Preparing for First Diverted Plasma Operation in the ST40 High-Field Spherical Tokamak

The ST40 tokamak [1], built and operated by Tokamak Energy, has recently been upgraded with upper and lower divertors to enable double null diverted operations with up to 1MA of plasma current and 2MW of neutral beam heating. ST40 is a high field spherical tokamak (BT=3T at R0=0.4m) with a goal to extend the high field spherical tokamak physics basis. Crucially, transport and confinement in high field, high temperature STs will be explored in support to the design of next step STs [2]. Extensive modelling activities have been undertaken to prepare for the exploitation of ST40. A range of plasma equilibrium in double-null configuration have been designed along with detailed scenario modelling, including 1.5D transport simulations and 2D SOL modelling. Gyrokinetic analysis has been performed to assess the level of expected turbulent transport. Building upon the NSTX pedestal database the pedestal width and height in the high performance ST40 scenarios have been predicted. MHD stability analysis and beta limit have been assessed. ST40 will be initially operated with 2 MW of NBI with ECRH planned for future operations. Careful analysis of the power deposited in the divertor during high performance operation has also been carried out. The most significant results of the modelling activities undertaken in preparation of ST40 exploitation are presented and summarized.