Targets for direct-drive fast ignition at total laser energy of 200–400kJ

Abstract

Basic issues for the design of moderate-gain fast ignition targets at total laser energy of 200–400kJ (with less than 100kJ for the igniting beams) are discussed by means of a simple integrated gain model. Gain curves are generated and their sensitivity to several parameters is analyzed. A family of scaled target is designed, based on 1D hydrodynamic simulations of the implosion stage and 2D model simulations of ignition and burn. It is found that ignition and propagating burn can be achieved by targets compressed by 100–150kJ, properly shaped laser pulses (with wavelength λc=0.35μm), and ignited by 80–100kJ pulses. This requires adiabat shaped implosions to limit Rayleigh-Taylor instability, at the same time keeping the fuel entropy at a very low level. In addition, the igniting beam should be coupled to the fuel with an efficiency of about 25%, and the hot-electron average penetration depth should be at most 1.2–1.5g∕cm2. According to the present understanding of ultraintense laser-matter interaction, this limits the wavelength of the ignition beam to λig≤0.5μm. With the same assumptions, energy gain G=100 can be achieved by targets driven by a 250kJ compression laser pulse and an 80–100kJ ignition pulse.

Cone-guided fast ignition withnoimposed magnetic fields

“…Our peak density = 450 g/cm 3 and r = 3.0 g/cm 2 give an ideal burn-up fraction of 1/3 and fusion yield of 64.4 MJ. Atzeni [12] has found from 2D hydrodynamic simulations with prescribed heating (not self-consistent fast electron dynamics) that the minimal heat deposited in the hot spot needed for ignition is 140 kJ/( /100 g/cm 3 ) 1.85 , which for our is 8.7 kJ. The fast electron source in Zuma is injected 20 m to the left of the cone tip at z = 0.…”

“…We first find the ignition energy E ig f for an artificially collimated ( = 10 • ), 1.5 MeV monoenergetic source. The optimal DT hot-spot depth [12] is z = 1.2 g/cm 2 , which removes at most 1.3 MeV from a fast electron. 1.5 MeV electrons mostly stop in this depth.…”

Systematic analysis of direct-drive baseline designs for shock ignition with the Laser MégaJoule

“…In this scheme, compression phase and ignition are separated. Usually, targets designs present high initial aspect ratio A, defined as the ratio of the deuterium-tritium (DT) ice-layer inner radius over the DT-ice layer thickness, around A = 7 for Fast-Ignition (FI) [9] or for Direct-Drive (DD) targets [1] and around A = 11 for indirect drive targets [4]. In our study, we explore low initial aspect ratios and moderate implosion velocities.…”

A specialized layering module for high rep-rate production of free standing HiPER targets

“…The conceptual baseline target design (Baseline Target-2) for the HiPER project is of two types [6]. The dimensions are as follows: (1) BT-2 is a 2.094-mm diameter compact polymer shell with a 3-m thick wall.…”