Alcator C-Mod Weekly Highlights April 26, 1999 Three plasma run days last week were focused primarily on bringing up the four ICRF transmitters and conditioning the three antennas. A forth run dedicated to the scaling of the rotation velocity with plasma current, in H-mode discharges, was undertaken on Friday. Physics: The Tuesday, Wednesday, and Thursday runs were dedicated to RF conditioning of the antennas, and the work required to debug and bring up the third and forth transmitters during plasma operation. A total input power of 3 MW was coupled to the plasma from the D and E antennas. Testing of the J-port antenna into vacuum was begun and up to 140 kW of power has been injected. Protection circuitry needs to be tested before significant power can be applied. On Friday a run to study the scaling of plasma rotation with plasma current during H-modes was scheduled. The plasma current ranged from 0.4 to 1.4 MA. However, the quality of the H-modes was erratic probably because of lack of conditioning of the RF antennas following boronization done the previous night. Some results were obtained, including edge temperature pedestal profiles in H-mode at high current, and impurity confinement scalings with plasma current. We are finding, for example, that the height of the edge temperature pedestal clearly increases with Ip. Further analysis of the rotation velocities will be forthcoming. Vacuum conditioning of all antennas is proceeding in preparation for this week's set of runs. The first images of carbon 'plumes' where recorded during piggy-back experiments last week. In these experiments, trace amounts of ethylene gas (approx. 10^17 molecules) are injected over a 10 msec period by the F-port vertical scanning probe. Two fast-gated (0.2 msec exposure) CCD cameras (on loan from PPPL and LANL) were used to view the resulting emission patterns of CII or CIII light. One camera views the plume from the top (along -Z direction) while the other views from the side (along -R). Video images were captured using the newly installed Matrox color frame grabber system and IDL-based widget interface. Based on the success of this frame grabber system system, another one is begin put together for divertor imaging. Plumes of both CII and CIII emission appear to be extended along the magnetic field line in both directions. Asymmetries in the pattern suggest a reversed plasma flow (flow out of the divertor) for injections near the separatrix. The plumes also indicate a strong cross-field plasma drift near the separatrix in a region where the ExB poloidal drift is expected to be high. These preliminary experiments show that the ethylene injection does not affect the discharges in any detectable way. A comparison of CII signals before and after a series of discharges with ethylene injection showed no change. Consequently, these experiments may be continued in a 'piggy-back' mode of operation. Plans for further experiments with ethylene include a reduction and optimization of ethylene puff and camera exposure. Progress is underway towards a full 3-D reconstruction of the emission plume from the two camera images. We reported last week on the first operation of the inner wall rangefinder diagnostic. Measurements reported at that time of 4 to 6 nm should have been reported as 4 to 6 um. Several weak disruptions (halo currents<= 100 kA) during last week's operation have now produced measurements in the 20 to 30 um range. Comparisons with the strain-gauge at the same inner wall location are now being made. Engineering: All four transmitters are now operational and work is focused on conditioning the antennas for plasma operation. Up to 3 MW of power was delivered to the plasma last week from the D and E antennas. The J-port antennas has been operated into vacuum at low power levels to test fault detection and condition the antenna for plasma operation. Boronization on Thursday evening degraded the performance of both D and E antennas. The cause of this effect is under investigation. Vacuum conditioning over the weekend has prepared them for operation this week. Work on the DNB last week included bench tests of the mod/reg tube regulator board. This system is now complete except for calibration. Details of the mod/reg cage component mounting and wiring were completed. Work has begun on the MCL/PLC HV supply and MOD/REG interface designs. Travel and Visits: Gary Taylor from PPPL was here last week to continue taking data with the GPC2 ECE diagnostic. He also brought on line new higher bandwidth Te data for this instrument. Raffi Nazikian, also from PPPL, visited to work with Yijun Lin on the C-Mod reflectometer. Raffi and Yijun also took a trip to Millitech to discuss new hardware for the reflectometer upgrade to be done in collaboration with PPPL. The DOE C-Mod Quarterly Review was held last Thursday, 4/22, via teleconfence. DOE, MIT, and UTexas were all linked together with talks presented from both the MIT and UTexas sites. Talks on Ohmic H-modes, the outer divertor flappers, high spatial resolution pedestal diagnostics, the status of the RF and DNB systems, and the Lower Hybrid proposal were presented from MIT. The status of the DNB diagnostics was presented by UTexas.