Kinetic tandem concept: theory and computer simulations of the potential barriers

摘要

The Kinetic Tandem fusion plasma confinement concept is a member of the class of211u001eopen magnetic confinement systems whose magnetic topology is that of a tube of 211u001emagnetic flux open at both ends. In open-ended systems the central problem is 211u001ethat of limiting the rate of plasma losses out the ends. In a conventional tandem 211u001emirror system end-plugging is accomplished by the generation of positive 211u001epotential barriers within special short mirror cells located at each end of a 211u001elong central confinement cell. The kinetic tandem concept accomplishes the same 211u001eend result by employing dynamic effects, but without the necessity of special end 211u001ecells. The field employed in the kinetic tandem is a simple axially symmetric 211u001esolenoidal field whose intensity tapers to low values at the ends. Since the 211u001efield line curvature is everywhere positive such a field is stabilizing for MHD 211u001einterchange modes. Into each end are injected ion beams that are aimed nearly 211u001eparallel to the field line direction. The ions from these beams then are radially 211u001ecompressed, stopped, and reflected back by magnetic mirror action in climbing up 211u001ethe magnetic gradient. In this way ion density peaks are formed between which the 211u001eplasma is to be confined. As in the original tandem mirror concept, a localized 211u001eambipolar potential arises to maintain quasi-neutrality between the ions and the 211u001eelectrons. provided the plasma density in the plugs is higher than that of the 211u001eplasma contained between them the ions of the central plasma will be confined 211u001ebetween the plugs by the positive potential barriers represented by the plugs. 211u001eThe plasma electrons will at the same time be confined by the overall positive 211u001epotential of the plasma with respect to the ends. In this report some analytical 211u001ecalculations of the formation of the plugs will be given. These calculations were 211u001ethen confirmed and extended by computer simulations, using the LLNL code ICEPIC. 211u001eWithin the assumptions made in the theoretical calculations and in the code 211u001erepresentation, fusion-relevant plug plasma parameters were achieved, and no 211u001eevidence of unstable behavior was detected in the simulations.