Experimental observations on the characteristics of an anode spot onset

Experimental observations of the characteristic features of anode spot onset and stabilization in response to a stepped voltage applied to an anode immersed in a low pressure (100 mTorr) helium afterglow are reported in this poster presentation. These observations include spatial and temporal evolution of metastable species measured by planar Laser induced fluorescence (PLIF), electron densities as measured laser-collision induced fluorescence (LCIF) and electric fields around and in the spot as measured by laser-induced fluorescence-dip (LIF -dip) spectroscopy. Oscillations observed during spot formation process are correlated to transient response of the host plasma induced by sudden loss of electron species by the spot. This work was supported by the Office of Fusion Energy Science at the U.S. Department of Energy under contracts DE-AC04-94SL85000 and DE-SC0001939.