Fifth CW and High Average Power RF Workshop

Mar 24, 2008, 7:00 PM → Mar 28, 2008, 6:00 PM Europe/Zurich

40-S2-C01 (CERN)

Daniel Valuch (CERN), Doug Horan (Argonne National Laboratory)

The Fifth CW and High Average Power RF Workshop will be held at CERN, Geneva, Switzerland, March 25 - 28, 2008. The goal of this workshop is to share experiences among designers and users of CW and high average power RF systems that utilize high-power klystrons, gridded tubes, combined solid-state architectures, high-voltage power supplies, high-voltage modulators, power couplers and tuners. New ideas for high-power RF system upgrades and novel ways of RF power generation and distribution will also be discussed.

Tuesday, March 25

8:30 AM → 9:45 AM Registration

9:45 AM → 10:00 AM Welcome

slides CWRF08_welcome.pdf CWRF08_welcome.ppt

10:00 AM → 12:30 PM Tuesday morning

4 talks, lab talks

10:00 AM LHC RF system

Design, parameters, building, commissioning, performance, controls. Longer talk (60 min).

Speaker: Mr Luca Arnaudon (CERN)

Slides Arnaudon_CWRF08.pdf Arnaudon_CWRF08.ppt

10:30 AM LHC superconducting cavities

Design, conditioning, experience, performance

Speaker: Mr Pierre Maesen (CERN)

Slides

• Maesen_ppt2003.pdf
• Maesen_ppt2003.ppt
• Maesen_ppt2008.pdf
• Maesen_ppt2008.pptx

11:00 AM break

11:15 AM Status of the Advanced Photon Source (APS) Radio Frequency System*

A. Nassiri, D. Bromberek, D. Horan,G. Trento The Advanced Photon Source, Argonne National Laboratory 9700 S Cass Ave, Argonne, Illinois 60439 U.S.A E-Mail: nassiri@aps.anl.gov

Speaker: Dr Alireza Nassiri (Argonne National Laboratory - DOE)

Slides Nassiri_APS_RFSystems-final.pdf

11:45 AM CW Operation of the Superconducting LINAC "ELBE"

H.Buettig, A.Arnold, A.Buechner, F.Gabriel, M.Justus, U.Lehnert, P. Michel, C.Schneider, R.Schurig, G.Staats, J.Teichert, Abstract: The superconducting CW-LINAC of the Radiation Source ELBE, based on 1.3 GHz-TESLA cavities, has been operational since 2001. An overview of the ELBE facility and of the RF-system of the superconducting CW-LINAC are presented. It is reported on different improvements on RF components to ensure stable operation of this user facility and on experience gathered during 7 years of CW- operation.

Speaker: Hartmut Büttig (Research center Dresden-Rossendorf (FZD))

Slides CWRF2008_HB.pdf CWRF2008_HB.ppt

12:30 PM → 2:00 PM Lunch

2:00 PM → 6:25 PM Tuesday afternoon

6 talks

2:00 PM Performance Of the Advanced Photon Source 350-MHz 1MW CW Klystrons

The Advanced Photon Source (APS) utilizes five 350-MHz/1MW CW klystrons to supply rf power to a 7GeV Booster-Synchrotron and Storage Ring. The performance of these klystrons during the last two years of APS operation will be discussed, along with troubleshooting techniques used to identify klystron-related problerms that interfere with accelerator operation.

Speaker: Mr Doug Horan (Argonne National Laboratory)

Slides CWRF08_350MHz_Klystron_Performance_Horan.pdf CWRF08_350MHz_Klystron_Performance_Horan.ppt

2:40 PM CERN SPS 200MHz/4MW tetrode power amplifier

CERN SPS 200MHz power amplifier, 4x1MW, tetrodes 125kW, tetrodes 35kW, long time (25yr) operation statistics, experience...

Speaker: Mr Eric Montesinos (CERN)

Slides CWRF2008_v18.pdf CWRF2008_v18.ppt

3:20 PM Implementation of new 352 MHz RF amplifiers and cavities in the frame of a general upgrade of the ESRF

A ten year upgrade programme has been set up at the ESRF to enhance its scientific capabilities for new research by renewing X-ray beam lines, their instrumentation and the X-ray source. As part of this programme, the photon flux and brilliance of the source will be increased by means of longer insertion device straight sections, a higher electron beam current, a reduced vertical emittance and the implementation of top up mode for few bunch fillings. A higher photon beam stability and an enhanced durability of the accelerator complex are further objectives of the source upgrade. New HOM damped RF cavities are being developed to replace the existing five-cell cavities. They will allow to increase the stored current from 200 to 300 mA without active stabilization of HOM driven longitudinal multibunch instabilities. In order to sustain the increased RF power of about 2 MW and to maintain or even improve the operation reliability, also the RF transmitters will be refurbished. Different solutions have been investigated, including additional higher power klystron transmitters, new medium power klystrons, IOTs and solid state amplifiers. The best choice for the ESRF upgrade will be discussed at the workshop.

Speakers: Mr Jean-Maurice MERCIER (ESRF), Dr Jörn JACOB (ESRF)

Slides

• JJ_CWRF_2008.pdf
• JJ_CWRF_2008.ppt
• Mercier_CWRF2008.pdf
• Mercier_CWRF2008.ppt

4:00 PM break

4:15 PM Operational experience with the SOLEIL 352 MHz RF systems

The 352 MHz RF accelerating systems for the SOLEIL booster and storage ring are in operation since mid 2006. In the booster, a 5-cell copper cavity of the CERN-LEP type is powered with a 35 kW solid state amplifier. In the storage ring, the required RF accelerating voltage (up to 4.4 MV) and power (560 kW at full beam current of 500 mA) will be provided by two cryomodules, each containing a pair of superconducting cavities, specifically designed for SOLEIL. The parasitic impedances of the high order modes are strongly attenuated by means of four coaxial couplers, located on the tube connecting the two cavities. The first cryomodule is operating on the ring, while the second one, which is under fabrication, should be implemented in August 2008. Both cryomodules are cooled at 4.2 K with liquid helium from a single 350 W liquefier and each cavity is powered by a 190 kW solid state amplifier. Using a single cryomodule and two amplifiers, the first objective of storing 300 mA stable beam was successfully achieved in 2006 and operated routinely in 2007. The operational experience with the different parts of the equipment is reviewed, after more than one year of running.

Speaker: Mr Patrick Marchand (SOLEIL synchrotron)

Slides Marchand_CWRF2008.pdf Marchand_CWRF2008.ppt

4:35 PM High Power Solid state amplifiers for the SOLEIL Synchrotron

In SOLEIL, 5 solid state amplifiers provide the required RF power at 352 MHz : 1 x 35 kW for the booster cavity and 4 x 190 kW for the 4 superconducting cavities of the storage ring. Based on a design fully developed in house, they consist in a combination of a large number of 330 W elementary modules (1 x 147 in the booster and 4 x 724 in the storage ring) with MOSFET transistors, integrated circulators and individual power supplies. Although quite innovative and challenging for the required power range, this technology is very attractive and presents significant advantages as compared to the more conventional vacuum tubes, klystrons or IOTs. The booster and two of the storage ring power plants have been successfully commissioned and the first operational experience is quite satisfactory. The amplifiers proved to be very reliable as well as easy and flexible in operation. The commissioning of the two other amplifiers on the second cryomodule is scheduled for August 2008.

Speaker: Mr Ti Ruan (SOLEIL)

Slides CWRFA08b.pdf CWRFA08b.ppt

4:55 PM 500MHz Solid State Power Amplifier Development at PSI - Preliminary Results

We present a progress report about the commissioning and construction of our first 4.5KW Solid State Power Amplifier Prototype. We show how the expansion up to much higher power will be made based in our modular approach. A brief description of the design and performance of the basic components and some preliminary results will also be presented.

Speaker: Mr marcos gaspar (Paul Scherrer Institut)

Slides 500MHz_Solid_State_amplifier_5TH_CWRF_Cern_1.0.pdf 500MHz_Solid_State_amplifier_5TH_CWRF_Cern_1.0.ppt

5:35 PM RF Power improvement of AlGaN/GaN based HFETs and MOSHFETs

High Power and high temperature electronics applications is one of the reasons for the enormous effort and progress which has been made in the development of III-nitride semiconductor material. A lot of investigations were done with regard to DC/RF dispersion since it influences the RF-performance of devices extremely. Significant performance improvement was achieved by application of a passivation layer on conventional AlGaN/GaN based HFETs. In a second step the introduction of a thin insulation layer underneath the gate to reduce the gate leakage current leads to the MISHFET or MOSHFET.

Speaker: Mr Alfred Fox (Research Center Juelich)

Slides A_Fox_CWRF2008.pdf A_Fox_CWRF2008.ppt

6:15 PM → 7:15 PM Working group 1

Solid State RF PA. Practicality, Cost, Potentials, Feasibility, Trend and Outlook

slides Workgroup_SSPA_5TH_CWRF_Cern_1.0.pdf Workgroup_SSPA_5TH_CWRF_Cern_1.0.ppt

7:15 PM → 8:15 PM Welcome drink

Wednesday, March 26

8:00 AM → 12:30 PM CERN visits

12:30 PM → 2:00 PM Lunch

2:00 PM → 6:55 PM Wednesday afternoon

2:00 PM RF Systems for NSLS-II

The NSLS-II is a new 3rd generation light source being designed at Brookhaven. A key design feature is a large circumference with soft (25m radius) bends which enable damping wigglers to reduce the emittance from 2.1nm-rad to <1nm-rad. The RF power requirement is dominated by the wiggler radiation, and the storage ring RF system is installed in stages as damping wigglers are added. The booster RF requirement of 60kW-80kW is well matched to an IOT amplifier, and klystron amplifiers have been selected in the project baseline to provide the 300kW per storage ring system, staged in from 1 to 4 systems. Alternate approaches to provide the RF power such as a solid state amplifier for the booster and either solid state or combined IOT's for the ring systems are being explored and will be discussed.

Speaker: Mr James Rose (Brookhaven)

Slides Rose_CWRF08.pdf Rose_CWRF08.ppt

2:40 PM Elettra RF System Upgrade: Commissioning and Operation of the 500 MHz 150 kW Plant

The first phase of the upgrade of the RF System of Elettra is completed. The 500 MHz 150 kW cw plant has been installed and is in operation on the machine. The 150 kW amplifier is based on the combination of two 80 kW IOTs. After a recall of the targets of the project, this presentation gives a review of the performances of the system and reports on the experience during the commissioning and operation of the new plant.

Speaker: Dr Alessandro Fabris (Sincrotrone Trieste)

Slides CWRF08_Elettra.pdf CWRF08_Elettra.ppt

3:20 PM Vector Control Algorithm for Efficient Fan-Out RF Distribution *

A fan-out power distribution algorithm with RF vector control using reactive transmission line circuit parameters for maximum power efficiency is presented. If a fixed power splitting system with individual cavity voltage control at each cavity input is used, the power efficiency becomes lower since the RF power source must deliver more power than needed by cavities. The proposed fan-out power distribution system is considered valuable for large scale SRF accelerator systems to save costs in construction and operation. In this fan-out system, feeding multiple accelerating cavities with a single RF power generator can be accomplished by adjusting phase delays between the load cavities and reactive loads at the cavity inputs for independent vector control of cavity RF voltages. A set of RF control parameters is determined for a whole fan-out system to deliver a set of required cavity RF voltage vectors. The reactive loadings and phase shifts can be realized using high power RF phase shifters. *This work was supported by SNS through UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U.S. DOE.

Speaker: Dr Yoon Kang (Oak Ridge National Laboratory)

Slides Kang_vector_control_algorithm.pdf Kang_vector_control_algorithm.ppt

4:00 PM Coffee break

4:15 PM ALBA RF amplifier system based on Inductive Output Tubes (IOT)

The ALBA RF accelerating cavities are powered up to 150 kW cw at 500 MHz. This power is obtained by combining the power from two 80 kW IOTs with a cavity combiner (CaCo). CaCo is a new development, designed and built in close cooperation between CELLS and Thales Electron Devices (TED). Thomson Broadcast & Multimedia (TBM) designed the amplifier system including the power supplies and local control system. During the system design phase for the sake of operational power margin, TED, TBM and CELLS agreed to develop a ruggedized IOT version, based on the standard IOT (TH 793) which is rated for maximum power of 80kW cw. The new IOT version, TH 793-1, dedicated for scientific applications demonstrated cw operation up to 90 kW at 500 MHz, giving more power flexibility and the highest quality of service for the ALBA operating conditions. To keep additional reliability margin, it has been specified for 85kW cw. Technologies used in TH793-1 open the door for higher power in the future. In association with the new IOT version, a TH18973 LS (Light Source) cavity has also been developed in order to evolve from broadcast wideband operation to single frequency. The new TH18973 LS features a 6”1/8 coaxial RF output, an optimized cooling system and allows for centred operation at 500 MHz with 7 MHz instantaneous bandwidth and +/- 5 MHz tuning capabilities. In parallel to the IOT design work TBM developed a new amplifier system for this application. The amplifier was developed to achieve a high reliability and performance. Each IOT is powered by an individual power supply based on the Thomson Pulse Step Modulator (PSM) technology. The amplifier control system was designed based on a PLC controller with the possibility to interface with the Tango system used for the accelerator control. The first amplifier system was delivered to ALBA in summer 2007 and was placed in the RF test hall and is already in use for the conditioning and testing of the first accelerator cavity. The remaining 13 amplifier systems will be delivered in summer 2008. This presentation is giving an overview on the system design and the operation performance as measured during commissioning and cavity testing.

Speaker: Mr Paco Sanchez (CELLS)

Slides ALBA_Sanchez.pdf ALBA_Sanchez.ppt

4:55 PM LHC RF Embedded SC Cavity Conditioning System

The LHC RF system consists of 16 supra-conductive cavities each individually driven by a 300kW klystron with its associated cavity controller electronics modules. The cavity conditioning system has been embedded in the cavity controller by addition of an independent VME controlled DDS based, versatile dual FM signal generator. The combined generator outputs are gain controlled and interlocked through an onboard failsafe digital vacuum level driven RF attenuator and an FPGA controlled RF VGA. The FPGA can create RF pulses with programmable width and strength at a 50Hz rate through the VGA control. The cavity controller software implements the conditioning mode by connecting the conditioning DDS output to the klystron RF pre-driver, setting up of the conditioning DDS module’s parameters and switching the Tuner Loop module to conditioning mode. In this mode the tuner loop module is able to maintain the cavity on tune even with the RF signal being pulsed and swept in frequency. At the same time the tuner loop acquisitions allow the software to measure the amount of RF power delivered to and the E-field created in the cavity during the RF pulses. The software running in the front-end CPU is synchronized with the process through IRQs generated by the conditioning DDS module. A labview application has been created that allows control and supervision of the entire process through a user-friendly graphical interface.

Speaker: Mr John Molendijk (CERN)

Slides Molendijk_CWRF08.ppt.pdf Molendijk_CWRF08.ppt.ppt

5:35 PM Vacuum Electron Device Limitations for High Power RF Sources

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Speaker: Mr Thomas Grant (Communication and Power Industires)

Slides CWRF2008numbered.pdf CWRF2008numbered.ppt

6:15 PM → 11:15 PM Workshop dinner

Teaser Workshop_dinner.pdf Workshop_dinner.ppt

Thursday, March 27

8:00 AM → 12:30 PM Thales visit

12:30 PM → 2:00 PM Lunch

2:00 PM → 7:35 PM Thursday afternoon

2:00 PM Status of the RF-system for the proton accelerator facility at PSI

PSI's proton accelerator facility currently produces a 1.2 MW beam. The extraction energy of the Ring cyclotron is 590 MeV and the beam current is 2 mA. It is planned to increase the beam current to 3 mA requiring several upgrades of the RF-system. The replacement of the 4 aluminum cavities in the ring cyclotron by copper cavities is a milestone in this program. The last 2 cavities have been installed recently during shutdown 2008. Beam dynamics calculations show that the flattop cavity in the ring cyclotron can eventually be replaced by introducing a buncher in the beamline between injector 2 and the ring. This buncher will be driven by a 506 MHz / 30 kW amplifier. First test results of this system will be presented. At the Injector 2 cyclotron it is planned to replace the flattop cavities (150 MHz) by accelerating cavities (50 MHz). This will allow to increase the turn separation at extraction with lower beam losses. Due to the fact of changing the resonance frequency of the cavities new amplifier chains have to be built. An overview of the new system will be given.

Speaker: Mr Markus Schneider (Paul Scherrer Institut)

Slides CWRF2008_Schneider.pdf CWRF2008_Schneider.ppt

2:40 PM PSI-XFEL RF-System

The X-ray Free Electron Laser (XFEL) is a new development in laser and accelerator-technology intended to introduce the excellent characteristics of conventional laser systems into the x-ray spectral region. The XFEL is labeled the next or 4th generation light source after the current state of the art 3rd generation light source like the Swiss Light Source (SLS). The commissioning of the High Voltage Pulser started in September 2007. The Pulser will accelerate the electrons emitted from a photocathode or a field emitter across a gap to the energy of 500 keV. In phase 1 the generation of electrons is done by photoemission with a laser. In phase 2 which already started, the installation of a 1.5 GHz two-cell cavity and an upgrade of the Pulser from 500KV to 1.MV is planned. The Modulator for the 1.5 GHz / 20MW System is installed and tested with the klystron in diode-mode. Further we plan to replace the two-cell cavity with a two-frequency standing wave cavity which works at 1.5 GHz and 4.5 GHz simultaneously. A second modulator to supply the 4.5 GHz at 4 MW has already been ordered. The concept of the RF-System for the XFEL and an overview of the current state at the test stand will be presented.

Speaker: Mr Christian Geiselhart (Paul Scherrer Institut)

Slides CWRF08_Geiselhart.pdf CWRF08_Geiselhart.ppt

3:20 PM 1MW/200MHz CW Source for IFMIF

Speaker: Prof. Richard Carter

Slides Carter_IFMIF_RF_Power_Source.pdf Carter_IFMIF_RF_Power_Source.ppt

4:00 PM Coffe break

4:15 PM High-Power Testing of a Normal-Conducting Single-Cell RF Cavity Utilizing Two Input Couplers

High-power tests were conducted on a normal-conducting single-cell copper rf cavity fitted with two H-loop input couplers in order to determine the capability of the cavity system to operate reliably at 200kW CW total input power. The Advanced Photon Source 350-MHz RF Test Stand was utilized to conduct the tests. Performance data and highlights of the conditioning process leading to sustained 200kW CW operation will be presented.

Speaker: Mr Doug Horan (Argonne National Laboratory)

Slides CWRF08_Two_Coupler_Test_Horan.pdf CWRF08_Two_Coupler_Test_Horan.ppt

4:55 PM New generations of RF amplifiers: from gridded tubes to dual technology solutions

The aim of the present paper is to show that new generations of RF amplifiers do exist with different technologies. Thales has a very long experience in gridded tubes and klystrons for science and broadcast applications as well as solid state solutions for broadcast applications. This experience in both technologies has been applied to RF amplifiers in order to take benefit of these different technologies for high power requirements Vacuum electron devices and solid state technologies should not be taken as two opposite options, or the old and the new ones, or the low and high power ones but as two technologies that have to be considered together to derive the best solutions for a defined requirement. As far as gridded tubes are concerned, the main evolution in that technology has been the Diacrode concept. In order to avoid the power limitation of conventional gridded tubes due to RF losses, Diacrodes do use folded grids. This option has been proven for TV broadcast over the years and for some specific science and industrial applications. The knowledge of both klystron and gridded tube technologies has allowed to derive the Inductive Output Tubes (IOT). After being extensively used for TV broadcast (in a pulse mode, in a certain sense), it has been installed in cw operation scientific systems for years now. The need for distributed sources in synchrotrons has increased the number of possible IOT installations (Elettra, Diamond, Boomerang or Alba). Examples at 500 MHz, 800 MHz and 1300 MHz are presented. Solid State Device (SSD) solutions do present some very interesting features but also some drawbacks that need to be taken into account, especially for systems that will operate for several decades. SSD are based on the use of single transistors: their single power capability is the prime parameter to derive high power amplifiers. Evolutions of SSD will be shown. These different technologies, gridded tube, Diacrode, klystron, IOT and SSD should be considered as building blocks that can be combined in order to fulfill a defined need. Examples of such combinations are shown and discussed.

Speaker: Mr Michel Caplot (Thales Electron Devices)

Slides Caplot_CWRF08.pdf Caplot_CWRF08.ppt

5:35 PM Development, Processing, and Installation of RFQ Input Power Coupling System*

A new RF coupling system for the RFQ structure in the SNS linac front-end has been developed for upgrade of input power coupling to the RFQ. The coupling system employs two coaxial loop couplers for 402.5 MHz operation; the two couplers are used in parallel to power the accelerating structure with up to 800 kW total peak power at up to 7% duty cycle. Each coupler has a coupling loop through a coaxial ceramic window that is connected through a coaxial to waveguide transition to each output of a magic-T waveguide hybrid splitter. The coaxial loop couplers have been designed, manufactured, and high power processed. The cavity structure is retuned for the installation of new coupling system. This paper presents the followings: RF and mechanical designs of the couplers and the coupling system, procedure and result of high power RF conditioning, and installation, test, and operation results of the upgrade. * This work was supported by SNS through UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U.S. Department of Energy.

Speaker: Dr Yoon Kang (Oak Ridge National Laboratory)

Slides Yoon_Kang_Thursday_RFQ_Coupler.pdf

6:15 PM Upgrades at Jefferson Lab

The design of High Power Amplifiers for an energy upgrade to 12 GeV is underway at Jefferson Lab. Eighty 13 kW 1.497 GHz amplifiers with required power supplies and waveguide components will be added to the existing accelerator, expanding on the 340 5 kW sockets. Klystrons and IOTs are being considered, with each having advantages and disadvantages. While JLab’s 340 5 kW klystrons have proven reliable over the past 18 years, the device’s overall efficiency is low. With energy deregulation and subsequent increasing costs, options to reduce energy consumption were evaluated. Changes to operating modes and replacement of the present klystron with a higher efficiency device were considered. To be cost effective, any replacement klystron or IOT would need to be priced right and be adaptable to the existing hardware with minimal modifications to existing equipment. The outcome is that no changes are planned at this time.

Speaker: Mr Richard Nelson (Thomas Jefferson National Accelerator Facility)

Slides Nelson-CWRF08-JLab_Updates.pdf Nelson-CWRF08-JLab_Updates.ppt

6:55 PM Development of a High Power Test System for New Power Grid Tubes for 200 MHz

A new high power 201.25 MHz RF system is being developed for the Los Alamos Neutron Science Center (LANSCE) proton drift tube linac (DTL). A planned upgrade will replace parts of the DTL RF system with new-generation components. When installed for the LANSCE-R project, the new system will reduce the total quantity of gridded power tubes from twenty-four to eight in the RF powerplant. The 3 MW final power amplifier will use a Thales TH628 Diacrode ?. This high-average power device eliminates the large anode modulator of the present LANSCE triode RF system. It will be driven by a new tetrode intermediate power amplifier. For the largest DTL tank, a pair of TH628 power amplifiers will be combined to provide additional peak power capability. A prototype system is being constructed to test components, using some of the infrastructure from previous high power RF projects at Los Alamos. High voltage DC power became available through innovative re-engineering of a LEDA klystron beam power supply. A summary of the design and construction of the power amplifiers, power supplies, and overall test setup and results will be presented.

Speaker: Mr John, T. M. Lyles (LANL)

Slides Lyles.pdf Lyles.ppt

7:35 PM → 8:35 PM Working group 2

Clean RF power. High voltage switching PS, RF phase noise, impact on beam lifetime.

slides CWRF08_WG2__Clean_RF_Power_Horan.pdf CWRF08_WG2__Clean_RF_Power_Horan.ppt

slides LHC_Polar_loop.ppt

slides Tuckmantel_CWRF08.pdf

Friday, March 28

9:00 AM → 12:40 PM Friday morning

9:00 AM High power, wideband, solid-state amplifiers for LEIR and J-PARC RF systems.

Starting from a basic 120 W building block covering the frequency range 0.1-80 MHz, amplifiers with power levels ranging from 1 kW to 9 kW have been designed at CERN for LEIR and J-PARK Rapid Cycling Synchrotron and Main Ring RF systems. About 1000 basic 120 W modules have been built and are now in operation. The design options, splitting and combining techniques, powering, cooling and servicing choices will be discussed. A short discussion will also be dedicated to ultra-wideband couplers/splitters.

Speaker: Mr Mauro Paoluzzi (CERN)

Slides Paoluzzi_Solid-state_amplifiers.pdf

9:40 AM RF Tests of Chemical Additives for Water Cooled RF Loads

This paper discusses the RF performance of high power RF water loads at 201.25 MHz for the LANSCE RF system using chemical additives to ionize the cooling water. RF loads at 201.25 MHz that dissipate the RF power directly into the water usually use some kind of additive to increase the number of free ions in the water and thus, increasing the RF absorption. Presently cooling water from a cooling tower is used in our 201.25 MHz load. The additional ions are obtained as the water passes through the evaporative cooling tower and is exposed to the outside elements. This water works well as an RF absorber, but it is very dirty and builds up a sludge in the water system that requires a cleaning every two years. The cleanings are time consuming and cleaning abrasives can potentially damage the components. In addition, a water glycol mixture has been historically used in loads, but this mixture can be difficult to dispose of because of environmental requirements. Two chemical additives, Corrshield MD401, made by GE, and West C-441, made by West, Inc, were tested in a high power RF water load at 201.25 MHz. The Corrshield MD 401 is the American equivalent to the European available Corrshield MD4151, tested by Ebert and Ullrich at DESY. It is a sodium molybdate based chemical used for corrosion protection in water systems. West C-441 is a sodium nitrate based chemical, that was developed by WEST, Inc for our specific application. Both of these chemicals are more environmentally friendly and easier to dispose of than options such as a water glycol mixture and do not create buildup problems like the cooling tower water. The RF performance was characterized by measuring the match of the RF load. This paper summarizes the low power test results of the two chemical additives.

Speaker: Dr Karen Young (LANL)

Slides Young_Chemical_Additives.pdf Young_Chemical_Additives.ppt

10:20 AM New IPA Design for 500 MeV TRIUMF Cyclotron

A new intermediate power amplifier (IPA) is currently being designed to improve the reliability of the main rf system of the 500 MeV Cyclotron at TRIUMF. A four-way matching pi-network circuit divides the power output from the present 100 KW IPA which drives four power amplifiers to produce 1 MW of rf power. Poor isolation between the four outputs makes it difficult to tune the power amplifiers. This deficiency can be overcome by using four independent 25 KW IPA. This paper describes design of such a 23 MHz 25 KW CW amplifier using EIMAC 4CW25000A tetrode. EIMAC tube performance computer has been used to establish the dc and rf parameters of the amplifier. As an alternate to the EIMAC performance calculation, accurate model in SPICE was investigated. The advantage of the SPICE model is that the circuit elements and inputs can be modified easily and the results can be seen in the simulation almost immediately. SPICE Subcircuit Architecture was developed to model the tube’s constant current curves. The results from PSPICE and EIMAC tube performance are presented. The output cavity of the amplifier is 23 MHz quarter wave resonator. Ansoft HFSS has been used to simulate the output cavity and compute shunt impedance and Q of the cavity and also design the coupling loop and the tuning elements for frequency tuning. Solid Works and HFSS helped to optimize both mechanical and electromagnetic design of the output cavity. Input circuit and neutralization of the amplifier are also discussed here. Prototype design of output cavity provides three alternative frequency tuning elements: movable shorting plate, vacuum variable capacitor and passive rotating tuning loop. Final option for output cavity frequency tuning will be defined after the tests. HFSS has also being used to compute parasitic modes of the amplifier.

Speaker: Mr amiya mitra (TRIUMF)

Slides Mitra_IPA_Presentation_for_CWRF08.pdf Mitra_IPA_Presentation_for_CWRF08.ppt

11:00 AM Coffee break

11:15 AM CEA-Saclay high voltage modulator for pulsed klystrons

The need for new RF power sources operating at different frequencies implies to develop HV sources to match their specifications. Two pulsed klystrons are employed at Saclay Supratech platform for R&D on superconducting accelerating cavities at 704MHz and 1300MHz and for 704MHz power couplers processing. A hard tube modulator that was at first developed for the 1300MHz klystron operation has been modified to generate the HV pulses shapes for a second klystron at 704MHz. The goals were to enable the use of a floating HVPS three times more powerful instead of the single ended old one, to increase the duty cycle by a factor of five, and to improve the mechanical aspect in order to simplify the remove of the electronics from the oil tank. The modulator, electronics and mechanicals, modifications are described. The first results of the HV measurements performed on the 704MHz klystron and measurements performed on the 1300MHz klystron will be presented.

Speaker: Mr Abdallah HAMDI (CEA/Saclay)

Slides Hamdi_cea.pdf Hamdi_cea.ppt

11:55 AM Update of Operating Experience and Reliability of Klystrons at Jefferson Lab

This talk is an update of the operating experiences and reliabilty of over 350 klystrons at Jefferson Lab over the past 15 years. We experienced a serious failure mode in the klystron, but were able to indentify the causes and find good solutions to these problems. Analysis and pictures will be shown to demonstrate the problems. Reliability data will be given on the results of the changes that were made to improve the reliability of these klystrons.

Speaker: Richard Walker (Jefferson Lab)

Slides Walker-CWRF08-Klystron_Update.pdf Walker-CWRF08-Klystron_Update.ppt

12:35 PM Short session on "Development of power amplifier modules for the ACOL stochastic cooling systems"

Speaker: Dr Fritz Caspers

Slides CERN_85-10__Caspers.pdf

12:35 PM → 2:00 PM Lunch

2:00 PM → 5:30 PM Friday afternoon

2:00 PM Resonant Ring Test Bench for Warm Window and Coupler Tests at ELBE.

Resonant Ring Test Bench for Warm Window and Coupler Tests at ELBE. G. Staats, A. Buechner, H. Buettig, P. Michel, R. Schurig, J. Teichert, A. Winter A new coupler test bench based on a resonant ring has been built at ELBE in Dresden-Rossendorf to run warm window as well as coupler tests with RF power up to 190 kW (warm window tests up to 250kW) in CW operation. The ring is driven by a 10 kW klystron. This test bench also includes liquid nitrogen cooling of the ceramic cold window of the RF-coupler which allows testing under almost real conditions. A special waveguide to coupler transition was designed to match couplers with different antenna tips. At the beginning with the test bench it was possible to test the warm windows used at ELBE. It has been shown that the used warm windows are usable up to 70kW of CW-RF power with additional air cooling, much more than the 10kW CW used at ELBE. After this test the coupler used at the ELBE cryomodules was tested, in CW operation a power level of about 20kW was reached. More tests are in program and in near future some improvements are planned.

Speaker: Dr Gerald Staats (Forschungszentrum Dresden-Rossendorf)

Slides cwrf2008_testbench_final.pdf cwrf2008_testbench_final.ppt

2:40 PM Development of Solid State Long Pulse Klystron Modulators

Development of Solid State Long Pulse Klystron Modulators Framework and report on the first prototype

Speaker: Mr Carlos DE ALMEIDA MARTINS (CERN)

Slides Martins_SolidStateKlystronModulators_CWRF08.pdf Martins_SolidStateKlystronModulators_CWRF08.ppt

3:20 PM Improved Operation of TRIUMF ISAC RFQ

The TRIUMF ISAC radioactive ion beam facility has been in operation since 2001. The room temperature linear accelerator comprises sixteen independent rf systems and RFQ is the first major system which was installed. The 35 MHz RFQ is designed to accelerate ions of A/q up to 30 from 2 keV/u to 150 keV/u in cw mode. The RFQ structure is 8 meters long and the vane-shaped rods are supported by 19 rings spaced 40 cm apart. The maximum operating inter-vane voltage is 74 kV, which requires 85 kW from the power amplifier. The power amplifier is capable of 150 kW of peak power for pulse rf conditioning. In order to improve reliability of beam delivery and reduce downtime due to rf devices, many improvements have been implemented to the rf amplifiers. In particular, RFQ amplifier has undergone major upgrades over last few years. Dedicated ramping circuit for smooth start up of the HV power supply has made it more reliable. Improved crowbar trigger circuit using two high power SCR has been installed which has made high power conditioning of the RFQ tank lot more easier. A new monitoring system for all relevant parameters of all ISAC-I rf amplifiers was designed and implemented. It consists of a Modicon Momentum PLC system and distributed Advantys I/O system. EPICS interface was established so as to operate and run the rf amplifiers from main control room over PLC interface. During the 2008 Spring Shutdown, new signal samples were added to the RFQ amplifier monitoring, and interface wiring was modified to incorporate this new PLC system. The updated system is undergoing rigorous test. The RFQ tank also went through major repair work. The RFQ vacuum deteriorated from 2*10-7 to 2.7*10-6 between 2003 and 2006 due to small water leaks inside the RFQ tank. The tank was opened and two rings were replaced with identical spare rings. Also water leaks in the supply and return lines were plugged. A cryo pump was installed which improved the vacuum to 1.5*10-7 Torr at full RF power.

Speaker: Mr Zheng Ting Ang (TRIUMF)

Slides CWRF2008-CERN.pdf CWRF2008-CERN.ppt

4:00 PM Coffee break

4:15 PM Workshop summary

Slides CWRF08_summary.pdf CWRF08_summary.ppt