Measurements of Lateral Diffusion Coefficients and First Townsend Coefficients for Electrons in Helium by an Electron-Density Sampling Method

Abstract

Direct experimental measurements of electron diffusion coefficients $D$ in helium have been carried out at 300\ifmmode^\circ\else\textdegree\fi{}K in the range of $0<~\frac{E}{N}<2.7\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}16}$ V ${\mathrm{cm}}^{2}$ ($0<~\frac{E}{{P}_{0}}<10$ V ${\mathrm{cm}}^{\ensuremath{-}1}$ ${\mathrm{Torr}}^{\ensuremath{-}1}$) by an improved electron-density sampling method. Absolute errors less than \ifmmode\pm\else\textpm\fi{} 0.5% are claimed in the range $0<~\frac{E}{N}<9\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}17}$ V ${\mathrm{cm}}^{2}$ and less than 1.5% in the range $9\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}17}<\frac{E}{N}<2.7\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}16}$ V ${\mathrm{cm}}^{2}$.The obtained values of $D$ are in agreement with those of Crompton, Elford, and Jory in the range of $2.124\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}19}<~\frac{E}{N}<~3.03\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}17}$ V ${\mathrm{cm}}^{2}$ studied by these authors. Also measurements of $\ensuremath{\alpha}W$ (where $\ensuremath{\alpha}$ is Townsend's first coefficient and $W$ the drift velocity) have been performed in the range $9.03\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}17}<~\frac{E}{N}<~2.6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}16}$ V ${\mathrm{cm}}^{2}$ (corresponding to $3.2<~\frac{E}{{P}_{0}}<~10$ V ${\mathrm{cm}}^{\ensuremath{-}1}$ ${\mathrm{Torr}}^{\ensuremath{-}1}$). Values of $\ensuremath{\alpha}$ with an accuracy evaluated at \ifmmode\pm\else\textpm\fi{} 10% are obtained by dividing $\ensuremath{\alpha}W$ by the $W$ values found in the literature. These $\ensuremath{\alpha}$ values are to be compared with those of the literature, which are dispersed by a factor of 3 in the above range.