The effect of increasing toroidal magnetic field in the Globus-M spherical tokamak

Abstract

In the final Globus-M experimental campaign B tor and I p were raised by 25% up to 0.5 T and 250 kA, respectively, expanding available range of experimental parameters. In these experiments an overall improvement in plasma performance was observed, plasma total stored energy and neutron rate increased significantly. The energy confinement time dependence on B tor and n e was close to linear. L-H transition threshold was 5–10 times higher than threshold predicted by the scaling. Despite the small plasma-wall distance, the level of radiation losses in the main plasma volume was relatively small and decreased as B tor rised. An increase in B tor and I p led to a decrease in the sawtooth-induced losses. While a rise in the plasma current led to a decrease of fast ion losses per TAE burst at the same amplitude; frequency of bursts and their amplitude increased. Doppler backscattering, applied to study TAE localization for the first time, revealed that TAE fluctuations are localized in the region of normalized minor radii ρ = 0.5–0.75. A new movable 9-pin head probe provided data, necessary for power decay length scaling investigation. Significant power decay length contraction, stronger than predicted by Eich’s scaling, was observed.

Tokamak research at the Ioffe Institute

“…Investigation of the toroidal Alfvén eigenmodes (TAE) identified in earlier experiments with NBI heating on Globus-M [20,21] were continued at the increased magnetic field and plasma current values of 0.5 T and 240 kA, respectively. We observed that the TAE-induced particle losses per burst of equal amplitude decrease with the increase of B T and I p [22]. The plasma current increase plays a decisive role in reduction of the losses, probably due to a decrease of the fast particle Larmor radius in the poloidal magnetic field [23].…”

Review of Advanced Implementation of Doppler Backscattering Method in Globus-M

“…These oscillations of the magnetic field lead to the fluctuations of the E × B velocity that is measured using DBS, which means that the amplitude of the Alfven perpendicular velocity, radial electric field can be extracted from the measurements. Studies were conducted in the Globus-M tokamak with early neutral beam injection at the stage of growth of the plasma current [66,67]. Initially, the detection of toroidal Alfven eigenmodes (TAE) using DBS was confirmed by comparing the experimentally obtained frequency of the fluctuations presented in Table 7 to the Alfven continuum frequency gaps f TAE = v A /4πqR, where v A = B/µ 0 ρ D is the Alfven velocity (B-magnetic field, ρ D -mass density of plasma ions), q is the safety factor, and R is the major radius [68].…”

Первые Результаты Исследования Переноса Тепла И Частиц В Сферическом Токамаке Глобус-М2 При Инжекции Пучка На Стадии Роста Тока

“…На токамаке Глобус-М [9,10] (аспектное отношение A = 1.5, большой радиус R = 0.36 m, малый радиус a = 0.24 m, тороидальное магнитное поле до 0.5 T [11], ток плазмы до 270 kA) в результате экспериментальных исследований режимов с инжекцией пучка атомов на фазе роста тока плазмы были обнаружены внутренние транспортные барьеры (ВТБ) [12,13] в условиях, когда минимальное значение запаса устойчивости в пламенном объеме превышает единицу (q min > 1). Область плазмы с пониженным переносом частиц формировалась в зоне отрицательного магнитного шира (обращенного профиля q).…”