|
|
|
|
|
3D
WARP simulation of a novel merging-beamlet
ion beam injector. On the order of 100 beamlets
are independently accelerated to 1.2 MeV and
then merged to form a single beam with
a current of 0.5 A. The transverse phase space,
(x, vx/vz) projection at 1.6 m after
the end of the accelerating Pierce column,
shows the beamlets as they begin to mix. The
particles are color coded based on the beamlet
they began in.
|
|
Alex
Friedman, William M. Sharp, and David P. Grote, Lawrence
Berkeley National Laboratory
Research
Objectives
To
model beam dynamics for heavy-ion fusion (HIF) in accelerators and in
fusion chambers.
Computational
Approach
A
hierarchy of codes is used for numerical simulation of beam dynamics in
heavy-ion accelerators. IBEAM is first used for global optimization. A
truncated-moment beam module in WARP is then used for refining the physics
design and for generating the fields for beam acceleration, compression,
and longitudinal control. Detailed accelerator simulations are done mainly
with the electrostatic particle-in-cell (PIC) modules of WARP. A 2D semi-Lagrangian
Vlasov code is being developed to study halo questions and to corroborate
the PIC modeling. Beam transport modeling in the fusion chamber has been
done with the axisymmetric PIC code BICrz and with the more modern 2D/3D
code BPIC. Mission Research Corporation will use their parallel 2D/3D
electromagnetic PIC code LSP to investigate chamber-transport scenarios
using higher plasma densities.
Accomplishments
Much
of the simulation work has focused on developing the physics design of
the Integrated Research Experiment (IRE). WARP simulations of several
representative layouts were made to quantify such phenomena as emittance
growth, beam halo formation, and transverse-longitudinal coupling. Simulations
examining the effects of quadrupole offsets and idealized steering were
also carried out. Initial steps have been taken to design and simulate
a drift compression system.
Simulations
were also used to design and support other experiments. For beam injectors,
extensive simulation was carried out to determine the sensitivity of the
2 MeV injector to changes in geometry, voltage, and source uniformity.
A multiple-beamlet injector has been designed that promises a higher average
current density than a single large-aperture beam injector. Simulations
were also done for the High-Current Experiment (HCX), the Scaled Final-Focus
Experiment, the University of Maryland electron ring experiment, and the
European approach to heavy-ion fusion.
Finally,
simulations were used to study several basic questions of accelerator
physics, including beam splitting and halos. A preliminary investigation
of impedance effects on longitudinal instability found that a coasting
beam under some conditions remains stable through hundreds of accelerating
modules.
Significance
The
U.S. HIF program is charged with developing an accelerator and focusing
system capable of igniting inertial-fusion targets at a cost that is competitive
with other long-term energy sources. Achieving this objective requires
significant advances in beam physics and in accelerator science and technology.
Numerical simulations are essential for all aspects of the HIF program,
including interpreting the results of ongoing experiments and developing
and optimizing the designs of future experiments.
Publications
A.
Friedman, D. P. Grote, E. P. Lee, and E. Sonnendrucker, "Beam simulations
for IRE and driver: Status and strategy," 13th Inter-national Heavy-Ion
Fusion Symposium, 1217 March 2000, San Diego, CA; Nuclear Instruments
and Methods in Physics Research (in press).
D.
P. Grote, A. Friedman, G. D. Craig, W. M. Sharp, and I. Haber, "Progress
toward source-to-target simulations," 13th International Heavy-Ion Fusion
Symposium, 1217 March 2000, San Diego, CA; Nuclear Instruments and Methods
in Physics Research (in press).
E.
Sonnendrucker, A. Friedman, J. J. Barnard, D. P. Grote, and
S.
M. Lund, "Simulation of heavy ion beams with a semi-Lagrangian Vlasov
solver," 13th International Heavy-Ion Fusion Symposium, 1217 March 2000,
San Diego, CA; Nuclear Instruments and Methods in Physics Research (in
press).
|