Beam Final Transport and Direct-Drive Pellet Implosion
in Heavy Ion Fusion
Shigeo Kawata, Tetsuya Someya, Aleksandar I. Ogoyski
*,
Koji Shimizu, Takashi Nakamura, Jun Sasaki
Department of Energy and Environmental Science,
Graduate School of Engineering, Utsunomiya University,
Yohtoh 7-1-2, Utsunomiya 321-0932, Japan.
kawata
cc.utsunomiya-u.ac.jp
*
permanent address
Tech. University of Varna, 2 Studentska Str., Varna 9010, Bulgaria.
Key issues of heavy ion beam (HIB) inertial confinement fusion (ICF) include an efficient beam transport, beam focus, uniform fuel pellet implosion, and so on. In this paper we focus on HIB final transport and a direct-driven fuel pellet implosion by computer simulations in HIB ICF.
In order to realize a fine focus on a fuel pellet, space charge neutralization of incident focusing HIBs is required at HIB final transport, and the HIB should be transported stably in a reactor gas. In this paper, an insulator annular tube guide is proposed at the final transport part, through which a focusing HIB is transported. The physical mechanism of HIB charge neutralization based on an insulator guide is as follows: the local electric field created by HIB induces the local discharges, and a plasma is produced on the insulator inner surface. Then electrons are extracted from the plasma by HIB net space charge. The emitted electrons neutralize the beam space charge and move together with the HIB. After the final transport of the insulator guide, the HIB enters a reactor gas. The two-stream and filamentation instabilities are also analyzed for the propagation through background reactor plasma. The estimation result shows that the HIB is not influenced seriously by both the instabilities. The annular insulator guide may be placed at the HIB final transport area just outside a ICF reactor wall. An additional role of the insulator guide may be a protection of a HIB accelerator against a reactor gas exhausting from a beam port to the accelerator side, when the insulator guide is made of a ceramic material. The ceramic insulator guide may absorb the exhausting reactor gas, which can be ionized by the HIB space charge and can be re-used as a plasma source.
We also performed direct-driven DT pellet implosion simulations. The simulation results present a density valley formation by a Pb HIB deposition in a fuel pellet energy absorber layer and a radiation-smoothing effect along the density valley. The density valley plays a role of radiation confinement, and we have confirmed that the beam non-uniformity can be smoothed along the valley. We also estimate the growth of the Rayleigh-Taylor instability in the implosion process.
