Optimization of cone target geometry for fast ignition

中村 龍史*; 坂上 仁志*; 城崎 知至*; 長友 英夫*; 三間 圀興*; Koga, J. K.

Physics of Plasmas, 14(10), p.103105_1 - 103105_7, 2007/10

https://doi.org/10.1063/1.2789561

Electron energy characteristics generated by the irradiation of ultra-intense 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 those with 30 degree cone angles with a 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 4 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.