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 (q(95)similar to 4.3) and medium density (n(e)similar to 3x10(19)m(-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 n(e)=3-4x10(19)m(-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 (V-L similar to 0.15V) discharges. Low plasma current operation and rather high effective charge (Z(eff)similar to 3) lead to modest current drive efficiency (eta=0.5-0.65x10(19) A.W(-1)m(-2)). Long pulse operation (similar to 30s) with high LHCD power (P-LH=2.7MW) is achieved with stationary parameters, in particular electron and impurity densities, with the upper water-cooled tungsten divertor.