LHCD experiments in high performance plasmas in JET

Lower Hybrid Current Drive (LHCD) has been used for current profile shaping in the shear optimisation experiments in 1996/97 in JET. ${\mathrm{P}}_{\mathrm{LH}}\mathrm{\lesssim 3MW}$ has been applied in the initial current ramp-up in order to control the internal inductance. An internal transport barrier with improved central electron confinement has been produced in this phase with LHCD alone. This has resulted in a peaking of the electron temperature profile and ${\mathrm{T}}_{\mathrm{e0}}$ above 10keV at ${\mathrm{n}}_{\mathrm{e0}}{\mathrm{⩽1.5\times 10}}^{\mathrm{19}}{\mathrm{\hspace{0.17em}m}}^{\mathrm{-3}}.$ The profile of the LH driven current, as determined by hard X-ray mesurements, is peaked at approximately mid-radius in these conditions. Good coupling of the LH waves has been obtained by the use of a near gas feed. This method reduces the risk of plasma-launcher interaction, since the launcher can be positioned in the shadow of the poloidal limiters. A reflection coefficient of 5% has been maintained at a plasma-launcher distance of 8 cm and ${\mathrm{P}}_{\mathrm{LH}}\mathrm{=5\hspace{0.17em}MW}$ has been coupled to divertor plasmas in L-mode with this method.