Overview of Globus-M2 spherical tokamak results at the enhanced values of magnetic field and plasma current

Abstract

The paper provides an overview of the results obtained on the spherical tokamak Globus-M2 in 2019–2020. The experiments were performed with the toroidal magnetic field up to 0.8 T and plasma current up to 0.4 MA (80% of the design values). The temperature of electrons 1 keV and ions 800 eV at the plasma density of 1020 m−3 were recorded at neutral beam injection (850 kW, 28.5 keV). Heat conductivity analysis was made by means of the codes ASTRA 7.0, NCLASS, SPIDER, NUBEAM, 3D fast ion tracking algorithm on the basis of the experimental data. A scaling for spherical tokamaks, which demonstrates strong τ E dependence on magnetic field and moderate dependence on plasma current, has been confirmed for the magnetic field up to 0.8 T. For Globus-M/M2 it is . The dependence of the normalized energy confinement time (B T τ E) on collisionality (ν*) in a wide range 0.02 < ν* < 0.2 was determined as . A non-inductively driven current was recorded during the launch of the electromagnetic waves of the lower hybrid frequency range (2.45 GHz) with the help of a toroidally oriented grill. The fraction of noninductively driven current has exceeded 70% in the discharge with a total current of 0.2 MA. The achieved values of efficiency η = (0.15–0.4) × 1019 A m−2 W−1 are comparable with the results obtained on conventional tokamaks. This paper presents the results of experiments on the study of Alfvén modes. The resulting scaling for the loss of fast ions caused by toroidal Alfvén eigenmodes demonstrates their decrease with increasing magnetic field and plasma current. Observation of Alfvén cascades made it possible to apply the method of MHD spectroscopy to determine the evolution of q min in a discharge. Also presented are the results of SOL investigation. Attention is also paid to the development of diagnostics.

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

“…A double increase in the plasma current and toroidal magnetic field results in four-fold T e increase in the plasma core that led to rise of the plasma total stored energy, see figure 1(b). The first reason of such plasma performance is the enhancement of the fast ion confinement in comparison with Globus-M discharges with lower I p [26], and recently observed in the experiment [27]. The second is an increase of the thermal insulation efficiency.…”

“…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).…”

NSTX-U theory, modeling and analysis results

“…New simulation and modeling capabilities have been developed to predict boundary turbulence, which influences particle and heat loads to divertor targets, and to predict operational limits of PFCs. The recent results in analysis, simulation and modeling of NSTX and NSTX-U, as well as future experiments on NSTX-U and other STs [154,[157][158][159], continue to advance the physics basis and technical solutions required for optimizing the configuration of next-step steady-state tokamak fusion devices.…”

Исследование Температуры Поверхности, Контактирующей С Плазмой, Методом Двухцветной Пирометрии

“…Эксперименты по бесконтактному измерению температуры взаимодействующей с плазмой поверхности производились на токамаке Глобус-М2 [10].…”