Fusion Generated Fast Particles by Laser Impact on Ultra-Dense Deuterium: Rapid Variation with Laser Intensity

摘要

Nuclear fusion D+D processes are studied by nanosecond pulsed laser interaction with ultra-dense deuterium. This material has a density of 10~(29) cm~(-3) as shown in several previous publications. Laser power is <2 W (0.2 J pulses) and laser intensity is <10~(14) W cm~(-2) in the 5-10 μm wide beam waist. Particle detection by time-of-flight energy analysis with plastic scintillators is used. Metal foils in the particle flux to the detector remove slow ions, and make it possible to convert and count particles with energy well above 1 MeV. The variation of the signal of MeV particles from D+D fusion is measured as a function of laser power. At relatively weak laser-emitter interaction, the particle signal from the laser focus varies as the square of the laser power. This indicates collisions in the ultra-dense deuterium of two fast deuterons released by Coulomb explosions. During experiments with stronger laser-emitter interaction, the signal varies approximately as the sixth power of the laser power, indicating a plasma process. At least 2 × 10~6 particles are created by each laser pulse at the maximum intensity used. Our results indicate break-even in fusion at a laser pulse energy of 1 J with the same focusing, in approximate agreement with theoretical results for ignition conditions in ultra-dense deuterium. Radiation loss at high temperature will however require higher laser energy at break-even.