Characteristics of X-ray Emission from a Micropinch Discharge at Different Polarities of the Discharge Electrodes

Plasma Physics Reports - The measurement technique and results are presented from studies of the X-ray spectra and X-ray yield from micropinch discharge plasma in a low-inductive vacuum spark...     

Studies of the structure and dynamics of the radiating plasma of a micropinch discharge

Space-resolved X-ray spectra and electron emission spectra from a micropinch discharge are measured with the help of tracking detectors. Results from measurements of the discharge optical emission with a high temporal and spatial resolution are also presented.     

Spatial structure of the neck and acceleration processes in a micropinch

It is shown that the spatial structure of the micropinch neck during the transition from magnetohydrodynamic to radiative compression and the bremsstrahlung spectrum of the discharge in the photon energy range of up to 30 keV depend on the configuration of the inner electrode of the coaxial electrode system of the micropinch discharge. Analysis of the experimental results indicates that the acceleration processes in the electron component of the micropinch plasma develop earlier than radiative compression.     

Generation of superthermal electrons in a micropinch discharge

Results are presented from experimental studies of the formation of the superthermal electron component in a micropinch discharge plasma. Radiative collapse in a Z-pinch is found to affect the energy of the accelerated electrons. That the radiative collapse has been reached may be inferred from the energy of the emitted hard X-ray photons.     

Formation of an anisotropic electron velocity distribution function and production of multicharged ions in the micropinch discharge plasma

Analysis of the results of polarimetric measurements of X-ray line radiation of multicharged ions in a Z-pinch discharge indicates that the formation of an anisotropic electron velocity distribution in the neck of the current channel and the generation of highly charged ions are separated in time. The generation of a fast electron beam in the longitudinal ohmic electric field in the stage of plasma compression in the neck results in the polarization of X-ray bremsstrahlung continuum. In the stage of expansion of the hot dense micropinch plasma, the radial electric field prevails, due to which X-ray line radiation of multicharged ions becomes linearly polarized.     

Effect of the anode material on the X-ray spectrum of micropinch discharge plasma

The effect of the elemental composition of the anode material on the parameters and X-ray spectrum of micropinch discharge plasma have been studied using a low-inductance vacuum spark device. It is shown that the plasma electron temperature T _e and intensity of hard X-ray emission increase with increasing nuclear charge number Z of the anode material of the discharge system.     

Study of the contributions of the electrode materials to the plasma of a high-current vacuum spark

The contribution of the electrode material to the formation of the plasma of a low-inductive high-current vacuum spark and its influence on the process of discharge micropinching were studied using X-ray spectroscopy and laser diagnostics. Electrode system configurations are determined in which the contributions of the materials of both electrodes to the plasma emitting X-rays are comparable and in which the contribution of one electrode is dominating. It is found that discharge pinching occurs primarily in the vapor of the pointed electrode independently of its polarity. The experimental results indicate the formation of a suprathermal electron beam in the micropinch region.     

Study of the Spectral Composition of X-ray Emission from Different Regions of Micropinch Discharge Plasma

Plasma Physics Reports - The measurement technique and results are presented from studies of the spectral composition of X-ray emission from different regions of micropinch discharge plasma in a...     

Correlation between the parameters of ion and X-ray emissions from the plasma of a micropinch discharge

Ion emission from the plasma of a micropinch discharge is studied by analyzing the plasma flow from the discharge region with the help of time-of-flight technique and probe diagnostics. Concurrently, soft Xray emission from the micropinch is recorded. The experimental data are interpreted using the radiative contraction model.     

Polarization properties of bremsstrahlung continuum and line emission of multicharged ions in a micropinch

The polarization properties of X-ray emission from micropinch discharge plasma in the spectral range corresponding to the K-lines of iron were studied experimentally. It is shown that emissions of different nature differ in the preferred orientation of polarization. The mechanisms responsible for the emission polarization are discussed.     

Current scaling for the radiative characteristics of a micropinch discharge

The absolute VUV and soft X-ray (hν > 100 eV) yield from a micropinch discharge is measured for a fixed current of 150 kA. The current scaling in the range of 30–250 kA is found for a number of the discharge parameters: the VUV and soft X-ray yield, the electron temperature, the effective temperature of suprathermal electrons, and the energy of bremsstrahlung emission from thermal electrons. The experimental data are in good agreement with the simulations performed by using the model of radiative collapse in fast Z-pinches in plasmas of high-Zelements.     

Peculiarities of the spatial structure and dynamics of the plasma of a fast Z-pinch produced in the high-Z medium of a high-current vacuum spark

The spatial structure and dynamics of the plasma of a high-current vacuum spark is investigated using pulsed shadowgraphy. Anisotropy of the plasma outflow from a micropinch region has been revealed. The existence of cavities in the sausage-type instability in the final stage of pinching has been recorded. The formation of a filamentary plasma structure at the discharge periphery is revealed.     

Experimental study of the spatial structure of high-energy ion sources in micropinch

Images of ion sources in the plasma of a micropinch discharge were recorded. The most intense ion source was found to be a ⩾1-mm-diameter 3-mm-long anode region. The main contribution to the images is made by single-charged ions of the plasma-forming element with energies of 10–50 keV.     

Comparative study of the spatial structure of the X-ray and ion emission sources in the micropinch discharge plasma

Images of ion emission sources in the micropinch discharge plasma are obtained by the pinhole camera technique. A region that is the source of the most intense ion emission has a length of about 3 mm along the discharge axis and a width of ≤1 mm. It seems that the image of the emitting region recorded in the axial direction reflects the action of the discharge current magnetic field on the directional pattern of the ion flow.     

X-ray spatial distribution of a low-inductance vacuum spark discharge

The paper presents the results of X-ray source spatial distribution measurements of a low-inductance vacuum spark discharge based on the analysis of helium-like ions spectral lines structure. The intensities of spectral lines of FeXXV ions and dielectronic satellites with spatial resolution were measured. The polarization of satellite line 1s2p ^{2 2} D _5/2-1s ²2p ² P _3/2 was found. The obtained dependence of maximum plasma parameters during micropinch events from initial plasma line density in discharge corresponds to the radiative collapse model.     

Measurements of the gas-kinetic pressure in plasma flows emerging from a micropinch discharge by means of laser interferometry

A new method for measuring the gas-kinetic pressure in pulsed plasma flows is developed in which an acoustic line in the form of a thin rod built in the optical scheme of a laser interferometer is used as a detector. The time evolution of the gas-kinetic pressure in particle flows emerging from a micropinch discharge (a low-inductance vacuum spark) was studied. Due to the wide dynamic range of the method (～10⁵), it can be applied in various plasma devices with a wide range of parameters.     

Measurements of the parameters of a condensed deuterated Z-pinch on the angara-5-1 facility

Results are presented from measurements of the parameters of high-temperature plasma in the Z-pinch neck formed when a current of up to 3.5 MA flows through a low-density polymer load. To enhance the effect of energy concentration, a deuterated microporous polyethylene neck with a mass density of 100 mg/cm³ and diameter of 1–1.3 mm was placed in the central part of the load. During the discharge current pulse, short-lived local hot plasma spots with typical dimensions of about 200–300 μm formed in the neck region. Their formation was accompanied by the generation of soft X-ray pulses with photon energies of E > 0.8 keV and durations of 3–4 ns. The plasma electron temperature in the vicinity of the hot spot was measured from the vacuum UV emission spectra of the iron diagnostic admixture and was found to be about 200–400 eV. The appearance of hot plasma spots was also accompanied by neutron emission with the maximum yield of 3 × 10¹⁰ neutrons/shot. The neutron energy spectra were studied by means of the time-of-flight method and were found to be anisotropic with respect to the direction of the discharge current.     

Suprathermal electrons in a vacuum spark discharge

Results of experiments on the detection of suprathermal electron beams in the plasma of a highcurrent low-inductance vacuum spark by means of space-resolved spectral X-ray polarimetry are presented. It is shown that the observed polarization of bremsstrahlung may be caused by an ~100-keV electron beam propagating along the discharge axis from the pinching region toward the anode. The influence of the discharge initiation conditions on the parameters of the generated electron beams is analyzed.     

Generation of hard X-ray emission by the electron beam in plasma focus facilities

The results of measurements of the temporal characteristics of hard X-ray emission generated at plasma focus (PF) facilities are presented. Mechanisms of electron beam generation in the PF pinch are analyzed. On the basis of the known mechanisms and experimental data on the measured temporal characteristics of hard X-ray pulses, a mechanism of fast electron generation that takes into account both the effect of the anomalous pinch resistance and the current redistribution in the near-pinch region is proposed. The processes occurring in the pinch plasma are simulated on the basis of the proposed mechanism by using the MicroCap code. It is shown that only a small fraction of the discharge current (1–10%) can be transformed into the electron beam current.     

Microwave processes in the SPD-ATON stationary plasma thruster

Results of experimental studies of microwave processes accompanying plasma acceleration in the SPD-ATON stationary plasma thruster are presented. Specific features of the generation of microwave oscillations in both the acceleration channel and the plasma flow outgoing from the thruster are analyzed on the basis of local measurements of the spectra of the plasma wave fields. Mechanisms for generation of microwave oscillations are considered with allowance for the inhomogeneity of the electron density and magnetic field behind the edge of the acceleration channel. The effect of microwave oscillations on the electron transport and the formation of the discharge current in the acceleration channel is discussed.