On priorities of cathode and anode contaminations in triggering the short-pulsed voltage breakdown in vacuum
ABSTRACT Modern theoretical notations on electrical breakdown in vacuum consider cathode triggering mechanisms to be most responsible on short-pulsed (<1 μs) breakdowns while anode mechanisms to be responsible in a part on DC and long-pulsed breakdowns. Following those notations, we tried to reveal conditions at which either mechanism steps aside to another one. The study involved several experimental techniques including the anode-probe surface scanning, pulsed electron-beam surface melting in vacuum for surface cleaning, and intentional dust particle contamination of electrode surfaces. Breakdown tests were performed using a pulser capable of producing 220 kV quasi-square pulses that were adjustable to ∼30 to 80 ns pulse length. Our experiments showed that cathode emission sites are responsible for breakdowns at relatively low hold-off fields. At higher electric fields of up to 1 MV/cm, the anode share in the mechanism of triggering breakdown becomes probably more significant than the cathode mechanism.
Conference Paper: Development of compact high-voltage electronic vacuum devices[Show abstract] [Hide abstract]
ABSTRACT: The issues of improvement of hold-off capability and reliability of high-voltage vacuum tubes, for example, X-ray tubes were studied. Two methods are suggested for improvement of the tubes operation. The first method is based on deposition of special coatings on the inner surface of tube isolator in the regions where electric field strength is high. 752 These coatings have bulk electric conductivity higher than for isolator material but their surface conductivity is almost equal. The second method is based on pulsed surface melting of the tube electrodes with non-relativistic, high-current electron beam. Pulsed surface melting drastically reduces parasitic field emission, which results in the decrease of the charge density both in the bulk and surface of isolator providing high hold-off voltages through the tube. The tests of 160-kV and 250-kV X-ray tubes made utilizing the new above mentioned technologies have shown that parasitic currents do not exceed 1 μA and conditioning time decreases from 5 hours to 15 minutes. The new technology also allows to reduce dimensions of the tube.Power Modulator and High Voltage Conference (IPMHVC), 2012 IEEE International; 01/2012
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ABSTRACT: Using an electron-transparent anode (titanium foil), the behavior of prebreakdown emission centers on a cathode made of 12X18H10T stainless steel is studied for the case of vacuum gap excitation by 100-ns-wide voltage pulses with an amplitude of 200 kV. To raise the working electric field to 1 MV/cm or higher, the electrodes are preprocessed by a low-energy high-current electron beam in the surface melting mode. It is found that prebreakdown emission centers may be stable and unstable. The stable ones arise at an electric field strength of 0.4–0.6 MV/cm, and their activity grows with voltage up to breakdown. As the electric field increases, new unstable emission centers occur at sites other than those observed at the previous voltage pulse. Reasons for the appearance of unstable emission centers are discussed.Technical Physics 09/2012; 57(9):1289-1296. · 0.54 Impact Factor
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ABSTRACT: The electrical and tribological properties of multicomponent surface alloys (stainless steel (SS)-Cu) formed on copper substrate with a low-energy (20-30 keV) high-current (10-30 kA) electron beam (LEHCEB) of microsecond pulse duration (2-4 μm) have been investigated. Formation of surface alloys has been performed using deposition of SS films by means of magnetron sputtering followed by a LEHCEB liquid-phase mixing. A thickness of formed SS-Cu alloys was ranging from 1 to 10 μm. Investigation of properties of copper electrodes with SS-Cu alloy at the surface showed almost three times increase in the electrical strength of vacuum insulation (1 MV/cm) compared with that for initial copper electrodes (0.35 MV/cm). The reached electrical strength of vacuum insulation appear to be close to that for electrodes made of SS. Moreover, scratch tests revealed the significant improving of adhesion of coating to a substrate for surface alloys compared with that for the magnetron deposited coating.Discharges and Electrical Insulation in Vacuum (ISDEIV), 2012 25th International Symposium on; 01/2012