The work presents the results of the energy confinement study carried out on the compact spherical tokamak Globus-M2 with a toroidal magnetic field 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. Compared to the previous experiments carried out with a toroidal magnetic field as high as 0.4 T plasma total stored energy was increased by a factor of 4. The main reason or this phenomenon is a strong dependence of the energy confinement time 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 has also been shown that the enhancement of the energy confinement in Globus-M2 with collisionality decrease is associated with an improvement of both electron and ion thermal insulation.

Hot ion mode was recently achieved at the Globus-M2 spherical tokamak when the toroidal magnetic field was as high as 0.9 T and plasma current 0.35 MA. The injection of two neutral beams with a total power of 0.7 MW and an energy of 30 keV into a plasma with major radius 0.36 m and minor radius 0.22 m (aspect ratio 1.6) made it possible to heat the plasma ions up to 4 keV, while electron density in the plasma center was as high as 8 × 10¹⁹ m⁻³. The achievement of high temperatures became possible due to the good thermal insulation of the plasma.

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.

Divertor Thomson scattering (DTS) and Laser-induced Fluorescence (LIF) are both laser aided diagnostics well suited for combining with common probing and collecting optics that is the most sophisticated and expensive part of any ITER optical diagnostic. The combined DTS / LIF used for simultaneous measurement of local electron (Te, ne), ion (Ti, nHeII) and atom (nHeI, nH(D,T)) parameters provides the basic information on rates of electron and ion processes to have basic understanding of the physics of divertor plasma detachment. The measured parameters permit to calculate rates of ionization and recombination using Te, ne, Ti,, ni, nHeI, nH(D,T); emission intensity Te, ne, ni, nHeI, nH(D,T); frictional force of the plasma flow due to collisions with neutrals Ti, ni, T0, nHeI, nH(D,T) and pressure of the incoming plasma flow Te, ne, Ti, ni. The paper discusses the benefits of DTS and LIF integration, suggests new approaches to estimation of DTS capability, LIF implementation and ways of further diagnostic development.