RU2313848C1 - Heavy-current electron gun - Google Patents

Abstract

FIELD: heavy-current electron beam generation for pulsed heavy-current electron accelerators and for surface treatment of materials and products.

SUBSTANCE: proposed heavy-current electron gun disposed in external driving magnetic field has explosion-emissive cathode, reflective-discharge anode, grounded diaphragm installed between cathode and anode, diameter of its hole being smaller than that of cathode, and collector; diaphragm is manufactured from material characterized in high emissive capability in strong electric fields.

EFFECT: enhanced service life, provision for recovering cathode emission capability.

1 cl, 2 dwg

Description

The invention relates to techniques for generating high-current electron beams (BOT) and can be used to create pulsed high-current electron accelerators, as well as for surface treatment of materials and products with these beams.

Known electron gun according to the method [1], containing an explosion-emission cathode and anode of the reflective discharge (OR) of the Penning type. The anode plasma generated in the OR pre-fills the accelerating gap and the space of the beam drift, i.e. the space between the cathode and the collector. When the accelerating voltage pulse is subsequently applied to the cathode, the electric field is concentrated in the near-cathode layer of the space charge of the anode plasma ions. Explosive emission is excited at the cathode with the formation of clots of a dense cathode plasma - an electron emitter. After that, the applied voltage is almost completely concentrated in the double electric layer between the cathode and anode plasmas, in which the electron beam is accelerated and formed. The presence of an anode plasma significantly increases the perveance of the electron flux compared with the flux in the vacuum gap of the same length, which ensures the production of SEPs even at relatively low accelerating voltages (tens of kV). To prevent pinching of the beam, the electron gun is placed in a leading magnetic field. The disadvantage of this gun is the presence of current leaks in the radial direction. These leaks are caused by the penetration of a magnetron discharge plasma arising between the anode and the electron gun body into the region between the cathode and the gun body. The magnetron discharge is ignited almost simultaneously with the main (Penning) discharge. Current leakage leads to a reduction in the duration of the SEC pulse, a decrease in its energy, and also to a deterioration in the stability of the beam parameters from pulse to pulse.

Closest to the technical solution to the claimed invention, selected for the prototype, is an electron gun with an explosion-emission cathode and a plasma anode based on reflective discharge [2]. The OR electrode system consists of a ring anode, to which a positive voltage pulse is applied, as well as a gun and collector cathode, which are OR cathodes. The axial driving magnetic field needed to ignite the OP and to transport the beam is created by a solenoid located externally. The use of a grounded diaphragm with a hole diameter smaller than the diameter of the cathode located between the anode and the explosion-emission cathode increases the stability of the beam parameters from pulse to pulse, since the diaphragm prevents the appearance of plasma in the region between the gun body and the cathode and, consequently, the formation of a channel for radial current leakage.

The disadvantage of the electron gun of this design is the degradation of the emissivity of the explosive emission cathode as a result of deposition of a film from the material of the irradiated sample or product on its surface if the sample or product is made of a material with low emissivity in strong electric fields, for example, nickel or stainless steel, containing nickel in significant quantities. Particularly fast degradation of the cathode emissivity occurs if the work is carried out in an oil-free vacuum. As a result of cathode degradation, the overhaul life of the electron gun is reduced, the beam energy is reduced, the stability of the SEC generation is deteriorated until idle trips occur, in which, despite the supply of an accelerating voltage pulse, explosive electron emission at the cathode is practically not excited and the beam is not generated. The appearance of idle trips is undesirable not only because of a violation of the processing mode, but also because as a result of such idle tripping, breakdown may develop on the surface of the high-voltage insulator. This, in turn, can lead both to contamination of the processed materials with the products of insulator erosion, and, ultimately, to destruction of the insulator itself.

The problem solved by the invention is to increase the service life of the gun, increasing the stability of the parameters of the EPA.

The technical result of the claimed invention is to increase the service life of the explosive emission cathode.

The specified technical result during the implementation of the invention is achieved by the fact that in a known high-current electron gun located in an external driving magnetic field and includes an explosion-emission cathode, an anode of reflective discharge, a grounded diaphragm with an opening diameter smaller than the diameter of the cathode, installed between the cathode and the anode, and the collector according to the invention, the diaphragm is made of a material having high emissivity in strong electric fields. As such materials, copper, magnesium, graphite, and several others can serve.

As experiments show, despite the focusing effect of the magnetic field, the diaphragm is subjected to intense bombardment by electrons emitted from the peripheral part of the explosive emission cathode. As a result of evaporation and transfer of the material of the diaphragm to the surface of the explosive emission cathode, a film of this material is formed after each pulse. If the diaphragm is made of a material having high emissivity in strong electric fields, this ensures an increase in the service life of the explosive emission cathode.

Figure 1 shows a schematic structural diagram of the proposed high-current electronic gun. The OP cathodes are, on the one hand, an explosion-emission cathode 1 and a diaphragm 2, and on the opposite side, a beam collector 3. A diaphragm 2 is placed between the explosion-emission cathode 1 and anode 4. Anode 4, to which a positive voltage pulse is applied, is a thin-walled metal ring . The axial driving magnetic field is created by a sectioned solenoid 5 located outside the casing of the electron gun 6. The high-voltage bushing 7 is made of porcelain. The case of the electron gun is vacuum tightly connected to the working chamber 8, to which are also connected systems of vacuum pumping and stationary inlet of the working gas. For power supply of the OR, the solenoid and the cathode of the electron gun, a discharge power supply unit (BPS), a solenoid power supply unit (BPS), and a pulse voltage generator (GIN) are used, respectively, which are controlled by control unit commands.

The electron gun works as follows. After pumping the volume of the electron gun to a pressure of not more than 0.005 Pa, the working gas (argon in our case) is stationaryly introduced into it to a pressure of the order of 0.05 Pa. Then, the BPS is turned on, and a leading magnetic field is created in the electron gun, which provides not only the ignition of the OR, but also the subsequent transport of the solar cells to the collector 3. At the maximum magnetic field, a pulse of positive polarity with an amplitude of 4-5 kV from the BPR is applied. After the OR passes into the high-current stage with a set delay, an accelerating voltage pulse of negative polarity with an amplitude of 12-36 kV is applied to the cathode 1 of the electron gun. After the initiation of explosive electron emission, the accelerating voltage is concentrated in a double electric layer between the cathode and anode plasmas. The electron beam accelerated in the double layer is transported in the anode plasma to the collector 3, on which the processed samples or parts can be located.

Experimental observations of the “autographs” of the SES on the diaphragm showed that the diameter of the beam with an energy density sufficient to sputter even such a material that is difficult to spray with a pulsed electron beam, like copper, exceeds the diameter of the diaphragm by 10-15 mm, if the diameter of the cathode is not less than the diameter of the hole in aperture. The explosion-emission cathode with a diameter of the emitting part of 65 mm was made of the same copper wire braid, pressed into a holder of stainless steel with a diameter of 75 mm. The diameter of the hole in the diaphragm was 60 mm. Thus, the conditions for the transfer of the diaphragm material to the cathode surface were ensured.

Figure 2, a shows the experimental data on the resource tests of the explosive emission cathode with diaphragms from different materials and in its absence. We specifically investigated the dependence of the probability of idling of the explosive emission cathode η _xx on the total number of gun shots, N. The tests were carried out under the following conditions: residual pressure - not higher than 0.001 Pa, working gas pressure (argon) - 0.04 Pa, collector material - stainless steel 12Х18Н10Т, the SEP energy density on the collector was from 6 to 12 J / cm ² , irradiation was carried out in series from 30 to 200 shots in one vacuum cycle. As the material of the diaphragm, stainless steel of the grade 12X18H10T and copper of the grade M0B were used. The criterion for developing the resource of the explosive emission cathode is an increase in the probability of blank shots up to 10% of the total number of shots.

From the data of Figure 2, a shows:

- the use of a stainless steel diaphragm reduces the service life of the explosive emission cathode by about 1.7 times in comparison with the case of its absence;

- the use of a copper diaphragm at the moment has allowed more than three times to exceed the cathode life compared to the case of its absence and more than five times compared to the case of stainless steel diaphragm. At the same time, there are no signs of developing the resource of the explosive emission cathode yet.

The use of a copper diaphragm also made it possible to restore the emissivity of the cathode. This is illustrated by the graph in Figure 2, b. The first 1,700 rounds were fired without a diaphragm, and at the end of this series n _xx reached 10% (AB section), the cathode surface was dusted with collector evaporation products (stainless steel). Then a copper diaphragm was installed, and after a series of 300 shots (aircraft section), the cathode emission stability improved dramatically (CD section). A direct consequence of the improvement in the cathode emission ability was an increase in the stability of the electron gun.

Information sources

1. RF patent No. 1706329, IPC H01J 3/02. A method of forming electron beams using an explosive emission electron gun. G.E. Ozur, E.M. Oke, D.I. Proskurovsky. Claim 01/09/89 // BI No. 10, 1994.

2. RF patent No. 2237942, IPC H01J 3/02. High current electronic gun. G.E. Ozur, D.I. Proskurovsky, K.V. Karlik. Claim 03.24.2003 // BI No. 28, 2004.

Claims (1)

A high-current electron gun located in an external driving magnetic field and including an explosive emission cathode, a reflective discharge anode, a grounded diaphragm with an aperture diameter smaller than the cathode diameter, installed between the cathode and the anode, a collector, characterized in that the diaphragm is made of a material with high emissivity in strong electric fields.

Images