Effect of tailored density profiles on the stability of imploding z-pinches at microsecond rise time megaampere currents

To study the effect of the radial density profile of the material of a metal-plasma Z-pinch load on the development of magneto-Rayleigh-Taylor (MRT) instabilities, experiments have been performed at the Institute of High Current Electronics with the GIT-12 generator produced microsecond rise time megaampere currents. The load was an aluminum plasma jet with an outer plasma shell. This configuration provides the formation of a uniform current sheath in a Z-pinch load upon application of a high voltage pulse. It was successfully used in experiments with hybrid deuterium gas-puffs [Klir et al. 2020 New J. Phys. 22 103036]. The initial density profiles of the Z-pinch loads were estimated from the pinch current and voltage waveforms using the zero-dimensional "snowplow" model, and they were verified by simulating the expansion of the plasma jet formed by a vacuum arc using a two-dimensional quasi-neutral hybrid model [Shmelev et al. 2020 Phys. Plasmas 27 092708]. Two Z-pinch load configurations were used in the experiments. The first configuration provided tailored load density profiles, which could be described as ρ(r) ≈ 1/r^s for s > 2. In this case, MRT instabilities were suppressed and thus a K-shell radiation yield of 11 kJ/cm and a peak power of 0.67 TW/cm could be attained at a current of about 3 MA. For the second configuration, the radial density profiles were intentionally changed using a reflector. This led to the appearance of a notch in the density profiles at radii of 1–3 cm from the pinch axis and to magnetohydrodynamic instabilities at the final implosion stage. As a result, the K-shell radiation yield more than halved and the power decreased to 0.15 TW/cm at a current of about 3.5 MA.

Estimation of Amount of Scattered Neutrons at Devices PFZ and GIT-12 by MCNP Simulations

Our work is dedicated to pinch effect occurring during current discharge in deuterium plasma, and our results are connected with two devices – plasma focus PFZ, situated in the Faculty of Electrical Engineering, CTU, Prague, and Z-pinch GIT-12, which is situated in the Institute of High Current Electronics, Tomsk. During fusion reactions that proceed in plasma during discharge, neutrons are produced. We use neutrons as instrument for plasma diagnostics. Despite of the advantage that neutrons do not interact with electric and magnetic fields inside device, they are inevitably scattered by materials that are placed between their source and probe, and information about plasma from which they come from is distorted. For estimation of rate of neutron scattering we use MCNP code.

The Construction of the Fast Resistive Bolometer for a SXR Measurement on the GIT-12 Facility

A lot of kinds of instruments are used for the SXR measurement at pulsed power facilities, but most of them are difficult to calibrate absolutely. For the determination of the energy of SXR radiated by the discharge on Z-pinches, it is possible to use the bolometer which can be calibrated analytically. The bolometer can be constructed with the sufficient sensitivity and, at the same time, with the time resolution in the order of nanoseconds. This bolometer was designed and constructed for the measurement on the 5MA facility GIT-12 at the Institute of High Current Electronics (IHCE) of the Siberian Branch Russian Academy of Sciences in Tomsk. The experiments on GIT-12 with the neon and deuterium gas-puff load were diagnosed by the copper bolometer with the time resolution of 4 ns and the sensitivity of 12 V cm2 J-1.