Space Charge Effects in the Cavalleri Determination of Electron Diffusion Coefficients in Gases

A theoretical analysis shows that positive ion space charge effects can dominate the Cavalleri experiment. It is, however, confirmed that on operating in a linear regime, corresponding to normal experimental conditions, very accurate values for the electron diffusion coefficient can be obtained by extrapolating to zero X-ray pulse intensity. Both primary effects, associated with ions produced by the initiating ray pulse, and secondary effects, associated with ions produced by the RF sampling pulse, are taken into account.