P. S. Antsiferov

Plasma production by means of discharge in a spherical cavity

The work is devoted to the study of plasma, appearing as a result of cumulation of shock wave with form close to spherical. The shock wave was obtained by triggering of fast discharge (dI/dt about 1012 A/s) on inner surface of cavity, made from insulator. Spherical cavity with radius 4.5 mm was filled with Ar at 80 Pa. Inductive storage with semiconductive opening switch was used as a current driver. Spherical plasma with diameter about 1 mm, emitting in vacuum ultraviolet (vuv), was detected by means of pinhole measurements with time gated microchannel plate camera, starting about 50 ns from the beginning of the discharge. vuv spectra have shown the presence spectral lines of ArV–ArVIII ions, which gives the estimation of electron temperature as 30 eV. The plasma ball reveals no instabilities, keeps its characteristics and emits vuv radiation during 300 ns. After 600 ns from the beginning of the discharge plasma emits a flux of electrons with energies about 1 keV with temporal structure about 100 ns.

Dynamics of a plasma in a capillary discharge driven by a plasma focus operated in the mode of a plasma switch opening.

A compact and simple type of current driver based on a plasma focus working in the mode of a plasma opening switch was used for excitation of a capillary discharge in Ar pressures in the range 0.1-0.5 Torr. A current of up to 50-60 kA with a rise time of about 200 ns was achieved in the capillary. The Ar plasma was compressed from an initial diameter of 5 mm to a diameter of 1 mm. The dynamics of compression have been studied using time-resolved VUV pin-hole diagnostics. Time-resolved VUV spectra show that the plasma consists mainly of the Ne- and F-like ions Ar IX and Ar X. A spectral line at 468.7 A, which was identified as the transition in Ne-like Ar IX, has an anomalously high intensity compared with other 3-3 transitions of Ar IX.

Plasma erosion opening switch for fast discharges with current growth rate about 1012 A/s1

The article presents the construction of a plasma erosion opening switch, capable of creating the discharge with electrical current of several tens kiloamperes and a growth rate up to 1012 A/s in the circuit with the inductive load up to 100 nH. The results of test experiments with imitator of load are presented. The discharge circuit under consideration will be used for the experiments for creation of shock waves in plasma.

Fast discharge in a plasma gun with hemispherical insulator

A method of creation of hot dense plasma is proposed. It is based on cumulation of a shockwave, which originates on a hemispherical surface of insulator of plasma gun. The results of first experiments are presented. The shock wave is driven by fast electrical discharge (dI/dt>1012 A/s). The inductive storage with semiconductor opening switch is used as a current driver. Time resolved pin-hole images and vacuum ultraviolet (vuv) spectra are studied. Shockwaves from hemispherical insulator with 4 mm radius create plasma with a form of column about 1 mm diameter and 3–4 mm length. vuv spectra contain the lines of Ar ions that corresponds to the electron temperature about 20 eV. Possible practical application is discussed.

Plasma focus as a current switch for a capillary discharge

Experiments are described in which a plasma focus is used simultaneously as an inductive store and a current switch. The obtained rates of current growth on a load of 0.01 Ω is 1012 A/s, and the maximum values of the switched current lie in the range 50–100 kA. The technique is seen as promising for employing a capillary discharge as a source of laser medium for the soft x-ray region.

Application of bent microchannel plates in recording systems of grazing-incidence spectrometers

The design of the grazing-incidence spectrometer, in the scheme of which microchannel plates (MCPs) elastically bent along the Rowland circle are used, is described. This scheme allows one to improve the matching of the spatial resolution of the MCP and the real spectral structure as compared with the outof- Rowland recording. The performed tests demonstrated the fivefold increase in the spectral resolution of the spectrometer.

Experimental investigation of the shock wave in a fast discharge with cylindrical geometry

The work is devoted to the registration and the study of the properties of cylindrical shock waves generated in the fast discharge (dI/dt ∼ 1012 A/s) inside the ceramic tube (Al2O3) filled by argon at pressures of 100 and 300 Pa. The shock wave appears at the inner wall of the insulator and moves to the discharge axis with a velocity of about (3−4) × 106 cm/s with subsequent cumulation. The plasma behind the front is heated enough to produce radiation in the vacuum ultraviolet (VUV) region, which makes it possible to study its structure by means of a pinhole camera with a microchannel plate detector. The time resolution of the registration system was 10 ns. The analysis of VUV spectra of the plasma shows that the electron temperature behind the shock wave front is about several eV; after the moment of cumulation, its temperature increases to 20–30 eV.

Specific features of the intensity alternation in different orders of a grazing-incidence diffraction grating

The behavior of the intensity distributions over the height of a spectral line in different orders of a concave diffraction grating used in the grazing-incidence scheme is studied. These distributions are considerably different for even and odd orders, which may help in the identification of spectral lines in complicated spectra and should be taken into account in the construction of spectral systems with spatial resolution.

Evolution of a Capillary Discharge Induced by a Semiconductor Current Generator

Results are presented from the intermediate stage of work on creating a current generator in a circuit with an inductive energy storage and a semiconductor opening switch made of 40 SDL-800 diodes. A six-diode generator prototype has been created with a current pulse amplitude of ∼4.5 kA and a leading edge duration of ∼10–20 ns at an inductive load of 30–35 nH. The generator was used to study discharges in capillaries filled with argon or hydrogen. It is shown that, in a 2-mm-diameter capillary, the initial azimuthal asymmetry of a structure arising during the breakdown ceases as the discharge evolves, whereas in a 0.8-mm-diameter capillary, it is retained. Time-resolved spectroscopic studies of the plasma reveal the presence of line emission of highly ionized argon (ArVII and ArVIII) in the hottest phase of the discharge, which indicates that a temperature of 20–40 eV has been achieved.

Scaling of a fast spherical discharge

The influence of the discharge cavity dimensions on the properties of the spherical plasma formed in a fast discharge was studied experimentally. The passage of a current pulse with an amplitude of 30–40 kA and a rise rate of ~1012 A/s (a fast discharge) through a spherical ceramic (Al2O3) cavity with an inner diameter of 11 mm filled with argon at a pressure of 80 Pa results in the formation of a 1- to 2-mm-diameter spherical plasma with an electron temperature of several tens of electronvolts and a density of 1018–1019 cm–3. It is shown that an increase in the inner diameter of the discharge cavity from 11 to 21 mm leads to the fourfold increase in the formation time of the spherical plasma and a decrease in the average ion charge. A decrease in the cavity diameter to 7 mm makes the spherical plasma unstable.