Current Density Profile Measurements in the Proto-Cleo Torsatron

Current density profile measurements were obtained in the Proto-Cleo torsatron (R = 40 cm, a = 5 cm, I = 3, BT = 3 kG, n? ~ 1011 cm-3, Te ~ 20 eV) by using a small back-to-back flat double probe. Three different operating circuits used with this probe are presented, along with experimental results, all showing good agreement. Current is seen to flow only within the separatrix, in channels which follow the magnetic surfaces as they move radially inward with time due to changing vertical magnetic flux.