Reconstruction of Edge-Plasma Density Profiles by Neutral Beam Probe Spectroscopy

Thermal neutral beam probing combined with a spectroscopic technique is numerically developed to reconstruct electron-density profiles of edge plasmas. Although the reconstruction has been performed by assuming all beam atoms to have a thermal velocity, the influence of a beam-velocity distribution has not received as much attention. It is shown that the method which neglects the beam-velocity distribution reconstructs electron densities lower than the true values by a factor of ∼2 in the density range up to ∼1×10 13 cm -3 , while the procedure which takes into account the velocity distribution yields true density profiles in the same density range. Some results of the beam probe mounted in the Heliotron-E device are also described, and good agreement with Langmuir probe measurements is found.