On the spectrum of Z-pinch plasma neutrons
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MA DYNAMICS
On the Spectrum of ZPinch Plasma Neutrons V. V. Vikhrev and A. D. MironenkoMarenkov National Research Centre Kurchatov Institute, pl. Akademika Kurchatova 1, Moscow, 123182 Russia Received July 22, 2011; in final form, September 16, 2011
Abstract—Generation of neutrons from Zpinch discharges in a deuterated gas medium has been studied. It is shown that a powerlaw energy dependence of the number of highenergy deuterons in Zpinch plasma explains the observed broadening of the neutron spectrum in these systems. It is established that, at an average ion energy below 3 keV in Zpinch plasma, neutrons are mostly generated due to the interaction of high energy (~100keV) deuterons with the main plasma components. DOI: 10.1134/S1063780X12030087
1. INTRODUCTION Generation of neutrons in Zpinch discharges has been studied for more than half a century. The interest in this phenomenon is related to prospects of creating energy sources based on nuclear fusion reactions pro ceeding directly in the Zpinch plasma. Results of the first investigations of nuclear fusion in highcurrent discharges were presented by Kur chatov [1]. It was found that neutron generation in Zpinch discharge took place, the energy spectra of neutrons were measured, and it was established that these neutrons appeared due to collisions of high energy deuterium ions (with energies on the order to ~100 keV) and plasma (with much lower energies of particles). Original data on the generation of neutrons in pinched discharges have been also reported in [2– 4]. In recent years, the knowledge about neutron gen eration from Zpinch discharges has significantly increased, in particular, due to the measurements of deuteron energy spectra in pincheddischarge plasma [5]. It was found that Zpinch discharges were not accompanied by the formation of a monoenergetic ion beam that could be expected for ions accelerated in a longitudinal electric field; on the other hand, the ion energy distribution in the pinch also did not strictly obey the Maxwell law. The aim of this study was to explain features of the observed spectra of neutrons generated in Zpinch plasma by the presence of a slowly decaying “tail” in the energy distribution of ions. 2. DISTRIBUTION OF ION ENERGIES IN EXISTING NUCLEAR FUSION FACILITIES It should be noted that none of the existing con trolled thermonuclear fusion facilities exhibits purely Maxwellian distribution of ion energies in the high energy region. This circumstance can be explained by
the fact that the time of plasma confinement in these facilities is insufficient for the thermalization of ions (Maxwellization of ion distribution) with energies about 100 keV and above, which are predominantly involved in the nuclear fusion reactions. Indeed, although Coulomb collisions in nuclear fusion reac tors are frequently sufficient to produce Maxwelliza tion of the main plasma component, these collisions cannot ensure the Maxwell distribution of ions with high energies (100 keV and above) for the achieved times of plasma
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