Tenfold increase in the fusion triple product caused by doubling of toroidal magnetic field in the spherical tokamak Globus-M2

Abstract

The current work reports on the significant rise of the fusion triple product in experiments carried out on the compact spherical tokamak (ST) Globus-M2 with a twofold increase in the toroidal magnetic field. A tenfold rise in the n . T . τ E product was recorded during an increase in the magnetic field from 0.4 to 0.8 T and the plasma current from 0.25 to 0.4 MA at an unchanged auxiliary heating power value. Limited reasons may affect this positive trend, among which are energy confinement improvement and an increase in the efficiency of neutral beam heating. Despite the increase in the magnetic field, the neutral beam injection (NBI) led to clear and reproducible transition to the H-mode accompanied by a decrease in the turbulence level at the plasma edge. It was experimentally confirmed that strong dependence of the energy confinement time on the magnetic field value is conserved at a higher magnetic field approaching 0.8 T. Enhancement of energy confinement is connected to a collisionality (ν *) decrease. While for conventional tokamaks the confinement dependence on collisionality becomes weaker with decreasing ν * dependence, in the ST, in contrast, we observe its strengthening.

Energy confinement in the spherical tokamak Globus-M2 with a toroidal magnetic field reaching 0.8 T

“…Transition to H-mode, accompanied by an increase in density and a decrease of D α emission, usually occurs a few milliseconds after injection of NB. Examples of the plasma parameters time traces indicating the transition were recently published, see figure 1(b) in [27] for B T = 0.8 T case, figure 1 in [23] for B T = 0.7 T and figure 10 in [5] for B T = 0.4 T. The results of the LH transition study at Globus-M2 investigated by Doppler backscattering (DBS) method was also recently presented in [23]. Comparison of the main plasma parameters for discharges obtained in Globus-M/M2 with a nearly fixed q (I p /B T ) are shown in figure 1(a).…”

“…This work represents the first results of plasma heating experiments using neutral beam at the Globus-M2 ST with the toroidal magnetic field as high as 0.8 T [22]. The device was designed to operate with the toroidal magnetic field on a geometric axis of the vacuum chamber up to 1 T. The preliminary results devoted to NBI experiments with B T as high as 0.7 T where recently published [23]. The main objective of this paper is more detailed review of plasma thermal energy confinement in Globus-M2 focusing on regimes with I p = 0.4 MA and B T = 0.8 T and a comparison with the existing data from other STs.…”

Calibration of neutron counters at the Globus-M2 tokamak

“…This provided an opportunity to increase the toroidal magnetic field and the plasma current. In the first experimental campaigns of 2019−2020 at the Globus-M2 tokamak, the field and current values of 0.8 T and 400 kA were achieved [4]. The design values (1 T and 500 kA, respectively) are to be achieved in 2022.…”

Калибровка Нейтронных Счетчиков Токамака Глобус-М2

“…Во время первых экспериментальных кампаний 2019−2020 гг. на токамаке Глобус-М2 удалось достигнуть значений поля 0.8 T и тока 400 kA [4]. Достижение проектных значений (1 T и 500 kA соответственно) запланировано на 2022 г. Вследствие повышения поля и тока улучшилось удержание быстрых ионов, возникающих при инжекции пучка атомов высокой энергии.…”