Double Electric Layer of a Helium Discharge in Modulation Mode

The positive column of a helium gas discharge in modulation mode has been investigated. It has been revealed that the contribution of the stepwise ionization to population of the 3 1 D 2 level is low due to small population of metastable levels at weak discharge currents (20–100 mA). With increasing discharge current, the metastable atom population increases and hence, the modulation depth of spectral line intensities of metastable levels also increases. At high currents (>100 mA), the modulation depth of spectral line intensities decreases because of saturation of metastable level population.