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.
Electrostatically trapped electrons in thermal-barrier tandem mirrors
Electron confinement in the plug regions of thermal-barrier tandem mirrors is examined. Analytical and numerical (Fokker-Planck code) approaches are presented for small-to-intermediate mirror ratios including the effects of passing particles and electron heating. Steady-state trapped-electron densities and mean energies from the theory and code agree to within 20% for mirror ratios 0 ≤ R ≤ 2.2 with and without passing particles. Electron heating and detrapping by strong RF diffusion is demonstrated computationally for parameters expected in the TMX-U experiment.
A relativistic multiregion bounce-averaged Fokker-Planck code for mirror plasmas
We have developed a unique Fokker--Planck code to study the physics of plasmas that are trapped in magnetic and potential wells of general shape on a collisional time scale. The code was designed primarily to apply to mirror machines, either a simple mirror or a tandem mirror. A plasma confined in a mirror machine generally consists of various groups of particles trapped magnetically and/or electrostatically depending on their energy, magnetic moment, and axial position. Characteristic features of such a plasma are: first, that the bounce times of trapped particles are much shorter than the collision times; and second, that particles trapped in different axial locations can have the same energy and magnetic moment. The former feature allows us to perform bounce-orbit averaging of the kinetic equation, and the latter feature indicates that the distribution function can be multivalued. The code solves a relativistic Fokker--Planck equation averaged over bounce orbits for all the trapped-particle groups. In addition to the Coulomb collision operator, the code includes a synchrotron radiation term, a quasilinear rf diffusion operator, and source and loss terms. The numerical method consists of a mapping technique and a Galerkin finite-element method. Example results using the code for electron-cyclotron resonant heatingmore » and neutral beam injection in a tandem mirror are also presented.« less