Drift compression and final focus for intense heavy ion beams with nonperiodic, time-dependent lattice

Abstract

In the currently envisioned configurations for heavy ion fusion, it is necessary to longitudinally compress the beam bunches by a large factor after the acceleration phase. Because the space-charge force increases as the beam is compressed, the beam size in the transverse direction will increase in a periodic quadrupole lattice. If an active control of the beam size is desired, a larger focusing force is needed to confine the beam in the transverse direction, and a nonperiodic quadrupole lattice along the beam path is necessary. In this paper, we describe the design of such a focusing lattice using the transverse envelope equations. A drift compression and final focus lattice should focus the entire beam pulse onto the same focal spot on the target. This is difficult with a fixed lattice, because different slices of the beam may have different perveance and emittance. Four time-dependent magnets are introduced in the upstream of drift compression to focus the entire pulse onto the same focal spot. Drift compression and final focusing schemes are developed for a typical heavy ion fusion driver and for the integrated beam experiment being designed by the Heavy Ion Fusion Virtual National Laboratory.

Kinetic description of neutralized drift compression and transverse focusing of intense ion charge bunches

“…Of considerable practical importance for heavy ion beam applications to high energy density physics and fusion is the axial compression and transverse focusing of the (initially long) charge bunch to a small spot size at the target location. Indeed, considerable technical progress has been made in analytical and numerical studies of the axial drift compression and transverse focusing of long, unneutralized charged bunches [10 -22], including the recent development and application of a self-consistent warm-fluid model, optimization of the axial pulse shape, and the lattice design for transverse focusing to a small spot size [18,19,21,22]. At the very high space-charge intensities characteristic of intense heavy ion beams, one of the major challenges is compressing the charge bunch axially (against space-charge forces) to the very short pulse length ideal for maximizing the beam intensity (number density) focused on the target.…”

Drift Compression and Final Focus Options for Heavy Ion Fusion

“…Our solution to this difficulty is to vary the strength of the four magnets in the very beginning of the drift compression phase for different z such that the desired scaling holds at the end of the last magnet. In a recently published paper [7], we demonstrated this technique using the parabolic longitudinal drift compression scheme for a typical unneutralized heavy ion fusion beam. We considered a Cs + beam with 2.43 GeV kinetic energy, and 5.85 m initial beam half length.…”

“…Heavy ion fusion designs require that different slices are focused onto the same focal spot at the target. In this paper, we study these basic questions of drift compression and final focus [1][2][3][4][5][6][7]. In the transverse direction, a set of envelope equations is adopted.…”

Centroid and Envelope Dynamics of High-intensity Charged Particle Beams in an External Focusing Lattice and Oscillating Wobbler

“…For example, unstable breathing modes can be described by envelope instabilities [1,6], and the two-stream electron cloud instability [7,8] and beam-beam interactions [9] are effectively modelled by following the centroid dynamics. Envelope dynamics is also employed to design beam focusing systems [10,11], while the purpose of studying centroid dynamics in most cases is to suppress instability or minimize the oscillation of the beam centroid around the design orbit [12]. As a general remark, the dynamics of the beam centroid has not been extensively explored for practical applications.…”