Experiments and simulations to achieve high values of plasma parameters at the Globus-M spherical tokamak (ST) at moderate auxiliary heating power (0.2-0.8 MW) are described. Important distinguishing features are the low edge safety factor range, which is unusual for spherical tokamaks, 2.7 < q < 5 and small plasma-outer wall space (3-5 cm). High ion heating efficiency with NB injection was demonstrated. Results of numerical simulation of fast ion trajectories are described and fast ion generation during NB injection and ICR heating is discussed. Also results on their confinement and slowing down processes investigation are presented. Reasons for achievement of high IC heating efficiency are outlined. Reliable H-mode regime achievement is described. Transport ASTRA modeling demonstrated that during NB heated H-mode ion heat diffusivity remains neoclassical and the particle diffusion coefficient inside transport barrier decreases significantly. RGTi divertor tile analysis was performed after irradiation by plasma during big number of shots (10000 shots in average). Mixed layer composition is measured and deuterium retention in different tokamak first wall area is estimated. Plasma jet injection experiments with upgraded plasma jet are described. Jet penetration to the plasma center with immense increase of density and temperature drop is proved and analogy with pellet injection is outlined.

The experimental and theoretical results obtained in the last two years on the interaction of neutral particle beams and high-frequency waves with a plasma using the spherical tokamak Globus-M are discussed. The experiments on the injection of low-energy proton beam of ∼300 eV directed particle energy are performed with a plasma gun that produces a hydrogen plasma jet of density up to 3 × 1022 m−3 and a high velocity up to 250 km s−1. A moderate density rise (up to 30%) is achieved in the central plasma region without plasma disruption. Experiments on high-energy (up to 30 keV) neutral beam injection into the D-plasma are analysed. Modelling results on confinement of fast particles inside the plasma column that follows the neutral beam injection are discussed. The influence of the magnetic field on the fast particle losses is argued. A neutral beam injection regime with primary ion heating is obtained and discussed. The new regime with fast current ramp-up and early neutral beam injection shows electron temperature rise and formation of broad Te profiles until the q = 1 flux surface enters the plasma column. An energetic particle mode in the range of frequencies 5–30 kHz and toroidal Alfvén eigenmodes in the range 50–300 kHz are recorded in that regime simultaneously with the Te rise. The energetic particle mode and toroidal Alfvén eigenmodes behaviour are discussed. The toroidal Alfvén eigenmode spectrum appears in Globus-M as a narrow band corresponding to n = 1. The first experimental results on plasma start-up and noninductive current drive generation are presented. The experiments are carried out with antennae providing mostly poloidal slowing down of waves with a frequency of 920 MHz, which is higher than a lower hybrid one existing under the experimental conditions. The high current drive efficiency is shown to be high (of about 0.25 A W−1), and its mechanism is proposed. Some near future plans of the experiments are also discussed.

A new Compact Neutral Particle Analyzer (CNPA) [1] has been developed at A.F. Ioffe Physical-Technical Institute. The CNPA is an energy and mass spectrometer of reduced size (169´302´326 mm). It is designed for the simultaneous analysis of H 0 (0.8 -80 keV) and D 0 (0.66 -36 keV) fluxes emitted by plasma. Significant reduction of spectrometer size and weight (42.5 kg) is achieved by two innovations: 1) employing of stripping in a thin (100 Å) diamond-like carbon foil instead of the traditional stripping in gas; 2) using a high-fieldstrength (1 T) NdFeB permanent magnets instead of the traditional electromagnets for generation of the analysing magnetic field. An acceleration of particles scattered in the stripping foil is employed in the CNPA, which together with a magnetic field configuration providing two-coordinate focusing is used to achieve a better detection efficiency. The CNPA has the following significant advantages in comparison with conventional NPAs:1) The compact spectrometer can be installed practically at any position around plasma machine. It can be easily moved or replaced in the case of need.2) The CNPA shielding against n-gamma radiation and against stray magnetic field can be made more compact.3) The arrays of such instruments for a purpose of multichord diagnostic can be easily formed.4) The CNPA has a high detection sensitivity (10-100 times higher than for conventional NPAs) due to wide solid angle of observation and high detection efficiency.5) The CNPA does not require its own high-vacuum pumping system (because of absence of gas inlet) and does not require magnet power supply (because of permanent magnets usage).The CNPA has been tested on the Wendelstein 7-AS stellarator at IPP,

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The article reports the results of experimental campaigns on plasma ohmic heating performed during 1999-2000 on the spherical tokamak Globus-M. Later experimental results with the tokamak fed by thyristor rectifiers are presented in detail. The toroidal magnetic field and plasma pulse duration in these experiments were significantly increased. The method of stray magnetic field compensation is described. The technology of vacuum vessel conditioning, including boronization of the vessel performed at the end of the experiments, is briefly discussed. Specific features of neutral gas column breakdown in spherical tokamaks by applied inductive voltage are outlined. Also discussed is the influence of ECR preionization on the breakdown conditions. Experimental data on plasma column formation and current ramp-up in different regimes of operation with the magnetic flux of the central solenoid limited to ∼100 mWb are presented. A significant reduction of the background density after boronization (below 2 × 1018m-3) allows the density to be completely controlled with external gas puffing and makes the influence of the wall negligible. The magnetic flux consumption efficiency is discussed. The results of magnetic equilibrium simulations are presented and compared with experiment. Ramp-up of the plasma current of 0.25 MA for a time interval of about 0.03 s with about 0.02 s flat-top at a toroidal field strength of 0.35 T allows the conclusion that the target design parameters of Globus-M could be achieved in a double swing regime.

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