Overview of recent Alcator C-Mod research

Experiments have been carried out to investigate the triggering and control of ITBs, using multiple frequency ICRF tools. It is found that the ITBs can be reliably triggered using off-axis ICRF minority heating; the addition of on-axis heating at a second frequency can be used for control of the particle transport, leading to quasi-steady operation. Cross-field particle transport in the SOL been shown to be very rapid in Alcator C-Mod usually dominating over the parallel transport into the divertor with very important implications for our understanding of particle recycling and ash removal. Detailed explorations of the quasi-coherent mode (QCM) that appears to be responsible for particle transport across the EDA H-mode barrier have revealed that the QCM has a magnetic component, and comparisons with MHD stability calculations are consistent with the hypothesis that it is due to a resistive ballooning instability. In preparation for long-pulse discharges which will be sustained non-inductively we have produced discharges up to 3 seconds in length confirming that all systems can be operated for at least 5-second shots, which corresponds to about 5 current relaxation times at 5 keV. (author)