Capillary Discharge Research Articles

Pulsed Jets for Dense Plasma Generation in an External Magnetic Field

In this work, results of numerical simulation of the interaction of pulsed capillary discharge plasma jets at atmospheric pressure are presented. The interaction of the pulsed plasma jets with a shock wave is considered. Modes with plasma jets created by the capillary discharge with a vaporizing wall expiring through a magnetic nozzle are simulated. Results obtained for several plasma channels are presented together with calculated plasma jets in the capillary discharge with a vaporizing wall.

Frequency Characteristics of a Subnanosecond Plasma Switch

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.

Theoretical study of wakefield acceleration of electrons in capillary Z-pinch plasma waveguide

The theoretical investigation of wakefield acceleration of electrons by CO2-laser pulse with central wavelength of 10.6 μm and input peak intensity of ∼1017 W/cm2 in transient hydrogen-plasma waveguide has been conducted. The plasma waveguide is produced by the fast Z-pinch discharge inside a 3 mm inner diameter and 50 mm long capillary. The waveguide properties of the capillary Z-pinch plasma were obtained from the space and frequency dependent wave equation that combines the attenuated charged particle inertia and the light wave effects in the plasma for the ideal Gaussian laser beam. For simulation of temporal and spatial evolution of electron density and other plasma variables during the capillary discharge, we used a standard one-fluid, two-temperature one-dimensional magnetohydrodynamic (MHD) model complemented with atomic data of hydrogen. Simulations showed that the guiding channel occurs far from capillary wall and exists for a few nanoseconds. In terms of laser driven plasma wakefield accelerators (LWFA), the Z-pinch waveguide is able to extend the acceleration length over the whole capillary, assuming that a single-mode transmission takes place. To quantify such ability of the channel, a correlation coefficient was introduced and computed at different input beam spot sizes. An optimal beam spot size was determined by taking maximum of time average of the coefficient over the channel lifetime. At the end of the guiding channel existence, the repetitive focusing and defocusing patterns were observed with intensity increase at the focal points. For simulation of the wakefield acceleration of electrons in the different waveguiding regimes we used the particle-in-cell (PIC) combined with the aforementioned MHD model. Influence of the waveguiding regimes on the electron acceleration was demonstrated.

Impact of pre-pulse current and delay time on 46.9 nm laser with larger inner diameter alumina capillary

In this Letter, we firstly, to the best of our knowledge, demonstrated the influence of pre-pulse current and delay time on the intensity of a discharge pumped Ne-like Ar soft X-ray laser operating at 46.9 nm by employing an alumina capillary having an inner diameter of 4.8 mm. Specifically, the delay time was changed from 8 to 520 μs in small intervals. The pre-discharge current was increased from 25 A to 250 A through small steps, while keeping the main discharge current constant. Usually, a small pre-discharge current is applied to an Ar-filled capillary to attain a plasma column having sufficient pre-ionization before the injection of the main current. The pre-discharge current of 140 A was declared the best current to obtain lasing with a 4.8 mm diameter capillary. The laser spots were captured at best time delays for the pre-discharge currents of 25, 45, 80, 140, and 250 A, which support the experimental results. We observed that by applying the pre-discharge current of 140 A, the laser spot exhibits small divergence, higher symmetry, and uniformity, which is clear evidence of strong amplification. The laser spot obtained at 140 A is cylindrically symmetric and has a better structure than those reported by all other groups in the literature. Hence, the laser spot indicates that the laser beam is highly focusable and beneficial for the applications of the 46.9 nm laser. Results of this Letter might open a new way to enhance applications of a 46.9 nm capillary discharge soft X-ray laser.

Study of Thermal Effect in the Interaction of Nanosecond Capillary Discharge Extreme Ultraviolet Laser with Copper

Interaction of Extreme Ultraviolet (EUV) laser with matters is an attractive subject since novel phenomena always occur under the effect of high energy photons. In this paper, the thermal effect involved in the interaction of a capillary discharge 46.9 nm laser with copper was studied theoretically and experimentally. The temperature variation of the laser-irradiated region of copper was calculated. According to the results, the copper surface was ablated obviously and presented the trace of melting, evaporation, and resolidification, which suggested the thermal effect occurred on the surface during the laser irradiation.

Effects of wire materials on radiative heat flux and spectral characteristics of a capillary discharge plasma jet

Capillary discharge plasmas have been widely used in many fields. This paper investigates the influence of different explosion wire materials on the radiative heat flux and spectral characteristics. Three kinds of wire (aluminum, copper and nickel) with 0.3 mm diameter were used as initiation wires to produce an electrothermal plasma, with a capacitor charging voltage of 3 kV. A thin-film calorimeter with high response speed was used for the measurement of the radiative heat flux. At the same time, spectral analysis was performed using a spatially resolved spectrometer with an ICCD. Based on the results, the electrical energy transported to the plasma that is calculated from the voltage and current traces follows the order Cu > Al > Ni, while the radiative heat flux follows the order Al > Cu > Ni. The trends can be explained by the secondary combustion (chemical reaction with the air) of Al and the fact that the dissipated energy is smaller than the vaporization energy for Ni but larger for Al and Cu, resulting in a bad performance in jet heat flux due to the incomplete vaporization of Ni wires. For the Cu and Al cases, a four-stage evolution process of the emitted radiation, which describes the emission, absorption and decay processes, can be found from the spectral analysis.

Fast Ionization Waves in Extended Capillaries Initiated by High-Voltage Pulses With Varying Rise Rates: A Numerical Investigation

This article presents the results of numerical investigations of initial stages of a fast capillary discharge—initiation and propagation of a fast ionization wave and consequent formation of a conducting plasma channel. Simulations were performed for the case of a 10 cm-long narrow capillary filled with argon at 270 Pa. The wave was created by voltage pulses of negative polarity with an amplitude of 10 kV and rise times varying in the 5–40 ns range, which is comparable with switching times of conventional switching devices based on gas discharges. Obtained spatio-temporal distributions of main discharge parameters were used to study the wave dynamics in general and the structure of the wavefront and the plasma channel. Simulations have revealed that the total wave propagation time is comparable to the voltage rise-time and varies linearly from 10 to 30 ns for the considered rise-time range. It is further shown that for longer voltage rise-times, it is possible for the wavefront to reach the anode well before the applied voltage reaches the maximum, which can potentially result in suboptimal initiation of a fast capillary discharge with lower current rise rates and less effective energy input.

Modeling and diagnostics for plasma discharge capillaries.

In this paper, we show how plasma discharge capillaries can be numerically modeled as resistors within an RLC-series discharge circuit, allowing for a simple description of these systems, while taking into account heat and radiation losses. An analytic radial model is also provided and compared to the numerical model for plasma discharge capillaries at thermal equilibrium, with corrections due to radiation losses. Finally, diagnostic techniques based on visible spectroscopy of plasma emission lines are discussed both for atomic and molecular gases, comparing experimental results with numerical simulations and theoretical calculations.

Plasma Flows of High-Current Discharge in a Capillary and Their Propagation Across a Magnetically Insulated Line

The characteristics of sources of plasma flows formed by high-current discharges in polyethylene, teflon, and ceramic capillaries are presented that allow high-velocity flows of high-density plasma to be obtained. The influence of the initial voltage on the capillary, rate of current growth, and current amplitude on the parameters of the formed plasma bunches and on the service life of the capillaries made of the examined dielectrics is shown. Experimental data on propagation of bunches in crossed electric and magnetic fields of a magnetically insulated transmission line are presented.

Hypersonic plasma flows created by a pulse capillary discharge

The possibility of producing by a pulsed capillary discharge the quasi-stationary high-speed plasma flows in a wide range of Mach numbers (M=3-20), electron number densities (ne∼1011-1015 cm-3) and temperatures (Te∼3-10 eV), rotational and vibrational temperatures (Tr=3800-6000 K and Tv=9000-15000 K), which can be used for setting up plasma aerodynamic experiments on small laboratory facilities, is shown. The most suitable for this purpose is a mode close to supersonic outflow into a vacuum, the transition to which occurs when the total pressure ratio exceeds N = p0/p∞ >5·103. This mode permits to obtain wide-aperture flows (D >10 cm) with spatially extended weakly inhomogeneous segments sufficient to accommodate tested bodies of a centimeter scale.

Switching devices – EPTRON with 100 kV operating voltage and sub-nanosecond switching times

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.

Influence of voltage pulse rise-time on initiation and propagation of fast ionization waves in extended capillaries

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.

Pulsed plasma jet interaction with a metal targets

The results of experimental studies of the interaction of plasma jets, created by a pulsed capillary discharge with an evaporating wall, with metal targets are presented. It is shown that the main mechanism of targets destruction is the material melting and the subsequent removal of the melt under the dynamic pressure of the plasma jet. The main sources of energy transmitted to the target are: the high-speed flow of high-enthalpy plasma created inside the capillary, and the fluxes of charged particles accelerated in the near-electrode layers. The energy transport provided by charged particles does not exceed ∼0.1–0.2 of the total energy input onto the target. The enthalpy transport is capable to provide heat flux densities of ∼5-6 kW/mm2, an order of magnitude exceeding the values achievable in welding arcs.

Wall ablation effect on the recombination pumping of EUV laser in pinching capillary discharge

Magnetohydrodynamic simulations of plasma evolution in nitrogen-filled alumina capillaries, taking into account the ablation of capillary walls, are reported. Time dependences of the ionization state and populations of the selected energy levels of nitrogen ions are evaluated by the kinetic code FLYCHK, used as a postprocessor. Plasma properties, including the spectral characteristics, simulated according to experiments done in different laboratories, are in good agreement with experimental results. We made some estimations of the wall evaporation, showing that capillary wall ablation may play a significant role. We show that ablation of the capillary material is a serious barrier on the way to 13 nm nitrogen laser recombination pumping by the capillary pinch.

Spectral Analysis and New Visible and Ultraviolet Lines of Ar v

Abstract A capillary discharge tube was used to record the Ar spectrum in the region of 330–4400 Å. We analyzed a set of 109 lines of Ar v, with 10 of them being classified for the first time. Part of these newly identified lines (six in total) corresponds to electric dipole transitions in the visible and ultraviolet regions of the spectrum. We calculated weighted transition rates (gA) for all experimentally observed lines and the corresponding lifetimes using a relativistic Hartree–Fock method with configuration interaction. The equations were modified to consider core polarization (CP) effects. A study on the Si isoelectronic sequence found that considering CP effects is essential for the correct description of the Ar v structure.

Impact of discharge currents on the intensity of 46.9 nm capillary discharge soft X-ray laser.

In this article, capillary discharge Ne-like argon 46.9nm soft X-ray laser has been firstly manifested with 4.8mm inner diameter alumina capillary for higher discharge currents. We have designed and installed capillary discharge setup for 4.8mm inner diameter alumina capillary to achieve intense 46.9nm laser. One dimensional Langragian Magneto-hydrodynamics (MHD) code was used to simulate the plasma conditions at the lasing time. The MHD code was used to perform the parametric studies of Z-pinch argon plasma, such as electron temperature, electron density and Ne-like argon ion density. The intensities of capillary discharge 46.9nm laser emitted from 4.8mm inner diameter alumina capillary were measured at 30, 36 and 40kA main discharge currents. According to the results, when the main current amplitude was increased from 30kA to 36kA and 40kA, the intensity of laser produced at optimum pressure increased up to 1.5 and 2 times, respectively. Moreover, we also studied the influence of predischarge current by increasing the predischarge current from 25 to 250A and investigated 140A as the best predischarge current for lasing. Hence, increasing the amplitude of main current using a comparatively larger inner diameter capillary is an effective way to improve intensity of capillary discharge 46.9nm soft X-ray laser. The maximum energy of 46.9nm laser was observed approximately 1.5mJ under best discharge conditions. The discussion has been made on the enhancement of 46.9nm laser intensity for higher main discharge currents and best predischarge current with experimental and simulated results. This is the first observation of 46.9nm laser with 4.8mm inner diameter alumina capillary.

A Compact Pulse Power System for Capillary Discharge Plasma-Based Soft X-Ray Laser

A compact pulse power system has been developed and successfully tested for soft X-ray lasing at 46.9 nm in argon plasma generated by fast capillary discharge scheme. The system has been designed with the aim to generate high current with a high rate of rise in the gas-filled ceramic (Al2O3) capillary (radius 1.4 mm and length 150 mm). The electrical parameters for the compact system were fixed using circuit simulation and the setup design was optimized using electrostatic field simulation software. A 10-stage 100–400 kV, 6-nF Marx generator is used to pulse charge the 3.2 nF, 35-nH water filled coaxial capacitor. The improvement in the output laser energy has been observed due to faster rise time of discharge current. The highest current observed was 70 kA, achieving a rate of rise of current $\sim 2\times 10^{12}$ A/s in 97 mm long, 2.8 mm inner diameter capillary. We strongly believe that the performance of the system is suitable for study of discharge plasmas from gasses other than the argon for exploring recombination-based X-ray lasing at wavelengths shorter than 46.9 nm.

Numerical investigation of dynamics and gas pressure effects in a nanosecond capillary sliding discharge

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.

Specific Features of the Longitudinal Distribution of Plasma Parameters in the Initial Segment of a Supersonic Jet Formed by a Pulsed Capillary Discharge

Specific Features of the Longitudinal Distribution of Plasma Parameters in the Initial Segment of a Supersonic Jet Formed by a Pulsed Capillary Discharge

Petawatt Laser Guiding and Electron Beam Acceleration to 8GeV in a Laser-Heated Capillary Discharge Waveguide.

Guiding of relativistically intense laser pulses with peak power of 0.85 PW over 15 diffraction lengths was demonstrated by increasing the focusing strength of a capillary discharge waveguide using laser inverse bremsstrahlung heating. This allowed for the production of electron beams with quasimonoenergetic peaks up to 7.8GeV, double the energy that was previously demonstrated. Charge was 5pC at 7.8GeV and up to 62pC in 6GeV peaks, and typical beam divergence was 0.2mrad.