The Globus-M spherical tokamak has demonstrated practically all of the project objectives during the 15-year period of operation. The main factor limiting further progress in plasma performance is a relatively low toroidal magnetic field. The maximum toroidal magnetic field achieved on Globus-M was 0.4 T with the exception of a limited number of shots with 0.55 T, which led to damage of the toroidal field coil in 2002. The increase of the magnetic field up to 1.0 T together with the plasma current up to 0.5 MA will result in the significant enhancement of the operating parameters in the upgraded Globus-M2 machine. The experimental program will be focused on plasma heating and non-inductive current drive and will contribute to the creation of a physical and technological base for the compact fusion neutron source development. In the article a brief overview of the physical background for the machine upgrade is outlined. The current status of the project implementation is described. First experimental results on moderate magnetic field increase from 0.4 T up to 0.5 T in the existing Globus-M machine are discussed. The improvement of plasma confinement as well as enhancement of efficiency of the beam driven current is observed.

The main parameters and design of the Globus-M spherical tokamak are described, including the modifications introduced after construction was completed. The experimental program and possibilities for...

The targeted plasma parameters of the compact spherical tokamak (ST) Globus-M have basically been achieved. The reasons that prevent further extension of the operating space are discussed. The operational limits of Globus-M together with an understanding of the limiting reasons form the basis for defining the design requirements for the next-step, Globus-M2. The recent experimental and theoretical results achieved with Globus-M are discussed, the operational problems and the research programme are summarized and finally, the targeted Globus-M2 parameters are presented. The magnetic field and plasma current in Globus-M2 will be increased to 1 T and 0.5 MA, respectively. The plasma dimensions will remain unchanged. With auxiliary heating at a high average plasma density, the temperatures will be in the keV range and the collisionality parameter with ν* ≪ 1 will define the operational conditions. Noninductive current drive will be a major element of the programme. The engineering design issues of Globus-M2 tokamak are discussed and the technical tokamak parameters are confirmed by thermal load and stress analysis simulations. The experimental results obtained on Globus-M2 and the limits of its performance should clarify the feasibility of an ST-based super compact neutron source.

Experiments and simulations to achieve high values of plasma parameters at the Globus-M spherical tokamak (ST) at moderate absolute auxiliary heating power (up to 0.8 MW) and high specific heating power (up to 2–3 MW m⁻³) are described. Important distinguishing features are the low edge safety factor range, which is unusual for STs, 2.7 <q< 5 and small plasma–outer wall space (3–5 cm). High ion heating efficiency with neutral beam injection (NBI) was demonstrated. Results of numerical simulation of fast ion trajectories are described and fast ion generation during the NBI and ion cyclotron resonance heating is discussed. Investigations on their confinement and slowing down are also presented. Reasons for achievement of high IC heating efficiency are outlined. Reliable H-mode regime achievement is described. Transport ASTRA modelling demonstrated that during NB heated H-mode ion heat diffusivity remains neoclassical and the particle diffusion coefficient inside transport barrier decreases significantly. Analysis was performed of divertor tile and special probe surfaces after irradiation by plasma during a large number of shots (3000–10 000 shots). Mixed layer composition is measured and deuterium retention in different tokamak first wall areas is estimated. Plasma jet injection experiments with upgraded plasma jet are described. Jet penetration to the plasma centre with immediate increase of density and temperature drop is proved and analogy with pellet injection is outlined.

The paper provides an overview of the results obtained on the spherical tokamak Globus-M2 in 2019-2020 years. 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). Temperature of electrons of 1 keV and ions of 800 eV at the plasma density of 10^20 m^(-3) was recorded at neutral beam injection (850 kW, 28.5 keV). Heat conductivity analysis was made by means of the codes АSТRА 7.0, NCLASS, SPIDER, NUBEAM, 3D Fast Ion Tracking algorithm on the base of experimental data. A scaling for spherical tokamaks, which demonstrates strong τ_E dependence on magnetic field and moderate on plasma current has been confirmed for magnetic field up to 0.8 T. For Globus-M/M2 it is τ_E^GLB~ I_p^(0.43±0.22) B_T^(1.19±0.1). The dependence of the normalized energy confinement time (B_T τ_E) on collsionality (ν*) in a wide range 0.02<ν^*<0.2 was determined as B_T τ_E~ν*^(-0.74). 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)10^19 A m^(-2) W^(-1) are comparable with the results obtained on conventional tokamaks. The paper presents the results of experiments on the study of Alfvén modes (AM). The resulting scaling for the loss of fast ions caused by toroidal Alfvén eigenmodes (TAE) demonstrates their decrease with increasing magnetic field and plasma current. Observation of Alfven cascades (ACs) 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.

Experimental results showing evidence for the development of filaments in plasma of the Globus-M spherical tokamak have been obtained by the method of Doppler reflectometry. The correlation between...