Photoelectron transmission efficiency in Ar–CH 4 and Xe–CH 4 mixtures: Experimental results

Abstract

The transmission efficiency of photoelectrons emitted from CsI photocathodes operated in Ar–CH 4 and Xe–CH 4 mixtures is experimentally investigated and compared to Monte Carlo simulation results; the ratio between the number of photoelectrons collected in the gas media and in vacuum is determined as a function of the pressure-reduced electric field E/ p at the photocathode surface, for irradiation with the VUV photons from an Hg(Ar) lamp. The addition of a small percentage of CH 4 to Ar and Xe results in a significant increase of the photoelectron transmission, in particular for electric fields below E/ p∼1 V cm −1 Torr −1. Below E/ p∼0.5 V cm −1 Torr −1 the transmission efficiency f in Ar–CH 4 mixtures reaches values higher than in pure CH 4, going through a maximum in the range of 10–30% CH 4. The addition of 5% and 20% CH 4 to Xe increases f by a factor of about 2 and 3, respectively, when compared to pure Xe.