First lower hybrid current drive experiments on the WEST tokamak

The first lower hybrid current drive experiments in the full tungsten WEST tokamak are reported. Good wave coupling is found at rather low plasma current (q95∼4.3) and medium density (ne∼3×1019m-3). Reflection coefficient is in agreement with the expectation from the linear theory of coupling. With low reflection coefficients, 5MW was coupled for 2 seconds. High central electron temperature, up to 5keV, is achieved at ne = 3-4×1019m-3. Flat and even hollow profiles of tungsten density are derived from the bolometry diagnostic. The stored thermal energy follows the H96-P scaling law with very slight degradation with density. The current drive efficiency has been assessed in low loop voltage (VL∼0.15V) discharges. Low plasma current operation and rather high effective charge (Zeff∼3) lead to modest current drive efficiency (ƞ = 0.5-0.65 × 1019 A.W−1m-2). Long pulse operation (∼30s) with high LHCD power (PLH=2.7MW) is achieved with stationary parameters, in particular electron and impurity densities, with the upper water-cooled tungsten divertor.