A numerical simulation of a cylindrical plasma bunch with non-equilibrium ionic composition under the action of an external laser pulse is carried out. The pulse parameters are varied. An unsteady one-dimensional two-temperature radiation-hydrodynamic model is used. The model and its results are of interest for research in the field of active media formation of lasers in the extreme ultraviolet and soft X-ray ranges.

Based on the results of numerical simulation using a nonstationary one-dimensional two-temperature radiation hydrodynamic model, the main physical processes have been analyzed that govern the formation of cylindrical plasma bunches with a nonequilibrium ionic composition containing ions of high ionization multiplicity under laser intensities of QL ≤ 1014 W/cm2 and energies of EL ~ 10 J/cm. The work is aimed at the creation of active media for lasers generating in the extreme ultraviolet and soft X-ray spectral ranges.

We numerically studied stimulated Brillouin scattering processes up to the 5th order is microcavities with various realistic diameters and Q-factors made of standard telecommunication fibres. Pump power thresholds were simulated for different parameters of the system. The larger the microcavity and lower Q-factors, the higher pump power thresholds are. It is also shown that thresholds strongly depend on pump detuning. For a microcavity with a diameter of 200 μm and Q-factor of 5×10 7 , threshold pump powers for the 1st order stimulated scattering are 0.3 and 30 mW for pump detunings 0 (exact resonance) and 20×2π MHz, respectively.

Based on the numerical simulation results in the framework of a nonstationary one-dimensional (1D) two-temperature (2T) radiative hydrodynamic (RHD) model, the main physical processes that determine the formation of cylindrical plasma bunches with a non-equilibrium charge containing high ionized ions at laser intensity QL≤10^14 W/cm^2 and energy EL~10 J/cm are analyzed. The results of the work are devoted to the creation of active media for lasers generating in the extreme ultraviolet (EUV) and soft X-ray (SXR) spectral ranges.

The paper presents a numerical study of laser radiation interaction with cylindrical plasma medium. The model has been described in detail. Non-equilibrium sodium ions were chosen as the active medium and a CO2-laser as an external irradiator. The calculations used the one-dimensional two-temperature single-fluid radiative-hydrodynamic approximation tak-ing into account the non-equilibrium ionic composition and the radiation absorption by plasma due to the inverse bremsstrahlung effect. In the calculations, the used laser pulse characteristics belonged to the range well-studied experimentally; e.g. the intensity of the incident laser ra-diation was about 100 TW/cm boolean AND 2. The performed calculations were aimed at the development of research on the creation of active laser media based on the multicharged ions' transitions working in the extreme UV and soft X-ray bands

This work is dedicated to a method for preionization of a laser medium (that is the most popular ones-CO 2 - and CO-lasers) using X-ray radiation created by a nanosecond sliding discharge (NSD). An experimental study has been carried out on the influence of the initial pressure and the composition of the gaseous medium on the intensity of X-ray bremsstrahlung. In order to estimate this intensity, a special sensor is used; it can measure free electron density that, in our, case is created during photoionization by X-ray radiation from an NSD. It is shown that in case an X-ray emitter is filled with argon, the photoelectron density in the vicinity of a cathode is about 15 times higher than in case the X-ray emitter is filled with helium. Moreover, when the gas volume of the X-ray emitter is filled with argon, the energy spectrum of the “runaway” electrons shifts to the region of lower values of their energy.

The results of experimental studies of a compact high-voltage pulse generator are presented. The generator is based on two artificial double forming lines in a collapsed circuit, which are switched by gas spark gaps; it also contains a peaking gas spark gap, transmission lines filled with a liquid dielectric, and a load equivalent. The characteristics of this generator were studied in the charging-voltage range of up to 100 kV. When the voltage pulse duration from the forming line was 100 ns, current pulses with an amplitude of 18 kA and a rise time of ~18 ns were obtained across an ohmic load.

Приведены результаты экспериментальных исследований высоковольтного многоканального генератора на напряжение до 100 кВ с длительностью импульса 100 нс и фронтом 8 нс. Рассмотрены варианты оптимизации выходных параметров с использованием численного моделирования схемы замещения генератора.

The possibility of stepwise formation of the active laser medium on a plasma of multicharged ions is shown based on the numerical simulation results. Practically, such compression can be carried out with a high-voltage generator, storage and forming lines. It is presented that at conditions I m ≥ 200kA in stepwise pumping mode, it is possible to obtain Xe-plasma parameters with an electron temperature Te>400 eV and a concentration Ne>10 20 cm −3 . Such plasma is a good medium for amplification of spontaneous radiation at several transitions in the spectral region λ≈10 nm in a Xe-plasma of Ni-like ions: it can provide a gain at the transitions g+~ ∼ 1-2 cm −1 .

The results of experimental studies of a high-voltage multichannel generator for a voltage of up to 100 kV with a pulse duration of 100 ns and a front of 8 ns are presented. Options for optimizing the output parameters using a numerical simulation of the generator equivalent circuit are considered.

The paper presents the numerical simulation results of the energy characteristics of a laser based on no equilibrium plasma of multiply charged ions. Plasma is created in a small inductive extended Z-discharge with a power system on heterogeneous forming lines. The requirements for the distribution of the lines parameters providing the creation of the energy density and power density necessary for the generation of radiation in the “water window” region have been established.

The paper presents the results of a numerical investigation of a fast ionization wave in a non-preionized gas as the initial stage of a nanosecond capillary discharge. The wave was created in a 5 cm long narrow capillary filled with nitrogen at a pressure p = 2 Torr by applying a nanosecond voltage pulse of negative polarity, which was supplied by an electric circuit consisting of a preliminary charged capacitor, a thyratron switch and a cable. Propagation of the wavefront along the capillary and formation of a conducting plasma channel were simulated using the fluid approach to description of processes in low-temperature plasma. Including electrical circuit into consideration allowed obtaining realistic voltage pulse shapes as well as current rise-rates in the system immediately after the ionization wave has reached the grounded electrode. The latter was used as a parameter indicating the efficiency of the consequent initiation of a capillary discharge. Obtained dynamics of wave propagation and structure of the wavefront are discussed. Influence of dielectric permittivity of the capillary material on the wave properties in general and on the capillary discharge initiation is analyzed.

X-ray lasers based on transitions in highly-charged Ni-like ions generating in the “water window” wavelength range can be pumped by compact laboratory discharge sources. In this paper, we report the results of numerical simulations of the plasma dynamics and kinetics in an X-ray laser based on transitions in Ni-like xenon ions. The laser active medium is created by an extended low-inductive high-current Z-discharge capable of producing two successive electrical pulses. The nonequilibrium multicharged ion-plasma dynamics is studied numerically using a nonstationary 1D two-temperature radiation (MHD) model, which describes plasma hydrodynamics, nonstationary ionization, transfer of the continuum and line radiation, as well as processes in the pumping electrical circuit. The ionicenergy-level populations are calculated in the quasistationary approximation. The simulation results allowed to determine the electrical and energy-pumping parameters needed to obtain a weak signal gain for the working transitions of the order of g+∼ 1 cm−1. We demonstrate that plasma with the electronic temperature of more than 400 eV and the density of more than 1019 cm−3 can be created by a low inductive two-step discharge with peak current exceeding 200 kA.

The report presents the results for numerical modeling of the active medium of short-wavelength radiation sources. The main interest was paid to transition 3-2 in He-like nitrogen ions. With the help of the developed level kinetics model and non-stationary one-dimensional two-temperature magneto-radiation-hydrodynamic code the inversions of ion level populations and amplification coefficients were calculated.

Creating stable and efficient compact X-ray sources based on fast capillary discharges that do not incorporate preliminary ionization circuits poses additional restrictions on parameters of voltage pulses and capillary geometry. Applying a voltage pulse with a rise rate of the order of 1 kV/ns results in gradual breakdown of non-ionized gas in the capillary which takes the form of an ionization wave that initiates at the powered electrode and propagates with typical velocities of 1 cm/ns. After the wave reaches the grounded electrode, a plasma channel with gradually increasing conductivity is formed. The current onset therefore appears only after a certain time delay after beginning of the voltage pulse. The ratio between the delay and the applied voltage rise-time will eventually influence the current rise rate that defines plasma heating and compression. It is therefore necessary to have the ability to estimate this delay time for a given capillary geometry and understand its dependence on the properties of a voltage pulse. In this work numerical simulations of fast ionization waves created in an extended Al2O3 capillary filled with nitrogen at 2 Torr were performed for cases of voltage pulses of negative polarity with rise-times varying in the range 10-50 ns. The numerical model was based on fluid approach with drift-diffusion approximation for charged particle fluxes. Influence of voltage rise-time on initiation and propagation of a fast ionization wave as well as on consequent rate of current rise is investigated.

The features of the multicharged ion plasma dynamics in the extended low-inductive high-current discharge with power supply system based on high-voltage generator and transmission lines was analyzed. It is shown that the power supply systems of the considered type allow one to obtain the stepwise plasma compression and heating, which creates additional programming possibilities for physical and spectroscopic characteristics, in particular, of the ionic composition of the plasma.

Nowadays capillary discharge is considered as the main way to create compact sources of EUV and soft X-ray radiation. Radiation in this range with such discharge is generated at the stage of magnetic plasma compression, when the current flowing through the system reaches values of the order of several kiloamperes. The initial conditions for the flow of such current are created by the so-called sliding discharge. In addition to pre-ionization, the role of such discharge is in stabilization during compression stage [1] and potential X-ray generation during the transition from a sliding discharge to a high-current one [2]. A complete picture of the physical processes that accompany the transition is not yet available. Consistent numerical modeling can significantly clarify the situation. We present the results of a numerical study of a sliding discharge at low pressures and applied voltages with nanosecond durations and amplitudes of several kilovolts in a long dielectric tube of small radius. The propagation dynamics of the sliding discharge along the capillary tube was reproduced, the role of the transverse field on the dynamics of the whole capillary discharge was evaluated, the values of propagation speed and degree of ionization were analyzed depending on different pressures and pulse parameters.

The paper presents the results of a numerical investigation of the dynamics of a sliding discharge in a capillary with spatial dimensions similar to those typically used in X-ray sources based on fast capillary discharges. The discharge is created in argon at pressure p = 9 Torr by applying a voltage pulse of negative polarity with an amplitude of 5 kV, a rise time of 5 ns, and a duration of 20 ns. Obtained distributions of main discharge parameters reproduce basic characteristics of a sliding discharge and reveal the mechanism of discharge propagation. The electric field in the front of the discharge is defined by a negative space charge, which at a given moment during discharge propagation is localized in a narrow region along the dielectric surface. For the considered case, discharge propagation is accompanied by full charging of the dielectric surface. The influence of gas pressure on discharge is investigated within range p = 2–25 Torr. Extrema in dependencies of total discharge time and front velocity on gas pressure are obtained in simulations and analyzed.

Peculiarities of the dynamics of multicharged ion plasma in extended longitudinal low-inductance high-current discharge with a power supply system based on a high-voltage generator and transmission line have been analyzed. It is shown that, using power supply systems of this type, it is possible to manage stepwise compression and heating of plasma, which provides additional possibilities in programming the physical and spectroscopic characteristics of plasma, including its ion composition.