Foreign Collaborators

Dr. Charles Neumeyer, PPPL, Princeton University, USA

Dr. Walter Joss, High Magnetic Field Grenoble, France

№ -0133 A New Employment of the Electrical Discharge in a Vacuum

Full Title:	A New Employment of the Electrical Discharge in a Vacuum
Technology Field(s):	OTH-ELE: Other / Electrotechnology PHY-PLS: Physics / Plasma Physics

Contributors

Dmitry I Proskurovsky	Institute of High Current Electronics (HCEI) 4, Akademichesky ave., Tomsk, Tomsk reg., 634055, Russia Phone: 7+3822+259709; 7+3822+258544 Fax: 7+3822+259410 pdi@lve.hcei.tomsk.su
Evgeny A Litvinov	Institute of Electrophysics (Inst of Electrophysics) 34, Komsomol'skaya, GSP-387, Ekaterinburg, Sverdlovsk reg., 620219, Russia Phone: 7+3432+499088; 7+3432+745953 Fax: 7+3432+745051 litvinov@ief.intec.ru

Present Status of Research

Brief Description of Research

Electrical discharges in a vacuum are used in various technologies. Numerous applications of completed discharges (vacuum arcs) are described in the “Handbook of Vacuum Arc Science and Technology, Fundamentals and Applications” (Ed. R.L. Boxman, D.M. Sanders, and P.J. Martin Noyes Publications, Park Ridge New Jersey, USA, 1995). The incomplete discharge (explosive electron emission) is discussed in detail in the book by G.A. Mesyats and D.I. Proskurovsky, “Pulsed Electrical Discharge in Vacuum” (Berlin - Heidelberg, Springer-Verlag, 1989).

During a discharge, the electrodes erode and an electrode plasma is produced which fills the electrode gap to produce a conducting medium necessary for the discharge formation. In an incomplete discharge, when the electrode plasma has not filled the entire gap, a high potential difference can be applied to the discharge diode. This makes it possible to extract from the electrode plasma accelerated charged particle (ion or electron, depending on the technological purposes) beams directly in the diode. In particular, X-ray pulses can be produced directly in a diode.

The electrode plasma are jet-like in character. In other words, plasma jets having velocities of a factor below 10 multiplied by 10⁶ cm/s propagate from electrodes into the electrode gap. We believe that it would be interesting and promising to make an attempt to create low-propulsion plasma jet microengines for correcting the spatial position of space objects. An attempt can be made to form a rarefaction corridor in front of a vehicle in the upper atmospheric layers using electron and ion beams.

A problem in this area concerns the service life of the electrodes. The use of liquid-metal cathodes (LMCs) makes it possible to extend substantially the parameter range of the explosive-emission sources of particles and plasma jets to the region of lower operating voltages and higher pulse repetition rates. Swanson (J. Appl. Phys., 1978, v. 49, pp. 5655-5662) has shown that the operating frequency of LMCs may reach 80 kHz. With that, the cathode lifetime is entirely determined by the liquid metal portion of the cathode material and may reach significant values. However, the long response time of LMCs and, hence, their ability to stable operate only at voltages being only slightly over the threshold voltage, has restricted for a long time their use in electron sources.

We have solved the problem of stable operation of an LMC at significant overvoltages using an original concept for the power supply of the LMC. On this basis, a special-type power source has been developed.

Of greatest interest from the physical and practical viewpoints are point-capillary-type cathodes. When a refractory-metal point cathode is operating, a thin (in the order of 1 micro meter) continuously regenerating liquid-metal film is present. With operating explosive-emission centers, a film like this shows the least erosion of the liquid metal (10 micro g/C).

Legal Aspects

Patents:

A.V. Batrakov and D.I. Proskurovsky, “Design of the power supply for an electron source with an explosive-emission liquid-metal cathode.” Useful Model No. 1393. Bulletin of Useful Models and Prototypes (in Russian), No. 12 (1995).

A.V. Batrakov and D.I. Proskurovsky, “A pulsed X-ray tube.” Useful Model No. 1572. Ibid., No.1 (1996).

Special Facilities

We have performed investigations that have made it possible to develop a series of laboratory prototypes of electron beam sources capable of operating with a high pulse repetition rate, namely:

a) A source of pulsed X-radiation based on an LMC sealed-off X-ray tube with a pulse repetition rate of up to 1 kHz and the operating voltage range 15 to 40 kV. The X-radiation intensity at a distance of 5 cm from the extraction window of the tube is 5 mR/pulse at an operating voltage of 25 kV. b) A source of pulsed X-radiation based on an LMC X-ray tube with the pulse repetition rate up to 200 Hz and the operating pressure range 70-120 k. The X-radiation intensity at a distance of 5 cm from the extraction window of the tube is 100 mR/pulse at an operating voltage of 70 kV. c) A source of an electron beam extracted into the air based on an LMC sealed-off electron tube with the pulse repetition rate up to 200 Hz and the operating voltage range 70 to 120 kV. The amplitude of the current pulses of duration 20 ns at a distance of 2 cm from the extraction window of the tube is 100 A at an operating voltage of 70 kV. d) A wide-aperture electron beam source based on a multipoint LMC with the pulse repetition rate up to 1 kHz and the operation pressure range 10 to 20 kV.