Heating and Confinement Study of Globus-M Low Aspect Ratio Plasma

Results on plasma heating in experiments with neutral beam injection (NBI) and ion cyclotron resonance heating (ICRH) at the fundamental harmonic of hydrogen minority in deuterium plasma in the Globus-M spherical tokamak are presented. Numerical simulation of fast ion trajectories was performed in the plasma configurations reconstructed from magnetic measurements with the help of the EFIT code. Energy spectra of slowing down fast ions were measured with tangentially and perpendicularly directed neutral particle analysers in a wide range of energies. Reliable H-mode transition was achieved after the change of the toroidal magnetic field direction. The ion drift now is directed towards the lower X-point, which exists inside the vessel even in a limiter configuration. The most stable H mode transition was achieved in NBI experiments. Also L-H transition was observed in ohmic heating (OH) regime and at ICRH in limiter and divertor magnetic configurations. By means of multi-channel multi-pulse Thomson scattering (TS) diagnostic we observed a formation of a steep density gradient after the L-H transition. Flat density distribution in the plasma bulk was sustained during all the H-mode period. Modeling of transport processes in the L and H-modes was performed with the help of the ASTRA code. The calculated energy confinement times are consistent with the ITER scalings. It is shown that in the ion heat conductivity remains neoclassical the H-mode and no barrier is formed for the ion temperature profile. The particle diffusion coefficient is reduced sufficiently inside the transport barrier region.