Fast Ignition without Hole Boring

Abstract

A fast-ignitor scheme for inertial confinement fusion is proposed which works without hole boring. It is shown that a thermonuclear burn wave starts from the pellet corona when an adequate amount of energy (typically 10 kJ) is deposited in the critical layer by a petawatt laser ("coronal ignition"). Burn efficiencies as high as predicted for standard central spark ignition are achieved. In addition, the scheme is surprisingly insensitive to large deviations from spherical precompression symmetry. It may open a new prospect for direct drive.

On the inefficiency of hole boring in fast ignition

“…The energy balance 2pR 2 q e t ϭ 15 kJ leads to q e ϭ 2.1 ϫ 10 20 W cm Ϫ2 . Surprising enough, this value agrees with the hydrodynamic beam calculations without flux limit~Hain & Mulser, 2001; see Fig. 2 therein!.…”

“…However, they contrast with the fact that the laser can deposit its energy at densities not exceeding the critical density r c , respectively particle density n c . As a consequence, electrons of relativistic energies must provide for the energy transport to the dense compressed fuel in an efficient way, that is, good collimation, and on a time scale of several tens of picoseconds~e.g., 70 ps; Hain & Mulser, 2001!. Essentially three scenarios have been proposed to achieve the goal:~1!…”

Nonlinear electron-magnetohydrodynamic simulations of three dimensional current shear instability

“…These instabilities, known as sausage or kink instabilities, have been studied extensively in magnetohydrodynamic (MHD) approximation 1 valid for macroscopic length and time scales (much larger than the ion scales). In recent years, with the increasing capabilities of resolving shorter and shorter space and time scales in laboratory experiments, space observations, and computer simulations, the role of current shear instabilities on the microscopic space and time scales is being identified in a number of physical situations like plasma opening switches, 2-4 fast magnetic reconnection, [5][6][7][8][9][10][11][12] fast Z-pinches, 13,14 fast ignition (FI) concept of laser fusion 15,16 etc. For example in FI, sheared current channels form as current of hot electrons generated at the surface of a D-T pellet flows towards the core of the pellet and is compensated by the return current of cold electrons provided by the background plasma.…”

Difference between relativistic petawatt-picosecond laser-plasma interaction and subrelativistic plasma-block generation

“…lead to volume ignition~Hora et al, 1998!. One remarkable alternative is the use of peripheral ignition of a highly precompressed plasma~Hain & Mulser, 2001;Mulser & Bauer, 2004;Mulser & Schneider, 2004;Deutsch, 2004! or the generation of very high density 5 MeV electron beams from petawatt irradiation of a high density precompressed DT plasma, where the electron beam will ignite a controlled fusion reaction wave in a large amount of nearly uncompressed DT fuel producing a very high gain~Nuckolls & Wood, 2002!.…”