Pre-plasma effects on core heating and enhancing heating efficiency by extended double cone for FIREX

Abstract

The effect of pre-plasma on core heating in cone-guiding fast ignition is evaluated by two-dimensional particle-in-cell (PIC) and Fokker–Planck (FP) simulations. If the long-scale pre-plasma exists in the cone, the generated fast electron energy becomes too high for effective core heating. As a result, the energy coupling from laser to core ηL→core is reduced by 80% compared with the case without a pre-plasma. Even for the case without a pre-plasma, ηL→core obtained in the simulation is smaller than that required for 5 keV heating in FIREX-I. In order to enhance ηL→core, we propose a new target design ‘extended double cone with short inner cone wall’ for fast electron guiding to imploded core and show sufficient improvement of heating efficiency using this new cone on the basis of PIC and FP hydro-simulations.

Fast electron beam guiding for effective core heating

“…The fast electron beam divergence was evaluated by 2D PIC simulations [2], where the Au cone with open angle of 30 degree was irradiated by intense laser with intensity of 3 × 10 19 W/cm 2 and duration of 1 ps, and the fast electron distribution function f fe (E, , y, t) (E, , y and t are energy, pitch angle, transverse position and time) were observed at the cone tip. The details of simulation condition and results are shown in Ref.…”

“…The details of simulation condition and results are shown in Ref. [2]. The "particle" and "energy" angular distributions of fast electron beam are evaluated by f f e,n ( ) = f f e (E, , y, t)dtdydE and f fe,E ( ) = E · f fe (E, , y, t)dtdydE.…”

“…Though a high-Z material, such as Au, is preferable for generating the strong magnetic field, the energy loss and scattering of fast electrons become large in the high-Z material. So, we estimate the guiding performance for different cone materials (Au, Cu, Al, DLC) by Fokker-Planck simulations where we used the fast electron beam profiles obtained from 2D PIC simulations [2] for 30 degree cone without pre-plasma and spherically compressed CD core (Gaussian density profile with 200 g/cm 2 density at the core, R = 0.12 g/cm 2 and uniform temperature of 300 eV) was assumed ( Fig. 2(a)-(b)).…”

“…According to the previous work [2], the fast electron beam has large beam divergence (full angle of ∼ 100 degree). Such a large beam divergence could be one of the main factors for lowering the core heating efficiency.…”

“…Such a large beam divergence could be one of the main factors for lowering the core heating efficiency. There are some ideas on beam guiding using self-generated magnetic fields, e.g., extended double cone [2] and layered cone with guiding wire [3]. The other idea is the guiding by externally applied magnetic fields along to the beam propagation direction [4].…”