First long pulse experiments with the actively cooled W-divertor in WEST

WEST is a full tungsten (W) superconducting tokamak with large aspect ratio (\textasciitilde 5), whose mission is to assess power exhaust with ITER actively cooled divertor technology and to master long pulse operation in a metallic environment. Repetitive and reliable long L-mode X-point discharges (\textasciitilde 30 s) have been achieved in WEST, accumulating \textasciitilde 20 minutes of plasma over two days. They were performed in upper single null configuration on the actively cooled W-divertor, using 2.7 MW Lower Hybrid (LH) power and nitrogen seeding in some discharges. The plasma radiation and density remained constant during the long pulses, indicating that no W-accumulation was taking place. In short pulses, 5.0 MW of LH power has been coupled in L-mode discharges. The central electron temperature increases linearly with the input power and reaches 5 keV with 5.0 MW of LH power. Loop voltage \textless 0.15 V is achieved for line average density$_{\mathrm{\thinspace }}$\textless 4*10$^{\mathrm{19}}$ m$^{\mathrm{-3}}$, with no sign of loss of LH current drive efficiency at the highest density. In the experiments, the heat load pattern on the divertor target is monitored with a unique set of PFC diagnostics (infrared systems, Langmuir probes, thermocouples, Fiber Bragg gratings).