Solving the stand-off problem for MTF: plasma streams as disposable electrodes
Author: Dmitri D Ryutov
Submitted: 2005-12-20 20:17:21
Lawrence Livermore National Laboratory
7000 East Avenue
Livermore, CA 94551
A challenging problem of magnetized target fusion (as well as Z-pinch fusion) is delivering the energy of the order of tens of megajoules to the target situated at a distance of 3-6 m from the walls of the reaction chamber. In the past, several ways of solving this problem have been considered, including the insertion of a disposable transmission lines, using fast projectiles to drive the magneto-compressor generator, using particle beams in combination with the inverse diode, etc. In this paper we consider an approach prompted by the concept of a plasma liner . Specifically, we suggest using a set of plasma sources situated at the walls of the reaction chamber, to create two disc-shaped plasma flows converging on the axis of the chamber, where they would be intercepted by two axisymmetric electrodes mounted on the target. The target we envisage would have a local spherical blanket of the type described in Ref.  with the outer radius of order of 50-75 cm. The collecting electrodes will be of a comparable scale and will have a thickness of only ~ 1 mm, so that their mass will be very small compared to the mass of the blanket. The current collected by the on-board electrodes will drive the MTF liner (or Z pinch) situated in the center of the blanket. In every cycle, the blanket with all the inner elements gets evaporated and partially ionized; the conducting gas may, in principle, be used to drive an MHD generator . We analyze a variety of the plasma physics issues related to the performance of the plasma electrodes: the hydrodynamics of converging disc flows, the magnetic insulation between the two discs, radiative balance, resistive losses in the plasma, and the role of the sheath resistance at the interface between the plasma streams and electrodes. We find that such a system is capable of delivering tens of megajoules within the time ~ 2-3 microseconds, at a voltage ~ 1 MV. We discuss the on-board circuitry (situated inside the spherical blanket) in the context of possible power amplification.
This work was performed for the U.S. DoE by UC LLNL under contract # W-7405-Eng-48.
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