Suppression by low-energy thermionic electrons of instabilities in the transport of a high-power electron beam in the forevacuum pressure range.

We report here the results of our studies on the effect of injection of low-energy thermionic electrons on the suppression of instabilities of the beam-plasma discharge type in a beam-plasma during the transport of a powerful continuous electron beam generated by a plasma-cathode electron source in the forevacuum range of pressure. As result of thermionic electron injection, the plasma electron temperature decreased to 0.3 eV and the plasma density decreased by an order of magnitude to 10^15 m-3. The minimal thermoelectron current required for suppressing the beam-plasma discharge increases with increasing emission current and decreases with increase of the beam accelerating voltage.

Numerical simulation of low-current vacuum arc jet considering anode evaporation in different axial magnetic fields

As the main source of the vacuum arc plasma, cathode spots (CSs) play an important role on the behaviors of the vacuum arc. Their characteristics are affected by many factors, especially by the magnetic field. In this paper, the characteristics of the plasma jet from a single CS in vacuum arc under external axial magnetic field (AMF) are studied. A multi-species magneto-hydro-dynamic (MHD) model is established to describe the vacuum arc. The anode temperature is calculated by the anode activity model based on the energy flux obtained from the MHD model. The simulation results indicate that the external AMF has a significant effect on the characteristic of the plasma jet. When the external AMF is high enough, a bright spot appears on the anode surface. This is because with a higher AMF, the contraction of the diffused arc becomes more obvious, leading to a higher energy flux to the anode and thus a higher anode temperature. Then more secondary plasma can be generated near the anode, and the brightness of the ‘anode spot’ increases. During this process, the arc appearance gradually changes from a cone to a dumbbell shape. The appearance of the plasma jet calculated in the model is consistent with the experimental results.

Influence of electron emission on operation of a constricted arc discharge in a pulsed forevacuum plasma-cathode electron source

The research of influence of electron emission and processes associated with the formation of a pulsed large-radius electron beam on operation of a constricted arc discharge, which forms emission plasma in a forevacuum plasma-cathode electron source, is presented. Processes, occurring in case of generation of the electron beam at forevacuum pressure range 3–20 Pa, provide lower operating voltage of the constricted arc discharge. The constricted arc voltage decreases with increasing pressure and increasing accelerating voltage. However, at pressure more than 15 Pa, the arc voltage decreases until a certain minimum value is reached, and then arc voltage is almost independent on pressure and accelerating voltage. This minimum value of the constricted arc voltage is on average 1.5–2 times higher as compared with voltage of the cathodic arc at the same discharge current. The observed decrease of operating voltage of the constricted arc is most likely caused by accelerated back-streaming ions, which move toward the emission electrode from beam-produced plasma. These accelerated ions partially penetrate into the hollow anode of discharge system through the mesh emission electrode and facilitate formation of the arc plasma, and thus provides lower voltage of the constricted arc.

Influence of accelerating gap configuration on parameters of a forevacuum plasma-cathode source of pulsed electron beam

The research of influence of accelerating gap configuration on parameters of a forevacuum plasma-cathode source of a pulsed low-energy (up to 10 keV) large-radius electron beam is presented. An increase in cell sizes of a mesh emission electrode increases electron emission efficiency, but leads to a decrease in electric strength of an accelerating gap. Larger cell sizes of a mesh extractor provide higher electron beam current. An increase in the length of the accelerating gap first leads to an increase in the electron emission efficiency, but when optimal value is reached, a further increase in the length leads to a decrease in the emission efficiency. This optimal length of the accelerating gap is about 25 mm. However, the electron emission efficiency changes relatively small (within 15%). The dependencies of maximum emission current and maximum operating gas pressure on the length of acceleration gap is similar to the dependence for the emission efficiency, but the gap length much stronger influences on these maximum values. Moreover, the optimal length, at which maximum emission current or maximum pressure is provided, is depended on gas pressure (for current) or emission current (for pressure), accelerating voltage and pulse duration.

Surface modification of hypereutectic silumin subjected to a millisecond modulated electron beam treatment

In this work, using a unique feature of the “SOLO” electron source with a grid plasma cathode based on a low-pressure arc discharge, which consists in the possibility of controlled operation of the beam power during a pulse of submillisecond duration, and, accordingly, the rate of energy input into the sample surface, we investigated the modes irradiation of samples of hypereutectic silumin. The irradiation modes had the same energy density during the first 200 μs of the pulse, equal to 20 J/cm2 and differed in different durations of further maintaining the surface temperature at 600°C for a time of up to 1 ms. The results of tribological tests and methods of diffraction microscopy of the investigated defect structure, the elemental and phase composition, the morphology of the strengthening phases of the modified layer of the hypereutectic silumin samples are presented.

Methods of increasing the dielectric strength of the accelerating gap in an electron source with a plasma cathode

This work represents the investigations for decreasing acceleration gap breakdown probability of plasma source of electrons SOLO, with grid stabilization of the boundaries of the arc cathode plasma. We increased the distance to the treated target, bent the transportation channel of the electron beam, created additional plasma in the anode space, and increased the beam front. The effect of the above measures on the breakdown probability when the target is exposed of a low-energy electron beam with a power density of up to 0.5 MW/cm2 with a diameter of 2.5 cm was investigated separately. Beam deflection is most effective at relatively long pulse durations of 150 μs and accelerating voltage of 20 kV, rather than a lower one. It was possible to double the maximum power for the same beam transport length applied to a low-melting target. Preionization in the anode proved to be effective for relatively short beams of 15 μs duration.