Alcator C-Mod Weekly Highlights May 3, 2004 Research operations continued at Alcator C-Mod last week. We have now accomplished 72 days (18 weeks) of research operations, which satisfies our JOULE Milestone SC7-6a for FY2004. During the course of the week we also extended C-Mod plasma performance to 2MA at 8 tesla, in satisfaction of C-Mod Milestone #62 and FY2004 Program Execution Agreement Task #5. Experiments were carried out in support of RF Physics and MHD research, including one ITPA Joint Experiment in the MHD area. Progress also continued on preparations for the Lower Hybrid experiments, which will begin during the next experimental campaign. Operations ----------- Four and a half days of plasma operation were scheduled and completed last week, including a 12 hour (1 1/2 day) run on Tuesday. A total of 79 plasma discharges were produced, with a startup reliability of 88%. Thirty-two of these discharges were at high field (B>7.5T). A 12 hour run on Tuesday was devoted to two RF Physics experiments, MP#343A and 345, which deal with Mode Conversion Current and Flow Drive at 8 tesla. The phase contrast imaging (PCI) diagnostic successfully detected mode converted waves on essentially all shots. The mode conversion layer and structure seen from the PCI was moving in directions as expected with B field, He3 level, etc. The signal level of the MC ICW appeared to be affected by the distance of the MC layer to the magnetic axis (B_pol effect). More analysis is required. The HIREX viewing chords were positioned around the mode conversion layer location in order to look for flow driven by the MC waves. No modulation of poloidal flow corresponding to the ICRF drive was seen in these experiments, suggesting that the flow, if any, is below the sensitivity/uncertainty of the HIREX measurement. More analysis is still underway. We also ran plasmas with low density and phased antenna for the MCCD study. There were some data from MSE with/without RF. Analysis is ongoing. On Wednesday, we successfully completed MP#371 to extend the C-Mod operating space to 2MA at 8 tesla. This accomplishment required making some modifications to the plasma control system gain parameters to prevent excessive demands on some power supplies, which were found to lead to loss of position control and high disruptivity early in the run. The A-coils were programmed to compensate for the estimated intrinsic non-axisymmetric error fields associated with the PF and TF coils, and this programming was apparently successful in preventing the locked modes which had previously limited high current operation. The high current ohmic discharges produced had central temperatures around 3keV and we were able to operate up to 2MA without approaching our maximum volt-second capability. On one 1.7MA, 8T shot an ohmic H-mode was produced. Halo currents during the disruptions we experienced were all below 150kA, well below the allowable levels with the presently installed divertor hardware. The high disruptivity did impact the startup reliability of subsequent shots. During the week, we also concluded our experiments on MP#361, the ITPA Joint Experiment on Locked Mode Thresholds carried out with JET and DIII-D. The JET experiments were completed in February, and the experiments at DIII-D are scheduled for next week. C-Mod experiments last week were carried out in the morning on Thursday and Friday, with Tim Hender (UKAEA) participating as co-Session Leader over an H323 remote connection from JET. Additional data were also obtained on Friday afternoon. On Thursday morning, we completed the evaluation at high density, up to approximately nebar~4e20/m^3. On Friday morning we completed the low-density range of the experiments. These experiments were all carried out with q95~3.2, Btor=6.3, using an equilibrium well matched to the JET shape and with an A-coil configuration producing a mode spectrum close to that of the JET EFCC coils. On Friday afternoon, these data were supplemented with a different A-coil configuration with a similar mode spectrum at a different toroidal phase. These additional points, in combination with the earlier data, provide further constraints on the phase and magnitude of the intrinsic error field in C-Mod, which needs to be accounted for in the analysis of the experiment. The experiment on Thursday afternoon was a continuation of MP#389, which is concerned with development of a new Compact Neutral Particle Analyzer. This work comprises part of the thesis project of an MIT graduate student. A power scan was carried out at low density (nebar~8e19/m^3); limiter discharges were used to avoid H-mode transitions, and attendant density increases, at the higher powers. The signal levels at the higher powers were small, perhaps due to lower charge exchange crossection for higher energy neutrals. Furthermore, the background signal during RF was significant. The data are being analyzed. The second experiment on Friday was concerned with completing the 1MA, 5.4T locked mode dataset in the standard C-Mod equilibrium. Threshold values at high (nebar~2.5e20/m^3) and low (.35