High Energy Density Plasma Diagnostics Using Neutron and Gamma Detectors

Abstract

Deuterium Z-pinches are e cient sources of pulsed soft and hard x-rays, fast ions, and neutrons. Many phenomena related to an acceleration of ions and neutron production on the Z-pinches have not yet been explained. Detailed understanding of these phenomena could be multidisciplinary important. Therefore, these phenomena are investigated in joint Czech-Russian experiments on the terawatt class GIT-12 device with the generator output voltage of 600 kV and current at stagnation of about 3 MA. These experiments are interesting since by using the novel experimental load composed of the deuterium gas-pu with outer plasma shell, the neutron yields were signi cantly increased from the order of 1011 to the order of 1012. Such relatively high neutron yields were earlier observed on the devices with signi cantly higher current as the Saturn generator with the pulsed current of about 10 MA. At the same time, in our experiments, hydrogen ions with an energy above 38 MeV were detected. Such results are unique in experiments on the generator with the abovementioned maximum current and voltage. The work reported in this thesis is focused on the diagnostics of Z-pinch plasma by neutron detectors and interpretation of the experimental results. The precise neutron diagnostics is in our experiments necessary because the produced neutron pulses carry the information about the deuterons which produced them. In this thesis, the extensive neutron detection system is presented. This system is based on several principally independent methods: neutron bubble detectors, scintillation neutron time-of- ight diagnostics, neutron activation diagnostics with the moderator (silver activation counter), and fast neutron activation diagnostics with various energy threshold. This diagnostic system was used to evaluate neutron yields, energy spectrum, and neutron uences at di erent distances and directions. The in uence of non-dd neutrons on the experimental results is discussed.