| Simulations
of Heavy Ion Beams in a Gaseous Fusion Target Chamber
For heavy-ion inertial confinement fusion, ion beams must
be transported and focused over several meters through the
chamber to the target. A sizable transport distance prevents
damage to the final focus section of the accelerator from
the target explosion. The selection of transport schemes impacts
the design not only of the accelerator but also of the fusion
target driven by the beams. Ballistic transport uses a final
focusing lens just outside the chamber to focus each beam
onto the target and a supply of electrons to provide neutralization.
Pinched transport uses a final focusing lens to focus each
beam to a small radius at the entrance to the chamber, and
then the beam propagates in the chamber at small radius to
the target.
 |
|
 |
|
| Figure
4 For the initial NBT plasma simulation,
the net current contained within the radius is plotted
with time moving clockwise: t = 14, 28, 42, 52 ns. The
legend unit is amps. |
|
Welch et al. have conducted state-of-the-art simulations
of three transport scenarios—neutralized-ballistic transport
(NBT, Figure 4), assisted-pinch transport (APT), and self-pinched
transport (SPT)—as they pertain to a thick-liquid wall
chamber (radius of 3 m). Their intent was to assess strengths,
weaknesses, and areas for future work.
No obvious showstoppers were uncovered for any of the transport
schemes. Given a judicious placement of plasmas, the simulations
suggest a nearly ballistic final spot can be achieved for
NBT. Outstanding physics issues for NBT include the 3D effects
of beam-beam interactions, target charging, and the interaction
with the flibe jets. The APT simulations are encouraging in
that nearly 90% energy transport is achieved; the discharge
channel naturally guides the beam from the chamber wall to
the target, unlike the two other schemes. Future work on APT
must include more realistic modeling of beam-plasma interactions
and gas chemistry. The meter-long SPT simulation is encouraging
in that a stable 2D equilibrium is found with tolerable late-time
erosion rate. A key issue may be the transport efficiency,
which appears to be degraded by transient beam evaporation.
INVESTIGATORS
R. Davidson, W. W. Lee, H. Qin, and E. Startsev, Princeton
Plasma Physics Laboratory; D. R. Welch, D. V. Rose, B. V.
Oliver, T. C. Genoni, and R. E. Clark, Mission Research Corporation;
C. L. Olson, Sandia National Laboratories; S. S. Yu, Lawrence
Berkeley National Laboratory.
PUBLICATION
D. R. Welch, D. V. Rose, B. V. Oliver, T. C. Genoni, R. E.
Clark, C. L. Olson, and S. S. Yu, “Simulations of intense
heavy ion beams propagating through a gaseous fusion target
chamber,” Phys. Plasmas 9, 2344 (2002).
URL
http://nonneutral.pppl.gov/best.htm
|
