A kinetic theory for the electron probe current is presented. The results allow us to infer the electron energy distribution function from the measured electron probe current and its derivatives over a wide range of pressures and magnetic fields.

The existing Globus-M machine [1] is a low aspect ratio compact tokamak (R = 0.36 m, a = 0.24 m) with high specific ohmic and auxiliary heating power. First plasma was achieved in Globus-M in 1999. The machine has demonstrated practically all of the project objectives ever since. Target design parameters (aspect ratio-1.5, 2 − X-point configuration, vertical elongation-2.2, traiangularity-0.45, average density-1.0•10 20 m −3 , plasma current-0.3 MA, toroidal beta-12%, auxiliary heating power-1 MW) [2] were achieved and some of them overcame [3,4]. Also Globus-M

The results of geodesic acoustic mode (GAM) studies in the spherical torus Globus-M via Doppler reflectometry are presented. The intermittent character of the GAM evolution is similar to the limit-cycle oscillation behavior of zonal flows. The evident correlation between the GAM rotational velocity and both Dα emission and plasma density oscillations is exhibited and discussed. The obtained experimental results are compared with those from tokamaks with large aspect ratios.

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.