Исследованы характеристики барьерного газового разряда в гелии при атмосферном давлении при возбуждении импульсами с фронтами нарастания напряжения 2.5-10 нс и частотой следования импульсов 5-100 кГц. В объемном режиме получен импульсный ток до 80 А с пиковой мощностью до 1.5 МВт и удельной мощностью до 250 Вт/см3. Увеличение крутизны импульсов возбуждения незначительно влияет на величину тока разряда, но позволяет сохранить объемный характер протекания тока до более высоких рабочих напряжений. Показано, что максимальный ток разряда ограничивается накоплением заряда на поверхности диэлектрика и, тем самым, увеличением её плавающего потенциала, что приводит к уменьшению разности потенциала относительно квазинейтральной плазмы. Показано, что увеличение разрядного промежутка и увеличение напряжения вызывает переход от однородного объемного протекания тока к шнурованию.

The experimental study of the laser on RM 4p2P3/2∘ - 3d2D5/2 (λ=854.2nm) and 4p2P1/2∘ - 3d2D3/2 (λ=866.2nm) transitions in a singly ionized calcium with active medium volume of 97 cm3 has been carried out. Excitation was performed with the periodic bursts containing 200 pulses each. It is shown that the laser pulse energy enters the steady-state mode during the burst. When the frequency of pulses inside the burst equaled to 90 kHz the steady-state value of the laser energy was 59 mJ, which corresponds to the average output power of 5.3 W. The measured power ratio between lines with λ=854.2nm and λ = 866.2 nm under optimum conditions amounted to 1.7, with radiation pulse duration of 20 ns. Experimental results for lasers on atom RM-transitions operating at pulse repetition frequency f≥100 kHz are reviewed. It is demonstrated that at such f values the energy characteristics of the Ca+ laser are comparable with those of lasers on atom RM transitions of other metals. An analysis of the mechanisms preventing further increase in the average output power when the pulse repetition frequency is increased above 100 kHz is presented.

The characteristics of barrier gas discharge in helium at atmospheric pressure are investigated when excited by pulses with voltage rise fronts of 3–10 ns and a pulse repetition rate of 5–100 kHz. The volumetric mode of the pulse current up to 80 A with a peak power of up to 1.5 MW and a specific power supply of an average power of up to 250 W cm−3 is realized. An increase in the steepness of the excitation pulses has little effect on the discharge current value but allows to maintain the volumetric nature of the current flow to the higher operating voltages. It is demonstrated that the maximum discharge current is restricted by an increase in ionization with an increase in the electron current from the cathode due to the ion–electron emission and charging of the dielectric surface, which increases the floating potential of the cathode surface relative to plasma.

The results of the investigation of the breakdown characteristics of the planar “open” discharge and open discharge with the generation of counter-propagating electron beams under excitation by pulses with nanosecond rise fronts are presented. The amplitude parameters of current and voltage and temporal characteristics of breakdown in helium, neon, and argon were measured. It is demonstrated that the breakdown in the open discharge is characterized by considerably larger electric field strengths at the same development delays as in the avalanche discharge. A similarity criterion based on the photoemission mechanism of electron generation, according to which the discharge development delay is inversely proportional to the squared working gas pressure, is obtained.

The abnormal discharge (AD) in pure helium and in helium containing molecular impurities was investigated. The obtained results were compared with the parameters of wide-aperture AD and different variants of ‘open’ discharge. It was shown that in all of the investigated types of discharges the current–voltage characteristics (CVCs) and, correspondingly, the emission properties of cold cathodes are determined mainly not by their material, but by the doping of cathodes with atoms of working gases and the purity of experimental conditions. With the impurity content less than 10 −4 % of the helium atom concentration, the CVCs begin to acquire S-shaped form, which is associated with a change in the electron emission mechanism. It was shown that the diversity of the CVCs is caused by uncertainty in the values of the secondary electron emission coefficients γ and the electron multiplication coefficient α in the cathode layer at reduced electric field strength E / N > 10 3 Td. The reproducibility of CVCs and, correspondingly, emission properties of cathodes can be ensured by high purity of the working gas and by maintenance of the cathode doping only by the working gas atoms.

We present the results of a study of the breakdown characteristics of a planar "open" discharge in helium when excited by pulses with nanosecond rise fronts. It is demonstrated that the development of the discharge is characterized by considerably larger values of the reduced electric field strength than in the avalanche discharge. A similarity criterion was obtained for discharges with a predominance of the photoemission mechanism of electron generation, according to which the rate of discharge development is proportional to the square of the working gas pressure.

We present the results of a study of the breakdown characteristics of a planar "open" discharge in helium when excited by pulses with nanosecond rising edge. It is demonstrated that the development of the discharge is characterized by considerably larger values of the reduced electric field strength than in the avalanche discharge. A similarity criterion was obtained for discharges with a predominance of the photoemission mechanism of electron generation, according to which the rate of discharge development is proportional to the square of the working gas pressure. Keywords: nanosecond gas discharge, breakdown, delay time, similarity condition.

We present the results of experimental studies of the output parameters of the lasers with a volume of 0.1 dm3 at RM transitions in barium and calcium ions. For Ca+ laser an average power of 4.5 W at a pulse repetition frequency of 100 kHz was achieved in the burst operation mode. For Ba+ laser the obtained steady-state average output power in the burst-mode operation amounted to 74 mW at a pulse repetition frequency 40 kHz. Typical laser pulse duration at half-maximum equaled correspondingly 13 and 5 ns for Ca+and Ba+ lasers.

Experimental results of the laser operating on the barium ion self-terminating transition 6p(2)P(3/2)(o) - 5d(2)D(5/2) at lambda = 614.2 nm investigations are presented. Through a series of tests, we demonstrated a significant improvement of the output characteristics of this laser by employing (i) a novel high-voltage nanosecond switch capable to operate at high pulse repetition frequency (more than 50 kHz), and (ii) hydrogen addition to the active medium. Achieved steady-state average output power in the burst-mode operation amounted to 125 mW with laser pulse duration of asymptotic to 5 ns at half-maximum.

Investigations of the operating parameters of a plasma-cathode switch based on a capillary discharge in helium and neon in the burst mode are presented. An increase in the efficiency of the switch is demonstrated when an additional preionization pulse is applied at a low pulse repetition frequency (5 kHz). The compression ratio of voltage pulses more than 300 is achieved at a pulse repetition frequencies less than 40 kHz.

Investigations of the operating characteristics of plasma switches based on the open discharge with the counter-propagating electron beams in helium, nitrogen, oxygen, and also in their mixtures have been carried out. In spite of the differences in the mechanisms of discharge burning for various conditions, which leads to the differences in switching characteristics, devices with switching times of 0.28–1.8 ns for design without a drift space and 1–2.5 ns with it are implemented. Even at a moderate voltage U ∼ 10 kV the obtained switching efficiency is in the range of 76%–95%, which exceeds values for the other gas-discharge devices, operating at high pulse repetition rate with ∼1 ns pulse leading front.

Comparative studies of the switching characteristics of devices based on an open discharge - kivotrons in molecular gases (nitrogen and oxygen), as well as their mixtures with helium - have been carried out. The choice of nitrogen and oxygen is due to the fact that the emission coefficients of electrons under the action of their heavy particles are much higher than for helium. It is shown that for this case, as well as with the predominance of the photoelectronic emission mechanism in helium, it is also possible to create fast switches. Their advantage is significantly lower requirements for the cleanliness of the working environment.

The results of investigation of the current-voltage characteristics (CVCs) and electron beam generation efficiency in continuous discharges in helium, its mixtures with oxygen and nitrogen, as well as in pure oxygen and helium are presented. Peculiarities of CVCs are singled out and interpreted in terms of a changed role of the principal emission mechanisms with an increase in the voltage. It is shown that a high efficiency of the electron beam generation of more than 80% can be achieved in glow discharges in helium, oxygen, and nitrogen. In helium, it is provided by the predominating photoemission, while in oxygen and nitrogen and their mixtures with helium – mainly by the kinetic emission under the impact of fast heavy particles.

The results of investigation of a new type of switch (eptron), which expands the opportunities of voltage waveform tailoring for low temperature plasma applications, are presented. This switch consists of the device with counter-propagating electron beams (kivotron), which acts as a plasma cathode, and capillary integrated with the kivotron into a single device. The main advantage of a discharge in a capillary is various mechanisms of charge neutralization at different plasma densities. At a low density (10(10)-10(11)) cm(-3), free transport of electrons to the walls of the capillary occurs, due to which a large delay in the development of the discharge is realized. At a high plasma density, due to Debye screening, a rapid charges multiplication occurs and fast switching is realized. Under optimal conditions corresponding to the maximum value of the Townsend multiplication coefficient, a switching time less than similar to 1 ns is achieved. The comparative characteristics of the kivotron and eptron due to different mechanisms of subnanosecond switching are considered. The kivotron has a much lower inductance, which allows it to receive currents of tens of kiloamperes. Eptron operates more efficiently with a small characteristic size of the capillary, preferably a few tens of millimetres square. As a result, plasma recombination in the capillary in the eptron in the interpulse interval is much faster than in the kivotron, which allows operating at pulse repetition frequency above 100 kHz and the operating voltage of tens of kilovolts. The subnanosecond switching time in the eptron is realized at currents up to similar to 1 kA. Nevertheless, eptron provides new opportunities of voltage waveform tailoring, specifically for pulses generating with a subnanosecond leading edge. Particularly, it is demonstrated that lasing characteristics of BaII and HgII lasers on self-terminating transitions are significantly improved in comparison with conventional power supply.

Novel opportunities of waveform tailoring for controlling plasma parameters based on the development of a high-voltage gas-discharge switch with a subnanosecond breakdown time and high pulse repetition frequency are discussed. The studies of characteristics and breakdown development mechanisms of the switch based on an ‘open’ discharge—kivotron are summarized. The discharge in the switch is carried out in conditions when counter-propagating electron beams in high electric field are generated. In this case, when using helium as an operating medium, firstly, atoms are effectively excited into the resonance state by fast particles. Secondly, due to the Doppler effect, resonant photons without reabsorption reach the cathode surface, maintaining the discharge current due to photoemission. Thirdly, fast heavy particles modify the cathode surface, thereby significantly (up to an order of magnitude) increasing the photoemission coefficient. The combination of these processes leads to an increase in the switching rate with an increase in the operating voltage U and helium pressure pHe. At U > 20 kV and pHe > 10 Torr, the switching time becomes less than 100 ps both in the experiment and according to the simulation. It is preferable to use planar geometry without a drift space as a switching device, in which, on the one hand, the most complete use of EB energy is realized in creating a plasma with a high charge density, on the other hand, a small wave impedance of the switch is realized. As a result, currents of tens of kiloamperes are achieved at voltages up to 100 kV. In an interpulse period plasma in the discharge gaps recombinates fast. As a result, switches can operate up to pulse repetition frequency 100 kHz. Together these achievements open new opportunities to control plasma parameters.

Results of comparative investigations of the pulse-switching characteristics of devices (kivotrons) based on the open discharge in molecular gases (oxygen and nitrogen) and their mixtures with helium are presented. The choice of oxygen and nitrogen is determined by the fact that the coefficients of electron emission under impact of their heavy particles are much higher as compared to that for helium. It is established that this factor, as well as the case of predominantly photoelectron emission mechanism operative in helium, makes the creation of fast switches possible. These switches are advantageous in posing lower requirements on the purity of a working gas medium.

Frequency characteristics of a subnanosecond plasma switch based on a combination of an open discharge or a discharge in a hollow cathode and a capillary discharge removed from the internal cavity of the plasma cathode are presented. It is shown that in the presence of an external screen that provides a capacitive discharge and hence, exclusion of the period of weak electron multiplication in the capillary from the delay mechanism of the discharge development, a high pulse repetition frequency is reached for different designs of the plasma cathode and the capillary section. It is demonstrated that at the voltage U = 30 kV, the pulse repetition frequency f = 100 kHz is reached for the capillary with round cross section at pHe ≤ 2.6 Torr and for the capillary with rectangular cross section at pHe ≤ 3.05 Torr.

The data on the experimental study of the characteristics of a gas-discharge switching device consisting of an open discharge section with generation of counter propagating electron beams acting as an electron emitter, and a capillary discharge section providing a large time delay for the development of the discharge τd and a rapid recombination of the plasma after the passage of the current pulse are presented. The ability of this device to operate at voltages up to 100 kV, while maintaining a delay time τd of the order of several hundred ns and subnanosecond capillary breakdown τsc, is demonstrated. The τsc voltage independence in the range of helium pressures pHe = 6–30 Torr was found.

The lasing characteristics of a copper vapour laser in a tube with forced heating, having a length of 50 cm and a diameter of 2 cm, excited by a train of pulses are investigated. Comparative studies of the frequency and energy characteristics of the laser are performed with a leading edge duration of the excitation pulse of ∼25 ns (when the capacitance discharges through a thyratron and a magnetic compression line) and ∼3 and 1 ns (using circuits with a high-speed switch – kivotron). It is shown that a decrease in the leading edge duration gives rise to an increase in the optimal pulse repetition rate up to ∼30 kHz, the generation efficiency up to 3.2 % and the generation power per unit length over 100 W m−1. The results obtained confirm the concept of limiting the frequency and energy characteristics of a copper vapour laser due to the insufficient rate of energy input into the plasma at high prepulse electron concentrations.