Collisional processes induced in the n=3 helium sublevels by electrons in a low-pressure plasma. Application to the electron density measurement

Quenching and excitation transfers in helium induced in the 3S, 3P and 4D states by electron collisions are investigated in a pulsed plasma by means of laser induced fluorescence (LIF) spectroscopy. The averaged cross sections compare well within a factor 1-3 with the Born-Bethe approximation and the Griem formulae. The dependence of these cross sections on the oscillator strength and the energy of the transitions are well fulfilled. Finally it is shown that from the measurement of the quenching rate of the 3889 AA LIF signal in a low pressure plasma it is possible to determine the electron density with a reasonable accuracy.