\begin{table}%t1
\caption{\label{t1}Summary of simulation parameters.} 
%\centering
\par
\begin{tabular}{ccc}
\hline \hline
Parameters & Symbol & Value\\
\hline
 Ion to electron mass ratio&$m_{\rm p}/m_{\rm e}$&$1836$\\
 Plasma density & $n=n_{\rm i}=n_{\rm e}$ &$10^{14}~{\rm m}^{-3}$\\
 Temperature&$T=T_{\rm e}=T_{\rm i}$&$10^{7}~$k\\
 Initial drift velocity &$v_{\rm d}$&$1.4v_{\rm e0}$\\
 Number of space grid points &$N_{z}$&$2000$\\
 Number of velocity grid points &$N_{\rm ve},N_{\rm  vi}$& $2500,400$\\
 Resolution of spacial grid &$\Delta z$&$0.5\lambda_{\rm De}$\\
 Resolution of velocity grid &$\Delta v_{\rm e},\Delta v_{\rm i}$&$0.01v_{\rm e0},0.05v_{\rm i}$\\
 Resolution of time&$\Delta t$& $0.003w_{\rm pe}^{-1}$\\
\hline
 \end{tabular}
\end{table}