Ivan S. Egorov

A high-repetition rate pulsed electron accelerator

A new electron beam accelerator with beam ejection into the atmosphere has been recently developed for radiation technology application. The high-voltage nanosecond pulse generator of the accelerator is based on a low-inductance pulse transformer. A cold cathode thyratron is used as a primary switcher. The diode consists of a cathode, which provides a high delay time in the plasma formation. The electron beam current pulse duration at half height is 75 ns. The kinetic energy of the electron beam is 450 keV. A cooling system is used for the anode, which makes it possible to extract an electron beam with the current density of 12 A/cm2 into the atmosphere. The accelerator is capable to operate in a long-term-repetition rate producing up to 40 pulses per second, which is possible due to the use of a built-in system of regeneration and cooling of the transformer oil. The results of shot-to-shot variation of the beam parameters in the repetitive mode are presented.

The Astra repetitive-pulse electron accelerator

The description and results of tests of the Astra pulsed electron accelerator are presented. A high-voltage pulse transformer with a pseudospark gap that serves as a switch of a capacitive storage is directly loaded into a vacuum planar diode, which is based on a metal-ceramic cathode with a long delay time of the electron explosive emission. The generated electron beam is injected into the atmosphere at a frequency of 50 Hz. The full width at half maximum (FWHM) duration of the injected beam current is 60 ns for an accelerating voltage of 370 ± 10 kV. The electron-beam energy is 19 J, when the accelerator operates into an internal target, and 4.5 J, when the electron beam is injected into the atmosphere and the low-energy fraction of beam electrons is cut off by a separating foil.

Principle and simulation of a high voltage bushing for a repetitive electron accelerator

A cylindrical graded bushing for the electron gun of the ASTRA-M pulsed repetitive accelerator was developed and simulated. In previous tests of the cylindrical graded bushing, primary reasons of electrical breakdown and degradation of dielectric elements were determined. Computational software was used to analyze the electric fields and simulate processes in the voltage grading system of the cylindrical bushing. This enabled proper modification and correction to the insulator structure for known problems. The new bushing has a conical structure instead of cylindrical one. The voltage graduation system uses nonsymmetrical voltage dividing for equal potential distribution along the grading electrodes. The grading electrodes provide shielding of organic dielectric surfaces from accelerated electrons and ultraviolet irradiation. Transmitted energy losses of up to 10% have been estimated in the nonsymmetrical voltage divider of conical bushing by simulating of high voltage pulse of 600 kV amplitude and 400 ns duration.

Thermal Stability of Iron Micro- and Nanopowders after Electron Beam Irradiation

Chemical activity of micro-and nanosized powders during open air heating after electron beam (up to 360 keV of electron kinetic energy) irradiation has been studied. A differential thermal analysis disclosed that an initial oxidation temperature for iron powders has been decreased to ~ 30°C after electron beam irradiation. Thus, the thermal oxidative stability of iron powders in air was improved without any detected changes in other activity parameters.

The Energy Stored in the Aluminum Nanopowder Irradiated by Electron Beam

The influence of the electron beam irradiation on the parameters of aluminum nanopowder oxidation by heating in air was studied. It was found that the oxidation starts at the temperature in the range from 410° C to 460° C and independent on the radiation dose. The degree of oxidation varied from 44.4 % to 58.3 % and its dependence on the radiation dose was not established. The heat energy release occurred in two stages: at the first stage (up to ~ 660° C) in general the increase of the thermal effect was observed. At the second oxidation stage of irradiated aluminum nanopowder the growth of the thermal effect also observed. The peak of heat effect achieved by irradiation (45.0 kGy absorbed dose) was 2576 J/g higher than the thermal effect for non-irradiated aluminum nanopowder. The energy stored is an additional motivating factor in the synthesis of composite materials, intermetallic compounds, hydrogen producing reactions and synthesis of various kinds.

A self-triggering system for a cold-cathode thyratron in a pulse voltage generator

A triggering scheme of the ТДИ high-voltage high-current switch of the pulse voltage generator for powering the vacuum diode of the Astra frequency electron accelerator is described. Its special feature is the automatic triggering mode of the switch, which is synchronized to the charging process of the high-voltage capacitive storage. The energy required for producing control pulses (1 J) is extracted in the process of charging the high-voltage capacitive storage using a pulse current transformer. The processes are synchronized by a peak transformer connected to the storage charging circuit. The components of the circuit are intended for the continuous operation with a repetition rate of up to 100 s−1.

Note: Numerical simulation and experimental validation of accelerating voltage formation for a pulsed electron accelerator.

This paper describes the development of a computation model of a pulsed voltage generator for a repetitive electron accelerator. The model is based on a principle circuit of the generator, supplemented with the parasitics elements of the construction. Verification of the principle model was achieved by comparison of simulation with experimental results, where reasonable agreement was demonstrated for a wide range of generator load resistance.

Influence of a Pulsed Electron Beam on the Sowing Quality of Wheat

Wheat grain has been irradiated by 200 keV and 305 keV of pulsed electron beams for changing of sowing parameters. Total microbial number, germination and germination energy were compared for both of electron kinetic energy settings for the same ranges of the energy input. The electron beam of 305 keV showed better disinfecting effect for energy input values of less than 4 J/g. That mode eliminates seed germination ability after irradiation of more than 2 J/g and can be used for grain storing. The mode of 200 keV beam keeps seed germination ability up to 5 J/g with the similar disinfecting effect after the irradiation energy input of more than 4 J/g. This mode can be used for pre-sowing seed treatment procedure.

Design and testing of fluid resistor for repetitive high-voltage pulse generator

The paper presents a design and the results of testing of the liquid resistive load for a repetitive high-voltage generator (200 kV, 0.5 ms). The load uses a sealed dielectric case, which is to be placed into a vacuum volume (5×10-4 Torr) for electrical strength ensuring. Repetitive testing of the generator with the load (10 pps) caused the electrolyte heating, the load resistance decreasing, and the changing of a generator mode. An expansion tank is used to compensate thermal expansion of the electrolyte, which makes it possible to absorb up to 1 MJ of energy in the load without seals breaking. A generator load curve can be obtained for one experiment with a help of the fluid load without any additional depressurization of the vacuum volume.

Multicapillary Carbon-Epoxy Tubes as a Cathode Material for a Pulsed Electron Accelerator

Paper presents the results of experiments on multicapillary carbon-epoxy as a candidate material for a cathode of a pulsed electron accelerator. A high voltage pulse of 350 kV, 350 ns (FWHM) was applied to the cathode. The pulse repetition rate was 20 pps. The optical image of the cathode surface after 4×104 shots of electron beam was changed as well as electrical characteristics of the electron diode.