A brief review and several new results on non-relativistic, high-current electron beams production in the guns based on the cathode unit with built-in resistively decoupled plasma sources based on vacuum arc triggered by dielectric surface flashover are presented. The production both planar-axial and radially converging wide-area, high-current electron beams has been demonstrated. It was shown that the sources of high-current electron beams based on such guns have several advantages in comparison with traditional sources with explosive-emission cathode and plasma anode: increased average current density, improved stability of the beam parameters and some others. The operation of the sources in the mode of vacuum, gas-filled and plasma filled diode has been investigated. It was founded that beam pulse energy is very sensitive to the working gas pressure and it decreases at some critical value because of beam-plasma discharge in the diode. For the case of radially converging beams, a method of the beam pulse energy increasing with the use of electrostatic screens limiting an outflow of charged particle and UV radiation towards surrounding space was proposed.

The dynamics of plasma glow in a high-current electron gun with explosive-emission cathode was investigated with the use of high-speed four-channel electron-optical camera. The cathode represented a copper disk of 5.8 cm in diameter with 69 resistively decoupled arc plasma sources located inside a 4.8 cm-diameter circle. It was found that all plasma sources are fired within less than 50 ns at the accelerating voltage pulse amplitude of 8 kV and higher. The influence of guide magnetic field on the number and localization of the cathode spots has been studied. In the presence of a guide magnetic field, the number of cathode spots during the pulse increases slightly, and the increase in the diode current is ensured mainly by their expansion, i.e. increasing the area of the emitting surface. In contrast, in the absence of a guiding magnetic field, a significant number of cathode spots are observed on the stainless steel screen electrode surrounding the cathode disk and electrically connected to it. This is due to the so-called “grab” effect, i.e. the appearance of new cathode spots under the plasma in contact with the cathode surface.

The present work is devoted to the study of current characteristics of a high-current, plasma-filled electron gun with multi-gap initiation of explosive emission by dielectric surface flashover at different accelerating voltages and densities of plasma preliminarily filling the space between the cathode and collector. Multi-gap initiation of explosive emission is performed with the use of resistively decoupled and operating in parallel arc plasma sources which are built-in to the disk explosive-emission cathode. Plasma anode was formed by high-current reflective (Penning) discharge or by hybrid discharge matching Penning discharge with vacuum arcs. Experiments have demonstrated good emissivity of a new cathode assembly, which is approximately 1.5–2 times higher than emissivity of traditional multi-wire copper explosive-emission cathode. Stable operability of this high-current electron gun is confirmed for the amplitude of accelerating voltage in the range of 5–30 kV in contrast to mentioned above traditional gun requiring, at least, 17– 20 kV for reliable operation of the cathode.

The distributions of the current and energy densities of low-energy (up to 30 keV), high-current (up to 20 kA) electron beam of microsecond duration have been studied with the use of thermal imaging and wide-band oscilloscope. It was shown that energy density distribution is quite uniform (inside the circle of 2.5 cm in diameter that is closer to the outer diameter of cathode emitting part) at the guide magnetic field compared or somewhat higher in induction to the beam self-magnetic field. In the case of low guide magnetic field or its absence, the beam focuses and its energy density distribution becomes sharp non-uniform. It was also shown that even low magnetic field (about 25 mT) stabilizes the beam position in cross section. Any micro- non-uniformities of millimeter scale were not observed in the energy density distributions.

Energetic characteristics of a high-current electron gun with a cathode assembly based on multi-gap initiation of explosive emission by dielectric surface flashover in the mode of vacuum and gas-filled diode were investigated. It has been shown that it is better to measure high-current electron beam pulse energy using a calorimetric (thermal imaging) method than to calculate it from the waveforms of accelerating voltage and beam current onto collector (target) since the beam current values may be essentially overstated because of decay current of a dense plasma emergent under the bombardment of a collector by the beam electrons. The best efficiency of the energy transfer from the capacitive storage of the high-voltage pulsed generator supplying an electron gun was observed in the case of gas-filled diode at a moderate pressure of the working gas (argon, 0.093 Pa).

The formation process and some characteristics of a high-current electron beam in dependence on pressure and working gas (argon, air, helium) filling the diode as well as on induction of an external guide magnetic field are investigated. The explosive emission is initiated with the use of arc plasma sources built into a copper disc cathode. It is shown that both the beam current and its pulse energy increase monotonically with the magnetic field induction. The beam pulse energy dependence on the gas pressure is, on the contrary, nonmonotonic. At first, the beam pulse energy increases with the pressure and then falls down due to the development of a beam-plasma discharge, which decreases both the diode impedance and the beam pulse duration.

Исследованы энергетические характеристики сильноточной электронной пушки с радиально сходящимся электронным пучком. Катодный узел пушки состоял из одной или двух кольцевых секций с внутренним диаметром 8 см, каждая из которых включала 18 резистивно развязанных дуговых источников плазмы, инициируемых пробоем по поверхности диэлектрика. Показано, что электростатическое экранирование, препятствующее выходу электронов и ультрафиолетового излучения из катодной и анодной плазмы в пространство за катодом, снижает вероятность развития пробоя вдоль резисторов дуговых источников плазмы и позволяет примерно вдвое увеличить энергию пучка, выделяемую в аноде. В двухсекционном варианте катодного узла ширина автографа пучка на аноде (следа оплавления) составила около 7 см при аксиальном расстоянии между центрами секций 4 см.

Исследованы характеристики сильноточной электронной пушки в зависимости от давления и рода рабочего газа (аргон, воздух, гелий), наполняющего пушку. Инициирование взрывной эмиссии осуществлялось с помощью дуговых источников плазмы, встроенных в дисковый медный катод. Транспортировка сильноточного пучка (5‒20 кэВ, 10‒25 кА, 2‒4 мкс) осуществлялась в ведущем магнитном поле индукцией 0.08 Тл. Показано, что зависимость энергии пучка в импульсе от давления газа является немонотонной: сначала она растёт с увеличением давления, а затем падает, что связано с развитием плазменно-пучкового разряда, приводящего к падению импеданса пушки и сокращению длительности импульса пучка.

Energetic characteristics of a high-current electron gun with a cathode assembly based on multi-gap initiation of explosive emission by dielectric surface flashover in the mode of vacuum and gas-filled diode were investigated. It has been shown that it is better to measure high-current electron beam pulse energy using a calorimetric (thermal imaging) method than to calculate it from the waveforms of accelerating voltage and beam current onto collector (target) since the beam current values may be essentially overstated because of decay current of a dense plasma emergent under the bombardment of a collector by the beam electrons. The best efficiency of the energy transfer from the capacitive storage of the high-voltage pulsed generator supplying an electron gun was observed in the case of gas-filled diode at a moderate pressure of the working gas (argon, 0.093 Pa).

Представлены некоторые характеристики электронной пушки с радиально сходящимся низкоэнергетическим (5–25 кэВ) сильноточным (до 30 кА) пучком микросекундной длительности, предназначенной для модификации поверхностных слоев протяжённых цилиндрических изделий и образцов. Катодный узел пушки включает кольцевой взрывоэмиссионный катод, в который встроены 18 резистивно развязанных дуговых источников плазмы, инициируемых пробоем по поверхности диэлектрика. Продемонстрирована работоспособность электронной пушки источника в режиме вакуумного диода (давление остаточных газов около 0.013 Па) и газонаполненного диода при давлении воздуха 0.05–0.09 Па. Показано, что плотность энергии пучка в импульсе достигает не менее 5–5.5 Дж/см2при зарядном напряжении генератора высоковольтных импульсов, питающего электронную пушку, 17 кВ, что является достаточным для оплавления подавляющего большинства металлов и сплавов.

The design and some characteristics of a source of radially converging low-energy (5–25 keV) high-current electron beams of microsecond pulse duration, which is aimed at surface modification of cylindrical parts and samples, are presented. The cathode unit of the source is a duralumin ring with an 8-cm inner diameter in which which 18 resistively decoupled arc plasma sources are built-in. The operability of the source electron gun in the vacuum-diode (with a residual-gas pressure of ~0.013 Pa) and gas-filled-diode modes at pressures of 0.05–0.09 Pa has been demonstrated. The beam energy density on the 1-cm-diameter anode is sufficient for surface melting of copper (the threshold of pulsed copper melting is 5–5.5 J/cm 2 at a pulse duration of 2–3 µs) at a 17-kV charging voltage of the high-voltage pulse generator that powers the electron gun.

The operating characteristics of an electron gun with a controlled explosive emission cathode have been investigated. The multichannel initiation of explosive electron emission from the (copper disk) cathode occurs due to the use of simultaneously operating resistively uncoupled arc plasma sources built in the cathode. Three gun operation options were tested, namely with a vacuum, a gas-filled, and a plasma-filled diode. In the last case, a plasma anode was formed using a high-current reflective (Penning) discharge or a hybrid discharge combining a Penning discharge with vacuum arcs. The cathode unit has shown a high emissive power (a factor of 1.5-2 higher than that of a conventional gun with a plasma anode and a multiwire copper explosive emission cathode). Stable operation of the gun was observed at an accelerating voltage of amplitude 5-30 kV, in contrast to at least 17-20 kV required for stable operation of the conventional gun. The gun operation with a vacuum and a gasfilled diode provided a considerably more efficient energy transfer from the power supply to the electron beam.

A new scheme of the cathode assembly of a high-current electron gun is presented. Initiation of explosive emission is performed with the help of sixty nine simultaneously operating spark gaps which electrodes and tube ceramic isolators are inserted into a disc explosive-emission cathode. The operability and high emissivity of the cathode assembly which exceeds by 1.5‒1.7 times the value inherent in traditional scheme of an electron gun with plasma anode and copper-braid explosive-emission cathode has been demonstrated.

The paper presents the results of a study of a glow spatial structure and temporal dynamics of a hybrid discharge combining a high-current reflective discharge with vacuum arcs at a voltage supplying the discharge up to 9 kV and working gas (argon) pressures of 0.1–1 mTorr. The possibility of forming a plasma anode with enhanced ion density at the periphery has been demonstrated with the use of this discharge. Preliminary results of measurements of the energy density distribution over the cross section of a low-energy (up to 30 keV) high-current (up to 25 kA) electron beam formed in an electron gun with explosive emission cathode and plasma anode based on the hybrid discharge are also presented. The promise of the proposed method for improving the beam homogeneity has been shown.

In the paper, the results of the study of space structure and temporal dynamics of a hybrid discharge matching a high-current reflective discharge with vacuum arcs initiated by surface dielectric flashover at the discharge supplying voltages up to 9 kV and working gas (argon) pressures of 0.1 – 1 mTorr are presented. The possibility of the formation of plasma anode with the density increased at the periphery including the use of an auxiliary screen has been demonstrated. The measurements of energy density distribution of a low-energy, high-current electron beam formed in an electron gun with explosive-emission cathode and plasma anode based on this hybrid discharge are also presented. The results obtained are comparable with those achieved with the use of magnetic field concentrators. Since the use of concentrators is not always possible, so the suggested method of the beam uniformity improvement looks promising.

A new scheme of the cathode assembly of a high-current electron gun is presented. The initiation of explosive emission is carried out using of 69 parallel triggered spark gaps, the electrodes and tubular ceramic insulators of which are built into the disk explosive-emission cathode. The efficiency of the proposed scheme and the high emissivity of the cathode assembly, which is approximately 1.5–1.7 times higher than the emissivity that is characteristic for a traditional gun scheme with a plasma anode and a copper-braided explosive emission cathode, are demonstrated.

The design and characteristics of resistively decoupled multi-emitter explosive-emission cathodes intended for high-current plasma-filled diodes are presented. The integral glow of the emission-center plasma, the energy-density distribution over the cross section of a nonrelativistic high-current electron beam, which is formed in the plasma-filled diode, and the operation lifetime of the cathode were studied. The best results were obtained for a cathode based on TVO-1 resistors, whose wire outputs serve as emitters.

The results of experiments on the use of permanent magnets shaped as a ring or square frame for the treatment of massive (thick) workpieces with a high-current electron beam are presented. It was shown that the placing of such magnets in front of the treated workpiece eliminates the beam defocusing caused by the ejecting of pulsed guide magnetic field because of skin-effect. This method provides the beam energy density to be sufficient for reliable and uniform melting of the workpiece surface layer which is needed for improvement of its physical-chemical properties: increasing corrosion resistance, smoothing microrelief (polishing), etc.

A possibility of the improvement of electrical insulation in vacuum by conditioning of each electrode with series of short-pulse breakdowns under plasma and further pulsed surface melting with low-energy, high-current electron beam has been studied. Such conditioning removes impurities limiting electrical strength of the vacuum gaps.