Design and characterization of a neutralized-transport experiment for heavy-ion fusion Page: 1 of 68
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Design and Characterization of a Neutralized-Transport
Experiment for Heavy-Ion Fusion
E. Henestroza, S. Eylon, P. K. Roy, S. S. Yu,
A. Anders, F. M. Bieniosek, W. G. Greenway, B. G. Logan,
R. A. MacGill, D. B. Shuman, D. L. Vanecek, and W. L. Waldron, LBNL
W. M. Sharp and T. L. Houck, LLNL
R. C. Davidson, P. C. Efthimion, E. P. Gilson, and A. B. Sefkow PPPL
D. R. Welch and D. V. Rose, MRC
C. L. Olson, SNL
In heavy-ion inertial-confinement fusion systems, intense beams of ions must be
transported from the exit of the final focus magnet system through the fusion chamber to
hit millimeter-sized spots on the target. Effective plasma neutralization of intense ion
beams in this final transport is essential for a heavy-ion fusion power plant to be
economically competitive. The physics of neutralized drift has been studied extensively
with particle-in-cell simulations. To provide quantitative comparisons of theoretical
predictions with experiment, the Virtual National Laboratory for Heavy Ion Fusion has
completed the construction and has begun experimentation with the Neutralized
Transport Experiment (NTX). The experiment consists of three main sections, each with
its own physics issues. The injector is designed to generate a very high-brightness,
space-charge-dominated potassium beam while still allowing variable perveance by a
beam aperturing technique. The magnetic-focusing section, consisting of four pulsed
magnetic quadrupoles, permits the study of beam tuning, as well as the effects of phase
space dilution due to higher-order nonlinear fields. In the final section, the converging
ion beam exiting the magnetic section is transported through a drift region with plasma
sources for beam neutralization, and the final spot size is measured under various
conditions of neutralization. In this paper, we discuss the design and characterization of
the three sections in detail and present initial results from the experiment.
The final transport section in a heavy-ion inertial-confinement fusion system poses major
challenges. After exiting the final-focus magnet system, intense beams of ions with a
current totaling tens of kiloamperes must drift without further external focusing to the
center of a target chamber, a distance of about 6 m in recent conceptual designs . To
obtain adequate target gain, these beams must all hit millimeter-sized spots on the ends of
the cylindrical fusion target.
From the very early days of heavy-ion fusion (HIF), final focusing has been a subject of
intense study [2, 3, 4], with perhaps the most comprehensive study being that of
HIBALL-II . These studies assumed that the chamber could have a sufficiently high
vacuum that beam ions would experience no forces other than their collective space
charge during the final transport to the target. In this final drift section, the beam space
charge acts to enlarge the focal spot, so the beam species, current, and energy in early
studies were chosen to make the space-charge blowup manageable. For example, Olson
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Henestroza, E.; Eylon, S.; Roy, P.K.; Yu, S.S.; Anders, A.; Bieniosek, F.M. et al. Design and characterization of a neutralized-transport experiment for heavy-ion fusion, article, March 14, 2004; Berkeley, California. (https://digital.library.unt.edu/ark:/67531/metadc787004/m1/1/: accessed April 23, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.