Alcator C-Mod Weekly Highlights September 27, 2004 FY 2004 weeks of operation planned: 18 weeks, completed: 18.9 weeks. We are currently up-to-air with the primary goal of installing the lower hybrid launcher. In addition, a large number of in-vessel activities are ongoing in support of ICRF and diagnostic systems. Physics ------- Analysis has been ongoing of C-Mod/JFT-2M H-mode comparison experiments. A primary goal of these experiments, which were proposed through the ITPA process (PEP-7), was to compare the C-Mod EDA regime with the globally similar- High Recycling Steady (HRS) regime. Shapes were developed which were similar in poloidal cross-section on the two machines, but at different aspect ratio (C-Mod 3.2, JFT-2M 4.9). JFT-2M carried out scans of plasma density at different q values in March 2004; results were recently published (Kamiya et al, Plasma Physics and Cont. Fus 46, 1745.). C-Mod carried out corresponding scans in April 2004. The most striking and significant result is that the access conditions in terms of edge collisionality nu* and q95 are nearly identical on the two devices. Above a certain nu*, which increases weakly for lower q95, C-Mod sees EDA H-mode while JFT-2M reports the HRS regime. This supports the earlier hypothesis that they in fact represent the same physical mechanism. At the lowest nu*, where JFT-2M sees discrete, large ELMS, C-Mod also sees large ELMs with no quasicoherent mode present. While not conclusively identified, these appear likely to be "Type I" ELMs, a significant result since this regime, common on other tokamaks, has been elusive on C-Mod. At intermediate nu*, both devices see a mixed regime with both small ELMS and indications of quasicoherent edge fluctuations. The edge fluctuations themselves, while broadly similar in nature, show some differences between the two devices that are not yet understood. For example, JFT-2M modes have a higher frequency (350 kHz vs 140 kHz) and the C-Mod fluctuations show two peaks separated in f and k by a factor of 2. Further analysis, and C-Mod experiments, are planned in FY 2005. Perry Phillips, UT-FRC, has done a re-examination of his core fluctuation measurements during ITB discharges which confirms his original conclusions that they are true core fluctuations. He has checked the suggestion that refraction of the electron cyclotron emission due to the QC mode might be causing spurious measurements. Extensive TORAY simulations indicate that while this effect could give some core fluctuations, they do not appear to quantitatively explain the observations, indicating the core fluctuations are likely valid fluctuation measurements. Some low level mid-radius fluctuations were shown to be of a magnitude which might be induced by edge refraction at the QC mode region. At least, that possibility could not be ruled out for the mid-radius fluctuations. Operations ---------- The new J-Hor flange with the new rf feedthroughs has been installed on C-Mod and successfully leak-checked. The J-Port antenna in-vessel assembly has begun. Striplines 1 and 4 have been installed along with the conductor covers. Maintenance on the transfer switch that provides backup power from the diesel generators has been completed, and the diesels have been enabled for normal operation. Having successfully completed tests of the new CRYO system PC to PLC software, we have begun work on the HEAT software. The HEAT PLC controls the 100 kW of heater power needed during vessel vacuum bakes, and to maintain the vessel near room temperature during operation. Lower Hybrid System ------------------- A 3-window prototype braze was successfully completed this week indicating that the preform braze material that is made to conform to the shape of the window channel does in fact work extremely well. We will use these preforms in the remaining couplers rather than braze wires bent to shape. This braze test also validated the use of the smaller radius of curvature corners needed for the five MIT and PPPL #4 couplers. On Friday the #2 PPPL coupler was brazed. A leak-check on Saturday indicated all 24 windows and the vacuum flange were leak-tight, and the quality of the braze was good. The #1 and #2 PPPL couplers will be prepared for installation on the launcher and will be the first to be used in high power launcher tests scheduled for next month. We continued work on the klystron filament voltage-to-frequency and frequency-to-voltage control system optical links. Fibers have arrived and will be run from the filament power supplies in the cart down to the lower level control rack. New panels are currently in process at the vendor, and should arrive late next week. A test stand is being developed to allow a careful characterization of our operational klystrons as well as refurbished ones. Following recommendations from Ron Koontz, the design will be similar to those developed at SLAC for their tubes. The procurement process has begun for high voltage power supplies and switches. ICRF System ----------- The FY2004 Alcator level 1 JOULE Target "SC6-1e Complete design of ICRF antenna for C-Mod", is complete, and a detailed target completion report was submitted to DoE-OFES on Monday of last week. The upgraded design for the FMIT #3 and #4 crowbar trigger chassis are complete and parts are on order. The water cooling system work for the fast ferrite tuners is complete and the power supplies will be tested this week. EIMAC has shipped one new 2 MW final amplifier tube which we expect in-house this week. Two more tubes are expected over the next few weeks. Long Pulse DNB -------------- Bob Granetz and Dexter Beals have received their visas, and plan to travel to Novosibirsk October 2 through October 10 to inspect and operate the new long pulse diagnostic neutral beam. The beam is currently being completed at the Budker Institute of Nuclear Physics, and scheduled for a November shipment to MIT. Travel and Visits ----------------- Miklos Porkolab was invited to Iowa State University on Sept. 20 to give a Physics Department Colloquium with the title: "Progress in the Physics of Magnetically confined Fusion plasmas and the Outlook for ITER". He also met with graduate students to discuss opportunities in plasma physics and fusion research, as well as discuss "plasma and fusion basics" prior to his lecture. This approach is highly recommended to anyone contemplating giving a talk at any institution with no courses on plasma physics. Earl Marmar traveled to PPPL to participate in the NSTX Research Opportunities Forum on Wednesday, Sept. 22. He gave a presentation entitled "Opportunities for C-Mod Collaborations and Joint NSTX Experiments". Last week Paul Bonoli was at PPPL for the entire week. He attended the NSTX Results Forum on Monday, Sept. 20. From Tuesday - Friday he attended the US-Japan Workshop on Integrated Modeling (with European participation). He gave a talk at the US Japan Workshop entitled "Status of RF Modeling in Integrated Simulations". He also attended and gave a talk at the NSTX Research Forum on Thursday afternoon, Sept. 23. The title of that talk was "RF Modeling Capabilities for NSTX: Edge Plasma and Non thermal Ion effects". _______________________________________________ Cmod_weekly mailing list Cmod_weekly@lists.psfc.mit.edu http://lists.psfc.mit.edu/mailman/listinfo/cmod_weekly