Collisional-radiative model for helium and its application to a tokamak plasma

We have reviewed the cross-section data of electron impact excitation for transitions starting from the ground and metastable states, and for those between different −l levels within the same n for neutral helium. We have taken into account the effect of the helium singlet and triplet wave function mixing caused mainly by the spin-orbit interaction. The dependence of the degree of the mixing on the magnetic field strength was also calculated. We have incorporated these data in our collisional-radiative model code and analysed the population of the 33P and 33D levels measured in the WT-3 tokamak plasma. The ground and 23S metastable state populations thus determined are compared with those given by the neutral transport code.