Abstract. As part of the work building a small heavy-ion induction accelerator ring, or recirculator, at Lawrence Livermore National Laboratory, a diagnostic device measuring the four-dimensional transverse phase space of the beam in just a single pulse has been developed. This device, the Gated Beam Imager (GBI), consists of a thin plate filled with an array of 100-micron diameter holes and uses a Micro Channel Plate (MCP), a phosphor screen, and a CCD camera to image the beam particles that pass through the holes after they have drifted for a short distance. By time gating the MCP, the time evolution of the beam can also be measured, with each time step requiring a new pulse.
A heavy ion linear induction accelerator is considered to be the leading driver candidate for an Inertial Fusion Energy reactor. To deliver a space-charge-dominated beam at the appropriate energy (several GeV), such an accelerator would be several kilometers in length. Since total length has a strong influence on accelerator cost, we are considering the potential advantages and practical implementation of a recirculating induction accelerator. To address the critical scientific and technical challenges of a recirculating space-chargedominated heavy ion beam, we have begun to develop the elements of a scaled "small recirculator". An operating recirculator must demonstrate full beam control including multi-lap operation, beam insertion/extraction, acceleration and pulse compression. At present, experiments have been conducted using a 2mA, 80keV Kf beam transported through a 45" bend; experiments on a 90" bend with five induction modulators will begin soon. This paper briefly summarizes the recirculator specifications and operational features and reports the latest experimental data as well as the developmental status of beam diagnostics.
As part of the small induction recirculator development at LLNL, we are testing an injector and transport line that delivers 4 p beams of potassium with repetition rates up to 10 Hz at a nominal current of 2 mA. The normalized K-V equivalent emittance of the beams is near 0.02 IE: mm-mad and is mostly determined by the temperature of the source (0.1 ev). K+ ions generated at 80 keV in a Pierce diode are matched to an alternating gradient transport line by seven electric quadrupoles. Two additional quads have been modified to serve as two-axis steerers. The matching section is followed by a transport section comprised of seven permanent magnet quadrupoles. Matching to this section is achieved by adjusting the voltages on the electric quadrupoles to voltages calculated by an envelope matching code. Measurements of beam envelope parameters are made at the matching section entrance and exit as well as at the end of the permanent magnet transport section. Beam current waveforms along the experiment are compared with results from a one-dimension longitudinal dynamics code.Initial experiments show particle loss occurring at the beam head as a result of overtaking. Except for this, the beam is transported with essentially no loss of current through the 4.8 meters of electric and magnetic focused transport. During transport the emittance increases by approximately 50% from the intrinsic emittance of the source. Some electron effects that have little apparent influence on transport have also been seen.The apparatus is also being used for the development of non or minimally intercepting diagnostics for future recirculator experiments. These include capacitive monitors for determining beam line-charge density and position in the
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