Linear induction accelerator requirements for ion fast ignition
Fast ignition (fast heating of DT cores afief compression) reduces driver energy (by 10 X or more) by reducing the implosion velocity and energy for a given fuel compression ratio. For any type of driver that can deliver the ignition energy fast enough, fast ignition increases the target gain compared to targets using fast implosions for central ignition, as long as the energy to heat the core after compression is comparable to or less than the slow compression energy, and as long as the coupling efficiency of the fast ignitor beam to heat the core is comparable to the overall efficiency of compressing the core (in terms of beam energy-to-DT-efficiency). Ion driven fast ignition, compared to laser-driven fast ignition, has the advantage of direct (dE/dx) deposition of beam energy to the DT, eliminating inefficiencies for conversion into hot electrons, and direct ion heating also has a more favorable deposition profile with the Bragg-peak near the end of an ion range chosen to be deep inside a compressed DT core. While Petawatt laser experiments at LLNL have demonstrated adequate light-to-hot-electron conversion efficiency, it is not yet known if light and hot electrons can channel deeply enough to heat a small portion of a IOOOxLD compressed DT core to ignition. On the other hand, lasers with chirped-pulse amplification giving thousand-fold pulse compressions have been demonstrated to produce the short pulses, small focal spots and Petawatt peak powers approaching those required for fast ignition, whereas ion accelerators that can produce sufficient beam quality for similar compression ratios and focal spot sizes of ion bunches have not yet been demonstrated, where an imposed coherent velocity tilt plays the analogous role for beam compression as does frequency chirp with lasers. Accordingly, it is the driver technology, not the target coupling physics, that poses the main challenge to ion-driven fast ignition. As the mainline HIF program is concentrating on induction linacs, the purpose of this memo is to explore possible new features and characteristic parameters that induction linacs would need to meet the stringent requirements for beam quality and compression (sufficiently low longitudinal and transverse thermal spread) for ion driven fast ignition. Separately, Ed Lee at LBNL is looking at heavy-ion synchrotrons to meet similar fast ignition requirements. Parameters relating to cost (e.g, total beam-line length and transport quads, total core volt-seconds and power switching) have to be considered in addition to meeting the challenging beam quality requirements for fast ignition compared to conventional HIF. The aim of this preliminary study is to motivate, after critical debate, taking a next step to do more detailed designs, particle simulations, and experimental tests of the most critical accelerator elements and focusing optics, to further assess the feasibility of ion-driven fast ignition.
- Research Organization:
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 304509
- Report Number(s):
- UCRL-JC-129618; CONF-980256-; ON: DE98057749; BR: DP0214000; TRN: 99:002106
- Resource Relation:
- Conference: 15. international workshop on high energy density in matter, Hirschegg (Austria), 2-6 Feb 1998; Other Information: PBD: 26 Jan 1998
- Country of Publication:
- United States
- Language:
- English
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