10th International Workshop on the Mechanisms of Vacuum Arcs (Hybrid MeVArc 2022)

Session

Experiments & Diagnostics

19 Sept 2022, 09:30

Chania, Crete

Conveners

Experiments & Diagnostics: Dislocation dynamics & Cryogenics

• Walter Wuensch (CERN)

Experiments & Diagnostics: Accelerators

• Sergio Calatroni (CERN)

Experiments & Diagnostics: DC Systems

• Antonio De Lorenzi (Consorzio RFX)

38. Observations of dislocations in Soft Cu samples exposed to high fields

Yinon Ashkenazy (The Hebrew University of Jerusalem (IL))

19/09/2022, 09:30

Experiments

Oral

It was proposed that breakdown nucleation can be explained as emanating from surface plastic activity due to collective dislocation dynamics within the surface layer of samples exposed to high electric fields. In the past, we have demonstrated that extensive mobile dislocation structures are routinely observed in soft large-grained OFHC copper. However, as of this day we are missing a clear...

43. Dislocation structures of Cu electrodes exposed to high fields

Inna Popov

19/09/2022, 10:00

Experiments

Oral

It was suggested that breakdown might result from collective dislocation effects within a surface of metal electrodes exposed to high electric fields. We applied scanning and transmission electron microscopy to check this assumption. In this talk, I present a picture of the lattice structural defects observed in soft and hard Cu – dislocation dipoles, stacking faults, twins, and grain boundaries.

17. Performance of electrical vacuum breakdown under cryogenic temperatures

Iaroslava Profatilova

19/09/2022, 10:30

Experiments

Oral

The cryogenic high-voltage pulsed DC system in FREIA laboratory continues the test series of copper electrodes to establish peculiarities of BDs craters occurred at low temperature down to 4K.
The system uses parallel plate 40 mm diameter anode and 62 mm diameter cathode with a tens micrometers inter-electrode space. 1 µs high-voltage rectangular dc pulses with a repetition rate up to 1 kHz...

5. Update on High-Field Research Activities at CERN

Mr Lee Millar (CERN)

19/09/2022, 16:00

Experiments

Oral

Alongside the numerous operational accelerators on the CERN site, several radio frequency (RF) and DC test facilities have been established to support the development of novel prototypes and investigate high-field phenomena. In these facilities, copper RF cavities are regularly operated at surface electric fields in excess of 200MV/m while DC electrodes of various materials have been tested to...

45. Application of Machine Learning to Breakdown Prediction in CERN’s High-Gradient Test Stands

Christoph Obermair (Graz University of Technology (AT))

19/09/2022, 16:30

Experiments

Oral

CERN has established several high-power RF test stands, to investigate high-field phenomena. Recently, a machine learning framework has been developed and applied to the high-gradient cavity test data from these facilities. The aim has been to search for the existence of previously unrecognized features related to the incidence of RF breakdowns. Preliminary results have shown two key features...

42. Status of High-Power Testing of X-band Parallel Feed Nb Accelerating Structures

Mitchell Schneider (SLAC National Accelerator Laboratory)

19/09/2022, 17:00

Experiments

Oral

This talk will present the status for developing high gradient X-band bulk niobium accelerating cavities. We optimized the cavity design to maximize the shunt impedance and reduce the peak surface magnetic fields. This means that a much higher gradient can be produced for the same quench field limit of niobium (230 mT), increasing the power loss to gradient2 ratio > 100 [mWm/(MV)^2]. We...

9. Recent results from the CERN pulsed DC systems

Ruth Peacock (Lancaster University (GB))

20/09/2022, 11:00

Experiments

Oral

There have been several pulsed DC system experiments ongoing including recent measurements of field emission current fluctuations associated with dislocation motion showing a variation in the number of events per pulse and a dependence on breakdowns. Also, results of a study comparing the optical spectra obtained during field emission experiments without breakdown from different materials,...

28. Microscopy investigation on different materials after pulsed high field conditioning and low energy H- irradiation.

Catarina Serafim (University of Helsinki (FI))

20/09/2022, 11:30

Experiments

Oral

During operation the LINAC4 RFQ (Radio-Frequency-Quadrupole) is exposed to high electric fields which can lead to vacuum breakdown. It is also subject to proton beam loss that can cause surface modification, including blistering, which can result in reduced electric field handling and an increased breakdown rate. An experimental study has been made to identify materials with high electric...

19. High Voltage Conditioning in high vacuum on concave electrodes. Developments and possible applications associated to accumulation points on electrode surfaces

Nicola Pilan

20/09/2022, 12:00

Experiments

Oral

Counterintuitive experimental evidences have been observed during High Voltage Direct Current (HVDC) tests of two concave, axial-symmetric, electrodes insulated by large vacuum gaps of 3 and 7 cm with voltages from 150 to 370 kVdc. The dissipation of microdischarge power during the conditioning procedure occurs mostly on the anodic side in a region close to the axis of the system where the...

22. X-RAY MEASUREMENTS REVEAL THE FINE DYNAMICS OF CURRENT MICRO-DISCHARGES IN A VACUUM HIGH VOLTAGE EXPERIMENT

Silvia Spagnolo (Consorzio RFX)

20/09/2022, 12:30

Experiments

Oral

The High Voltage Padova Test Facility (HVPTF) is an experimental device for investigating High Voltage (HV) insulation in vacuum, in support of the realization of MITICA, the prototype of a neutral beam injector for ITER. Inside a high vacuum chamber, two stainless steel electrodes, separated by a few centimetres gap, can achieve an HV difference up to 800 kV During the conditioning process of...

30. High Power RF Breakdown Test for Cryo-cooled Reentrant C-Band Copper Structure

Gerard Lawler

Experiments

Oral

High gradient RF structures capable of maintaining gradients in excess of 250 MV/m are critical in several concepts for future electron accelerators. Concepts such as the ultra-compact free electron laser (UC-XFEL) and the Cool Copper Collider (C3) plan to obtain these gradients through the cryogenic operation (<77K) of normal conducting copper cavities. Breakdown rates, the most significant...