak 805 MHz klystrons, each capable of 150 kW of average power. A prototype solid-state amplifier (SSA) feasibility study began in 2024, as reported at 13th CWRF Workshop in Oak Ridge. We are using high voltage Gallium Nitride (GaN) on Silicon Carbide (SiC) high electron mobility transistors to reduce the number of active devices and the complexity of power combing smaller amplifiers. These wide bandgap semiconductors can operate at high channel temperatures around 200 degC without shortened life. We are testing devices up 5 kW of peak power at 100 volts. Operating in saturation mode, outphasing modulation between pairs of amplifiers is used to maintain high device efficiency to reduce thermal dissipation, compared to conventional class AB linear amplifiers. The power supply requires stored energy with a capacitor bank. Power combining uses a combination of 2-way Gysel, 40-way radial and magic tee combiners in waveguide. Combiner testing has been underway. Cooling design is critical for such as high power-density amplifier. A new test lab is testing HEMT pallets, power supply/energy storage, and passive RF components for a medium power prototype. We have determined that a SSA can replace a klystron, while fitting within the existing footprint to use the same water-cooling plant.

Speaker: John Lyles

LANL SSA Lyles CWRF Lund.pdf

LANL SSA Lyles CWRF Lund.pptx

32 Recent Progress and Future R&D Plans of GaN-based 750 MHz Compact Pulsed Solid-State Power Amplifiers at IMP

The Institute of Modern Physics (IMP), Chinese Academy of Sciences, has recently developed a series of compact 750 MHz pulsed solid-state power amplifiers (SSPAs) with a total output power of 1.8 MW. These pulsed SSPAs with rated power ranging from 200 kW to 400 kW have been developed based on gallium nitride (GaN) 5 kW and 10 kW single transistor. This report will present the overall design of the SSPA system, focusing on the development of the 300 kW compact pulsed SSPA, together with lessons learned from prototype fabrication and commissioning. Furthermore, relying on the present work, this presentation proposes the general architecture design and phased development roadmap for a 750 MHz/500 kW high-duty factor SSPA.

Speaker: Dr Longbo Shi (Institute of Modern Physics, Chinese Academy of Sciences)

Progress and Future R&D Plans of Compact Pulsed SSPA in IMP Final.pdf

Progress and Future R&D Plans of Compact Pulsed SSPA in IMP Final.pptx

33 Operational Experience of Radio Frequency RF Power Stations (RFPSs) at ESS

The first section of the ESS superconducting linac is the Spoke linac. It consists of 26 superconducting Spoke cavities resonating at 352 MHz, installed in 13 cryomodules. Each Spoke cavity is powered by an RF Power Station (RFPS), with a maximum output power requirement of 400 kW. To achieve this power level, the outputs of two amplifiers based on TH595A tetrodes are combined.
Twenty-seven RFPSs were delivered by Elettra as part of the Italian in-kind contribution to the construction of ESS. The detailed design of the RFPS was jointly developed by ESS and Elettra [1].
Twenty-six RFPSs have been installed and commissioned in the ESS service gallery. Due to issues encountered during the initial operation, extensive soak testing was performed on eight RFPSs. Based on the results and operational experience from these tests, several improvements were implemented in both the RFPS design and the tetrodes. This paper presents details of these improvements. As a result of these modifications, together with improvements in operational procedures, the tetrodes have demonstrated significantly improved operating lifetimes. Currently, 7.5% of the tetrodes have accumulated more than 15,000 filament hours, 3.5% have accumulated between 10,000 and 15,000 filament hours, and 61% have accumulated between 8,000 and 10,000 filament hours. The paper also discusses issues encountered with the high-voltage anode power supplies and the corresponding possible mitigation measures.
The RFPSs were successfully used for cold coupler and cavity conditioning, as well as for the Beam on Dump 2 (BOD2) campaign. They will also be used for the Beam on Dump 3 (BOD3) campaign in 2026.
References:

1. Cristina Pasotti, ‘400 kW - 352 MHz Radio Frequency Power Station Technical Specification’, E-ST ESS RF TSD 002, 2017 (confidential document).

Speaker: Dr. Rutambhara Yogi (European Spallation Source (ESS) ERIC)

yogi-CWRF2026.pdf

yogi-CWRF2026.pdf

yogi-CWRF2026.pptx

34 RF Power Sources for Crab Cavities in HL-LHC

The LHC Crab Cavity System is powered by dedicated 400 MHz high-voltage RF stations based on IOT amplifiers. These systems were designed to provide reliable and stable RF power while meeting the stringent availability and machine protection requirements of the LHC and future HL-LHC operation.
The installation of the RF infrastructure in the LHC galleries required the integration of high-voltage equipment, RF transmission lines, cooling systems, and controls within a constrained environment.
Several years of operation have provided valuable feedback on the performance, reliability, and efficiency of the IOT-based RF power stations. Operational experience, maintenance activities, and lessons learned have contributed to continuous improvements in system robustness and availability.
The challenges associated with the linearization of IOT amplifiers at very low output power levels are investigated, and the solutions implemented to improve RF control performance are presented

Speaker: Mr Gino Cipolla (CERN)

14th_CW_HPRF_Workshop_Lund_2026_V2_.pdf

14th_CW_HPRF_Workshop_Lund_2026_V2_.pptx

10:15 Break

Session 9

Convener: Aditya Goel (Argonne National Lab)

35 Selected High Power RF and Particle Accelerator Capabilities at SLAC

The RF Accelerator Research (RFAR) department at SLAC National Accelerator Laboratory specializes in high-power RF and accelerator technologies, enabling new applications across science, industry, and medicine through breakthroughs in efficiency, size, and cost.
This presentation highlights RFAR's core competencies in the design, fabrication, and testing of accelerator structures, high-power RF sources, and integrated systems from decades of experience producing the 5045 klystron, SLAC's S-band source, alongside X-band klystrons, UHF-band klystrons, and prototype devices of various topologies. Emphasis is placed on RFAR's in-house manufacturing capabilities, including precision machining, furnace brazing, vacuum baking, coating, and high-power RF testing, and the lessons learned over time. In addition, opportunities for future collaboration and how RFAR's capabilities can support the broader accelerator and RF community are highlighted.

Speaker: Daniel Rowen

2026_09 RFAR Manufacturing Capabilities_Final.pdf

36 High Power RF Developments at FNAL’s PIP-II Project

Fermilab’s PIP-II project seeks to enhance its proton beam capabilities for scientific research by modifying the existing synchrotrons and replacing the linear accelerator with a superconducting linear accelerator. The PIP-II project has progressed from test stand development to component qualification and site installation, with additional test stands deployed in the former Tevatron RF gallery for 325 MHz and 650 MHz circulator and high power coupler testing. The PIP-II Injector Test (PIP2IT) facility was converted into a cryomodule test cave will be used for qualifying all the SRF systems to be installed at PIP-II.

Speaker: Victor Grzelak (FNAL)

CWRF14-PIP-II-HPRF-draft-v2.pdf

37 Direct Cavity Combiner for High Power Solid State RF Transmitter

The recent funding of multiple fusion startups is accelerating the development and integration of commercial fusion devices, systems, and architectures. In most fusion reactions, the plasma must be heated to great temperatures, and efficient current drive must be established. Ion Cyclotron Range of Frequencies (ICRF) has been demonstrated to be effective, and 60-240 MHz radio frequency (RF) systems are envisioned for high magnetic field devices.
There are only two ways to create this RF power – tubes and transistors. Conventional Vacuum Electron Devices (VED like tetrodes, aka vacuum tubes) have a finite life, and require replacements after months, have poor efficiency, and are subject to a fragile supply chain. Transistors, or solid-state amplifiers, are expensive, have large footprints at high power, and require costly power combining and cooling systems.
Diversified Technologies, Inc. (DTI) is building a novel, patented, Direct Cavity Combiner (DCC) VHF Transmitter in a single high power, compact, and efficient amplifier under a Department of Energy Small Business Innovative Research (DOE SBIR) grant for use as a high power solid state RF transmitter. This transmitter, designed to scale to 1.5 MW, is built from multiple RF amplifier modules combined in a single RF cavity, with high efficiency, low combining losses, and output power directly proportional to the number of RF modules feeding the cavity. This technology is an alternative to conventional megawatt-class VED RF sources, and overcomes the limited frequency range, reliability, and supply chain issues associated with tetrodes and similar VEDs. It enables high power output in a compact size, because it eliminates the power combining losses typical of conventional solid state amplifiers. The basic transmitter technology can be adapted to a wide range of frequencies, making it applicable to multiple applications beyond fusion, including high power microwave, high energy physics, radar, and broadcasting.
DTI has previously demonstrated the viability of the DCC concept at L-band and UHF. The current full-scale 120 MHz cavity combiner was partially populated with 31 modules, demonstrating 42.7 kW of output power at 81% efficiency. Additional octants are currently being populated to produce 100 kW RF output for at least 1 minute. Following this test, additional modules will be added to demonstrate 280 kW RF output at short pulse.

In this paper, DTI will report on the latest design and test results of the VHF RF cavity and modules, and the lessons learned during its development.

Speaker: Shannon Hunter (Diversified Technologies, Inc.)

Direct Cavity Combiner 9_16.pdf

Direct Cavity Combiner 9_16.pptx

12:00 Lunch

Session 10

Convener: Douglas Horan (Argonne National Laboratory)

38 Phase-Based Circulator Control and High Directivity Measurement Techniques for the HL-LHC Upgrade

In the framework of the high-power upgrade for the HL-LHC at CERN, developments are underway to enhance the performance and reliability of the RF systems operating at up to 350 kW continuous-wave power. This work presents two complementary developments aimed at improving RF system control and measurement accuracy.

First, a phase-based active control technique for high-power circulators is investigated, where the relative phase between circulator ports is continuously monitored and the ferrite magnetic bias is dynamically adjusted to maintain optimal tuning under varying operating conditions.

Secondly, a dual directional coupler architecture combined with digital signal processing is developed to improve coupler’s directivity. Initial results show that by digitally optimizing amplitude and phase relationships between two coupled signals, effective directivities exceeding 70 dB can be achieved. Experimental results, simulations, implementation details, and current performance limitations are presented, along with plans for further improvements.

Speaker: Martin Par Ankel

CWRF2026_Ankelv2.pptx

39 Countermeasures for Arc Discharge in 509 MHz High-Power Circulators at SPring-8

In the synchrotron radiation facility SPring-8, we have stably operated four 509 MHz, 1.2 MW high-power circulators to protect klystrons from reflections for the past 28 years. However, since January 2026, we have suddenly experienced frequent arc discharges inside the circulators. To mitigate this, we have taken countermeasures such as lowering the operating power and replacing them with spare circulators.
In order to investigate the causes of these arc discharges, we replaced the faulty circulator and conducted internal inspections, low-power RF measurements, and high-power tests. Through the internal inspections using a fiberscope, we found black dust on the ferrite plate surfaces, which was identified as silver compounds by elemental analysis. In the low-power measurements, no significant property changes or frequency shifts were observed compared to the factory test. In the high-power test, we reproduced arc discharges at a transmission power of around 500 kW. We used a high-speed camera to capture the light emitted during the discharge. We found that the discharges mostly occurred between the ferrite plates near the input port of the circulator. Based on these findings, we considered rotating the circulator by 120 degrees, to move the discharge-prone areas to Port-3, where the electric field is weaker. After we rotated the circulator by 120 degrees, we successfully operated with a power of 1 MW without any discharge. This demonstrated that rotating the circulator by 120 degrees is an effective new countermeasure.
In this presentation, we will report on these issues and countermeasures for the circulators.

Speaker: Takato Tomai (Japan Synchrotron Radiation Research Institute)

CWRF2026_Presentation_Tomai.pdf

CWRF2026_Presentation_Tomai.pptx

40 Operational and Lifetime Experience of High-Power Klystrons for Accelerator Facilities

High-power klystrons have been developed for accelerator applications requiring stable RF power generation and high reliability. The developed tubes have been deployed at accelerator facilities with different operational requirements and have demonstrated stable performance under long-term operation. Long-term monitoring data provided by accelerator facilities were analyzed to investigate klystron failure modes and evaluate tube lifetime characteristics. This talk presents the failure modes affecting klystron lifetime and possible countermeasures.

Speaker: RISA KIKUCHI (Canon Electron Tubes & Devices Co., Ltd.)

Operational_and_Lifetime_Experience_of High-Power_Klystrons_for_Accelerator_Facilities_Canon_rev0.pdf

41 New High Power RF Systems at FRIB

FRIB is one of the largest heavy ion accelerators in the world. As such it has many RF systems across many frequencies and power levels. The facility is constantly working to improve the performance and/or reliability of the systems. The focus of this talk will be on the improvements and updates that have been made to the RF systems in the last two years. We will provide an update on the commissioning and early operation experience of the 120 kW solid state amplifier (SSA), being used to replace the FRIB RFQ tetrode amplifier. We will also discuss the addition of a second RF transmitter (400 W SSA, 10 to 13 GHz) to improve the performance of the ARTEMIS ion source.

Acknowledgement: This work is supported by the U.S. Department of Energy Office of Science under Cooperative Agreement DE-SC0023633, the State of Michigan and Michigan State University.

Speaker: Shen Zhao (FRIB)

42 Improving SNS RF Master Oscillator Signal Level Stability Through Environmental Controls

The Spallation Neutron Source (SNS) Master Oscillator (MO) generates six continuous-wave, low-close-in phase-noise RF reference signals at 2.5, 10, 352.5, 402.5, 755, and 805 MHz for the low-level RF, diagnostics, and timing systems. A free-running ultra-low-noise 10 MHz oscillator provides the 10 MHz output; after low-noise distribution, this signal serves as the common source for direct analog synthesis of the other five frequencies. The frequency stability and phase-noise performance of the MO output signals have always been excellent. However, the MO output amplitude levels, while meeting specifications, have exhibited slow drifts and fluctuations typically in the ±0.25 dB range over the course of a several-month SNS neutron production run.

Observations showed that these amplitude variations correlate with changes in temperature, humidity, and airflow near the MO rack, which is located in the SNS klystron gallery building. When air temperature or relative humidity rises, the signal levels fall; when airflow increases (within a limited range), the signal levels rise. The klystron-gallery building temperature is normally regulated to ±1 °C, but relative humidity is uncontrolled and can range from as low as 10% in dry winter months to as high as 60% in warm, humid summer months. Changes in the positions of carts, equipment, or doors near the MO rack can also alter local airflow and thereby affect the output levels. The SNS linac low-level RF control systems are sensitive to small amplitude variations in the distributed reference signals, which can produce control errors and increased beam loss.

A simple, non-invasive environmental monitoring and control system was developed for the MO rack to improve output-level stability without modifying the existing MO RF hardware. The system comprises three variable-speed DC fans for controlled airflow, a 100 W resistive heater for supplemental thermal control, precision RF power meters, and temperature/humidity sensors. The automated controller compares selected amplified MO output levels with individual targets, forms a weighted error, and adjusts fan voltage (and, when needed, heater power) within safe operating limits. Configurable sampling intervals, averaging windows, gains, tolerance bands, and voltage-step limits govern the control loop; all key parameters and actions are displayed on the EPICS/EDM interface.

The airflow-control system was tested throughout the SNS production neutron run in the first half of 2026 and performed well, successfully keeping selected RF levels at or near their targets and substantially reducing amplitude drift and variations. The improved signal-level stability contributed to a more stable accelerator: after initial beam-loss tuning, losses did not drift upward as much during the run, requiring fewer ongoing manual adjustments by machine specialists. Operators and machine specialists reported high satisfaction with the improved stability provided by the MO airflow control system. The heater was added during the July 2026 outage, providing additional control margin. Both the airflow and heater systems are now operational. This contribution presents the diagnostic process, control architecture, production-run results, and operational safeguards of a practical retrofit that reduces environmentally driven amplitude drift while preserving the phase and frequency performance of the SNS RF reference system.

Speakers: Amith Hulikal Narayan (Oak Ridge National Laboratory), Chip Piller (Oak Ridge National Laboratory)

Sweden CWRF Workshop.pdf

43 Progress from Testing Facility for HPRF SSA System at LANSCE CCL

A new high-power RF test facility was developed at the Los Alamos Neutron Science Center (LANSCE) to evaluate components of a RF Solid-State Amplifier (SSA) system operating at 805 MHz and targeted for a final output power of 1.25 MW. The system is powered by a 100 V DC supply and stabilized with a capacitor bank to support transient power demands. The SSA utilizes Gallium Nitride (GaN) on Silicon Carbide (SiC) high electron mobility transistors (HEMTs) and uses water cooling to manage thermal loads and ensure stable operation under high duty-factor pulsed conditions. Multiple HEMT amplifier modules will be power combined to achieve the full 1.25 MW output, with the aim of enhancing reliability, modularity, and maintainability in accelerator RF infrastructure. Integrated protection procedures allow for secure shutdown of RF drive and DC power in the event of overvoltage, overcurrent, or thermal excursions. This project supports ongoing evaluation of solid-state amplifier performance, thermal handling, and integration with RF passive and active components under realistic operational conditions.

Speaker: Javier Vega

Vega_CWRFPoster.pptx

44 8 kW Solid State Amplifier System for the Cryomodule Test Facility

Jefferson Lab currently uses a four klystron amplifier system to provide up to 12 kW of RF power for cryomodule cavity and RF window testing. Due to the system’s age, the Cryomodule Test Facility is undergoing an upgrade that replaces klystrons with solid state amplifiers (SSAs). SSA specifications were selected with consideration for potential future klystron replacements across the CEBAF accelerator. This presentation will outline the status of the SSA installation, key technical challenges, and the implications for broader SSA adoption within the accelerator.

Speaker: Mark Wissmann (Jefferson Lab)

2026 CWRF_SSAsys For CMTF SLshow_final.pdf

2026 CWRF_SSAsys For CMTF SLshow_final.pptx

CWRF_Workshop_CMTF_MW.pdf

CWRF_Workshop_CMTF_MW.pptx

15:20 Break

Session 11

Convener: Amith Hulikal Narayan (Oak Ridge National Laboratory)

45 Status of the HIPA Injector 2 upgrade at PSI

The Paul Scherrer Institute (PSI) is upgrading its High Intensity Proton Accelerator (HIPA) facility to improve reliability and increase beam power. The upgrade of the RF system for the Injector 2 cyclotron has now been completed. To increase the energy gain per turn, the two 150 MHz flattop cavities were replaced with higher-voltage 50 MHz aluminum cavities. The project also included the replacement of the legacy low-level RF (LLRF) and amplifier systems for all four Resonators. The new amplifier chains are based on a hybrid architecture consisting of a 10 kW solid-state driver amplifier and a tetrode-based final power amplifier. Since the new amplifier systems were installed in an annex building, the coaxial transmission lines connecting the amplifiers to the cavities also had to be replaced.
The first of the new RF systems has been in routine operation since 2024. In 2025, the RF system for Resonator 4, corresponding to the second new cavity, was successfully integrated into routine beam operation. During the 2026 shutdown, the LLRF and amplifier systems for Resonators 1 and 3, the original 50 MHz double-gap cavities, were replaced.
This contribution summarizes the latest progress of the PSI Injector 2 upgrade project, with particular emphasis on the technical and operational challenges associated with the high-power RF systems.

Speaker: Markus Schneider

CWRF2026_Status_INJ2_upgrade_Schneider.pdf

CWRF2026_Status_INJ2_upgrade_Schneider.pptx

46 Development and high-current operation of the high-power RF system for the High Energy Photon Source

The High Energy Photon Source (HEPS), recently commissioned in Beijing, is a 6 GeV diffraction-limited storage-ring light source. It utilizes a double-frequency RF system to provide the required beam energy and power, while also facilitating bunch lengthening. The RF system comprises five 166.6 MHz SRF cavities and two 499.8 MHz third-harmonic SRF cavities, all developed in-house. The system is driven by solid-state amplifiers with a total installed CW RF power of 2.4 MW and is controlled by in-house developed digital low-level RF systems. A multi-stage installation and commissioning procedure was carried out. The RF system achieved stable operation at a beam current exceeding 100 mA using the nominal RF configuration in fall 2025, and has been in operation for one year. The beam current is planned to be ramped to the design value of 200 mA in fall 2026. This represents the first large-scale deployment and operation of 100-kW-class solid-state amplifiers in China. The development and high-power operation of the RF system will be presented.

Speaker: Pei Zhang (Institute of High Energy Physics)

CWRF2026-HEPS-HPRF-PeiZhang-final.pdf

CWRF2026-HEPS-HPRF-PeiZhang-final.pptx

47 Construction and applications of the 352MHz Test Stand at ESS

Preparation for BOD1 (Beam on Dump1) phase started in 2024. Since that time, it has been sure, that we will not be able to use current systems for testing new components. At the beginning of 2024 decision was taken to make additional effort to build separate test-stand for 352 MHz – RFQ, DTL and Spoke new components or checking not fully operate using equipment.
In order to measure the RF components mentioned above, used in the normal conducting section of the accelerator, e.g. RFQ, DTL, as well as the superconducting section - SPOKE, a test stand was first designed and then built at ESS.
Part of the existing infrastructure and equipment from the accelerator's spare resources were adapted for the needs of the test-stand, which simplified the design and construction process, allowed for faster commissioning of the test-stand and significantly reduced costs.
The design of the test stand allows for the connection and testing of many types of auxiliary RF parts, but each of the components of the stand itself, which is in fact an almost exact copy of the existing ESS infrastructure, can also be replaced, thus allowing for the testing and verification of each element and its integration with the existing system, which increases the versatility of the test-stand and makes it essential for support and ensuring the continuity of the accelerator's operation.
The construction and use of the above-mentioned stand is a model example of cooperation between the RF and the Linac groups during its construction, adaptation, current and potential uses.

Speaker: Agnieszka Zwozniak (European Spallation Source)

3. CWRF2026_Zwozniak.pdf

18:00 Guided Historical City Tour in Lund

18:00 Guided tour in Kulturen Open Air Museum

18:00 Guided tour in Skissernas Art Museum

19:15 Social Dinner

Thursday 17 September

Welcome

Session 12

Convener: Bruno Lagoguez (European Spallation Source ERIC)

48 CEPC High efficiency RF power sources development

The Circular Electron Positron Collider (CEPC) requires approximately 60 MW of beam power, making the efficiency of RF power sources a key determinant of overall project cost‑effectiveness. High‑power, high‑efficiency klystrons are therefore highly attractive due to their superior performance compared to alternative RF amplifiers.

At the Institute of High Energy Physics (IHEP), a 650 MHz continuous‑wave (CW) high‑efficiency klystron prototype, completed in 2024, has demonstrated an output power of 803 kW with a peak efficiency of 78.5 %. In parallel, a multi‑beam klystron (MBK) designed to achieve efficiencies exceeding 80 % is currently under development and is scheduled for high‑power testing in 2026.

Furthermore, an energy‑recovery klystron (ERK) targeting an efficiency above 85 % is under fabrication and is expected to undergo high‑power testing by the end of 2026.

In addition, a very high‑efficiency, high‑power "tristron" concept was proposed in 2024. IHEP has initiated the development of grid assemblies and other key enabling technologies to support future prototype fabrication.

Speaker: Prof. Zusheng Zhou (Institute of High Energy Physics(IHEP))

CEPC High efficiency RF power sources development.pdf

49 Operation of the ALBA RF systems and installation of a new active harmonic RF system

ALBA is a 3rd generation 3 GeV synchrotron light source located in Barcelona, Spain. The RF system of the Storage Ring provides 3 MV of accelerating voltage with six 500 MHz HOM-damped cavities fed by two 80 kW IOTs each. The Booster RF system comprises a 50 kW SSPA and a 5 cell PETRA cavity. This contribution describes the performance of these systems and the upgrades performed in the last years. Also we describe the recently installed components of the new active 3rd harmonic system in the framework of the upgrade of ALBA towards a 4th generation synchrotron light source: ALBA II. The system consists of four 1.5 GHz HOM-damped cavities fed by a 20 kW SSPA. The installation of the cavities, waveguides and LLRF is now complete. The commissioning and operation of the whole system planned to start next year, once the SSPA are installed, are also presented.

Speaker: Jesús Ocampo

JOcampo ALBA CWRF 2026.pdf

JOcampo ALBA CWRF 2026.pptx

50 High Average Power RF Source Developments at Calabazas Creek Research

Research at Calabazas Creek Research, Inc. (CCR) is focusing on high efficiency, high average power, RF sources. Recent programs included a 10 kW CW, 1.3 GHz magnetron system with frequency and phase control, a 700 MHz, 200 kW CW multiple beam inductive output tube, and a 1 MW CW gyrotron at 110 GHz. These projects have been described in peer-reviewed publications and RF conferences and workshops. This presentation will describe two on-going research programs relevant to the accelerator community.

200 kW Multiple Beam Klystron:
CCR is funded by the U.S. Department of Energy to develop a 200 kW CW, S-Band, multiple beam klystron (MBK) for industrial and environmental applications. The design uses the Core Stabilization Method (CSM) to achieve efficiencies approaching or exceeding 80%. The design uses six beams driving eight coaxial cavities, including two second harmonic and one third harmonic cavities. Analysis codes included KlyC, TESLA, Beam Optics Analyzer, TRAK, HFSS, and ANSYS Thermomechanical. A particular challenge is cooling the output cavity, where 12 kW of thermal power must be dissipated. Details of the design will be described.

200 kW Multiple Beam Power Grid Tube RF Sources
CCR began developing multiple beam power grid tubes to leverage their inherent high efficiency and extremely low cost for high average power applications. Single beam devices generate up to 25 kW of RF power at efficiencies approaching 90%. The power grid tube basically consists of a gridded electron gun driven by an RF input signal and an anode. The tube is surrounded by an output cavity to convert the beam power to RF power, similar to Class C operation. This provides high efficiency, similar to an IOT, but with relatively low gain, typically around 14 dB. Consequently, one must include the driver performance when comparing to other RF sources. Even so, the combined cost of driver and output tube is less than $1/watt, making them perhaps the lowest cost RF sources available. Another advantage is that only the beam line is under vacuum. It can be inserted into a multiplicity of output cavities operating at different frequencies. The output cavities operate at atmospheric pressure and can be mechanically assembled with fasteners. Mechanical tuning ranges can exceed 150 MHz.
strong text

Speaker: R. Lawrence Ives (Calabazas Creek Research, Inc.)

CWRF High Efficiency RF Sources at CCR.pdf

CWRF High Efficiency RF Sources at CCR.pptx

09:50 Break

Session 13

Convener: Alireza Nassiri

51 Commissioning of Standardized Solid-State Power Amplifiers for Particle Accelerators

This paper presents the installation and commissioning status of standardized solid-state power amplifiers (SSPAs) for the HIAF linac. All 36 SSPA cabinets and 103 transmission lines have been installed, with insertion losses below -0.02 dB. Commissioning results show that the RFQ front end operates stably at 56 kW CW and 98 kW pulse, supporting multi-species beam tuning. The QWR007 cryomodule achieved Epk > 28 MV/m for all cavities with 5 kW CW per channel. The new 162.5 MHz GaN-based SSPAs for HWR015 have passed factory tests and are under joint commissioning. Key issues such as phase-dependent reflection and measurement errors have been mitigated.

Speaker: zhengrong Wu

CWRF2026_finally(1).pdf

CWRF2026_finally(1).pptx

52 Progress on the High Power RF Systems for the Electron-Ion Collider

The Electron-Ion Collider (EIC) requires a diverse suite of high-power RF systems across the Acceleration Storage Rings and Electron Injectors to meet its performance goals for beam stability and luminosity. These RF systems, spanning frequencies from tens to hundreds of megahertz, support key functions including acceleration, bunching, bunch splitting, and synchrotron damping compensation. The progress and challenges of each system will be discussed. In particular, procurement is underway for two 591 MHz, 400 kW solid-state amplifiers that will enable high-power testing of the superconducting two-cell cavities planned for both the Hadron and Electron Storage Rings. Updates on this procurement effort, along with the associated test program, will be presented.

Speaker: Mark Hoffmann Wallner (Brookhaven National Laboratory)

Progress on the High Power RF Systems for the Electron-Ion Collider.pdf

Closing

11:35 Lunch

12:00 Departure with bus for Grimeton. Return 17.00 from Grimeton, back to Lund. Lunchbag from Stadshallen to bring at the bus

Return 17.00 from Grimeton, back to Lund
Lunchbag from Stadshallen to bring at the bus