Electron velocity distribution of (a) ﹩v_{x,e}/ v_{\mathrm{th}\,,e}﹩ and (b) ﹩v_{y,e}/ v_{\mathrm{th}\,,e}﹩ at ﹩\omega _{pe}t=150﹩. The velocity distribution functions are normalized by each maximum value. The bold solid curve along the distribution is the fitting one with the Gaussian function ﹩A_{0}+A\mathrm{exp}\,\left\{-\left[\left(v-v_{0}\right)/ v_{\mathrm{th}\,}\right]^{2}\right\}﹩.