Here, we report the latest results on the high-field application of a merging/compression (M/C) plasma startup in the ST40 spherical tokamak, using 96-channel 2D ion Doppler tomography and 30-channel Thomson scattering diagnostics installed over the past three years. The new findings and achievements are summarised as follows: (i) the new 96-channel 2D ion Doppler tomography clearly revealed ion heating in the downstream of the reconnection JET and its confinement/transport process. (ii) Electron density also increases in the same region, while electrons are heated around the -point (or magnetic axis) and the electron temperature profile forms a peaked profile. (iii) Quasi-steady sustainment/confinement of M/C startup plasma current and ion temperature has been demonstrated. (iv) Based on a series of M/C experiments, scaling was increased to kA. (v) Full pressure profile measurements lead to the evaluation of the energy conversion ratio of the dissipated magnetic energy to the reconnecting field and it was found that of released magnetic energy was converted to ion thermal energy. (vi) The previously demonstrated scaling has been successfully upgraded to for the first time and which was 10 times higher than the previous record in MAST was explored.
Reconnection heating experiments and simulations for torus plasma merging start-up