K-shell radiation and neutron emission from z-pinch plasmas generated by hybrid gas-puff implosions onto on-axis wires

Abstract

Z-pinches have been explored as efficient soft x-ray sources for many years. To optimize x-ray emission, various z-pinch configurations were tested. This paper presents data obtained with a hybrid gas-puff z-pinch imploding onto on-axis wires on a microsecond, multi-megaampere GIT-12 generator. In our previous experiments, the hybrid gas puff, i.e., an inner deuterium gas puff surrounded by an outer hollow cylindrical plasma shell, was used to produce energetic protons, deuterons, and neutrons up to 60 MeV [Klir et al., New J. Phys. 22, 103036 (2020)]. The behavior of the hybrid gas-puff z-pinch on GIT-12 was interpreted as a high-density plasma opening switch with a microsecond conduction time, 3 MA conduction current, nanosecond opening, and up to 60 MV stand-off voltage. These properties can be employed to transfer the current into an on-axis load with a high rise rate. In the recent experiments on GIT-12, we therefore placed single or multiple aluminum wires on the axis of the hybrid gas-puff z-pinch. Before a current sheath arrived at the axis, a coronal plasma was seen around the wire. A rapid increase in x-ray radiation was observed when the coronal plasma imploded onto the axis. The coronal plasma implosion resulted in a long (2 cm), narrow (∼mm) column radiating in the Al K-shell lines. With the single Al wire of 80 μm diameter, the K-shell x-ray output reached 5.5 ± 0.8 kJ in a 0.6 ± 0.1 TW peak power and 7 ± 1 ns pulse. The higher K-shell yield of 12 ± 2 kJ and peak K-shell power of 0.7 ± 0.1 TW were achieved with four 38 μm diameter Al wires. (Their cross section formed the corners of a square with 1 mm side.) The presence of the wires on the axis significantly suppressed ion acceleration and neutron production. Deuterium-deuterium (DD) neutron yields of about 1.2 × 1011 were 20 times smaller than the yields produced in shots without any wire. The DD neutron yield was increased up to 4.5 × 1011 when the Al wire was replaced by a fiber from deuterated polyethylene. A characteristic feature of the experiments with the (CD2)n fiber was a rapid expansion with the velocity approaching 900 km/s.

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

“…For both the PJ and PJR Z-pinch loads, due to the plasma shell produced upon application of a high-voltage pulse from the GIT-12 generator, the current sheath was formed at a radius R 0 = 14-16 cm [21]. This load configuration, as shown in [22,24], provided a substantially improved stability of an imploding Z-pinch load. For both load configurations, the cathode plane was formed by a stainless steel mesh, and the anode plane was partially covered with the same mesh (figures 1 and 3).…”

“…The difference in readings between XRD1 and XRD2 made it possible to estimate the K-shell radiation yields and powers with an error of about 20%. Details regarding the methodology for determining the sensitivity of the XRDs can be found in our paper [24].…”

Generation of Ar K-shell radiation using a hybrid gas puff with an outer plasma shell

“…Two of them were performed with the deuterium gas puff only. Based on the results of these shots, we could be convinced that the parameters of the plasma and deuterium shells provide us with the optimal implosion regime observed in our previous experiments [18,13]. The main criteria for the optimal regime for us were the neutron yield at the level of 10 12 neutrons per pulse, the amplitude of the voltage pulse in the final stage of implosion close to or even higher than 1 MV, and the characteristic behavior of the dI/dt oscillogram, which has two dips at the moment of pinch stagnation on the axis.…”

“…We observed something similar earlier in experiments with deuterium gas puffs and an aluminum wire located on the axis. In those experiments, light emission from the wire started 120-150 ns before the implosion of the deuterium gas puff [13]. Nevertheless, there is one significant difference.…”

“…Finally, in recent years, two more new types of loads have been studied on the GIT-12 generator for generating radiation in aluminum K-lines: a metal-puff Z-pinch with an outer plasma shell [12] and a deuterium gas puff with an outer plasma shell and aluminum wires located on the axis [13]. In both series of experiments, it was possible to achieve a high efficiency of the plasma radiation source at implosion times close to a microsecond.…”