Transportation of high-current electron beams in plasma and plasma-filled diodes

The results of a numerical simulation of the nonstationary processes in different charge-neutralization schemes of high-current electron beams and the results of a measurement of the beam parameters are presented. Most attention is paid to beams with a current higher than the limiting Alfven current.     

Characteristic features of the generation of large-diameter low-energy electron beams from a penning plasma source

A wide-aperture plasma source of low-energy electron beams on the basis of an electrically asymmetric reflex discharge is studied experimentally. The characteristic features of the generation of electron beams are investigated, and the boundaries of the generation regime are determined. The influence of the dimensions and shape of the discharge electrodes on the source characteristics is examined. A method for efficiently controlling the electron-beam current is proposed.     

Generating a low-energy high-current electron beam in a gun having a plasma anode

Research has been done on major physical processes governing the scope for generating magnetized low-energy high-current electron beams in a plasma-filled system. Conditions are considered for efficient excitation of the explosive electron emission at a large-area cathode at low accelerating voltages, together with the trends in beam formation in the nonstationary double layer formed between the cathode and anode plasmas, as well as the beam transport to the collector in the inhomogeneous guiding plasma. It is found that a gun having a plasma anode enables one to generate wide-aperture electron beams of microsecond duration having a mean electron energy of 10–20 keV and an energy density of up to 20 J/cm² or more, which goes with homogeneity sufficient for technological purposes.High-Current Electronics Institute, Siberian Branch, Russian Academy of Sciences. Translated from Izvestiya Vysshikh, Fizika, No. 3, pp. 100–114, March, 1994.     

Generation and transport of high-current, low-energy electron beams in a system with a gas-filled diode

Investigations of the generation and transport of a high-current, low-energy electron beam are performed in a system with a gas-filled diode based on a plasma cathode. At accelerating voltages of up to 20 kV and pressures of (1–5)×10⁻¹ Pa, a beam with an emission current of 600 A, emission current density of 12 A/cm² and pulse duration of 30 μs if obtained in a diode with a grid-stabilized emission opening having a diameter equal to 8 cm. The beam is transported in the absence of an external magnetic field over a distance of 20 cm. The beam is compressed by its self-magnetic field, and the current density at the collector reaches 100 A/cm² when the beam diameter is 3 cm. Zh. Tekh. Fiz. 68, 44–48 (January 1998)     

Ion acceleration in direct high-current electron beams

Conclusions The stream of research on collective methods does not dry up, just as the diversity of directions over which searches and investigations does not diminish. We observe this pattern for approximately the last 10 years. Moreover, qualitative shifts can be noted with respect to certain areas.Until recently, mainly research work (theoretical and experimental) on questions of principle in collective acceleration methods and on detection of appropriate collective effects has been conducted. In particular, it would be necessary to construct apparatus of significant scales and to develop diagnostic methods for the processes which occur. Mainly it would be necessary to obtain, at least, greater accelerating fields in experiment, if not greater energies. It cannot be said that greater accelerating fields are actually obtained in the set of methods examined here. The next stage has started, when it is necessary to develop appropriate accelerating systems by using the cumulative experience and the results obtained, and to try to optimize them in the fundamental parameters. It is here necessary to solve some difficult technological problems such as to obtain steep (or generally given) fronts of current and voltage growth in the accelerator-injector, beam monochromaticity, sufficiently high pulse repetition rate, etc. It is also necessary to solve the problem of tolerances in traditional accelerators. However, the results already obtained permit consideration of further progress in collective methods and, in the long run, their practical application in different regions.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 59–82, October, 1979.     

Generation of high-current electron beams by a hollow cathode with a ferroelectric plasma source

This paper presents results and analysis of an experimental investigation of the operation of a hollow cathode (HC) with an incorporated ferroelectric plasma source (FPS). It was shown that the use of FPS based on a BaTi solid solution allows one to ignite and to sustain a 10²-10³ A HC discharge with duration of 10^-3-10^-5 s at background pressure of 5 x 10^-3 Pa while keeping the HC design with small dimensions. It was found that the development of the HC discharge is accompanied by formation at the surface of the FPS of dense plasma which serves as a powerful (hundreds of kW) pulsed source of current carrying electrons. Parameters of the HC plasma (radial distribution of the plasma density and temperature and plasma potential) for different discharge current amplitudes and two types of FPS are presented. Application of the FPS as an electron source in a diode under an accelerating pulse 300 kV and pulse duration 400 ns showed that the latter operates in a plasma pre-filled mode with a current amplitude up to 1.6 kA. Parameters of the diode and electron beam for different experimental conditions are presented and discussed.Received: 10 April 2003, Published online: 12 August 2003PACS: 52.50.Dg Plasma sources - 29.25.Bx Electron sources - 52.25.Tx Emission, absorption, and scattering of particles     

Formation of narrow low-energy high-intensity electron beams

The process of formation of high-density low-energy (5–10 keV) pulsed electron beams of small diameter (on the order of a few millimeters) in a gun of the “channel-spark” type is studied. It is shown that beams with a rate of rise of the current exceeding 10¹¹ A/s and an amplitude exceeding the Alfvén current by a factor of 1.5–2.0 can be obtained in experiments with intense preionisation of the transport channel combined with a pulsed supply of the accelerating voltage to the cathode. In the optimal pressure mode, the current density at a distance of 2–3 cm from the gun outlet is 40–25 kA/cm², which will ensure ablation of most solid targets.     

Generation of a pulsed high-current low-energy beam in a plasma electron source with a self-heated cathode

The transition of a low-current discharge with a self-heated hollow cathode to a high-current discharge is studied, and stability conditions for the latter in the pulsed–periodic mode with a current of 0.1–1.0 kA, pulse width of 0.1–1.0 ms, and a pulse repetition rate of 0.1–1.0 kHz are determined. The thermal conditions of the hollow cathode are analyzed, and the conclusion is drawn that the emission current high density is due to pulsed self-heating of the cathode’s surface layer. Conditions for stable emission from a plasma cathode with a grid acting as a plasma boundary using such a discharge are found at low accelerating voltage (100–200 eV) and a gas pressure of 0.1–0.4 Pa. The density of the ion current from a plasma generated by a pulsed beam with a current of 100 A is found to reach 0.1 A/cm². Probe diagnostics data for the emitting and beam plasmas in the electron source are presented, and a mechanism behind the instability of electron emission from the plasma is suggested on their basis.     

Methods of optical diagnostics of electron-positron beams and interaction between plasma and high-current electron beam

Optical diagnostics is widely used, both in plasma-physics experiments and in measuring parameters of electron and positron beams in accelerators. In doing so, the approaches with the same methodological base are often applied, which is explained by similarity of certain properties of objects under study despite the fact that these fields of physics are absolutely specific and require using the specialized techniques. The possibility of close contacts and cooperation among scientists concerned with similar problems in different fields of physics contributes to the fruitful exchange of ideas and helps to overcome these problems. It is especially characteristic of the Budker Institute of Nuclear Physics, Siberian Branch of Russian Academy of Sciences, which is famous for pioneering works in the field of electron-positron colliders and controlled thermonuclear fusion. The first part of this paper presents a review of optical diagnostics of the stationary beam parameters in cyclic accelerators of electrons and positrons. The only techniques considered are those that became the recognized tools at colliders and storage rings of the latest generation, without which the routine operation of the facility is difficult to imagine. The second part of the paper describes optical diagnostics used in experiments of heating the plasma by a high-current electron beam.     

Formation and transportation of low-energy high-current electron beams in the plasma-filled diode under the effect of the external magnetic field

The mechanisms behind limitation of current of nonrelativistic high-current electron beams in the plasma-filled diode immersed in the external guiding magnetic field whose intensity is comparable with that of the beam self magnetic field are studied. It is shown that the beam current is limited by transmission capacity of the double layer between the cathode and anode plasma on the one hand and, on the other hand, by charge neutralization of the beam and by the decrease of the longitudinal velocity of the beam electrons under the action of the induced electric field and of the beam self magnetic field. The effect of the beam self fields on its cross-sectional current density and energy distributions is studied. Results of the numerical simulations are in good agreement with the experimental data.     

Structural phase changes in a titanium-silicon system modified by high-current electron beams and compression plasma flows

Structural phase changes in a titanium-silicon system treated by low-energy high-current electron beams (HCEBs) and compression plasma flows (CPFs) with the duration 100 μs and the energy density 12–15 J/cm² are studied. Scanning electron microscopy, X-ray diffraction and electron microprobe analysis are used in this work. The formation of a titanium-doped silicon layer 10–25 μm thick, titanium silicides (TiSi₂ under HCEBs and Ti₅Si₃ under CPF treatment), silicon dendrites, and needle-like eutectics (typical size of precipitates is about 50 nm) is revealed. It is shown via the results of numerical simulation that the thickness of the metal-doped layer is mainly controlled by the power density value and the surface nonuniformity of the heat flow over the target surface. The thermodynamic regularities of phase formation are discussed, taking into account heat transfer between the silicide nuclei and solid silicon.     

Two-pulse generation of high-current relativistic electron beams and their transportation in the gaseous medium of a plasmochemical reactor

Experimental results on two-pulse generation and transportation of high-current relativistic electron beams (REBs) through the gaseous medium of a plasmochemical reactor (PR) are presented. The generation of two consecutive high-current REB pulses with a duration of 60 ns was achieved at the Tonus accelerator with modified schemes of high-voltage pulse formation. The first version of the formation scheme enabled pulse powers of 2 and 4.0–9.6 GW with a time interval between the pulses of 500 ns. The second version enabled one to generate pulses with powers of 1.8 and 16 GW and time interval between the pulses of 160 μs. The transportation parameters of an REB injected into a 1.4-m-long PR filled with an N₂: O₂ gas mixture are studied. The conductance of the plasma produced under the action of the electron beams is measured. It is shown that the schemes proposed provide more efficient (by 35–45%) transportation of the REBs in the reactor volume as compared to single-pulse high-current REBs of the same power and pulse duration.     

Dislocation substructure formed by irradiating iron with a low-energy high-current electron beam

Calculations were made of the time variation of the temperature in iron at different depths from a surface irradiated with a low-energy high-current electron beam. The mutual relationship betwen the changes in the dislocation and grain structures of the iron polycrystals and the maximum temperature reached during irradiation was traced. The variation of the microhardness in the surface layers of the irradiated iron was found to be nonmonotonic.V. D. Kuznetsov Siberian Physicotechnical Scientific-Research Institute, Tomsk State University. Institute of Power Electronics, Siberian Branch of the Russian Academy of Sciences. Physics Institute of Strength and Materials Science, Siberian Branch of the Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 42–47, May, 1993.     

低能脉冲电子探束研究“气-固”界面

介绍了利用低能脉冲电子探束研究“气-固”界面的基本原理和方法，并实验研究了室温T=300K、1×10^-3Pa真空条件下， O₂，N₂-Ni，W“气-固”界面的相互作用，即吸附、脱附与置换作用，测量了电子诱导脱附产额、脱附截面和阈值能量，给出了实验结果分析与结论. 关键词： 脉冲电子探束 电子诱导脱附 阈值能量 脱附截面     

Stability of high-current beams of relativistic electrons in cyclic systems

Stability conditions of high-current thin beams of relativistic electrons against excitation of long-wave oscillations in a stellatron and modified betatron have been investigated theoretically. The influence of self electric and magnetic fields obtained from electron beam delayed potentials has been taken into consideration. The correspondent dispersion relation has been found. The electron beam of the modified betatron has been shown to be always unstable against excitation of the oscillations considered. Necessary and sufficient conditions for the elec-tron beam confinement in a stellatron have been found.     

Laser interferometry of acoustic fields generated by high-current electron beams in solids

We have developed a method for detecting acoustic fields in solids irradiated with dense electron beams. The method is based on laser Michelson interferometry. The electron source is a high-current DZhIN electron accelerator. The detection system features a short baseline Michelson interferometer located inside the experimental chamber with the sample, a stabilized initial beam pathlength difference within the interferometer, high temporal resolution, an analog-to-digital converter with output to a personal computer, and a program for reducing the interferometer data. We can measure both long pulses with minimum displacements of 10⁻¹⁰ m and durations of 10⁻⁸ sec, and flexure waves with large-amplitude displacements of 10⁻⁵ m and oscillation periods of 10⁻³ sec. We present results from studies of flexure waves in thin plates and rods of copper, silicon, alkali-halide crystals, quartz glasses, and D16T aluminum alloy irradiated by nanosecond high-density electron beams. Institute of High-Current Electronics, Siberian Branch of the Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 82–92, November, 1997.     

Computations of profiles of low-energy electron diffraction beams for arrays of ordered islands

In an attempt to determine the influence of the presence of adjacent islands on LEED beam profiles, an excluded area model has been proposed to describe the relative positions of ordered islands on a crystal surface. On the basis of this model, overlayers of different island density have been created on a finite lattice using a simple computer algorithm. The LEED from these overlayers has been calculated kinematically. Although the placement of the islands is not random, this does not perturb the LEED beam profile observably. Therefore, the kinematically diffracted intensity depends solely on the distribution of island sizes. Using this result, the intensity and half-width as functions of coverage have been calculated for one model of island growth.