Abstract
The High Current Experiment (HCX) at Lawrence Berkeley National Laboratory is part of the US program to explore heavy-ion beam transport at a scale representative of the low-energy end of an induction linac driver for fusion energy production. The primary mission of this experiment is to investigate aperture fill factors acceptable for the transport of space-charge-dominated heavy-ion beams at high space-charge intensity (line-charge density /spl sim/ 0.2 /spl mu/C/m) over long pulse durations (>4 /spl mu/s) in alternating gradient electrostatic and magnetic quadrupoles. This experiment is testing - at driver-relevant scale - transport issues resulting from nonlinear space-charge effects and collective modes, beam centroid alignment and beam steering, matching, image charges, halo, electron cloud effects, and longitudinal bunch control. We present the results for a coasting 1 MeV K/sup +/ ion beam transported through the first ten electrostatic transport quadrupoles, measured with beam-imaging and phase-space diagnostics. The latest additions to the experiment include measurements of the secondary ion, electron and atom coefficients due to halo ions scraping the wall, and four magnetic quadrupoles to explore similar issues in magnetic channels.
Highlights
The High Current Experiment (HCX) [1], located at Lawrence Berkeley National Lab and carried out by theHeavy-Ion Fusion Virtual National Laboratory (HIFVNL),1 is designed to explore the physics of intense beams in the context of developing a heavy-ion high-intensity accelerator for an inertial fusion power plant [2,3].At an injection energy of 1–1.8 MeV, a line-charge density, of 0:1–0:2 C m1, and a pulse duration of4 s, the HCX main beam parameters are in the range of interest for a fusion driver front end
The time dependence of the envelope parameters emerging from the matching section is driven by variations in the extraction voltage which controls most of the emission at the beginning of the injector
The energy perturbation is applied by raising the potential of the first matching section quadrupole with respect to its neighbors, which induces a perturbation in the gaps preceding and following the quadrupole, each perturbation resulting in two waves that propagate in opposite directions
Summary
The High Current Experiment (HCX) [1], located at Lawrence Berkeley National Lab and carried out by the. In the Single Beam Transport Experiment [15], the maximum generalized perveance was 2:2 103 —higher than generally envisioned for a fusion driver—but the linecharge density remained about 1 order of magnitude lower than for the HCX or a fusion driver front end. Greater fill factors enhance nonideal physics effects resulting from imperfect focusing optics, image charge and halo impacting material structures and releasing desorbed gases that interact with long-pulse beams, creating possible electron-cloud effects. These are intense beam physics issues that may be relevant to other accelerator applications requiring high intensity, such as spallation neutron sources and the production of rare isotopes.
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