Electric potential dynamics in OH and ECRH plasmas in the T-10 tokamak

摘要

New experimental observations of the plasma potential using the heavy ion beam probe diagnostic are presented together with a theoretical description of the formation of the electric field E_r in the T-10 circular tokamak (B_0 = 1-5-2.5 T, R = 1.5 m, a = 0.3 m). Ohmically heated (OH) deuterium plasmas with main plasma parameters n_e = (0.6-4.7) × 10~(19) m~(-3), T_e(0) ＜ 1.3 keV, T_i(0) ＜ 0.6 keV are characterized by a negative potential φ(ρ) with maximum negative values of φ(6cm) = -1400 V with respect to the wall. The potential profile monotonically increases towards the plasma edge. A density rise due to gas puff is accompanied by a plasma potential that becomes increasingly negative. When the density approaches values in the range n_e = (2.5-3.5) × 10~(19) m~(-3), the value of the plasma potential saturates, while the energy confinement time still increases up to a saturation value that is obtained at a slightly higher density. With auxiliary heating by electron cyclotron resonance heating (ECRH) up to 1.2 MW, T_e(0) increases (up to 3 keV) and the absolute value of the plasma potential decreases. In some cases the plasma potential changes its sign and becomes positive at the edge. The radial profile of E_r and its dependence on n_e and T_i are qualitatively explained by a neoclassical model in the core, and a turbulent dynamic model (Braginskij magnetohydrodynamic equations) in the edge.