Alcator C-Mod Weekly Highlights April 10, 2000 Plasma operations continued on Alcator C-Mod last week. Three run days were scheduled and completed. A total of 39 plasma shots were produced with a reliability of about 80%. The bus work had been re-connected in the normal field direction (toroidal field and plasma current both negative). The primary goals were to re-establish operation with normal (negative) field; continue machine conditioning with tokamak plasmas; and proceed with checkout and commissioning of diagnostics. Plasma operation was readily obtained, but conditioning is still incomplete. High disruptivity was experienced except at low density (nebar<1.e20), and numerous molybdenum injections were observed on the bolometer and spectroscopic diagnostics. The observed behavior is not atypical of previous campaigns at this stage of the startup process. This week will be a maintenance week at Alcator C-Mod. No plasma runs are scheduled; electron cyclotron discharge cleaning (ECDC) will be carried out consistent with other activities. The principal focus will be on readying the ICRF and DNB systems for operation into plasma. Physics --------- A second array looking at neutral deuterium Lyman alpha radiation is now operational. This array uses a photodiode array and a very narrow filter at 1215 Angstroms. The radiation gives the local ionization rate and neutral density with information of the electron density and temperature. Initial results indicate that the Lyman alpha radiation is approximately 10 times larger near the inner wall compared to the radiation near the outer midplane. Detailed analysis of the measured profiles is under way. The new limiter particle-flux probes are now operating. Particle flux densities to the sides of the A/B and G/H limiters are recorded at 8 different locations (4 on each limiter) by Langmuir probes operated in an ion-saturation mode (Isat). The probe geometry is designed so that each probe element integrates the cross-field profile of Isat from the leading edge of the limiter far into the limiter shadow. ICRF Systems: -------------- Efforts continued in bringing up the ICRF transmitters for the resumption of operation into plasma. Transmitter tuning for maximum output power had been hampered by residual telemetry waveform and calibration issues, but these are being resolved. Lack of transmitter access resulting from C-Mod plasma operation has added delays, but this will be alleviated by the scheduled maintenance week of 4/10. Chris Brunkhorst from the PPPL rf engineering group will come for the week once more to help. DNB System: ----------- Preparation for operating the DNB into C-Mod continued. A problem with the arc crowbar was bypassed, allowing consistent formation of the source plasma. An interaction between the C-Mod magnet supplies and the DNB HV supplies was corrected, allowing a beam to be fired into the dump plate during a C-Mod shot. The DNB software was further checked during C-Mod operation. The RGA was made operational in preparation for opening the DNB gate valve. Diagnostic activities this week included installing the full set of BES fibers in the MSE/BES image dissector, installing the MSE polarizer, checking the PEM control units, and calibrating the filter temperature controls. The BES system is now ready to make measurements of the radial profile of the absolute level and fluctuations of the beam emission. Howard Yuh, an MIT graduate student, is continuing to write software to do calibrations and set the timing for automated and interactive data taking. The filter control calibrations were both tests of Howard's programs and system calibrations aimed at anticipated 5.3 T plasma and 45 keV hydrogen DNB operations. Lower Hybrid Fabrication ------------------------- Work on the lower hybrid test stand continued. Mechanical assembly is now 98% complete, and wiring 90% complete. Power was applied to the focus magnet, and testing of the fast-off fault circuits was begun. Travel and Visitors -------------------- Randy Wilson (PPPL) came to MIT for the week to help with transmitter tuning and debugging. Joel Hosea(PPPL) came 4/6-7 to contribute to the ICRF startup and for discussions with Ron Parker on the LHCD project. Norton Bretz(PPPL) was at MIT 4/3-5 for the MSE work. Ron Bravenec (UTx) visited C-Mod to work on the BES system. Perry Phillips also visited C-Mod and worked on hardware for the Texas ECE system. Dave Winslow is presently at C-Mod working on hardware for the Texas turbulence probe. Dr. Nobuyuki Asakura, from the JAERI JT-60U experiement, visited the PSFC for the period March 28 through April 8. He spent his time primarily on issues to do with transport in the SOL. More specifically the question of how wall recycling on different machines scales was addressed. This involved comparing data on midplane pressure and D_alpha, as well as plasma profiles in the SOL for different experiments. We compared not only C-Mod and JT-60U, but also data found in the literature for ASDEX Upgrade and JET. For the most part midplane pressures, which represent the ion flux to the walls (ion flux to wall = neutral flux back towards the plasma) scale with the operating density of the experiment. Some differences among experiments became apparent. All of the data will be analyzed further. Montgomery Grimes (MIT) traveled to CPI (the manufacturer of the LH high-power klystrons) to discuss the klystron operation in this application. Miklos Porkolab, Ian Hutchinson, and Earl Marmar attended the OFES Field Work Proposal Meeting in Germantown, Md., on April 5,6 . Bob Childs attended the Executive Council Meeting 85, chaired the Vacuum Science Division meeting of IUVSTA and attended the Program Committee meeting for the International Vacuum Congress 15 to be held in San Fransisco October 2001. These meetings where held in Namur, Belgium from Friday March 31, to April 2, 2000