Divertor modelling for the design of the HT-7U tokamak*

The B2.5 code is applied for modelling SOL plasma in the HT-7U superconductor tokamak in order to construct a database for the design of a divertor for the device. The plasma parameters at the core-SOL interface set as the boundary conditions for B2.5 modelling are varied extensivelyin order to survey the operation of the divertor over a wider range of plasma parameters. Detailed distributions of the plasma heat flux and the other plasma parameters in the SOL, especially at the target plate of the divertor and the outer wall, are found by modelling, and a detailed analysis for the power balance in the SOL is carried out. The modelling results show that most of the electron heat flux and a small part of the ion heat flux arrive at the target plate of the divertor, while a part of the ion heat flux and a small part of the electron heat flux arrive at the outer wall. For the same boundary conditions the SOL physics widths λTe, λTi and λne,i increase with SOL thickness DSOL and the peak values of plasma heat flux and some other plasma parameters at the target plate of the divertor decrease with increasing DSOL. For a boundary density Nedge of 2×1019 m-3, a boundary temperature Tedge of 300 eV and DSOL = 5 cm, the peak value of the electron heat flux at the target plate is 3.92 MW/m2, with 52.81% of the electron heat flux and only 4.20% of the ion heat flux arriving at the target plate. The modelling results form a database for the preliminary design of the HT-7U tokamak divertor.