Instability and Emittance Growth in High-Current Heavy Ion Beam Bunching

Abstract

Summary form only given. In a heavy ion inertial fusion (HIF), the generation and transport of intense heavy ion beams are important issues, because the required beam parameters are far from those of the conventional particle accelerator system. Since there are no sufficient data for the system design, the study of space-charge-dominated beams is crucial in HIF. Especially, in the final stage of HIF driver system, the beam pulse must be longitudinally compressed from ~100 to ~10 ns. Induction voltage modulators, based on a pulsed power technology, are proposed for this purpose. The pulsed power technology serves a precise waveform controllability and repetition capability. A beam buncher by the induction modulator can apply bunching voltage so as to make a considerable velocity tilt between the head and the tail of the beam bunch. Although the whole HIF driver design is under construction, the final beam bunching is indispensable in all of the suggested HIF accelerators. We investigate the beam dynamics under a strong space charge effect during the longitudinal bunch compression in the final beam bunching by using the multi-particle numerical simulation. During the final beam bunching, a beam instability is induced by the strong space charge effect. The beam instability can cause the emittance growth. We study the emittance growth mechanism induced by the beam instability with two types of the transverse focusing lattice system, i.e. alternating gradient (AG) focusing and continuous focusing (CF) configurations. In the beam transport with the AG focusing lattice, the beam instability can be induced rather than in the case with the CF lattice configuration