Alcator C-Mod Weekly Highlights June 27, 2005 FY2005 weeks of research operations Planned: 17 weeks Completed: 10.5 weeks The 3rd quarter milestone is complete for the FY2005 C-Mod Joule target, "Measure plasma behavior with high-Z antenna guards and input power greater than 3.5 MW". This milestone, "Assess operation with significant auxiliary input power for L-Mode and H-Mode plasma regimes" due June 30, 2005, was completed ahead of schedule, on June 22, 2005. The milestone completion report can be found at http://www.psfc.mit.edu/cmod/sciprogram/FY05_level1_targets/q3_complete.pdf Operations ---------- Plasma operations continued at Alcator C-Mod last week. Five run days were scheduled and 4 1/2 days completed. A total of 129 plasma discharges were produced, with an overall reliability over 85%. Experiments were carried out in support of research in the Transport topical science area, and as part of the on-going program in support of our Level 1 JOULE target - "Measure plasma behavior with high-Z antenna guards and input power greater than 3.5 MW". Fresh boronizations were carried out over Tuesday and Thursday nights. A computer problem on Tuesday night prevented the usual post-boronization ECDC procedure from being carried out, and Wednesday's run was therefore delayed by 4 hours to allow the standard preparation to be conducted. Plasma Operations are planned to continue this week. Run Summaries ------------- On Monday, we devoted 15 shots to MP#296 "Confirmation of Thomson scattering density calibration using ECE cutoffs", in order to correct for a change in the TS laser energy measurement. A set of absolute calibration coefficients was derived for both TS core systems based on the ECE cutoff data. The derived calibration coefficients were applied retroactively to shots back to May 24, 2005. Shots from June 10, 14, 15, and 20 (shots 1-10) are not recalibrated yet, since we had different optical setup in TS lab those days. This work is in progress at the moment. The second half of the run on Monday was devoted to MP#419, "Fiducial wall pumping measurements for comparing operating conditions", which supports the Level 1 Target. This was the first operation dedicated to this MP since the temporary removal of the Lower Hybrid launcher in mid-May. Three pieces of information were obtained from this run: 1)Continued repetition of the same shot did not lead to saturation of the wall-pumping; if saturation of the wall is taking place it is doing so slowly. 2) Changing the "wetted surface" does lead to changes in the wall pumping rate. When the divertor strike point is shifted from the outer vertical plate to the floor tiles the pumping rate dropped by a factor of 2.5 to 3. Upper null discharges exhibited a pumping rate similar to those with the strike on the lower vertical plate. Some inner wall limited discharges were also run, but these shots were disruptive and the pumping rates are therefore not directly comparable. An outboard-limited discharge was run and exhibited the highest pumping rate observed, but since this single example shot followed a series of several disruptions this result requires further confirmation. 3) The values for wall-pumping with the strike point on the vertical plate were similar to those measured on April 12, before boronization and before dust from the lower hybrid launcher was released, indicating that this aspect of machine operation is "normal". Tuesday's run was devoted to MP#415 "Rotation and H-mode Power Threshold for LSN and USN at Different IP and ne". This run was successful in determining the core rotation velocity and H-mode power threshold for both LSN and USN discharges at three currents, 0.6, 0.8 and 1.0 MA, at a single value for the target electron density, nl04 of 1.0e20/m2. The core rotation velocities in L-mode for both LSN and USN at 1.0 MA were the same, yet the threshold ICRF power was very different, in contrast to findings at 0.8 MA. A partial boronization was carried out over Tuesday night. The intent was to only boronize the antennas and outer limiters and see if that is effective in reducing Mo sources. Only half the usual amount of diborane was used, and the ECDC resonance was swept from 0.78m to 1.03m in major radius. The evaluation (MP#417) was carried out over the remaining half-day on Wednesday. Re-conditioning of the RF was relatively rapid, although steady RF pulses were not produced until later in the run. Radiated power was observed to rise more rapidly during H-mode than following the previous boronization, leading to back transitions. The conclusion is that either the partial boronization was not as effective in preventing Mo influx or we are encountering Mo sources in different areas. On Thursday we carried out MP#397 "Comparison of C-Mod EDA regime with JFT2-M HRS regime." N. Oyama and K. Kamiya from JAERI participated remotely from Japan (despite the 13 hour time difference). This run repeated some cases (q95=3.5)from the April 7 run of this MP, which took place in an unboronized machine. The current was then decreased to carry out a density scan at q95~4.8. At the higher densities we obtained long steady H-modes which had the global appearance of EDA, but without a strong QC mode visible on the PCI diagnostic. At intermediate density a steady QC mode was observed, while at the lowest densities it became intermittant and the H-modes less steady. Finally, we returned to q95~3.5 and revisited the conditions of low density, low nu* which had previously exhibited large ELM's. Under these conditions a series of discrete ELMs were reproducibly obtained. The fast camera was successfully triggered to capture images of these ELMs, which are being analyzed. MHD precursors were clearly observed on the fast magnetics diagnostics and are also being analyzed. These experiments contribute to ITPA Inter-machine Experiment PEP-12; results will be presented at the IAEA meeting on H-mode and Transport barriers in St Petersburg in September. Friday's run, which followed a fresh boronization over Thursday night, was devoted to MP#410, "Extension of pedestal scalings". The purpose of this run was to vary machine parameter space in current and field and examine pedestal profiles at each data point. Some shots from run 1050428 were repeated for purposes of comparison, since we began with a fresh boronization, and the previous run was far from well-conditioned. Radiated power was low at the beginning of the day, and good EDA H-modes were obtained using 2--3MW ICRF. As the day progressed, radiated power increased, even for shots that should have been solidly EDA, such as the 5.4T, 0.9MA shot 19. Large D2 puffs from the NINJA system were administered into several discharges, resulting in reduced radiative power and steadier H-modes. However, at lower Ip, and thus lower pedestal density, the gas injections tended to cause back-transitions to L-mode. Good edge Thomson and PCI data were obtained, as well as background D-alpha from the GPI camera. The range of parameters covered was 0.4