Research at the

Virtual National Laboratory for Heavy-Ion Fusion

The Virtual National Laboratory for Heavy-Ion Fusion (HIF-VNL) was established in 1999 to develop heavy-ion accelerators capable of igniting inertial-fusion targets for electric-power production.  The collaboration, which presently involves Lawrence Berkeley National Laboratory (LBNL), Lawrence Livermore National Laboratory (LLNL), and Princeton Plasma Physics Laboratory, is funded through the Office of Fusion Energy at the US Department of Energy.  According the memorandum creating the partnership, the HIF-VNL is chartered with "promoting more rapid progress in the development of heavy ion drivers through technical management integration of the laboratories scientific staff, equipment, and experimental facilities."  The current focus of HIF-VNL research is the design of an Integrated Research Experiment (IRE), a multiple-beam induction accelerator that would address, at a smaller scale, many of the critical technological and physics issues of a inertial-fusion driver.  Induction accelerators are used for several reasons.  They can handle much higher currents than the radio-frequency (rf) accelerators used for high-energy physics, and they allow a beam to be beam to be compressed during acceleration, eliminating the need for storage rings.  Also, induction accelerators have a lower-cost development path than rf accelerators because the critical physics questions occur a low energies, allowing them to be studied on small-scale experiments.  Initial studies have shown that this approach should have significant cost advantages over designs based on rf accelerators.

The IRE is intended as an integrated experiment to test simultaneously all aspects of a driver-scale accelerator, the injecting, transport through electrostatic and magnetic quadrupole lattices, final focusing, and transport through a reactor chamber.  Together with the target-physics database from laser-based  National Ignition Facility, the IRE should provide the scientific and technological basis for an Engineering Test Facility, the final step toward an inertial-fusion demonstration power plant.  To a large extent, this goal determines the scale of the experiment.  A hundred or more lattice periods are needed to demonstrate an understanding of beam dynamics in a transport lattice.  In order for beam loading to resemble that in a driver, the total current at the end of the IRE must be about 100 A, and tens of parallel beamlets are needed to carry this amount of current.  To allow useful focusing experiments, the ion energy must be 100 MeV or greater, the final perveance must be in the range 10-5 to 10-4, and the normalize emittance must be less than about 15 mm-mrad.  Finally, to validate beam-target interaction physics, the target temperature must reach about 50 eV, requiring a flux of 3 x 1012 W/cm and a total beam energy exceeding 1 kJ.   The precise accelerator requirements will, of course, emerge as design work proceeds.

A wide range of HIF-VNL research is currently underway to develop the physics and technological understanding needed to design the IRE.  This research falls into three general categories.

Small-scale experiments to study aspects accelerator physics of an IRE.  These experiments include the High-Current Transport Experiment (HCX) and Multiple-Beamlet Injector Experiment, both currently being planned, as well as recent projects like the Scaled Final-Focus Experiment, the  Beam-Combiner Experiment, and the  Plasma-Lens Experiments.

Theory and simulation using analysis and a variety of numerical models, ranging from zero-dimensional systems codes to 3-D particle-in-cell simulations.  The numerical tools are able to model all parts of an accelerator from source to target at an appropriate level of detail, and they are used now both to design the IRE and supporting experiments and to help understand experimental results.  In the accelerator, the areas presently being studied  include beam matching, emittance growth, lattice-error tolerances, beam-halo formation, and bunch compression.  Beam transport in the reactor chamber is also being examined to determine the best ways to neutralize the beam and to minimize the focal spot.

Engineering research and development work to develop the innovative approaches to fabricating affordable and reliable accelerator components.  The evaluation of low-cost magnetic-core materials and the design of superconducting magnetic-quadrupole arrays are active areas of IRE reasearch.

Work in these areas is co-ordinated through frequent teleconferences involving the HIV-VNL partners and through frequent internal reviews.  It is expected that conceptual-design work on the IRE will begin early in 2002.

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This document was written by W. M. Sharp and D. P. Grote, and has been reviewed and approved by HIF-VNL Director Roger Bangerter and by the AFRD Director William Barletta.  For comments or questions contact or  Work described here was supported by the Office of Fusion Energy at the U.S. Department of Energy under contracts  DE-AC03-76SF00098 and W-7405-ENG-48.  This document was last revised February, 2000.