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

Abstract

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 ne = (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(6 cm) = −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 ne = (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.

ECRH effect on the electric potential in toroidal plasmas (Overview of recent T-10 tokamak and TJ-II stellarator results)

“…Plasma potential profile evolution in the regimes with Te and ne changes is consistent with Neoclassical expectations [6].…”

“…Broadband electrostatic oscillations (up to 200 kHz) are strongly excited by ECRH in low-density plasmas of TJ-II, while for high-density plasmas, obtained in T-10 the effect found is opposite [6]. It was found in T-10 that the GAM frequency fGAM increases with ECRH in accordance to the theoretically expected dependence on the electron temperature for the turbulence driven fGAM ~ Te 1/2 [7].…”

3D structure of density fluctuations in the T-10 tokamak and new approach for current profile estimation

“…Small scale density fluctuations were measured using ordinary mode correlation reflectometry [1] with new T-10 antenna set and 5 channel Heavy Ion Beam Probe diagnostic (HIBP) [5]. The 5 channel HIBP measured plasma density and potential fluctuations at 5 adjacent points along the beam pass at Low Magnetic Field Side (LFS) equatorial area of tokamak [6]. The positions of reflectometry antennas and HIBP are shown schematically in IAEA-CN-EX/10-2 from LFS equatorial plane) and allowed to investigate the radial distribution of the fluctuation amplitudes for each poloidal angle.…”

Investigations of the Peripheral Plasma by Langmuir Probes on the T-10 Tokamak

“…На токамаке Т-10 характеристики периферийной турбулентности и турбулентные потоки частиц ис-следовались с помощью подвижных зондов Ленгмюра и зондирования пучком тяжёлых ионов (HIBP) [7]. Токамак Т-10 имеет большой радиус R 0 = 1,5 м, рельсовый лимитер на радиусе 0,30 м и круговой лимитер радиусом 0,33 м. Эксперименты проводились в омическом дейтериевом разряде.…”