Alcator C-Mod Weekly Highlights Jan 25, 1999 Alcator C-Mod resumed plasma operation this week. C-Mod is now in a start-up and conditioning phase, which is scheduled to last two to three weeks. During this period, we will be carrying out conditioning and calibration runs, including commissioning of new experimental systems. Major activities will be clean-up and wall-conditioning, and conditioning of the D- and E-port ICRF antennas. Phsyics runs are scheduled to begin in February. Pre-operations power systems tests were carried out on Wednesday and Thursday. All power supplies were run under both PLC and Hybrid control (the "Hybrid" is the C-Mod real-time control system). The pulsed gas system was also checked out under Hybrid control. Magnetics diagnostics, particularly those used for feedback control and equilibrium analysis were tested. Following completion of power testing on Thursday, we began plasma attempts. Breakdown was obtained on the fourth attempt. This result was encouraging in that it confirms that the diagnostic, analysis, and control systems are functioning correctly, and that the operating point is close to that used in the previous campaign. Spectroscopic measurements during the breakdown flash indicated that the machine was still quite dirty, as was expected since we had done very little (< 20 hours) discharge cleaning. About 12 hours additional ECDC was carried out overnight, and plasma attempts resumed on Friday. Breakdowns were obtained routinely, and after some field and voltage adjustments we successfully obtained a current rise to about 300 kA. Spectroscopic measurements indicated the machine was still dirty, with Zeff of around 3, and the loop voltage indicated the plasma was indeed very resistive. A total of three shots with currents above 200kA were obtained on Friday. This result is consistent with previous experience in bringing the machine online following an extended vacuum break. Further clean-up will require additional ECDC followed by conditioning with tokamak discharges. Initial results from several diagnostic systems were obtained during these runs. The H-port ECE diagnostics, including the Princeton GPC2 instrument, are now operational. The new H/D ratio diagnostic, based on Balmer-alpha emission, obtained data; the hydrogen fraction was observed to rise during the run (the working gas is D2). The HIREX xray spectrometer observed chlorine emission. The "flappers", a new system which provides control of the bypass conductance between the divertor and the main chamber, was successfully run for the first time last week during power tests. On Friday, the physicist in charge of these experiments operated the flappers remotely from his home in Toronto. Diagnostics and controls for the DNB continued to move ahead. Ron Bravenec, UT-FRC, began an extended visit to setup the diagnostic space for the BES system, to install the data acquisition, and to continue work on the BES fiber optics. Work on the DNB controls continued with completion of layouts for circuit board manufacture and with required improvements in the water flow to the Mod/Reg tube. We have begun testing and conditioning antennas in D and E-port into vacuum this past week. After testing the rf data aquisition system we began vacuum conditioning. Initially a significant gas pulse was associated with each RF test pulse. After about one hundred 20 msec, 15 kW shots, the antenna condition was significantly improved. The antennas were conditioned up to ~25 kV for 0.5 sec without arcing in the antenna. A comparison of two independent power measurements were consistent within 3% (22.2 kW versus 21.6 kW). The resonant loop are now pressurized with SF6, and we can continue conditioning up to 40 kV. We also obtained calibration factors required for matching the antenna to plasma loads. D and E-port antennas can now be tested into plasmas. We received a new 2274 vacuum tube, on loan from PPPL, last week. This loan allows us to avoid delays caused by EIMAC's failure to meet their delivery schedule of our tubes, which we sent in for repair last summer. We hi-pot tested the tube successfully and have it installed in FMIT#4. We briefly tested the tube's filament current. We will begin testing and tuning FMIT#4 early this week into the dummy load. The remaining 6" coax needs for J-port are: two 30" lengths, two crosses, two 6", and one tee. Two 9" coax lengths are also needed to complete the power feed. The remainder of the coax should be at MIT by week's end. A simple multi-channel detector is under design to look at deuterium Lyman alpha emission near the outer midplane of C-Mod. Using a wide-band silicon detector and a Lyman alpha filter, we are planing to resolve emission with a ~3 mm resolution near the separatrix, a region where the emission is expected to be the largest. The detector consists of 20 channels, and should cover approximately 6 cm at the tangent point. The results should give us the ionization rate near the midplane, and with local Te and ne, it would also give us a neutral density profile. Exact details and signal levels are still being worked on, and we hope to field the first version of this system during this run campaign. Travel and Visitors ------------------- Martin Greenwald attended the PAC meeting for the fusion SSI (Scientific Simulation Initiative) project held at PPPL. The purpose of the meeting was to get feedback on a whitepaper that had been prepared by the management team and to begin planning for the proposal process. The PAC, which was unusually large, consisted of 13 specialists from both inside and outside the fusion community. Their response to the whitepaper was generally quite favorable, though they made numerous suggestions for improvements. The final version of the whitepaper is due by Feb. 28. Assuming a formal announcement of the initiative (expected from Vice President Gore sometime real soon) OFES will publish a "notice of interest" by April 15. Proposals will be due by July 1. Ian Hutchinson visited IPP-Julich in Germany to present an invited series of graduate student lectures on plasma diagnostics as part of the "GraduiertenColleg" program in plasma physics at German Universities. He also had discussions regarding experiments being carried out on ECDC at a small dedicated toroidal facility. Topics discussed with the TEXTOR group included the possibility of studying rotation in ICRF-only TEXTOR discharges, to compare with results obtained on C-Mod; RI-mode results from TEXTOR; perpendicular velocity measurements with Mach probes, and results of siliconization experiments on TEXTOR. He presented a research colloquium on "Plasma Velocity Measurements on Alcator C-Mod". Perry Phillips, UT-FRC, visited C-MOd for the week to install the radiometer for the high resolution ECE system.