Beam dynamics studies with the heavy-ion linear induction accelerator MBE-4

Abstract

Current amplification of heavy-ion beams is an integral feature of the induction linac approach to heavy-ion fusion ͑HIF͒. In this paper we report on amplification experiments conducted on a single beam of the Multiple Beam Experiment ͑MBE-4͒, a heavy-ion ͑Cs ϩ ͒ induction linac. Earlier MBE-4 experiments ͓H. Meuth et al., Nucl. Instrum. Methods Phys. Res. A 278, 153 ͑1989͔͒ had demonstrated up-to-9ϫ current amplification but had been accompanied by an up-to-2ϫ increase of normalized transverse emittance. Experiments to pinpoint the causes of this emittance growth indicated various factors were responsible, including focusing aberrations and mismatch difficulties between the injector diode and the accelerator transport lattice, a localized quadrupole misalignment problem, and the interaction of transversely large beams with the nonlinear elements of the focusing lattice. Following ameliorative measures, new current amplification experiments, both with and without acceleration, showed that current amplifications of up to 3ϫ and line charge density increases of up to Ϸ2ϫ could be achieved without increasing the beam's normalized transverse emittance. Finally, both the transverse beam dynamics, and beam current and energy measurements were accurately modeled by numerical particle-in-cell simulations and longitudinal dynamics codes, respectively.

Research and development toward heavy ion driven inertial fusion energy

“…The multiple beam experiment combined induction acceleration with a velocity ramp on a high space-charge Cs þ beam. It showed little emittance growth while the line charge density of the beam increased by factor of a few, similar to that required in the driver [26]. Later, in NDCX, the addition of plasma neutralization in conjunction with a AE15% velocity ramp furnished beams of a few nanoseconds duration, corresponding to 50-fold bunch compression and current amplification.…”

Intense Ion Beam for Warm Dense Matter Physics

“…Longitudinal space charge limits the beam compression ratio R, the ratio of the initial-to-final current, to ≤ 10 and an experiment reported R ∼ 5 [70]. If the beam space-charge is perfectly neutralized only two factors limit the axial compression, the velocity tilt ∆v o and the velocity spread ∆v z of the uncompressed beam bunch.…”

Results on intense beam focusing and neutralization from the neutralized beam experiment

“…Pulsed power is provided by a Marx generator that was used in the Multiple Beam Test Experiment (MBE-4) [34]. A timed crowbar switch on NTX produces pulses with 0.5 ---1 µs rise time and a 10-µs "flat-top".…”