\begin{table}%t2
 %\centering
\par
 \caption {\label{t:Xnull}Gradient and curvature drift velocities (in \rm{m/s}), gradient and curvature
 scales (in \rm{m}) and Larmor radii (in \rm{m}) of both protons and electrons at the reference null.}
  \begin{tabular}{llllll}
 \hline\hline
 \noalign{\smallskip}
 At the null & $V_{\rm grad}$ & $V_{\rm curv}$ & $R_{\rm grad}$ & $R_{\rm curv}$ & $R_{\rm Larmor}$ \\
 \hline
 $200~\rm{eV}$ proton & $36.9$ & $21.6$ & $8778$ & $75807$ & $422.34$ \\
 $200~\rm{eV}$ electron & -- & -- & -- & -- & 9.85 \\
 $2~\rm{keV}$ proton & $369$ & $216$ &-- & -- & $1335.6$ \\
 $2~\rm{keV}$ electron & -- & -- & -- & -- & 31.2 \\
 $10~\rm{keV}$ proton & $1850$ & 1080 & -- & -- & 2986.4 \\
 $10~\rm{keV}$ electron & -- & -- & -- & -- & 69.7 \\
 \hline
 \end{tabular}
 \end{table}