Density dependence on negative corona onset voltage in helium

This paper presents the results of experiments in gaseous helium, in point cathode-plane geometry, for a wide range of densities (3.10¹⁹-2.10²¹) cm^-3. A current instability occurs at a threshold voltage V_S. For V>V_S, a space charge limited current is observed. The nature of charge carriers deduced from their mobility value and the variation of V_S with density is discussed as a function of helium purity