Reactor Confinement Theory and IEC Reactor Visions

Abstract

Basic IEC theory was described earlier in Chaps. 1 and 2. We now turn to issues related to confinement theory for extension to a high flux neutron source or a power reactor. Work on reactor grade confinement for an IEC is closely tied to formation of a deep potential well and trapping of ions in that well sufficiently long enough (i.e., sufficient confinement time) to meet the Lawson Criteria. For D–T fuel, this is approximately given by n i τ i = 1014 s/cm3 at about T i = 25 keV (varies with fuel, e.g., about 1016 at T i ~ 150 keV for p–B11) [1, 2]. Here, n i is the ion density, τ i is the ion confinement time, and T i is the average ion temperature, or, for a non-Maxwellian plasma, the average ion energy. This applies to both electron-injected and ion-injected IEC configurations. However, due to ion beam convergence in typical spherical geometry, the ion density peaks strongly in the center region making it difficult to estimate the appropriate average density, n. In addition, it is generally hoped that beam–beam fusion collisions will dominate rather than Maxwellian reactions or beam–background gas reactions. In view of these considerations, the Lawson Criteria, which assumed a Maxwellian-type plasma for reaction rates, must be revised for the IEC. For a rough order of magnitude, assume that the converged region average density is around 1016 cm−3, then the confinement time needed is roughly 10−2 s. Radiation losses also need attention. The elimination of a magnetic field in the ion-injected case minimizes cyclotron radiation losses. Such losses are still encountered in “hybrid” magnetic trapping concepts such as the Polywell, but hopefully this radiation loss can be kept reasonably low with a relatively low magnetic field strength in the plasma trapping region.