Detailed study of nuclear fusion from femtosecond laser-driven explosions of deuterium clusters

Abstract

Recent experiments on the interaction of intense, ultrafast pulses with large van der Waals bonded clusters have shown that these clusters can explode with sufficient kinetic energy to drive nuclear fusion. Irradiating deuterium clusters with a 35 fs laser pulse, it is found that the fusion neutron yield is strongly dependent on such factors as cluster size, laser focal geometry, and deuterium gas jet parameters. Neutron yield is shown to be limited by laser propagation effects as the pulse traverses the gas plume. From the experiments it is possible to get a detailed understanding of how the laser deposits its energy and heats the deuterium cluster plasma. The experiments are compared with simulations.

Frequency dependence of level depletion in Na clusters and in C2H4

“…We mention here briefly the violent cluster dynamics induced by high-intensity infrared laser beams leading to emission of energetic electrons, ions, X-rays and even nuclear reactions, see e.g. [4,5,6,7]. Pulses in the fs range have opened a wide area of fs-spectroscopy allowing the detailed tracking of ionic dynamics in molecules and clusters, see e.g [8,9,10,11].…”

Optimization of the neutron yield in fusion plasmas produced by Coulomb explosions of deuterium clusters irradiated by a petawatt laser

“…After compression, the pulse continued in vacuum, directed to reflect off the f /40 spherical mirror that focuses the 22 cm diameter flat-top beam to a 200 μm diameter focal spot in the target chamber with a Rayleigh length of 2 cm. This created a relatively large interaction volume compared with previous experiments [1,3,[9][10][11][12][13][14] to increase neutron yields [16]. The spherical mirror could be translated along the laser propagation direction to adjust the distance between the optical focus and the position of the cluster-producing nozzle.…”

“…At high enough laser intensity, almost all of the electrons are removed from the cluster on a time scale short relative to the ion motion. What remains is a highly charged cluster of ions at liquid density, which promptly explodes by Coulomb repulsion.In experiments with peak laser intensities of 10 16 -10 18 W/cm 2 , deuterium ions with average kinetic energies up to about 10 keV have been observed, which were energetic enough to drive DD fusion events in a plasma with an average ion density near 10 19 cm −3 [9][10][11][12]. DD fusion can also occur when energetic ions collide with cold atoms in the background gas jet [13].…”

Using ultrasonic atomization to produce an aerosol of micron-scale particles

“…The gas forms clusters as it expands into vacuum, and these clusters have been measured up to sizes of ϳ100 Å for a deuterium gas cooled to 80 K at a pressure of 70 atm. 1 This is roughly the maximum cluster size that can be produced by this method because further cooling is negated by mechanical energy that is added to the system when the gas jet is activated. In these experiments, the neutron yield was measured to increase dramatically with increasing cluster size, rising from ϳ10 2 neutrons/ shot for 30 Å clusters to ϳ10 4 neutrons shot for 55 Å clusters.…”

“…For example, such particles will: improve neutron yield when used as laser targets in laser-driven fusion experiments; [1][2][3] serve as a testmedia for models of the nonlinear optical phenomena that arise when intense light interacts with a wavelength-scale particle; [4][5][6] and be used to test fluid models of droplet formation in a novel phase space. 7 We describe here an apparatus capable of producing a dense aerosol of micron-scale particles that will be useful in each of these studies.…”