Alcator C-Mod Weekly Highlights March 15, 2010 FY2010 weeks of research operations Base Target: 13 weeks Base Completed: 7.6 weeks ARRA Target: 5 weeks ARRA Completed: 5.0 weeks Plasma Shots: 1399 Operations ----------- Plasma operations continued at Alcator C-Mod last week. Four run days (Monday - Thursday) were scheduled and completed. Experiments supported research in the Boundary, ICRF Physics, and Transport topical science areas, and the Diagnostic Development activity. A total of 110 plasma discharges were produced with a reliability of 93%. A fresh boronization was performed on Wednesday night. Part of Thursday's experiment featured operation at 7.8 T. All C-Mod systems performed nominally last week, with minimal delays or interruptions of the experimental program. Research operations are planned to continue this week. Operation Details ----------------- Monday's experiment was devoted to MP#598 "Impurity Transport Studies in L and H-Mode Plasmas Using the Modified HIREX Sr. Spectrometer". This portion of the experiment was dedicated to the study of L-mode discharges, following the H-mode experiments conducted on the previous Friday. Laser blow-off (LBO) injections of CaF2 were again used in conjunction with the modification to the HIREX_SR spectrometer to allow radially and temporally resolved measurements of helium-like Ca brightness profiles. After inversion, these are used to infer calcium concentration evolution. Scans of plasma current (0.6 to 1.2MA) and Bt (3.3 to 6.6T) were performed, as well as scans of density and RF power. This experiment comprises part of the thesis research of an MIT graduate student. On Tuesday we carried out experiments in support of MP#562 "Characterization of the decay time of the fast-ion tail". Modulation of the ICRF power was used to allow measurement of tail energy and decay times in a range of target discharges. Power scans (0.75 to 4MW) and scans of plasma current (0.6MA to 1.2MA) were performed and documented using the Compact Neutral Particle Analyzers (CNPA). This experiment forms part of the thesis research of an MIT graduate student. On Thursday, we continued our experimental program in support of MP#591, "Boundary Layer Heat Transport Experiments in H-mode Plasmas", which supports the C-Mod contributions to the 2010 OFES Joint Facility Milestone on boundary and SOL heat transport. Thursday's experiments concentrated on obtaining heat flux footprint data at different toroidal fields. Datasets were obtained in stationary (EDA) H-mode discharges at 6.2 and 4.5 T, with RF power up to ~4MW. Some L-mode comparison discharges were also obtained at lower P_rf. Friday's run was dedicated to continuation of experiments under MP#579, "Characterization and optimization of I-mode". The primary goals of the day's experiment were completion of a shaping scan at 5.6T and preliminary exploration of I-mode access at B~8T, using D(He3) minority heating. Nitrogen seeding was also employed to try to reduce Mo influx and core radiation during the high power I-mode discharges. The seeding seemed to be successful in reducing, though not eliminating the steady core radiation, but the shaping studies were restricted by discharge terminating disruptions that seemed to be correlated with the motion of the inner strike point into the corner where the upper strike plate meets the inner wall. Good heating was obtained at B=7.8T, with steady discharges at Prf over 4.5MW using N2 seeding. However, no I-mode transitions were observed during these initial high-field experiments. ICRF Systems ------------ The FMIT#2 (E-port antenna) screen capacitor was replaced, and the driver was reassembled and returned to service on Tuesday. All ICRF systems performed nominally in support of experiments during the rest of the week. On Friday, we began converting the J-port antenna ICRF system to 70 MHz in preparation for this week's experiments. The network is set for [0,pi,0,pi] phase, and we plan to test a current drive network configuration at the end of the current run period. The transmitters were roughly tuned by using previously physical cavity dimensions. Completion of the frequency changeover is planned for Monday. Measurements made on the prototype current strap for the new four strap antenna found some deviations from the computer model. A second strap was fabricated to investigate the source of the discrepancy. The machining process was modified to prevent movement of the piece during manufacture, and the resulting second prototype strap was found to be a better match to the computer model predictions. Lower Hybrid System -------------------- Work continued last week on preparing the lower hybrid launcher for installation in the vacuum test stand where it will be baked and leak-checked. The back flange was removed and the o-ring surfaces were inspected and polished. This step was necessary following the window etching process to ensure that the chemicals used had not affected the seals. The flange has been reinstalled along with support plates, reflectometer waveguides, thermocouple leads, and other cabling. We continued the algorithm development needed to store and interpret the 64-bit fault status word generated by the Coupler Protection System (CPS). Work also continued on the electronics needed for the launcher rf probes with tests indicating low crosstalk between channels. ARRA Activities ---------------- Specifications and drawings are being developed for the water cooling system needed for the 4th lower hybrid cart. Procurement of water cooling system components has begun under ARRA funding. Diagnostics ----------- The polarimeter lower optical table was moved to the cell on Friday, and positioned into proper alignment with the beam-lines. We are now in the process of installing the FIR lasers and their support equipment including water cooling systems, power supplies, PLC, and fill gas and vacuum components. The polarimeter data system is also being brought on-line. Travel and Visitors ------------------- Martin Greenwald (FESAC Chair), Amanda Hubbard (FESAC member), Miklos Porkolab, and Jeff Freidberg attended the FESAC meeting March 9-10. Earl Marmar, Miklos Porkolab and Martin Greenwald attended the OFES Budget Planning meeting on March 11-12. Earl presented a summary of the C-Mod research plans detailed in the FY12 Work Proposal, which can be found at www.psfc.mit.edu/research/alcator/program/Work%20Proposals/FWP_FY10-12_Draft.pdf Miklos made a presentation on PSFC Institutional Issues. Robert Granetz attended an ITPA MHD meeting at the NIFS site in Japan. The two primary topics for this meeting were 3D MHD and disruptions. Dr. Guangjiu Lei from Southwestern Institute of Physics of China (SWIP) visited from Wednesday to Friday. Dr. Lei is the leader of tokamak heating on the HL-2A tokamak. The purpose of the visit was for Dr Lei to familiarize himself with the operation of our ICRF system. His group is planning to install ICRH their new tokamak, HL-2M. Syunichi Shiraiwa and Orso Meneghini participated in the US-Japan Workshop on RF Physics held at General Atomics in San Diego last week. Syunichi presented a paper on "Development of LH full wave simulation based on FEM" and Orso presented "Coupling core and edge plasma wave simulations". _______________________________________________ Cmod_weekly mailing list Cmod_weekly@lists.psfc.mit.edu http://lists.psfc.mit.edu/mailman/listinfo/cmod_weekly