Yu. V. Petrov

Fast particle behaviour in the Globus-M spherical tokamak

The behaviour of the fast particle population during 18 keV hydrogen and 26 keV deuterium neutral beam injection in deuterium plasmas is investigated. Experiments reveal large fast ion losses. The experimental results are confirmed using different types of modelling: simulation using the NUBEAM module, solution of the Boltzmann kinetic equation and solution of the 3D fast ion tracking algorithm. The dynamics of the energetic particle redistribution and losses during sawtooth oscillation and toroidal Alfven eigenmodes are studied. A method to decrease fast ion losses under the current conditions (0.4 T, 0.2 MA) is shown. The influence of the plasma parameters on the energetic ion confinement rate is investigated. Modelling for the Globus-M2 conditions (1 T, 0.5 MA) is performed.

Globus-M plasma physics research for fusion application and compact neutron source development

During the past decade, plasma physics research promoting the physics base of ITER and developing novel concepts such as a compact fusion neutron source has been conducted on the Globus-M spherical tokamak (ST) (R = 36 cm, a = 24 cm, I p ≤ 250 kA, B T ≤ 0.4 T). Tokamak reconstruction is imminent. The upgraded tokamak Globus-M2 will have the same vacuum chamber and an enhanced magnetic system to provide B T = 1 T and I p = 500 kA. In this paper we outline the most important research directions and the main results obtained on Globus-M and make some predictions about the possibilities and parameters of Globus-M2.

Tomography diagnostic of plasma radiated power on the spherical tokamak Globus-M

A diagnostic system for plasma radiated power tomography on Globus-M was upgraded with a new linear array based on silicon photodiodes. The hardware of the diagnostic system based on a 256-channel tangential matrix array and a 24-channel linear array is described. The algorithm for 2D tomographic reconstruction of plasma emissivity is presented. It uses the Tikhonov regularization method and anisotropic diffusion functional as a side constraint. Simulated plasma emissivity profiles were used to test and assess the capabilities of the developed algorithm. Data analysis was carried out in ohmic and neutral beam heated discharges to demonstrate the performance of the tomography diagnostic in plasmas with different parameters. The presented results illustrate the proper functioning of the tomography system that allowed to reveal and study various plasma phenomena, including magnetohydrodynamic mode.

Analysis of Dynamics of Plasma Current Quench in the Globus-M Spherical Tokamak

Data on the dynamics of the plasma current quench in the Globus-M tokamak are presented. The main current quench characteristics at different toroidal magnetic fields are compared. The distribution of the toroidal current induced in the vessel wall is determined from magnetic measurements, and the electromagnetic loads acting on the vessel wall during the current quench are calculated. By extrapolating the experimental data, the additional pressure on the vessel wall during the current quench in the upgraded Globus-M2 tokamak is estimated. It is shown that the current quench results in the appearance of bending stresses in the vessel domes. Using numerical simulations, it is shown that the best agreement between the measured and calculated plasma current dynamics during the current quench corresponds to the linear (in time) influx of the carbon impurity.

First Counter-NBI Experiments on the Globus-M Tokamak

A high-energy counter-NBI has been applied for the first time on the Globus-M spherical tokamak. An ELM-free H-mode has been obtained. However, no significant increase in the ion temperature and plasma energy content compared to ELMy H-mode has been observed. This is due to a high level of the fastion losses. Neither increase in the plasma current nor an increase in plasma-wall distance resulted in an increase in NB heating efficiency as it occurred during the co-NBI experiments.

Energy distributions of superthermal ions in regime with sawtooth oscillations during neutral beam injection at the Globus-M tokamak

Specific features of the energy distributions of fast ions during neutral beam injection at the Globus-М tokamak are considered. Different loss mechanisms that can lead to the formation of a specific shape of the energy spectrum of superthermal ions are analyzed. The effect of sawtooth oscillations on the loss of fast ions is discussed.

Globus-M2 NBI upgrade and updated NBCD results obtained on spherical tokamak Globus-M

The latest results are presented from NBCD experiments at the Globus-M spherical tokamak. The Globus-M2 NBI upgrade program is discussed, in particular, the analysis of the injection geometry and choice of the optimal experiment layout. The results from numerical simulations of plasma heating and current drive by two neutral beams in the Globus-M2 shots are also analysed.

Multipass/multipulse Thomson scattering on CDX-U (abstract)

A multipass/multipulse Thomson scattering system has been implemented on CDX-U in collaboration with the Ioffe Institute, St. Petersburg. The system consists of a low energy (1.5– 2.5 J), passively Q-switched ruby laser, and a multipass optical cavity enclosing the plasma. Multiple reflections of the beam within the cavity increase by about an order of magnitude the number of scattered photons, allowing temperature density to be measured with good accuracy even at very low plasma density. By feeding the returned beam back into the laser, the system can deliver several pulses over a 1 ms period. However, the experiments on CDX-U show that a mechanical shock wave reaching the multipass system affects the feedback and laser output per pulse drops significantly. Therefore we operate the system by fine tuning the laser cavity, so that output is practically independent of feedback from multipass cavity. Also, by optimizing the transmission of the passive Q-switch and the pumping power, we obtain that laser outp...