Expansion and nonlinear relaxation of a strongly magnetized non-neutral electron plasma due to elastic collisions with background neutral gas

The expansion and nonlinear relaxation of a non-neutral electron plasma due to elastic collisions with constant collision frequency nu(en) between the plasma electrons and a low-density background neutral gas are investigated theoretically. The model treats the electrons as a strongly magnetized fluid (omega(pe)(2)/omega(ce)(2) much less than 1) with isothermal temperature T=const immersed in a uniform magnetic field B0 (e) over cap(z); The model also assumes an axisymmetric plasma column (partial derivative/partial derivative theta=0) with negligible axial variation (partial derivative/partial derivative(z)=O). Introducing the scaled radial coordinate rho=r/r(0)(t), and the density profile shape function eta(rho,t) = [2 pi r(0)(2)(t)/N]n(r,t), a diffusion equation is derived that describes the nonlinear evolution and relaxation of eta(rho,t) in response to electron collisions with the neutral gas. A very important consequence of the present analysis is that electron-neutral collisions (nu(en)not equal 0) cause the electron density profile to relax to a (slowly expanding) quasiequilibrium state with identical profile shape eta(eq)(rho) to that which would be produced by relaxation to thermal equilibrium by electron-electron collisions in the absence of background neutral gas (nu(en)=0). (C) 1996 American Institute of Physics.