Q-profile measurement in tokamaks using fueling pellets

Fuel pellets ablating in a hot, magnetically confined plasma generate cold, self-luminous filaments which seem to orient themselves along the local magnetic field direction. This distinctive ablation pattern has been used for local measurements of the q profile. In the Texas Experimental Tokamak (TEXT), this technique was investigated experimentally, and the results were compared to other q-profile measurements to examine limits of applicability. It is found that the technique may be applied only to limited regions of the plasma. Although the mechanism which causes the filaments to align along the magnetic field lines is not completely understood, comparisons between this technique and other techniques tend to support its use. Inclination angle profiles for the local magnetic field and q profiles obtained on TEXT by this technique are presented. The q profiles are compared with predictions based on various resistivity models, specifically classical, neoclassical, and q-clamped