Results From The TCV Plasma EXhaust (PEX) Upgrade

To investigate the critical role of divertor neutral pressure in power exhaust, the TCV divertor was equipped with several sets of removable divertor gas baffles, altering neutral transport in and out of the divertor chamber. This upgrade was accompanied by diagnostic enhancements and plasma heating upgrades.

In line with simulation expectations, stronger divertor closure correlated with increased divertor neutral pressure, to date up to a factor of 5, although a quantitative mismatch remains between experiments and simulations, indicating more complexity. Increased plasma exhaust mitigation is also found. Electron temperature and density measurements in the divertor volume show a cooler and denser plasma with baffles. Target particle flux measurements further show that higher divertor closure facilitates detachment, with a typical reduction of ~30% in the core density required to obtain particle flux roll-over in baffled L-modes. Improved exhaust performance with baffling is also observed in H-mode, with a reduction in inter-ELM peak parallel heat flux for standard and alternative divertor configurations of up to ~40%.

Building on the performance of divertor gas baffles, a planned upgrade to the Swiss Plasma Center's installations will equip TCV with a tightly baffled, long-legged divertor. This will experimentally assess the concept, and further challenge available divertor models, improving our confidence in their predictions for future devices.