A laser-based measurement of electron collision rates for excited states of ionised helium in a plasma

Abstract

The total de-excitation rate out of the level (n=4) of singly ionised helium was measured using a dye laser to deplete the n=4 population; the rate being inferred from the relative depletion obtained for a given laser power. For the plasma parameters of ne=5*1014 cm-3 and Te=4.3 eV this rate will be dominated by the electron-ion collision rates to n=3 and n=5. The experimental results are compared with those predicted by a ten-level collisional radiative model using the hydrogenic electron-ion collision rate coefficients due to Seaton. Substantial agreement is achieved.