Low-impedance plasma systems for generation of high-current low-energy electron beams

The results of experimental investigation and numerical modeling of the generation of low-energy (tens of keV) high-current (up to tens of kA) electron beams in a low-impedance system consisting of a plasma-filled diode with a long plasma anode, an auxiliary hot cathode, and an explosive emission cathode. The low-current low-voltage beam from the auxiliary cathode in an external longitudinal magnetic field is used to produce a long plasma anode, which is simultaneously the channel of beam transportation by residual gas ionization. The high-current electron beam is formed from the explosive emission cathode placed in the preliminarily formed plasma. Numerical modeling is performed using the KARAT PIC code.     

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.     

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.     

Analysis of propagation of a high-current electron beam from a sectioned plasma-filled diode

We report on the results of analysis of propagation of an electron beam from a plasma-filled diode in the absence of the metal anode between the regions of beam generation and transportation. The diode parameters are 160 kA, 400 kV, and 50 GW. At a distance exceeding 10 cm behind the generation region, a beam current of 100 kA to the target and an energy density of 20 J/cm² are attained for the beam cross-sectional area of about 200 cm². The possibility of varying the beam current and energy density by changing the distance to the target is demonstrated.     

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.     

Analytic theory of formation of tubular electron beams of various thicknesses in high-current coaxial diodes with magnetic isolation

The problem of beam formation in a coaxial diode with a tubular cathode of various thicknesses in both infinitely strong and finite isolating magnetic fields is analyzed. A method is developed for the determination of principal beam characteristics on the basis of invariants of the formation problem and preliminary solution of the problem of transport of beams of quasi-homogeneous density with various generalized-momentum vortices. Necessary conditions are found for the formation of quasi-homogeneous beams, and the evolution of their characteristics with variation of the geometrical and electrical parameters of the system is traced.Institute of Applied Physics, Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 34, No. 9, pp. 1027–1040, September, 1991.     

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     

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.     

强流电子束二极管陶瓷真空界面

从绝缘和机械强度两方面优化设计了一种应用于强流电子束二极管的陶瓷真空界面。首先,依据真空沿面闪络机理及其影响因素,针对外径220mm的陶瓷板,应用ANSYS静电场模拟,通过对阴极电极形状和阳极外壳尺寸的调整,使得陶瓷沿面电场和阴、阳极三结合点场强均得到了有效控制。模拟结果显示:陶瓷沿面电场分布均匀,阴、阳极三结合点场强小于30kV/cm,电场线与陶瓷表面所成角度基本保持在45°;其次,针对陶瓷与电极的约束结构,通过静力和瞬态冲击分析,确定了该陶瓷界面可承受的最大静压和冲击波最大峰压分别为4.8MPa和60MPa;最后,在脉宽200ns的脉冲功率驱动源上进行了实验研究,陶瓷真空界面平均绝缘场强达到44kV/cm,二极管运行稳定,机械性能可靠,实验结果与理论设计相符。     

强流电子束二极管陶瓷真空界面

从绝缘和机械强度两方面优化设计了一种应用于强流电子束二极管的陶瓷真空界面。首先,依据真空沿面闪络机理及其影响因素,针对外径220 mm的陶瓷板,应用ANSYS静电场模拟,通过对阴极电极形状和阳极外壳尺寸的调整,使得陶瓷沿面电场和阴、阳极三结合点场强均得到了有效控制。模拟结果显示：陶瓷沿面电场分布均匀,阴、阳极三结合点场强小于30 kV/cm,电场线与陶瓷表面所成角度基本保持在45;其次,针对陶瓷与电极的约束结构,通过静力和瞬态冲击分析,确定了该陶瓷界面可承受的最大静压和冲击波最大峰压分别为4.8 MPa和60 MPa;最后,在脉宽200 ns的脉冲功率驱动源上进行了实验研究,陶瓷真空界面平均绝缘场强达到44 kV/cm,二极管运行稳定,机械性能可靠,实验结果与理论设计相符。     

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.     

Numerical study of the current-voltage characteristic of a plasma-filled high-current diode

A numerical study is performed of a one-dimensional model of a high current plasma-filled diode, connected in a circuit with a voltage generator. Flow of the plasma from an external source into the diode anode-cathode gap through the plane of the cathode grid proves to have a definite effect on the diode current-voltage characteristic. An estimate is made of the limiting current above which formation of a cathode double layer occurs. Generation of explosive emission at a high value of current or the time derivative of current causes rapid expansion of the cathode layer due to a lack of the majority, electron current component and the presence of a phase intensified by plasma erosion. Dependence of the current-voltage characteristic on density of cathode explosive emission centers is noted.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 48–53, October, 1988.     

Structure and phase composition of a chromium-silicon system modified by high-current electron beams

The results of studies of the structure-phase state of a chromium-coated silicon substrate system’s subsurface layer treated with low-energy high-current electron beams, 50–200 μs in duration and with an energy density of 15 J/cm², are reported. The data of raster electron microscopy and X-ray structural and spectral microanalysis revealed the formation of a chromium-doped silicon layer with a thickness of 2–38 μm, chromium-enriched silicon dendrites, chromium disilicide CrSi₂, and an amorphous eutectic layer (the characteristic cross-section size of the chromium-enriched phase extrusions is ∼50 nm). The structure-phase transformations are discussed taking into account the peculiarities of the distribution of temperature, diffusion and convective mass-transfer in the modified layer.     

Measurements of the transverse electron velocities in high-current microsecond relativistic electron beams in a strong magnetic field

An analyzer is created for time-resolved measurements of the electron pitch-angles in high-current microsecond relativistic electron beams in a strong magnetic field. The electron pitch-angles in a 500-keV relativistic electron beam with a current density of ∼1 kA/cm² and a 1-μs flat-top current profile are measured. The diode proposed previously by the authors allows one to produce a high-current electron beam in which pitchangles vary only slightly with time and over the beam cross section.     

Beam-halo measurements in high-current proton beams

We present results from an experimental study of the beam halo in a high-current 6.7-MeV proton beam propagating through a 52-quadrupole periodic-focusing channel. The gradients of the first four quadrupoles were independently adjusted to match or mismatch the injected beam. Emittances and beamwidths were obtained from measured profiles for comparisons with maximum emittance-growth predictions of a free-energy model and maximum halo-amplitude predictions of a particle-core model. The experimental results support both models and the present theoretical picture of halo formation.     

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)