Observation of Non-Circular Cross-Section for q=1 Magnetic Surface in Very Low-q Discharge (qa\lesssim2) of DIVA Tokamak

Abstract
Non-circular cross-section for q=1 magnetic surfaces were experimentally shown in stable very low-q discharge (q a \lesssim2; q a is the safety factor at the plasma surface) of DIVA tokamak with and without a divertor. Heat flux to the first wall due to the sawtooth disruption in low-q discharge will become a serious problem in future large tokamak if sawtooth disruption cannot be suppressed.