Radial Fokker-Planck model for plasmas confined by magnetic mirror fields

A time-dependent computer model has been developed for the spatially dependent distribution function f(r,v,t). An orbit averaged Fokker-Planck equation treats Coulomb collisions and various atomic physics processes. The motivation for the present code is to provide an accurate treatment of gyro-radius effects and realistic beam geometries which have been neglected in previous Fokker-Planck codes. Finite width beams may be offset from the plasma center to determine beam injection for build-up studies. The inclusion of a finite gyro-radius is essential for studying radial transport due to both quasilinear fluctuations and charge exchange collisions. Charge exchange with energetic beam atoms and plasma erosion due to charge-exchange collisions with thermal gas are both included. Quasilinear diffusion terms include the effects of turbulent diffusion in the model. The model has been used to study particle and energy confinement times in the 2XIIB experiment and in the mirror plug of the TMX experiment. Calculated values of T/sub e/ decrease from classical Fokker-Planck values (1000 eV for 2XIIB) to the 50 eV to 200 eV range observed in 2XIIB and TMX experiments. Radial density profiles and n tau scaling with plasma radius and magnetic field agree with experimental data