Overview of recent results from the ST40 high-field spherical tokamak

ST40 is a high-field spherical tokamak (ST) built and operated by Tokamak Energy Ltd., a privately funded company based in the UK. The goal of ST40 is to extend the high-field ST physics basis and test engineering solutions for future ST reactors.

ST40 Programme 2.2 (P2.2) operations began in March 2021 and are scheduled to run until January 2022. The target parameters for P2.2 are: BT=3T (with LN2 cooling of the Cu magnet system), IP=1MA, PNBI=1.5MW (0.8MW/50kV, 0.7MW/25kV), flat-top duration =200ms, A=1.6-1.9, and RGeo=0.4-0.5m. Operations are in hydrogen and both double null diverted (DND) and centre column limited configurations are possible. Plasma start-up is achieved via merging-compression (MC), where two high voltage in-vessel coils are used to initiate the plasma. ST40 diagnostics include: Interferometers, X-ray Crystal Spectrometer, Diagnostic Neutral Beam and Visible Spectrometer (for Charge Exchange Recombination Spectroscopy), Neutral Particle Analyser, Soft X-ray Camera/Spectrometer, Neutron and Hard X-ray Spectrometers, Divertor/Main Chamber IR Cameras, Magnetics and ECE Radiometer. A Thomson Scattering system is planned for later in 2021.

Some of the goals of ST40 P2.2 are to maximise central ion temperature, study hot-ion modes, achieve H-mode operation and investigate confinement in a high-field ST. To date, a plasma current of 800kA has been reached at a toroidal field of 1.9T. At 450kA, an ion temperature of around 2keV has been obtained with one neutral beam at 50kV.

This presentation will provide an overview of the ST40 high-field spherical tokamak and latest results from P2.2 operations.