Optimization of cone target geometry for fast ignition

Abstract

Electron energy characteristics generated by the irradiation of ultraintense laser pulses onto solid targets are controlled by using cone targets. Two parameters characterizing the laser-cone interaction are introduced, which are cone angle and the ratio of the laser spot size to the cone tip size. By changing these parameters, the energy absorption rate, laser irradiance at the cone tip, and electron acceleration at the cone tip and side wall are controlled. The optimum cone targets for fast ignition are 30° cone angle with double-cone geometry, and a tip size comparable to the core size, with the irradiation of a laser pulse with a spot size of about four times the cone tip size. Cone targets have the possibility to enhance the maximum energy of laser-accelerated protons by using a smaller angle cone depending on the laser f-number.

Fast electron generation in cones with ultraintense laser pulses

“…[6][7][8][9][10][11][12][13][14] This paper discusses our recent explorations in laser-cone interactions. Section II describes the experimental setup and relevant parameters.…”

High Energy Electron Generation by Laser-Cone Interaction

“…T mid is lower than the ponderomotive energy of incident laser pulse which is 2.5 MeV in the above condition, and higher than the ponderomotive energy calculated by taking into account the intensity decrease due to oblique irradiation, whose tendency is seen in targets of different cone angle with similar size. When the surface potential and laser electric field co-exist, electrons are effectively accelerated along the surface by wiggling inside the potential [12,13]. When the surface acceleration takes place, the effective temperature of high energy electrons becomes proportional to the laser spot size, i.e., lateral coordinate, which is not seen in the above simulation.…”

Enhanced surface acceleration of fast electrons by using subwavelength grating targets

“…PIC simulations indicate that the cone targets can focus the laser energy and concentrate the fast electrons to the cone tip and enhance the energy coupling from the laser to fast electrons [3,4]. Cone shape [5,6], pre-plasma scale-length [7], polarization [8] and focusing properties of laser beam [6,9] are investigated in order to increase the laser energy absorption and to concentrate more fast electrons to the cone tip.…”