Abstract
Experiments at the GARPUN KrF laser facility and 2D simulations using the NUTCY code were performed to study the irradiation of metal and polymethyl methacrylate (PMMA) targets by 100 ns UV pulses at intensities up to 5 × 1012 W cm−2. In both targets, a deep crater of length 1 mm was produced owing to the 2D geometry of the supersonic propagation of the ablation front in condensed matter that was pushed sideways by a conical shock wave. Small-scale filamentation of the laser beam caused by thermal self-focusing of radiation in the crater-confined plasma was evidenced by the presence of a microcrater relief on the bottom of the main crater. In translucent PMMA, with a penetration depth for UV light of several hundred micrometers, a long narrow channel of length 1 mm and diameter 30 μm was observed emerging from the crater vertex. Similar channels with a length-to-diameter aspect ratio of ∼1000 were produced by a repeated-pulse KrF laser in PMMA and fused silica glass at an intensity of ∼109 W cm−2. This channel formation is attributed to the effects of radiation self-focusing in the plasma and Kerr self-focusing in a partially transparent target material after shallow-angle reflection by the crater wall. Experimental modeling of the initial stage of inertial confinement fusion-scale direct-drive KrF laser interaction with subcritical coronal plasmas from spherical and cone-type targets using crater-confined plasmas seems to be feasible with increased laser intensity above 1014 W cm−2.
Highlights
Much effort is being expended worldwide on the creation of huge laser installations such as the National Ignition Facility (NIF) in the USA,[1] Laser Megajoule (LMJ) in France,[2] Shen Guang (SG III and IV)[3,4] in China, and UFL-2M in Russia,[5] with radiation energies over 2 MJ for implementation of controlled thermonuclear reactions on irradiation of spherical shell microtargets containing D–T fuel
Laser-driven experiments on ignition of inertial confinement fusion (ICF) performed at the only fully operating NIF facility adopting the indirect-drive scheme with conversion of laser light into x-rays have not yet succeeded in achieving a useful energy gain GT ≥ 1 in a target
In future ICF power plants, neutrons would have to release their energy in the reactor chamber blanket, producing inertial fusion energy (IFE).[9]
Summary
Much effort is being expended worldwide on the creation of huge laser installations such as the National Ignition Facility (NIF) in the USA,[1] Laser Megajoule (LMJ) in France,[2] Shen Guang (SG III and IV)[3,4] in China, and UFL-2M in Russia,[5] with radiation energies over 2 MJ for implementation of controlled thermonuclear reactions on irradiation of spherical shell microtargets containing D–T fuel. Laser-driven experiments on ignition of inertial confinement fusion (ICF) performed at the only fully operating NIF facility adopting the indirect-drive scheme with conversion of laser light into x-rays have not yet succeeded in achieving a useful energy gain (the ratio of output thermonuclear energy to laser energy) GT ≥ 1 in a target. Only rather low neutron and alpha particle yields ∼1016 have been obtained,[6,7] there has been some progress in achieving ignition conditions.[8] On absorption in the compressed target core, alpha particles with 3.5 MeV energy should sustain fuel burning, whereas 14 MeV neutrons would mostly lead to energy release in the form of a microexplosion. For the direct-drive ICF neutron source in such a hybrid reactor with a bilateral conical target and a neutron yield of 1016–1017, it has been proposed to use a 1 MJ KrF laser driver with long pulses of 100–250 ns[14] or a 1 MJ Nd-glass laser (second and third harmonics) with pulses of 10–20 ns.[15,16]
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