Vacuum breakdowns in DC conditions between the electrodes with large gap (several mms) are believed to initiate at anode. We have investigate the origin of anodic plasma by setting up DC experiments with the fast intensified charge-coupled device camera (ICCD) and combining our observations with theoretical calculations. We observe the evolution of light emission, analyze the typical waveforms...
Development of vacuum circuit breakers for high-voltage applications leads to continuous basic research in the field of vacuum arcs. Investigations of the arc plasma properties is an important instrument for understanding of basic phenomena and parameter optimization for corresponding applications. It is well known that the high-current anode phenomena have a distinct impact on contact erosion...
We present an overview of studies that examine the role of photo-assisted breakdown. Emphasis is placed on an experimental platform that subjects well-characterized platinum surfaces to pulsed UV illumination as functions of UV illumination and UV wavelengths spanning from 260 nm (4.77 eV) to 400 nm (3.11 EV), well below the 6 eV values often used for platinum. Application UV illumination is...
The High Voltage Padova Test Facility (HVPTF) is an experimental device for investigating HV insulation in vacuum, in support of the realization of MITICA, the prototype neutral beam injector for ITER. The experiments here described aim at understanding the physical phenomena underlying voltage holding in vacuum and specifically the electrode "conditioning" process. Two stainless steel...
Normal-conducting RF accelerating structures are hearts of many modern accelerators, where vacuum arcs in the structures could lead to breakdowns, that might limit accelerator performance. However, we do not know what the real source of breakdowns is, i.e., the breakdown-trigger mechanism is not yet well understood.
[Recently, based on direct in-situ observation method, we performed breakdown...
It has been suggested that BD can nucleate due to stochastic plastic activity induced in the cathode under extreme fields. The nature and type of plastic activity can be constrained from experimental observations on post-BD electrodes. I will present estimates to such constraints from transmission electron microscopy of samples exposed to high fields, discussing properties like dislocations...
Field emission and electrical breakdowns play a central role in the RF conditioning process of particle accelerating structures. However, actual mechanical changes in the copper surface and just beneath the surface are unclear. Ultrasound microscopy is an advanced method to measure mechanical properties point-by-point from the sample surface. High lateral resolution, 3.5 μm, can be achieved by...
The importance of microscopy analysis and observations have been proof over the last years over the post-mortem analysis of different structures. Here we will see as well its importance in other fields and pollution analysis, as it can be the origin of a breakdown, the analysis of bonded structures, to guarantee a good electrical contact and vacuum tightness.
Measurement of different aspects of high-field behaviour including pre-breakdown processes, breakdown events and parameters for conditioning of materials ongoing in pulsed dc systems at CERN are described. The system uses parallel plate electrodes with 40 and 62 mm diameter together with a well-controlled high-voltage high repetition rate generator up to 6 kHz. The dc pulsed experiments are...
Understanding the microscopical phenomena behind vacuum arc generation is crucial for being able to control the breakdown rate thus improving the efficiency of many applications where breakdown generation is a limiting factor.
Statistical properties of breakdowns, such as pulses between breakdowns, breakdown waveforms and changes in vacuum pressure, are studied using a Large Electrode DC...
After initiation of an arc, the plasma forming it must be fed by sputtering. The basic mechanisms of sputtering in the linear cascade regime are well understood from decades of theory and computer simulation development. However, under an electrical arc, the surface is either hot or molten, the plasma bombardment intensity very high, and the surface may have nanosize protrusions.
The...
