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

The work presents the results of the energy confinement study carried out on the compact spherical tokamak (ST) Globus-M2 with toroidal magnetic field (BT) as high as 0.8 T. A reproducible and stable discharge was obtained with the average plasma density (5-10) 1019 m-3. 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. NBI allowed effectively heat the plasma: electron and ion temperatures in the plasma core exceeded 1 keV. In comparison with the previous experiments carried out with BT=0.4 T plasma total stored energy was increased by a factor of 4. The main reason of this phenomenon is a strong dependence of the energy confinement time (τE) on the toroidal magnetic field in the spherical tokamak. It was experimentally confirmed that such kind of dependence is valid for ST with magnetic field up to 0.8 T. It also has been shown that the enhancement of the energy confinement in the Globus-M2 with collisionality decrease is associated with an improvement of both electron and ion heat transport.

Magnetic fields in the solar convection zone

It has been a prevailing picture that active regions on the solar surface originate from a strong toroidal magnetic field stored in the overshoot region at the base of the solar convection zone, generated by a deep seated solar dynamo mechanism. This article reviews the studies in regard to how the toroidal magnetic field can destabilize and rise through the convection zone to form the observed solar active regions at the surface. Furthermore, new results from the global simulations of the convective dynamos, and from the near-surface layer simulations of active region formation, together with helioseismic investigations of the pre-emergence active regions, are calling into question the picture of active regions as buoyantly rising flux tubes originating from the bottom of the convection zone. This article also gives a review on these new developments.

Development of a novel spiral antenna system for low loop voltage current start up atSteady State Superconducting Tokamak(SST-1).

In general, superconducting tokamaks require low loop voltage current start up for the safety purpose of its poloidal field coils. The loop voltage inside the vacuum vessel of Steady-state Superconducting Tokamak (SST-1) is low in nature since its central solenoid is located outside the cryostat. The low loop voltage current start up of the SST-1 is routinely performed by Electron Cyclotron Resonance (ECR) method at the toroidal magnetic field Bt=1.5T(first harmonic) and 0.75T(second harmonic). Recently, an alternative RF based plasma current start up system had been planned for operating the machine specially for higher toroidal magnetic field regime 1.5T ≤ Bt ≤3T. The system is already developed based on an antenna system, made of series combinations of two at spiral antenna, to assist plasma current start up at lower inductive electric field. It is already tested and installed in SST-1 chamber. The system testing had been performed without background magnetic field within frequency regime 35-60MHz at present. The test results show that it can produce electron density ne ≈1016m-3 measured by the Langmuir probe in expense of 500W RF power. The spectroscopy results indicate that its capability to produce plasma density higher than 1013 m-3 and electron temperature Te = 2 -6eV. In addition, it also shows that the presence of turbulent electric field of the order of 106V/m at antenna center and finite anomalous temperature of neutral particles. Calculations show that the obtained density is enough for SST-1 low loop voltage plasma breakdown. The antenna system is also capable to produce plasma at higher frequencies. This article will discuss the development of the prototype and the installed antenna system along with their test results in detail.

Измерение мощности радиационных потерь и эффективного заряда плазмы на токамаке Глобус-М2

This paper presents the measurement results of the radiated power Prad and the effective ion charge Zeff in a toroidal magnetic field of up to 0.7 T and a plasma current of up to 300 kA for a wide range of electron density, which were first obtained on the Globus-M2 tokamak. An analysis of the results demonstrated that the content of radiation losses relative to the input power decreased in the Globus-M2 tokamak compared to the Globus-M tokamak, and the measured profiles of Prad had a strong dip in the central region. In addition, a decrease of the effective ion charge Zeff with increasing electron density was observed.