Abstract
Deuterium-Deuterium fusion processes were generated by focusing the 3 TW PALS Laser on solid deuterated polyethylene targets placed in vacuum. Deuterium ion acceleration of the order of 4 MeV was obtained using laser irradiance Iλ 2 ∼ 5 × 1016 W μ m2 /cm2 on the target. Thin and thick targets, at low and high density, were irradiated and plasma properties were monitored “on line” and “off line”. The ion emission from plasma was monitored with Thomson Parabola Spectrometer, track detectors and ion collectors. Fast semiconductor detectors based on SiC and fast plastic scintillators, both employed in time-of-flight configuration, have permitted to detect the characteristic 3.0 MeV protons and 2.45 MeV neutrons emission from the nuclear fusion reactions. From massive absorbent targets we have evaluated the neutron flux by varying from negligible values up to about 5 × 107 neutrons per laser shot in the case of foams targets, indicating a reaction rate of the order of 108 fusion events per laser shot using “advanced targets”.
Highlights
The high intensity laser, of the order of 1016 W/cm2 or higher, transfers high ponderomotive energy to the electrons target, generating high electron emission and high electric fields in the developed non equilibrium plasma, which drives the ion acceleration mainly along the normal to the target surface [1]
A typical result obtained using the Thomson Parabola Spectrometer is reported in Fig. 2 for the Target Normal Sheath Acceleration (TNSA) plasma production, from 600 J pulse energy hitting a deuterated PE foil, 10 μm in thickness, using a laser focal position FP of -100 μm, i.e. focusing 100 μm in front of the target surface
The proton parabola is thicker and wider with respect to the others as a consequence of two proton contributions: the protons coming from the D-D nuclear reaction extended up to a maximum energy of 3.0 MeV and the protons coming from the ionized hydrogen absorbed in the deuterated PE polymer, characterized by a maximum ion acceleration of 2.4 MeV
Summary
The high intensity laser, of the order of 1016 W/cm or higher, transfers high ponderomotive energy to the electrons target, generating high electron emission and high electric fields in the developed non equilibrium plasma, which drives the ion acceleration mainly along the normal to the target surface [1]. The use of thick “advanced targets”, promoting the laser absorption and the ion acceleration, for example based on porous (foam) polymers, permits to enhance both ion energy and ion yield accelerating protons at energies of the order of some MeVs. Tailored foams, due to their low density (approximately 1-10 mg/cm3) and high porosity, can be employed as thick and thin films covering a substrate in order to enhance the laser illuminated area, to reduce the reflection component of the laser light, to increase the laser penetration in the under-critical produced plasma and. To induce self-focusing effect due to the high refraction index in the produced pre-plasma vapor [7]
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