Design and simulation of a multibeamlet injector for a high current accelerator

Abstract

A multibeamlet approach to a high current ion injector, whereby a large number of beamlets are accelerated and then merged to form a single beam, offers a number of potential advantages over a monolithic single beam injector. These advantages include a smaller transverse footprint, more control over the shaping and aiming of the beam, and more flexibility in the choice of ion sources. A potential drawback, however, is a larger emittance. In this paper, we seek to understand the merging of the beamlets and how it determines the emittance. When the constraints imposed by beam propagation physics and practical engineering issues are included, the design is reduced to a few free parameters. We describe the physics design of a multibeamlet injector and produce a design for an example set of parameters. Extensive use of 2D and 3D particle simulations was made in understanding the injector. Design tolerances and sensitivities are discussed in general and in relation to the example.

Envelope model for passive magnetic focusing of an intense proton or ion beam propagating through thin foils

“…(49)] in the continuous defocusing approximation is plotted in Fig. 6 as a function of the beam aspect ratio for Gaussian-and uniform-density beams.…”

“…(49) can be precalculated as a function of x =L on a grid over an adequate range and then F can be efficiently calculated to sufficient accuracy using interpolation to carry out the integrations without many evaluations of the form factor integral over K. Analogous comments apply to application to Eqs. (46) and (49) to model the evolution of r b for a uniform-density beam from specified initial conditions r b ðz i Þ ¼ r bi and dr b dz ðz i Þ ¼ r 0 bi . Note that if x !…”

“…This section presents a comparison of the envelope theory with particle-in-cell simulations using the WARP code [47][48][49]. Attention is restricted primarily to simulations aimed at verifying the envelope-model predictions and the departure from those results in cases where significant beam halo is generated, the beam pulse length is short, and/or and the beam under study is that of a finite-width energy slice of a much broader-energy-spectrum (and correspondingly higher-total-current) beam.…”

Overview of theory and simulations in the Heavy Ion Fusion Science Virtual National Laboratory

“…High-gradient tests with parallel beamlets were carried out, as were reduced-gradient scaled tests of a converging-beamlets system. WARP simulations were used to design the experiments, and results are in good agreement with those predictions [37][38][39].…”

Overview of theory and modeling in the heavy ion fusion virtual national laboratory

“…Another approach involves the merging of a large number (∼100) of micro-beamlets, each with high current density, offering the promise of a compact system [34]. However, the approach also poses physics and engineering challenges, as well as the computational challenge of a wide range of scales [35]. We are simulating all aspects of this approach.…”