Profile Control Experiments in JET using Off-Axis Lower Hybrid Current Drive

In lower hybrid current drive (LHCD) experiments in JET, up to 7.3MW LH power has been coupled to X-point plasmas, resulting in sawtooth suppression and full current drive up to 3MA. The current drive efficiency reached ηCD = 0.26x1020 m-2A/W in these experiments. The LH power deposition and driven current profiles can quite well be reproduced with the ray-tracing + Fokker-Planck code in JET, even when multi-pass absorption of the LH wave is dominant. Profile control with off-axis LHCD has been used for increasing q above 1, thereby suppressing sawteeth before and during the ELM-free hot ion H-mode. In optimised shear plasmas, a broad q-profile with central negative shear was formed with moderate LH power (≤2MW), applied in the low density phase during the current ramp-up. An internal transport barrier with improved electron confinement was produced, which resulted in a peaking of the electron temperature profile and Te0 up to 10keV at ne ≈ 1.0x1019 m-3. LHCD has assisted in producing the target q-profile required for high fusion yield in the optimised shear experiments.