A.G. Russkikh

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.

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.

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

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.

First microsecond K-shell PRS experiments on the GIT-12 generator

Summary form only given. We report the results of the first K-shell PRS experiments carried out on the GIT-12 generator in the microsecond implosion time regime. The GIT-12 generator operated without the plasma opening switch delivers the current directly to a Z-pinch load. Our experiments were performed with neon and argon multi-shell gas puffs (shell-on-shell-on-solid-fill) with the length of 18 mm. Two concentric annular gas jets had diameters of 160 mm (outer shell) and 80 mm (middle shell). The inner on-axis solid fill had the diameter of 22 mm. The shell masses and their ratio were varied in the experiments. The short-circuit current of GIT-12 rises to the peak value of 4.7 MA at 1600 ns. Depending on the shell masses, the peak implosion current was varied in the range from 3.1 to 3.6 MA, and the corresponding implosion times were 850 to 1000 ns in the experiments with neon, and from 2.2 to 3.4 MA (implosion times from 550 to 950 ns) in the experiments with argon. The maximum Ne K-shell radiation yield reached 11 kJ/cm in a 40 ns FWHM pulse. The diameter of the plasma column radiating in K-shell was less than 5 mm. The maximum Ar K-shell yield achieved in these experiments was 500 J/cm in a 15 ns FWHM radiation pulse. The diameter of the final pinch was 1.8 mm. The experimental data will be presented and discussed.

Influence of preionization on dynamics of a gas puff implosion

The experiments with both single and double Ar gas puff were carried out on the IMRI-4 (Trt=1.1 μs, Im=350 kA) and the GIT-4 (Trt=0.12 μs, Im=1.7 MA) generator. Two different system of preionization, a sparking flash of UV radiation and a Planar Magnetron Discharge (PMD) in the crossed E×H fields, were used. The process of current stratification and the dependence of gas puff implosion uniformity on the preionization were investigated.

Gas-puff-on-wire-array structured load experiments on the GIT-12 facility

Summary form only given. The use of structured loads is a promising approach to creation of a long implosion time plasma radiation source. Our previous experiments with gas-puff-on-wire-array loads on the GIT-4 generator (1.5 MA 120 ns) have shown significant increase in radiation power and decrease in radiation pulse duration due to fast switching of the pinch current from the outer RMS shell to the inner wire array. Our recent experiments carried out on the GIT-12 generator were aimed at obtaining a better understanding of the process of current switching from the outer gas shell to the inner wire array. In these experiments tungsten wire array was used for the inner shell. Different gases-argon, krypton, and xenon-were tested as a material of the outer gas puff. The experimental results and their discussion will be presented.

Stability and K-shell radiation of Z-pinches

Experiments of GIT-4 facility are shown that Rayleigh-Taylor instabilities destroy the cylindrical gas shell at low mass and the X-ray yield falls sharply. Double gas puff is the efficient load designs for plasma radiation source. A double gas puff can be efficiently only if the magnetic field diffusion is absent at the onset of the current. The problem of the skin layer production in the outer shell was decided using magnetron discharges. As a result a good reproducibility of K-shell generation was achieved for Ar double gas puff. The final plasma column demonstrated the absence of bright spots and produced 0.3 kJ/cm of the K-shell yield at the 1.7 MA current.