Time-of-flight measurements of deuterium ions and neutrons produced from laser-cluster fusion plasmas

Abstract

Previous studies have shown that, by irradiating deuterium containing clusters with intense laser pulses, one can generate deuterium ions energetic enough to create nuclear fusion reactions. The rate of DD fusion reactions increases with the relative velocity of the colliding ions. Therefore, measuring the ion temperature of fusion plasmas is essential for fusion research. We produced deuterium clusters with a high pressure (~50 bar), cryo-cooled (~87 K) deuterium gas using a supersonic nozzle with an orifice diameter of 0.79 mm and an expansion half angle of 5˚. We irradiated the cluster targets with intense laser pulses (10^16-10^18 Wcm^(-2)) and produced deuterium fusion plasmas. The average radius of deuterium clusters was about 10 nm based on our Rayleigh scattering measurements. We have designed and built our own neutron detectors to measure the fusion yields. We confirmed the production of 2.45 MeV fusion neutrons from the plasma using neutron time-of-flight technique. We have also built ion detectors using micro-channel plates, and have measured the time-of-flight of deuterium ions originating from the plasma. Our ion time-of-flight signals indicate that we produced deuterium plasmas with temperatures as high as 14 keV from the experiment. The yields of energetic deuterium ions and 2.45 MeV fusion neutrons are estimated to be 10^14 ions per shot and 10^5 neutrons per shot, respectively.