Alex Friedman, David P. Grote, Edward P. Lee, Christine M. Celata, Michiel DeHoon, George D. Craig, John J. Barnard, Steven M. Lund, and William M. Sharp,
Heavy Ion Fusion Virtual National Laboratory, LBNL/LLNL
Eric Sonnendrucker, Lawrence Berkeley National Laboratory and Université Louis Pasteur, Strasbourg, France
Irving Haber, Naval Research Laboratory
Rami A. Kishek, University of Maryland
Debra A. Callahan-Miller, Lawrence Livermore National Laboratory

Research Objectives

This project entails the numerical simulation of beam dynamics for heavy-ion fusion (HIF) in the accelerator and in the fusion chamber. Current activities include the exploration of basic accelerator physics questions, such as emittance growth and halo formation, the analysis of ongoing experiments, and the design and optimization of planned experiments.

Computational Approach

A hierarchy of codes is used for numerical simulation of HIF beam dynamics. A fast-running truncated-moment code, CIRCE, is used for design and optimization of accelerators, for generating fields for beam acceleration, compression, and longitudinal control, and for testing algorithms for pulse steering, shaping, and final focus. Detailed accelerator simulations are done mainly with the 2D and 3D electrostatic particle-in-cell (PIC) code WARP. A 2D semi-Lagrangian Vlasov code is being developed to study halo questions and to corroborate the PIC modeling. Beam transport in the fusion chamber is modeled with electromagnetic codes such as BICrz or BPIC. A 1D Lagrangian-fluid code, CYCLOPS, is being used to study a z-pinch for possible beam focusing.

Behavior of longitudinal waves on an intense ion beam in a heavy-ion fusion driver accelerator, as simulated using the WARP3d PIC code. A random initial perturbation to the beam velocity is applied, launching waves which propagate in both directions. The plots depict the change in line charge density (relative to its initial value) for two cases. In each, the upper frame is an overlay of traces at a number of observing stations, with a vertical offset corresponding to the separation between stations. The lower frame is a "cell array" wherein "peaks" appear in light color, "valleys" in dark. In the left column, the waves moving toward the tail of the beam are seen to be unstable; in the right column, the accelerating module capacitance has been increased, and the instability is effectively suppressed.

Accomplishments

Evaluation of possible layouts and acceleration schedules for the Integrated Research Experiment (IRE) included studies of multiple-beam injection, emittance growth due to misalignments and quadrupole rotations, the effects of applied-field non-linearities (anharmonicities), and beam dynamics during final focus. Separate studies were carried out to investigate a kinetic instability driven by a temperature anisotropy, to determine equilibrium distribution functions of beams in curved lattices, and, in collaboration with the HIF group at GSI in Germany, to investigate bunch compression in storage rings.

Numerical support was provided to several ongoing experiments, and simulations were made to assist the design of planned experiments.

Significance

Publications

S. M. Lund, et al., "Numerical simulation of intense-beam experiments at LLNL and LBNL," Nuclear Instruments and Methods A 415, 345 (1998).

D. P. Grote, A. Friedman, and I. Haber, "New Methods in WARP," International Computational Accelerator Physics Conference, Monterey, CA (1998).

A. Friedman, et al., "Beam dynamics studies for heavy ion fusion drivers," in Proceedings of the 1999 Particle Accelerator Conference, edited by A. Luccio and W. MacKay, (IEEE Service Center, Piscataway, NJ, 1999), p. 1830.