Development of vacuum circuit breakers for medium- and high-voltage applications leads to continuous basic research in the field of vacuum arcs. The diagnostics of the electrode surface plays an important role for understanding of basic phenomena and parameter optimization for corresponding applications since the electrodes provide the material for the arc plasma. It is well known that the...
The prevaling way of analyzing dark currents is by looking only at the mean current. While there have been some work to extract usefull information from that, there's a lot of data being ignored by neglecting the inherently statistical nature of the current.
In this talk, I will present a novel method for field estimation and its advantages as opposed to the current method of beta estimation...
Under sufficient high electric field, a breakdown process will be triggered in a vacuum insulation system, influencing the efficiency, reliability and even safety of the system. The transition to a vacuum arc, which is indicated by the formation of a conductive channel in the initial vacuum gap, is an important process for a deeper understanding of the vacuum breakdown. According to our...
Although electrical breakdowns are often reported as a single value, in general breakdowns for both vacuum and gases are in fact a distribution of values. This work measures the breakdown voltage distribution for two general contact arrangements (floating and fixed shield) using Cu-Cr contact material. Tests were performed using the lightning impulse voltage pulse, with a 1.2/50 µs...
High voltage platform are of widespread use in nuclear physics accelerator in order to provide the initial acceleration of ion. The ion source environment is particular challeging for high voltage holding, since discharge can be energized from source radiation or secondary particle generated by the ion beam.
Moreover spectrometers for charge to mass ratio of exotic nuclei requires a well...
Vacuum breakdowns are common phenomena in nature and gain their important role in modern technologies. Although a lot of effort has been done to reveal the nature of the breakdown, the dispute over the roles and physical processes of anodes in the initial stage is not over. The objective of the paper is to experimentally investigate prerequisites for appearing anodic glow and its role in a...
The contribute describes and analyses some recent experimental results obtained at the High Voltage Padova Test Facility (HVPTF)
The results of four voltage hold -off experiments adopting stainless steel electrodes are presented and discussed. The conditioning histories in high vacuum, obtained by a fully automatic procedure, have been compared and analysed. A marked total voltage effect has...
Post arc dielectric recovery process is an important stage when vacuum circuit breakers interrupt current, which has decisive effect on the whole interrupting process and causes much concern. much concern. The post arc dielectric recovery process, which contains the physical processes, e.g., the dissipation of residual plasma and metal vapor, begins at the moment of current zero and lasts...
V. Kolobov, D. Levko and R Arslanbekov
CFD Research Corporation, Huntsville, AL 35806
Operation of vacuum arcs involves multi-phase processes associated with melting, evaporation and ionization of electrode materials. In this paper, we will present simulations of vacuum arc ignition from the tip of a Taylor cone on the surface of liquid cathode made of GaIn. The formation of Taylor cone on...
In the ion accelerator or film deposition instruments, the ion beam may induce breakdown under the high voltage. In order to explain this phenomenon, a typical model of protons impacting the electrode is analyzed with the help of a PIC-DSMC code. The temporal and spatial distribution evolution of electrons, ions and neutrals with different electrode conditions are present. The critical value...
Useful models of arcing capable of predicting operating gradients in limited environments are beginning to be produced, but generalizing these models to many applications is coming very slowly. We will show how each stage of the arcing process can be explained by many possible mechanisms, each with its own parameter space and peculiarities, and outline how a general model, applicable to many...
We present a model in which electrical breakdown in high-voltage systems is caused by a critical transition, due to stochastic fluctuations of the mobile dislocation population in the cathode. Recent developments of the model, due to comparison with experiment and microscopic observations, are described. We propose a number of additional experiments to validate the model, and discuss its...
NUMERICAL SIMULATION OF THE INITIAL PHASE OF UNIPOLAR ARCING IN FUSION RELEVANT CONDITIONS
The results of experimental works on unipolar arcs, e.g. [1], suggest that there are two phases of unipolar arcing. An intense external energy flux, i.e., the laser pulse (or ELM), causes significant heating of a wide region of the surface of an isolated plate, current transfer is initiated and the...
Combining classical electrodynamics and density functional theory (DFT) calculations, we develop a general and rigorous theoretical framework that describes the energetics of metal surfaces under high electric fields. We show that the behavior of a surface atom in the presence of an electric field can be described by the polarization characteristics of the permanent and field-induced charges...
Direct field ionisation of neutral atoms may happen when they are immersed in an external electric field of magnitude comparable to the atomic electric field seen by the outer electron shells. The resulting ionisation probability may have a magnitude comparable to the usual electron impact ionisation probability, and thus this process should not be neglected in plasma simulations codes. In...
Pulsed DC systems dedicated to the study of electrical breakdown phenomenon and the conditioning process are part of the CLIC (Compact Linear Collider) project. There are two pulsed DC systems operational at CERN, as well as similar systems at Helsinki and Uppsala Universities. In the systems, two plane electrodes with large surface areas are placed parallel to each other with a separation of...
Field emissions and vacuum breakdowns are major limiting factors for the development of the compact particle accelerators. An extensive program of developing high-gradient X-band accelerating structures has been carried out at CERN. To complement these RF tests, a high repetition rate, pulsed DC system with large planar electrodes has been also operated. It proved that high-field behaviors in...
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 of a neutral beam injector for ITER. The facility investigates the physical phenomena underlying voltage holding in vacuum, such as the mechanisms causing breakdowns and the electrode conditioning process, along with testing...
The characterization of the X-ray energy spectrum during the high voltage conditioning of a multi electrode vacuum insulated system (such as the MITICA electrostatic accelerator) could be useful to understand which stage is causing the micro discharge onset. This technique seems particularly promising for measuring small dark currents (I< 10μA), which are generally difficult to be measured...
The surface flashover ion source based on MEMS technology is the component of the chip type neutron generator. In this paper, patterned titanium films are prepared on polished ceramic substrates and surface flashover ion source samples are obtained. The stability of the surface flashover ion source is studied by analyzing the extraction ion current. The relative standard deviation of ion...
Oxidation and other kinds of surface contaminants are one of the biggest unknowns in understanding the breakdown resistance and conditioning behaviour of Cu electrodes under frequent DC voltage pulsing.
Argon can be used to clean the electrode surfaces in situ under vacuum. In the process, Ar gas is inserted into the chamber and a constant DC voltage is used to ionize the gas in order to...
The CLIC project aims to establish an accelerating gradient of 100MV/m within novel high gradient X-band accelerating structures, this leads to surface electric fields on the order of 220MV/m. In this context, CERN have developed high power X-band RF test stands (Xboxes) to test the prototype structures for CLIC at high power. A summary and analysis of recent RF results from the test stands...
