Electron Swarm Parameters in Helium in a Strong Electric Field

Dependences of kinetic and transport coefficients of electrons in helium on the electric field strength E reduced to the atomic concentration N in the E / N range from 15 to 1000 of Td are calculated using the earlier developed Monte-Carlo code. The calculation results are compared to the published experimental data. It is shown that for the available experiments, significant inaccuracy is inherent in the range of high E / N magnitudes caused by electrons not being in equilibrium with the field in strong fields. It is shown that the diffusion–drift approximation for the space–time evolution of electron concentration in helium is not applicable above E / N ≈ 200 Td. The gas gain G of helium-filled proportional counter is calculated; the computed G magnitudes agree well with the measurement data. The discrepancy between the measured G values and previously published calculated G values is explained.