19th International Symposium on Heavy Ion Inertial Fusion

Manipulations for delivering HIF beams onto targets: (1) Smoothing by arc wobblers, (2) Differential acceleration in final beam lines

16 Aug 2012, 14:35

2h 40m

Boiler Room (Shattuck Plaza Hotel)

Poster Poster session

Speaker

Alex Friedman (LBNL)

Description

A. Friedman LLNL, Livermore CA 94550 USA and Heavy Ion Fusion Science Virtual National Laboratory We describe two techniques related to the delivery of the ion beams onto the target in a Heavy Ion Fusion power plant. (1) By manipulating a set of ion beams upstream of a target, it is possible to achieve a more uniform energy deposition pattern. We consider an approach to deposition smoothing that is based on rapidly “wobbling” each of the beams back and forth along a short arc-shaped path, via oscillating fields applied upstream of the final pulse compression [A. Friedman, Phys. Plasmas 19, 063111 (2012)]. Uniformity is achieved in the time-averaged sense; the oscillation period must be sufficiently shorter than the target’s hydrodynamic response timescale . This work builds on two earlier concepts: elliptical beams [D. A. Callahan and M. Tabak, Phys. Plasmas 7, 2083 (2000)]; and beams wobbled through full-circle rotations [e.g., R. C. Arnold, et al., Nucl. Instr. and Meth. A 199, 557 (1982)]. Arc-based smoothing remains usable when the geometry precludes full-circle wobbling, e.g., for the X-target [E. Henestroza, B. G. Logan, and L. J. Perkins, Phys. Plasmas 18, 032702 (2011)] and some distributed-radiator targets. (2) By accelerating some beams “sooner” and others “later,” it is possible to simplify the beam line configuration in a number of cases. For example, the time delay between the “foot” and “main” pulses can be generated without resorting to large arcs in the main-pulse beam lines. This may minimize beam bending, known to be a source of emittance growth in space-charge-dominated beams. It is also possible to arrange for the simultaneous arrival on target of a set of beams (e.g., for the foot-pulse) without requiring that their path lengths be equal. This may ease a long-standing challenge in designing a power plant, in which the tens or hundreds of beams entering the chamber all need to be routed from one or two multi-beam accelerators or transport lines. Work performed under auspices of U.S. DoE by LLNL under Contract DE-AC52-07NA27344.