George H. Miley
Inertial electrostatic confinement (IEC) with a non-Maxwellian-beam- dominated plasma for fusion was originally proposed in the 1950s,(1) but since then only sporadic work has been devoted to the subject. Still, several new approaches have been proposed to overcome what was seen as a key problem--namely, maintenance of the cathode grid in a power reactor. R.W. Bussard proposed the Polywell! system, which replaces the grid with a pseudo-spherical magnetic field;(2) D.C. Barnes proposed a modified Penning trap approach;(3) while the University of Illinois (UI) effort has retained grids but used ion "microchannel" formation to partly protect them.(4) Each of these approaches appear to allow scaling to a power unit, e.g. a preliminary conceptual design study of the UI partially protected grid system indicates the heat load can be handled with active cooling, while sputtering does not seriously reduce lifetime.(5) However, a number of physics issues remain--especially stability and ion confinement times relative to up-scattering out of the potential trap formed in the plasma core of the IEC. Stability studies to date are encouraging,(6) but there is considerable debate about the up- scattering issue; various predictions for resulting Q-values range from .01 to 10.(7,8) However, even if a Q-value of only about 1 or less is achieved, the IEC could still provide an attractive intense neutron source or a He3 breeder.(9) Since IEC experiments are relatively small and inexpensive, it would seem prudent to pursue the physics issues in several scaled-up versions of present devices. (Present IEC units at the UI, for example, are being developed for commercial applications as low- level neutron sources--see Ref. 10.) A fusion power plant would be the goal, with the other low-Q applications as a backup, or alternately, as a practical way to bridge the gap from present units to a power plant. The IEC power plant appears to offer many advantages, including good compatibility with advanced fuels and direct conversion, small size, and low cost.(2,11) Consequently, the IEC reactor must be viewed as an exploratory project with potentially high divedends. Fortunately, the near-term low-Q applications can provide an early return on the R&D investment.
1. R. Hirsch, J.Appl.Phys., 38, 4522 (1967).
2. R. W. Bussard, Fusion Technol., 19, 2, 273-293 (1991).
3. M.M. Schauer, et al., Bult. APS, 40, 11, 1737-1738 (1995).
4. G.H. Miley, et al., "Discharge Characteristics of the Spherical Inertial Electrostatic Confinement (IEC) Device,"
XVIIth ISDEIV, Berkeley, CA (July 21-26, 1996).
5. A. Satsangi, et al., 11th Symp. on Space Nucl. Power and Propulsion, eds. M.S. El-Genk and M.D. Hoover,
AIP Conf. Proc. 301, AIP Press, 1297-1302 (1994).
6. N.A. Krall, Bult. APS, 40, 11, 1665 (1995).
7. W.M. Nevins, Pl. Physics 2, 10, 3804-3819 (1995).
8. T.N. Tiouririne and D.C. Barnes, Bult. APS, 40, 11, 1665-1666 (1995).
9. L. Chac!n and G. H. Miley, "IEC-3He Breeder for D-3He Satellite Systems," ANS Topical on the Technology of Fusion Energy, Reno, NV (June 16-20, 1996).
10. G. H. Miley, et al., Dense Z-Pinches, Conf. Proc #299, AIP Press, NY, 675-688 (1994).
11. R.W. Bussard and N.A. Krall, Fusion Technol., 26, 1326-1336 (1994).