A. S. Shikanov

Amplification of spontaneous emission of neon-like argon in a fast gas-filled capillary discharge

The evolution of the CAPEX facility and its basic diagnostics are described. The experiments carried out in the last modification of this facility accomplished with the demonstration of amplified spontaneous emission of neon-like argon (Ar8+) at the wavelength 46.88 nm. The first version of the facility, CAPEX1, operated with a plastic capillary and had a short high-power passive prepulse and an imperfect gas-filling system. In the second version, CAPEX2, a ceramic capillary was used, the prepulse amplitude was lowered, and the gas-filling system was improved. In the third, most successful version, CAPEX3, the capillary bending was reduced, a longer external prepulse was used, and the gas-filling system was further optimized. For each version, results of X-ray measurements are presented and interpreted.

Influence of laser pulse parameters on characteristics of a source of multicharged metal ions based on laser-induced medium-power spark discharge

The dynamics of laser-induced vacuum spark discharge with storage energy not exceeding 25 J has been studied in a broad range of laser pulse energies and power densities. It is shown that, using discharge-initiating laser pulse of nanosecond duration, it is possible to obtain stable single pinching of cathode jet plasma at a storage voltage above 10 kV. Plasma pinching is accompanied by the generation of a beam of multicharged ions of the cathode material (aluminum) up to Al8+. The maximum energies of ions obey the scaling relation Emax = 5ZeU0 that has been obtained previously for a low-voltage discharge. An increase in the laser pulse energy leads to growth of the average beam charge and a sharp decrease in the ion energy.

Study of the radiation spectra of fast Z-pinches formed during the implosion of wire arrays in the Angara-5-1 facility

Results are presented from measurements of the radiation spectra of the Z-pinch tungsten plasma produced during the implosion of cylindrical wire arrays with a linear mass of 200–400 μg/cm and an initial diameter of 12–20 mm at a current of ∼3 MA in the experiments performed at the Angara-5-1 facility. The radiation spectra in the photon energy range of 50–900 eV were recorded on a UF-4 X-ray film by using a spectrograph with a transmission grating. The radiation spectrum in the photon energy range of 1–3 keV was recorded using a crystalline panoramic spectrograph. A curtain shutter was used to protect the transmission grating from fast microparticles produced due to the erosion of high-voltage electrodes. The total radiation yield was measured with a thermocouple calorimeter. It is shown that most of the tungsten plasma radiation energy is emitted in the photon energy range of 80–300 eV. Measurements of the spectral intensity of pinch radiation with a spatial resolution along the pinch radius showed that the effective transverse diameter of the pinch did not exceed 2 mm, which agrees with independent current measurements of the pinch size. The results of measurements of the spectral intensity of pinch radiation were compared with calculations per-formed under the assumption of a stationary homogeneous plasma.

Ion acceleration in a high-current cathode plasma jet expanding in vacuum

Ion acceleration in a high-current cathode plasma jet of a low-voltage vacuum spark discharge has been studied. It is established that an increase in the discharge current amplitude leads to a growth in both the density and velocity of the ion flux emitted from the discharge gap. The dependence of the ion velocity on the discharge current amplitude in the range below 10 kA is well described by a simple hydrodynamic model of the current-carrying jet with allowance for plasma compression by the intrinsic magnetic field of the discharge current. For discharge current amplitudes exceeding 10 kA, the ion velocity ceases to grow and exhibits a considerable scatter of values measured in different shots.

A three-channel polarointerferometer for diagnostics of magnetic fields in high-temperature plasma

A polarointerferometer designed for studying magnetic fields in high-temperature laser or electricdischarge plasma with the method of measuring the Faraday rotation of the plane of polarization of a probing laser beam is described. The instrument’s optical system allows three—shadow, polarization, and interference—images of an object to be formed in a single diagnostic channel, thereby making it possible to record plasma images using only one digital camera.

Properties of soft X-ray emission from a fast capillary discharge

Results are presented from experimental studies of the time resolved, spatially resolved, and spectrally resolved soft X rays emitted along the axis of a fast capillary discharge.

Methods and results of studies of the radiation spectra of megampere Z-pinches at the angara-5-1 facility

Methods and results of studies of the radiation spectra of high-current Z-pinches with different elemental compositions are presented. To examine a wide spectral range (Ehν = 30–3000 eV), two diagnostics tools were used—a transmission grating and a reflecting mica crystal. The radiation characteristics of the pinch are determined by its elemental composition. For currents of 2–3 MA and low-Z elements (aluminum), the hard end of the radiation spectrum is represented by spectral lines with clearly pronounced K lines, while for high-Z elements (tungsten), the spectrum lies in the softer photon energy range and is quasi-continuous. Two methods of spectrum processing were used to determine the plasma parameters. The parameters of aluminum plasma were traditionally determined from the intensity ratios of the K lines taking into account the plasma transparency for these lines. The spectra of tungsten plasma were compared with the results of computer simulations of pinch compression with allowance for both magnetohydrodynamic and plasma radiation processes. The applicability of these methods of spectral analysis is discussed.

Crater formation in a target under the action of a high-power laser pulse

The formation of craters in targets of various materials under the action of a high-power neodymium-laser pulse at radiation intensities from 1010 to 1014 W/cm2 was studied experimentally and theoretically. The interaction between the laser beam and solid targets is investigated to determine the efficiency of the ablation loading of various materials and the transformation of the laser energy into the energy of a shock wave.

Vacuum discharge instability at laser initiation of a cathode spot

The dynamics of fast (a current rise time of ≤1011 A/s) laser-induced vacuum discharges with moderate amplitudes of the current (≤10 kA) and voltage (≤20 kV), as well as medium storage energy (20 J), is studied. It is shown experimentally that the initial conditions specified by the energy and duration of laser radiation are a decisive factor governing the discharge dynamics. Two types of beam-plasma instabilities separated in space and time are discovered, and their occurrence conditions are analyzed. The first type of instability, observed early in the discharge, is associated with pinch structures at the front of the cathode jet expanding into a vacuum. The second type arises either at the peak or at the trailing edge of the current pulse and is accompanied by generation of hard (with an energy of ≥100 keV) bremsstrahlung from the anode region. The increase of the hard component energy over the current source potential is attributed to breaking due to plasma erosion.

Formation of a cathode plasma jet in a laser-induced vacuum discharge

The process of formation of micropinch structures in the plasma of a vacuum discharge initiated by a laser pulse on the cathode is studied. It is demonstrated that the micropinch formation takes place mainly in the substance evaporated by the laser pulse upon the discharge initiation. The size of the hot region of the plasma jet and the distance from the cathode to the micropinch increase with increasing laser pulse energy.