Nuclear Fusion with Reduced Coulomb Barriers
Author: John Perkins
Requested Type: Consider for Invited
Submitted: 2006-12-01 21:07:35
Co-authors:
Contact Info:
Lawrence Livermore National Laboratory
PO Box 808 (L-477)
Livermore, CA 94551
USA
Abstract Text:
The reserves of fusion fuels within the earth are truly unlimited providing a way can be found to exploit them economically. However, the route to a fully attractive commercial fusion reactor that can compete with advanced fission in the 21st century is not clear at this time. The size, cost and complexity of conventional thermonuclear fusion reactors -- both magnetic and inertial -- are fundamentally governed by the need to sustain a minimum value of the plasma temperature of ~10keV (100,000,000-degC) in the face of significant loss processes. This minimum temperature is necessary so that energetic ions in the tail of the thermonuclear Maxwellian plasma have sufficient energy to tunnel appreciably through the repulsive Coulomb barrier and, thereby, induce acceptable fusion reaction rates. For example, in the D-T fusion reaction, the cross section rises by nine orders of magnitude as the energy is raised from 1keV to 10keV; this is entirely due to increasing barrier transmission probability. Very modest changes in the Coulomb barrier geometry can have a profound impact on the fusion cross section and reaction rates. This suggests that one approach to achieving a fundamental step-change in the physics and, perhaps, the economics of fusion is to circumvent, at some level, this high temperature barrier threshold of the conventional (thermonuclear) cross section. This would be particularly advantageous if we are ever to realize economically attractive fusion reactors based on the so-called “advanced” fusion fuels.
In the spirit of a “skunkworks” talk, we will examine the nuclear physics of the fusion cross section both in terms of barrier penetration requirements and the “nuclear part” of the process that pertains at meson-coupling ranges of a few*1e-15m once barrier tunneling has occurred. We then summarize three barrier tunneling methods that have been proposed at some level:
(1) Muon catalysis. Here a muon acts as a very heavy electron. It orbits a D-T nuclear couplet at ~0.005A and hence screens the repulsive Coulomb repulsion down to this radius. The resulting optimum temperature for muon-catalyzed fusion reduces to only ~600-deg C.
(2) Shape-enhanced fusion in which a large enhancement (~factor of 10) of the fusion cross section may be realizable for certain advanced fusion fuels (e.g., p-11B) involving deformed nuclei with large quadrupole moments.
(3) Antiproton-catalyzed fusion where the bound state of an antiproton and a fusion fuel nucleus results in a dramatic reduction of the barrier width. Room temperature D-T fusion cross sections of ~1000barns have been calculated for this process which is twice the value of the uranium-235 neutron fission cross section at the same temperature
Finally, we pose the question of whether other methods of barrier penetration could be explored to these ends.
Characterization: D
Comments:
Skunkworks (oral talk prefered)
