LAUSR

Partial detachment is the desired regime for the baseline burning plasma scenario in ITER and next-step devices, as it allows to convert the majority of the energy carried by charged particles through the scrape-off-layer (SOL) is dissipated and thus deposition of localized heat fluxes in the divertor region is avoided. The COMPASS tokamak is equipped with an open divertor and has a relatively short connection length, both factors being unfavourable for access to detachment. As such, it only allows to approach naturally detached operation at very high line-averaged densities (> 10 m), which are incompatible e.g. with maintaining the ELMy H-mode regime. In order to achieve the detachment at lower densities, impurities (such as nitrogen) should be injected into the plasma in the divertor region. A series of experiments with impurity injection in the range of 1-9×1020 molecules per second at different locations in the divertor were performed with the aim to cool the plasma and influence the particle and heat transport onto the divertor targets and provoke partial detachment. Previously reported results [M. Komm et al, EPS 2017, P1.118] were largely extended by injection of nitrogen at the outer divertor target.