Scaling of Laser Fusion Experiments for DD-Neutron Yield

Josef Krása,Daniel Klír

doi:10.3389/fphy.2020.00310

Abstract

Yields of neutrons produced in various laser fusion experiments conducted in recent decades are compared with each other. It has surprisingly been found that there is a possibility to make an overall elucidation of the variance in the number of neutrons produced in the various experiments. The common method is based on definition of the energy conversion efficiency as a ratio between the energy carried out by neutrons produced through the fusion reaction and the input energy given by laser energy, E, focused on a target. The neutron-yield – laser-energy diagram is the basic chart used to interpret the spread of experimental data in terms of the experimental efficiency of the laser-matter interaction. Experiments carried out using a single laser system show that laser energy dependence of the yield can be well characterized by a power law, Y = QE^a, where Q is the parameter reflecting possible dependence on the pulse duration, laser intensity, laser contrast ratio, focal geometry, target structure, etc. Sorting the values of the neutron yields obtained in various experiments shows that the power law Y=QE^1.65 is suitable to determine lines in the Y-E diagram each of them, where the value of Q is associated with quality of experimental conditions. This sorting shows the order-of-magnitude differences in yields found in various experiments, which can be characterized by the value of the parameter Q. Due to the easy feasibility and the large number of DD fusion experiments performed, the overall Y-E diagram gives a chance to identify suitable laser systems for effective DD fusion experiments. It can, therefore, be assumed that some of the conclusions of these experiments could also be applied to the experimental arrangement suitable for optimizing p11B fusion.

Highlights

Many efforts have been devoted to optimizing the heating of fusion targets by laser pulses to initiate different fusion reactions producing e.g., neutrons and alpha particles through fusion DD, DT and p11B reactions that carry released energy [4,5,6]
If this factor is taken into account, the values of DT-neutron yields achieved at the OMEGA and NIF experiments are shifted to the YBL line that determine the results of standard DD-fusion experiments
Published experimental data made it possible to classify individual experiments within a metadiagram in such a way that the number of fusion reactions increases with increasing energy as E1.65 at the same value of the Q coefficient

Summary

INTRODUCTION

Many efforts have been devoted to optimizing the heating of fusion targets by laser pulses to initiate different fusion reactions producing e.g., neutrons and alpha particles through fusion DD, DT and p11B reactions that carry released energy [4,5,6]. We note that the values of the DT-neutron yield shown in Figure 3 are presented without a correction taking into account differences in DD and DT fusion reaction cross sections, in the case of a thermonuclear reaction at a certain temperature, the fusion probability of the deuterium-tritium reaction is nearly by a factor of 100 larger than that of the deuterium-deuterium reaction [29] If this factor is taken into account, the values of DT-neutron yields achieved at the OMEGA and NIF experiments (tagged with 11–15 labels) are shifted to the YBL line that determine the results of standard DD-fusion experiments. If we consider the possibility of increasing yield by using a high-quality laser, as mentioned above, the use of picosecond or shorter duration CPA- laser pulses that do not produce pre-plasma but initiate non-thermal fusion reactions in p11B plasma could help solve a key problem for controlled nuclear fusion energy generation [50, 51]

CONCLUSIONS

DATA AVAILABILITY STATEMENT