NUMERICAL HEATING IN HYBRID PLASMA SIMULATIONS

The numerical heating in hybrid particle-fluid simulations has been in vestigated with emphasis on the regime ZT(e)/T-i much greater than 1, where Z is the charge state of the ions and T-e and T-i are the electr on and ion temperatures, respectively. For the simple case of particle ions advanced in the ambipolar field due to quasineutral isothermal f luid electrons, the heating rate is observed to be weakly dependent on time step, inversely proportional to the number of simulation particl es per grid cell and strongly increasing with increasing ZT(e)/T-i. Ad ditional smoothing, due to finite Debye length, or introduced through numerical means such as higher order particle interpolation or smoothi ng of grid quantities, is observed to significantly reduce this heatin g. Both one- and two-dimensional results are presented. These results are important to hybrid particle simulations of laser generated plasma s, a regime where ZT(e)/T-i much greater than 1 is often encountered. As a relevant example, simulations of stimulated Brillouin scattering are presented illustrating the deleterious effect of numerical heating and attendant distortions to the particle distribution function. (C) 1997 Academic Press.