On the Alcator C-Mod tokamak, lower hybrid current drive (LHCD) is being used to modify the current profile with the aim of obtaining advanced tokamak (AT) performance in plasmas with parameters similar to those that would be required on ITER. To date, power levels in excess of 1 MW at a frequency of 4.6 GHz have been coupled into a variety of plasmas. Experiments have established that LHCD on C-Mod behaves globally as predicted by theory. Bulk current drive efficiencies, n20IlhR/Plh ~ 0.25, inferred from magnetics and MSE are in line with theory. Quantitative comparisons between local measurements, MSE, ECE and hard x-ray bremsstrahlung, and theory/simulation using the GENRAY, TORIC-LH CQL3D and TSC-LSC codes have been performed. These comparisons have demonstrated the off-axis localization of the current drive, its magnitude and location dependence on the launched n.

Alcator C-Mod is a high magnetic field tokamak with strong shaping capabilities. While compact in physical dimensions, C-Mod produces plasmas which overlap, in dimensionless parameters and absolute performance, with those produced in much larger devices. Auxiliary heating and current drive systems for C-Mod exclusively employ radio-frequency tools (Ion-Cyclotron and Lower Hybrid), naturally decoupling the heating, fueling and momentum sources. Routine operation at high absolute density, enabled by large B/R, allows C-Mod to explore regimes with fully equilibrated electrons and ions. Compactness also yields very high power densities and particle fluxes, expanding the available parameter space for scrape-off-layer and divertor physics and technology studies. C-Mod has always and exclusively used high Z metallic plasma facing components for all high heat flux regions. C-Mod produces the highest absolute pressure plasmas (at the ITER magnetic field and [beta]), with the current tokamak record for volume average plasma pressure (1.8x10^5 Pa).