Plasma Performance of the Central Cell of a Cat-D Tandem Mirror Reactor
A particle and power balance assessment of the central cell of a conceptual D-D tandem mirror reactor (TMR) is carried out using a two-dimensional (2-D) Fokker-Planck code and a zero-dimensional (0-D) simulation code. The two computational models produce excellent agreement except for the mean triton energy, the difference in which can be attributed to the fact that the 2-D code considers the long slowing-down time of the tritium. It is demonstrated that for an ion confining potential between 200 and 300 keV, a) the central cell of a catalyzed-deuterium (Cat-D) fueled TMR can achieve ignition in the temperature range of 40-60 keV, b) the alpha ash buildup must be strictly controlled to obtain an economical ratio of electrostatic confining potential to central-cell temperature ¿/T, allowing the exhaust tritium to beta decay to helium-3 prior to reinjection results in roughly the same net electrical power output, and c) injecting extra tritium beyond that bred in the plasma allows a drop in the minimum ion confining potential required for ignition. It is shown that the ion confining potential is minimized when Tic, = 50 keV; this results in a plasma Q of 26. A quantitative comparison with a D-T reactor scenario is presented. It is shown that under ideal operating conditions, a conceptual Cat-D TMR has a 35-40 percent higher power conversion efficiency than a D-T device; this must be weighed against the higher temperature and plugging requirements of Cat-D.
Multi-species Fokker-Planck calculations for D-T and D-3He mirror reactors
Values of the confinement parameter ntau and the figure of merit Q (the ratio of thermonuclear power to injected power) are obtained for postulated reactor conditions. The heart of the work is the numerical solution, under tested assumptions, of the coupled Fokker-Planck equations for as many as six charged species. A study is made of D-T and D-3He fuel cycles, including reaction products, in the following parameter ranges: mirror ratio, 2<or=Rm<10; injection energy, 50 keV<or=E0<or=1500 keV; equilibrium 3He fraction for the D-3He cycle, 0.05<or=fHe<or=0.35. The computed Q's fall in the ranges 0.5<QDT<1.5, 0.1<QDHe<0.3. The present results are compared with previous work, with analytical/empirical approximations, and with a separate code treating velocity space more rigorously for a single positive species.
Thermal barrier ion trapping rate in a tandem mirror
An analytic expression for the Coulomb collision induced ion trapping rate in the thermal barrier cell of a tandem mirror has been obtained. The overall system is assumed to be maintained in steady state by particle injection in the central cell and charge-exchange pumping in the barrier cell. For small ratios of bounce-to-collision time scales the problem reduces to a series of boundary value problems in the various regions of phase space. For conditions of interest, pitch-angle trapping is dominant and a Lorentz collision operator describes reasonably well the kinetic problem, which is solved using a square-well approximation. The analytic results are found to agree with numerical results within expected limits, on the order of the inverse of the barrier/mirror ratio (∼ 10 to 20%).