Charge conversion of alphas by refueling pellets

In this paper, the neutral gas surrounding a refueling pellet is considered as a charge changing medium for diagnostics of alphas below 1 MeV. Alphas may be neutralized so they escape the system entirely or excited He+ states can be created by electron capture and the doppler-shifted radiation observed. The neutral-shielding model was used to obtain radial profiles of neutral and plasma density and temperature surrounding the pellet. This model predicts plasma densities and temperatures in the collar plasma surrounding the pellet consistent with experiment. Conditions for a pellet injected into TFTR during a 33.5 MW neutral beam pulse are taken from a simulation. For such conditions ion and electron impact ionization in the collar plasma reduce the escape probability below 10 -7 and n αmust be ∼ 1011/cm3 for the doppler-shifted radiation near 1640 Angstrom to be equal to the free-bound bremsstrahlung from the collar plasma