Alcator C-Mod Weekly Highlights April 3, 2000 Plasma operation at Alcator C-Mod resumed last week. Four run days were scheduled and completed. All runs were devoted to machine startup and conditioning activities. In order to minimize time devoted to startup development for "reverse-field" operation later in the campaign, this first week of plasma runs was carried out with current and toroidal field in the reverse, i.e. positive, direction. A total of 31 plasma shots were produced, out of 69 attempts. Operationally, the machine performance was similar to previous startup weeks. Breakdown was readily obtained, with very minor adjustments from control settings used during the last campaign. The main difficulty was in machine cleanup (conditioning) which requires a significant number of tokamak discharges. The startup scenario in reverse field was improved by adjusting the vertical field ramp rate, and by the end of the week appeared to be satisfactorily robust. Full length (>1.6 sec) discharges at 5.4T and 800kA were produced. At the end of Friday's run, the walls were still not fully conditioned, as evidenced by the rate of gas evolution from the walls, the high H/D ratio, and the relatively high loop voltage. A partial flux loop, F28, which had been repaired during the last vent, failed early in the week, apparently due to disruption forces. The PCS control algorithms were modified to use a nearly redundant loop, F27, and operation was resumed. The bus work is being re-configured for normal (negative) field and current operation. This week will also be a plasma startup week, devoted to additional conditioning discharges. Physics: -------- The Thomson scattering diagnostic is ready for the run. Over the last weekend the laser beam was aligned, laser tuned up and tested, both core and edge spectrometers tested, and the diagnostic calibrated using Raman scattering in D2. ICRF: ----- Work on the transmitters has focused on operational safety and diagnostics. We have recently imported FPA and Driver tube models from C. Brunkhorst (PPPL). Currently, the measured data and model predictions significantly disagree. We have re-calibrated the anode voltage and current instrumentation on the Driver and FPA. We have re-calibrated the RF power measurements of the IPA, Driver, and FPA stages. Currently the transmitters produce 1.8 - 2.4 MW into dummy load. We plan to document the working status of the transmitters and compare them with the models. The PLC system has been investigated for FMIT#1. Programming modifications were implemented to improve the information required for operations. Future work is scheduled to transfer these improvements to FMIT#2-#4. A gas barrier in E-port's matched line section has failed and needs to be replaced. This work will begin this week. Lower Hybrid System Fabrication: -------------------------------- The first klystron has been installed in the test stand. The filament power supply has been tested successfully, and emission current measured in the tube. Diagnostic Neutral Beam ------------------------ We continued the conditioning of the beam and were able to operate in the 45 to 48 kV range with few arc downs. There are some problems with the plasma arc power supply. The connections in the oil tank appear to be intermittent. We tightened them, which appeared to result in temporary remediation, but the problem persists and will be addressed this week. We successfully tested the software that we use to fire conditioning shots between C-Mod shots. The software also detects the preparation for C-Mod shots and then synchs the beam with them. The software was demonstrated to work. Travel and Visitors: -------------------- John Rice attended the Atomic Processes in Plasmas Meeting in Reno Mar. 19-23 and presented a poster on Satellites to the Hign n Rydberg Series in Ar, Cl and S from Alcator C-Mod Plasmas. Amanda Hubbard attended a Workshop on Core and Edge Transport Barriers, held at JAERI in Tokai, Japan, and presented a talk on 'Conditions for EDA H-mode'. She also discussed with Drs. Kamada and Hatae ideas for comparing this regime with the 'grassy ELM' regime on JT60U. Yongkyoon In attended the Sherwood Fusion theory meeting, which was held in Los Angeles from March 27 through 29. Perry Phillips from the Fusion Research Center has been at MIT for the past week installing the high resolution ECE system. He will be here for another week to finish the installation. Norton Bretz was at PPPL this week working on MSE software and preparing final hardware adjustments. He will be back at C-Mod the week of 4/3. Gerd Schilling also spent the week at PPPL, tidying up remaining FWP issues, collecting fiber optic telemetry for the C-Mod ICRF transmitters, working on obtaining a replacement to man the MSE diagnostic next year, and trying to arrange for further and additional rf engineering help to finish off the remaining problems of the ICRF transmitters.