Alcator C-Mod Weekly Highlights July 1, 2002 Plasma operations continued on Alcator C-Mod last week. Four run days were scheduled and completed. A total of 31 plasma discharges were produced with a startup reliability of 45%. The purpose of this week's runs was continued clean-up of the tokamak, diagnostic alignment and calibration, and discharge development for the upcoming physics campaign. Progress also continued on ICRF, DNB, and Lower Hybrid Systems. Plasma operation is scheduled to continue next week. Operations ---------- Three days of plasma operations in support of tokamak conditioning and startup activities were carried out last week. In addition, one run day was devoted to beam-into-gas (no plasma) shots with programmed toroidal and vertical fields for calibration of the MSE diagnostic. Cleanup and conditioning of the machine is proceeding well. By Friday, the H/(H+D) ratio was down to less than 15%, and the startup reliability was above 60%. Disruptivity was also down, with 29 of 31 plasmas lasting into programmed rampdown. A problem with the discharge initiation sparker encountered the previous week has been remedied, and a new sparker system has been installed as a backup. Development of new equilibria for the physics campaign also made progress last week. A series of double null discharges (abs(SSEP)<2mm) were produced with both upper and lower triangularity>0.8 and elongations up to 1.85. These high triangularity configurations are possible due to the new lower inner divertor structure installed during the last year. Diagnostics ----------- Diagnostics continue to be brought online and calibrated. The ECE system was aligned on a series of constant-shape discharges. Both A and F-port scanning probes were exercised during plasma shots, as were the divertor flappers. The high-pressure in-vessel Penning gauge recently installed under the B-C outer divertor module was connected to a new high voltage bias circuit last thursday. The cathode/anode geometry of this gauge was custom-built with dimensions approximately a factor of 10 times smaller than the standard commercial units used at other locations in C-Mod. The miniature Penning gauge was designed to take advantage of the high magnetic field strengths in C-Mod, extending the useful pressure measurement range to the 10s of mtorr level and allowing a direct, fast time-response measurement of the high pressures under an outer divertor module. During last friday's run, the gauge was successfully operated, reporting divertor pressures of up to 100 mtorr during local capillary gas injection tests. Pressure readings taken during discharge 'fizzles' are found to generally agree with readings from other gauges connected to the vessel, lending confidence to the gauge's operation. The gauge appears to maintain a discharge at moderate to high neutral pressures which is more stable than the three other Penning gauges in the torus (commerical units). Thus, plans are already developing to replace the 3 commerical gauges with custom-built units. Experiments are planned to use the miniature gauge to calibrate divertor neutral leakage rates during the physics phase of the present run campaign. New capillaries in the upper and lower regions of the chamber are also operational, and should shed new light on plasma fueling and pumping. The visible continuum array diagnostic became operational last week. Additional new inner divertor diagnostics are also coming on-line. The halo and eddy current rogowski coils (20 coils) are now all operational. One of the two Gunn oscillators used for the upgraded reflectometer system was found to have failed and will be sent to the commercial vendor for repairs. TV plasma-imaging systems are being brought on-line, including two wide-angle views of the discharge from A- and F-ports, which will provide a nearly complete view of the plasma chamber; a divertor view; and a fast framing camera view used to image turbulence in the SOL region near the midplane. Problems with data acquisition for these cameras have apparently been resolved, and the image data are now being automatically stored in the MdsPlus tree. ICRF Systems ------------ The ICRF system is coming on-line. Following resolution of some issues in the new control and fault protection systems, the J-port four-strap antenna was vacuum conditioned up to 35kV on Friday. Low-power (~30kW) conditioning pulses into plasma were then obtained on the final few shots of the day. Plasma conditioning of the J-antenna should proceed this week. Operation of D- and E-port antennas is also imminent. DNB Systems ----------- The beam was operated on three days last week, On Tuesday and Wednesday, it was fired in synch with C-Mod pulses. On Thursday, a beam-into-gas experiment was completed for MSE calibration. The TF, and EF3 and EF4 coils were energized during these calibrations to simulate the fields due to plasma current. The BES system was operated for measurement of the beam width. On the last day of the week, there was a fault in the charging power supply circuit which is being evaluated. Blown fuses were found but operation of the beam will be continued only after consultation with the Budker team. Travel and Visitors ------------------- Miklos Porkolab visited the Ecole Polytechnique Federale De Lausanne/CRPP, Lausanne, after the EPS meeting, June 24, and gave the Colloquium with the title: The MIT Plasma Science and Fusion Center: A Paradigm of How to Operate a major Fusion Laboratory in a University Environment. The colloquium was well attended. Discussions followed by the Director, Prof. Tran and Dr. Appert, Associate Director, about possible collaborations between the two laboratories. Gerrit Kramer (PPPL) was at MIT 6/25-26 to check out the two-channel reflectometer upgrade and participate in MSE diagnostic startup with the RFX beam. Steve Scott (PPPL) has joined the C-Mod team; this was his first week onsite. Steve will be working on the MSE diagnostic. Gerd Schilling was at MIT 6/25-28 to participate in the ICRF startup.