Electromagnetic instability in plasmas heated by a laser field

Electromagnetic instability is investigated in homogeneous plasmas heated by a laser wave in the range alpha=v(0)(2)/v(t)(2)<= 2, where v0 is the electron quiver velocity and vt is the thermal velocity. The anisotropic electron distribution function that drives unstable quasistatic electromagnetic modes is calculated numerically with the Vlasov-Landau equation in the high ion charge number approximation. A dispersion relation of electromagnetic waves which accounts for further nonlinear terms on v(0)(2) from previous results is derived. In typical simulation with ion charge number Z=13, a temperature T=5 keV, a density n=9.8x10(20)cm(-3), and a laser wavelength lambda(laser)=1.06 mu m, growth rates larger than 10(12)s(-1) in the quasicollisionless wave-number range were found for alpha >= 1. In the same physical conditions and in the mildly collisional range a growth rate about 10(11)s(-1) was also obtained. The extent of the growth wave-number region increases significantly with increasing alpha.