Results of HIF R&D are reported in biannual Heavy Ion Fusion symposia and elsewhere. The last (13th) symposium was held under the auspices of Fusion Power Associates in March 2000 in San Diego, CA, and the next one is scheduled for May 2002 in Moscow.

Existing accelerator technology for use in high-energy or heavy-ion physics is highly developed. However, the application to heavy-ion inertial fusion requires considerable new R&D to produce the short, high-power beams that must be delivered to the fusion targets. Heavy ion beams with unprecedented currents of tens of kA, accelerated to several GeV, must hit the mm-size targets in short pulses of about 10 ns. These beams are essentially nonrelativistic, dominated by space-charge forces and must have very low emittance and energy spread. Simulation of the beams with special computer codes, verified by comparison with experiments, is a necessity for the staged development of a full-scale HIF driver. Heavy-ion induction linac experiments at the ampere level are being pursued at LBNL.

At the University of Maryland, two "table-top", low-cost experiments are being conducted with electrons to study major beam physics issues relevant to HIF drivers and to serve as testbeds for validating theory and computer simulation codes. Even though the electron energy is kept low (10 keV initially, 50 keV in the future), the beam is sufficiently intense to simulate the physics of nonrelativistic ion beams with several kA of current.

One of the two experiments, dealing with the longitudinal resistive-wall instability, which might adversely affect the beam quality in HIF drivers, has already produced significant results. It confirmed the predictions of linear theory, but also revealed nonlinear effects that are so far unexplained. Current research is aimed at understanding the evolution of energy spread using a new energy analyzer with highly improved resolution.

The second and major project, now under construction, is the 3.5-m diameter University of Maryland Electron Ring (UMER) for investigating the physics of space-charge dominated beams over a relatively long distance in the presence of dispersion by the bending magnets. The use of low-energy electrons keeps the size and cost relatively small and allows the use of innovative printed-circuit quadrupoles and dipoles. Progress, reported in seven papers at the recent Particle Accelerator Conference, includes excellent agreement of injector beam measurements with envelope calculations; descriptions of the beam diagnostics, controls and alignment system; electron gun simulations; and initial energy analyzer measurements.

Initial measurements of the 4x normalized emittance using the "pepper-pot" method yield a respectable value of 15 mm-mrad. The computer simulation code, WARP, originally developed at LLNL/LBNL, accurately reproduced experimental results, in particular the unexpected observation of radial space-charge waves, which gives confidence into the code's predictive capability. The ring will be fitted with induction gaps to provide longitudinal control of the beam bunches and, ultimately, acceleration. The ring will thus in effect be a recirculating induction accelerator, capable of acceleration from 10 keV to 50 keV (v/c=0.4) in 100 turns. Beam experiments are being conducted as construction proceeds. A wealth of new phenomena will be studied, including longitudinal-transverse coupling, resistive-wall instability, halo formation, resonance traversal, evolution of energy spread, and emittance growth due to several possible causes.

The electron beam physics laboratory at UMD is under the direction of Patrick O'Shea and Martin Reiser. It is funded jointly through the Office of Fusion Energy Science and the Office of High Energy and Nuclear Physics at DOE. Detailed information is available in the web site: http://www.ireap.umd.edu/umer. For further information, contact Patrick O'Shea (poshea@eng.umd.edu).