Alcator C-Mod Weekly Highlights January 24, 2011 FY2011 weeks of research operations Target: 15 weeks Completed: 9.5 weeks Plasma Shots: 1145 Operations ----------- Plasma operations continued at Alcator C-Mod last week. Four run days were scheduled and 3.3 completed. The experiments supported two miniproposals in the Transport area. A total of 106 plasma discharges were produced with a reliability of 90%. Five hours were lost on Tuesday morning due to a problem with the alternator drive system. The alternator was spun down in order to service a contactor, after which the system was successfully brought to operating speed and C-Mod operations resumed. No further difficulties were encountered with alternator operation during the week. Boronizations were carried out prior to the runs on Tuesday and Thursday. Plasma operations are planned to continue this week. Operation Details ----------------- Runs on Tuesday and Wednesday morning supported MP#521a, "ITB formation - Ti and profile rotation effects". EDA H-mode discharges with and without internal transport barriers were produced using ICRF heating at f=70MHz with the magnetic field scanned shot to shot from 5.5T to 3.9T. ITB's were obtained at the extremes of the field scan, with the hydrogen minority resonance located near r/a~0.5 on the low- and high-field sides. Detailed profiles of ion temperature and rotation were obtained using high resolution X-ray spectroscopy and CXRS measurements. The experiments on Wednesday afternoon, Thursday, and Friday supported MP#602, "Core Fluctuations and Transport in Two -Frequency ICRF Heated ITB Plasmas with Jogs and Modulated ICRF". Internal transport barrier discharges were produced using off-axis heating with f=70MHz at B=5.5T, which places the resonance on the low-field side. Modulated on-axis heating with f=80MHz was applied after formation of the ITB to control the evolution of the density peaking. Changes in core and edge fluctuations associated with the on-axis heating were documented, along with the evolution of the kinetic profiles. On Friday, we also successfully applied neon seeding to help control the impurity influx and reduce the occurrence of back-transitions. ICRF Systems ------------ J-port antenna (FMIT#3 and 4) operated successfully at 70 MHz in support of C-Mod experimental operations last week. A parameter entry error in the control software resulted in loss of about ten shots on Thursday during which the antenna phase control did not behave properly. The software has been modified to be robust against such errors in future. Following the run on Friday, the J-port coaxial transmission line was re-configured for 78MHz operation. We expect to complete the migration of the transmitters and diagnostics back to 78 MHz settings this week. Fabrication of the ARRA-funded rotated four-strap antenna made good progress last week. The bridges for all four straps have been machined and the short strip lines are nearing completion. The EDM machine has been repaired and successfully performed a set of test cuts. Three of four straps have now had their final EDM cuts made, and the fourth will be completed shortly. The straps showed only minor movement due to residual stress and do not need further heat treatment. The straps will next be glass bead blasted to remove EDM residue, in preparation for brazing and plating. Brazing the bridges and short strip lines to the straps is the next major fabrication step for the antenna straps. The external coax flange mating to the bellows tube was checked and found to require an adjustment for proper fit. The boron carbide resistors have been received and resistance versus temperature tests will be carried out shortly. The TZM side tile design has been completed and requests for quotation have been issued. The purchase order for the top/side/bottom plates has been issued. Lower Hybrid System -------------------- The LH system was not required for C-Mod operations last week. Efforts were focused on preparations for the 4th klystron cart and transmitter protection system (TPS) upgrades. Coaxial directional couplers for very low power (~1 W) measurements of antenna reflection coefficients were delivered. Coax to waveguide adapters for low power tests were modified to the correct bolt pattern. Travel and Visitors ------------------- Dr. Donald Batchelor from Oak Ridge National Laboratory visited the Alcator Group and the PSFC for three days last week. His visit was hosted by Paul Bonoli and John Wright. He gave a talk at the Turbulence Simulation Users Group Seminar on Tuesday, titled "Using the SWIM Integrated Plasma Simulator for multi-physics fusion calculations". He also gave a tutorial on how to use the Integrated Plasma Simulator (IPS). During Don's visit he had detailed discussions with Anne White, Amanda Hubbard, and David Mikkelsen on potential applications of the IPS. He also had discussions with Martin Greenwald, Josh Stillerman, Paul Bonoli, and John Wright on simulation data management and storage issues. Don, John, and Paul also spent time working on application of the IPS to simulations of discharges in Alcator C-Mod where sawteeth had been delayed by application of lower hybrid current drive. Prof. Rob Goldston (PPPL) visited MIT on Tuesday. He presented a C-Mod seminar entitled "Heat flux width scalings from a drift-based scrape-off layer model", as well as a presentation during the PSFC Program for MIT's Independent Activities Period (IAP) entitled "Climate Change, Nuclear Proliferation and Fusion Energy". He also participated in discussions with a number of C-Mod scientists. Other fusion related IAP presentations at the PSFC included "Fifty Years of Fusion" by Dale Meade, "An Alcator Chronicle, or What Happened to Alcator B" by Ron Parker, "The Challenge of Fusion Burn and ITER", by Steve Cowley (UKAEA Culham Laboratory), and "Diagnosing Plasma Turbulence in Tokamaks" by Anne White. Randy Wilson (PPPL) visited MIT on Thursday and Friday to work with the Lower Hybrid group. _______________________________________________ Cmod_weekly mailing list Cmod_weekly@lists.psfc.mit.edu http://lists.psfc.mit.edu/mailman/listinfo/cmod_weekly