A. V. Fedunin

Long time implosion experiments with double gas puffs

Long time implosion experiments with argon double gas puffs have been conducted on the GIT-12 [S. P. Bugaev et al., Izv. Vyssh. Uchebn. Zaved., Fiz. 40, 38 (1997)] generator at the current level of 2.2–2.4 MA. A double gas puff was used as one of the alternative ways to improve implosion stability at implosion times from 230 to 340 ns. The results of these experiments were compared with two-dimensional snowplow simulations. The experiments and the simulations show that the final pinch is sufficiently stable when the inner-to-outer shell mass ratio is greater than 1. The maximum argon K-shell yield obtained in the experiments is 740 J/cm with 220 GW/cm radiation power. At the long implosion times, the K-shell yield obtained in the double gas puff implosion is twice the K-shell yield of a 4-cm-radius single gas puff, with more than an order of magnitude increase in radiation power.

The K-shell radiation of a double gas puff z-pinch with an axial magnetic field

A double shell z -pinch with an axial magnetic field is considered as a K -shell plasma radiation source. One-dimensional radiation-hydrodynamics calculations performed suggest that this scheme holds promise for the production of the K -shell radiation of krypton ( h ν ≈ 12–17 keV). As a first step in verifying the advantages of this scheme, experiments have been performed to optimize a neon double-shell gas puff with an axial magnetic yield for the K -shell yield and power. The experiments show that the application of an axial magnetic field makes it possible to increase the K -shell radiation power and reduce the shot-to-shot spread in the K -shell yield. Comparisons between the experiments and modeling are made and show good agreement.

The Effects of Preheating of a Fine Tungsten Wire and the Polarity of a High-Voltage Electrode on the Energy Characteristics of an Electrically Exploded Wire in Vacuum

Results obtained from experimental and numerical studies of tungsten wires electrical explosion in vacuum are presented. The experiments were performed both with and without preheating of the wires using positive or negative polarity of a high-voltage electrode. Preheating is shown to increase energy deposition in the wire core due to a longer resistive heating stage. The effect was observed both in single wire and wire array experiments. The evolution of the phase state of the wire material during explosion was examined by means of a one-dimensional numerical simulation using a semiempirical wide-range equation of state describing the properties of tungsten, with allowance made for melting and vaporization

On stabilization of gas puff implosion: experiment and simulation

A double gas puff was used to study the mitigation of the magneto-Rayleigh-Taylor (RT) instabilities for long implosion times (up to 250 ns). The experiments have been performed on the inductive storage GIT-4 (1.7 MA, 120 ns) generator. Current division between the outer and inner shells was controlled using magnetron-discharge preionization. The implosion of the a double gas puff, with the improved preionization, results in the formation of a uniform plasma column. The results of two-dimensional (2-D) radiation-magnetohydrodynamic simulations support the experimental results: a double gas puff implosion mitigates the RT instabilities, leading to the development of only small-amplitude waves. The 2-D simulation allowed us to explain the halo effect seen in the experiments: the use of the low hybrid conductivity in the calculation demonstrated the existence of the high density plasma core surrounded by a low density plasma halo.

Gas-Puff-on-Wire-Array

Results of the experiments carried out on the GIT-12 generator at the current level of 3.5 MA and the Z-pinch implosion times from 700 ns to 1.1 mus are reported. A gas-puff-on-wire-array (triple-shell) load configuration with the outer double gas puff (neon) and the inner wire array (aluminum) was used in the experiments. In the course of the research, implosion dynamics of the triple-shell Z-pinch was studied, and the radiation yield in the spectral range of neon and aluminum K-shell X-rays has been measured. Optimization of the inner wire array parameters (masses and initial diameters) aimed at obtaining the maximum aluminum K-shell radiation yield has been carried out.

Z

Z-pinches with long time implosions is the subject of this paper. The experiments with neon, argon, krypton and xenon implosions have been conducted on a GIT-12 (Bugaev S P et al 1997 Izv. Vyssh. Uchebn. Zaved., Fiz 40 38) generator at a current level of 2.2-2.5 MA. The goal was to study an unstable gas puff of large diameter. Attention was focused on the dynamics of the implosion of such a gas puff, namely on the effect of the gas puff mass and atomic constitution on the macroscopic parameters of the implosion. It has been established that during the implosion the wavelength of RT oscillations increases, reaching a value of 0.8-1 cm at the final stage. As this takes place, bubbles appear in the plasma shell bulk. The unstable implosion of a gas puff with a large atomic weight is accompanied by an increase in the resistance of the gas puff in the run-in phase, to a value exceeding the Spitzer resistance by two or three orders of magnitude.

-Pinch Experiments on the GIT-12 Generator at Microsecond Implosion Times

Argon K-shell plasma radiation source experiments were carried out on the GIT-12 generator [Bugaev, S.P. et al., 1997, Russian Phys. Journal, 40, 38] for a long (300 ns) implosion regime. The performance of a shell-on-solid-fill double gas puff was characterized in the experiments with and without an external axial magnetic field. The maximum Ar K-shell radiation yield registered in the experiments without an axial magnetic field was at the level of 1100 J/cm. This yield is consistent with the theoretically predicted yield for a short (100 ns) implosion regime. The experiments showed that the initial magnetic field which provides stabilization of the shell-on-solid-fill double gas puff was lower than that required for stabilization of a single annular gas puff. Satisfactory stabilization of the double gas puff was observed at an initial axial magnetic field of 1.4 kG. The maximum Ar K-shell radiation yield registered in the experiments with the axial magnetic field did not exceed 400 J/cm. A sharp reduction of the K-shell yield cannot be explained only by taking into account the energy losses associated with the compression of the axial magnetic field.

Study of large-diameter gas puff implosions

Experiments with Ar-H/sub 2/ double gas puffs have been conducted on the GIT-12 generator at the current level of 2.1-2.4 MA and 250-350 ns implosion times. The argon-hydrogen mixture was used as a working medium in the outer shell of a double gas puff. The goal of the experiments was to verify whether the use of the argon-hydrogen mixture in the outer shell can improve the stability of a double gas puff implosion and provide increased argon K-shell radiation yields. The experiments showed that hydrogen admixture results in the change of implosion dynamics: decreased implosion velocities and compression ratios. The experimental data does not allow a conclusion that the use of an Ar-H/sub 2/ mixture in the outer shell of a double gas puff significantly improves the implosion stability. An increase in the hydrogen percentage in the outer shell leads to a decrease in plasma density and temperature, and as a result, reduced K-shell radiation yields and powers.

Formation of tight plasma pinches and generation of high-power soft x-ray radiation pulses in fast Z-pinch implosions

We propose a model that describes the neck formation and implosion in an X-pinch. The process is simulated to go in two stages. The first stage is neck formation. This stage begins with an electrical explosion of the wires forming the X-pinch, and at the end of the stage, a micropinch (neck) is formed in the region where the wires are crossed. The second stage is neck implosion. The implosion is accompanied by outflow of matter from the neck region, resulting in the formation of a “hot spot”. Analytical estimates obtained in the study under consideration indicate that these stages are approximately equal in duration. Having analyzed the neck implosion dynamics, we have verified a scaling which makes it possible to explain the observed dependences of the time of occurrence of an x-ray pulse on the X-pinch current and mass.

Experimental study of an argon-hydrogen Z pinch plasma radiation source

Results of the experiments carried out on the GIT‐12 generator at the current level of 3.5 MA and the Z‐pinch implosion times from 700 ns to 1.1 μs are presented. A multi‐shell (triple‐shell) load configuration with the outer gas puffs (neon) and the inner wire array (aluminum) was used in the experiments. In the course of the research, implosion dynamics of the triple‐shell z‐pinch was studied, and the radiation yield in the spectral range of neon and aluminum K‐lines have been measured. Optimization of the inner wire array parameters aimed at obtaining the maximum aluminum K‐shell radiation yield has been carried out. As a result of optimization of the gas‐puff‐on‐wire‐array Z‐pinch load, the aluminum K‐shell radiation yield (hv> 1.55 keV) up to 4 kJ/cm in the radiation pulse with FWHM less than 30 ns has been obtained. Comparison of the experimental results with the results of preliminary 1D RMHD simulations allows a conclusion that at least 2/3 of the generator current is switched from a gas puff to a...