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 present director of the HIF-VNL is Grant Logan and the other members of the executive staff are found on the organization chart.
The US heavy-ion fusion program is developing induction accelerators as inertial-fusion drivers. 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 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 at 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 current focus of HIF-VNL research is a series of small-scale experiments to study aspects of intense-beam physics. These experiments include high-brightness injector experiments to study the generation of beams with high current density and low emittance, a High-Current Experiment to investigate questions of beam transport, acceleration and steering, and a Neutralized Transport Experiment (NTX) to model aspects of beam transport in a fusion chamber. Engineering work is continuing in parallel with these experiments 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. A suite of computer codes is used to design the experiments, model details of their performance, and to analyze the data. These codes which range from zero-dimensional systems codes to 3-D particle-in-cell simulations, are able to model all parts of an accelerator from source to target at an appropriate level of detail. 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.
The current series of experiments is expected to culminate in an Integrated Beam Experiment (IBX), a single-beam induction accelerator combining beam injection, electrostatic and magnetic transport, acceleration, steering, and chamber transport in a single machine. The IBX will provide the physics and technology basis for designing a multiple-beam Integrated Research Experiment (IRE), which we hope to construct around 2009. 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.
Work in these areas is co-ordinated through frequent teleconferences involving the HIV-VNL partners and through frequent internal reviews.
For comments or questions contact WMSharp@lbl.gov or DPGrote@lbl.gov. Work described here was supported by the Office of Fusion Energy at the US Department of Energy under contracts DE-AC03-76SF00098 and W-7405-ENG-48. This document was last revised June, 2002.