Variance of DD-neutron yield in laser fusion experiments

⎯ This contribution deals with experimental observations of the yield of DD fusion in deuterated plastic targets irradiated by 300-ps 3-TW laser system PALS. To perform the analysis of variance for neutron yield values, Yn, in the range of 10 5 10 observed in a relatively narrow range of laser energy E from 500 700 J, the observed yield values were included in a neutron-yield – laser-energy (Yn−E) diagram showing general trends in the energy yield scaling Yn (E). This dependence is characterized by a power law, Yn = Q E , where Q is the parameter reflecting possible dependence on the pulse duration, laser intensity, laser contrast ratio, focal geometry, target structure, etc. [1]. The analysis we present shows that, despite shot-to-shot fluctuations, the variance of Q values from 14 – 5.210 for the narrow range of laser energy obtained in PALS experiments can be elucidated by the influence of some nonlinear processes affecting ion acceleration. The law of laser energy scaling for the yield of neutrons, YN, generated by intense lasers is derived from a series of experiments performed on various laser systems [1]. In general, this law is related to the energy and number of fusion ions. YN depends on the number densities of reacting nuclei and the fusion averaged reactivity, <v>, where (v) is the cross section defined as the number of reactions per target nucleus per unit time when a unit flux of projectile particles hits the target [2,3]. It is generally known that it is not possible to directly obtain experimental information on the flow of ionized species accelerated forward into the target volume, and to determine the number densities of reacting nuclei. Only in the case, for example, of deuterons is it possible to 47 EPS Conference on Plasma Physics P2.2001