Measuring spatial distributions of residual gas density electric potential in a plasma

A method for determining density profiles of molecular and atomic components of a residual gas in a plasma volume of is suggested. The method is based on the charge exchange of the beam of fast hydrogen or deuterium ions, introduced in the plasma. Simultaneously, the measurements of the shift of the energy spectrum of atoms produced are used to obtain the profile of the electric potential distribution in the plasma. The results of the measurements in weakly ionized helium and hydrogen plasmas of the Penning discharge are presented. The total accuracy of the determination of the residual gas density is better than 50 % and depends mainly on the accuracy of the literature data on the charge exchange cross sections