Alcator C-Mod Weekly Highlights July, 24, 2006 FY2006 weeks of research operations: JOULE Target: 14 weeks Completed: 15.9 weeks Operations ---------- Plasma operations resumed at Alcator C-Mod last week. Four run days were scheduled and 3.5 days completed. A heat emergency declared by the local electric utility necessitated an early shut-down on Tuesday. Overnight boronizations were carried out before the runs on Wednesday and Friday. Experiments were carried out in support of research proposals in Lower Hybrid Current Drive Physics, Transport Physics, and Integrated Scenarios topics. A total of 92 plasma discharges were produced with a reliability over 95%. C-Mod research operations are scheduled to continue this week. Run Summaries -------------- Runs on Tuesday and Thursday were devoted to MP#455 and MP#418, from the lower hybrid physics group. Randy Wilson (PPPL) was at MIT to participate as co-Session Leader for these experiments. The total net power coupled to the plasma was successfully increased to 800kW. A phase scan was taken at 600kW with launcher phases set to 60, 90, and 120 degrees (co-current drive). The measured reflection coefficients were similar for 60 and 90 degree phasing, and higher at 120degrees. At a phase of 60 degrees and 750kW the loop voltage was reduced by almost a factor of four, to ~0.25V, with a total plasma current of 700kA. Lower hybrid pulse lengths up to 0.6 sec were achieved. Wednesday's run was devoted to MP#456 "Particle Transport in Low Density ITBs" and MP#403 "Core turbulence in low density ITB plasmas". David Mikkelsen (PPPL) was at MIT and participated as co-Session Leader for this experiment, and Gerrit Kramer (PPPL) was also at MIT for this run, studying the turbulence data with the refectometer diagnostic. Perry Phillips (U. Texas) also participated in the run from his home institution. The purpose of this experiment was to investigate transport phenomena in ITB plasmas at low density. Following up on previous observations, the target plasmas for the experiment used the low elongation, high triangularity equilibrium originally developed for the JFT2-M comparison experiments. Initially low density ELMy discharges were produced with on-axis ICRF heating at 5.3T, and the target density was lowered. The field was then reduced to 4.5T, placing the ICRF resonance about half-way to between the axis and the high-field side edge. Some parameter adjustment was required to produce H-modes under these conditions. At the end of the day we were successful in producing low density discharges with strong density peaking, with n0/nped up to 4. There was no clear ITB foot inside the pedestal, perhaps because an anomalous pinch, previously postulated to be present at low collisionality, was acting over the entire crossection. The next steps will be TRANSP analysis to look at local transport, then gs2 simulations to try to understand the physics. The run on Friday supported MP#454 "High Bootstrap Current Fraction Plasmas" submitted through the Integrated Scenarios for ITER thrust. Chuck Kessel (PPPL) was at MIT to serve as co-Session Leader for this experiment. The goal of this first run under this MiniProposal was to establish the feasibility of obtaining high bootstrap fraction plasmas using controlled ITBs at low current, via off and on-axis heating. The experiment was carried out using a standard LSN equilibrium with off-axis heating on the high-field side (B=4.5T, f=80 and 80.5MHz), and on-axis heating at 70MHz applied after formation of the ITB. The plasma current was reduced on successive discharges from 800kA to 600kA and then to 450kA. Unfortunately, the lowest current discharges had to be run without central heating, due to a fault in the FMIT#3 (J-port) crowbar trigger cabinet that terminated operation of the 70MHz system for the day. ITB discharges with strong density peaking were obtained that appear to be suitable targets for further develoment under this MP; they will require central heating to sustain the duration of the ITB phase. ICRF System ------------ D- and E-port antenna systems (FMIT#1 and 2, 80 and 80.5MHz) operated as requested for plasma operations last week. The J-port system (FMIT#3 and 4, 70MHz) was unable to operate into plasma on Wednesday as a consequence of a brief power outage on Tuesday night. The J-port system was back in service as required on Friday, but a fault in the FMIT#3 crowbar trigger cabinet forced a HV shutdown at about 14:30. The trigger circuit will be repaired during Monday maintenance and is expected to be back in service this week. Lower Hybrid System -------------------- Replacement of the circulator on klystron #1 was completed, and drive and montitor leg calibrations of this system at 45kV were also carried out. All twelve klystrons were available for plasma operations last week. The lower hybrid system was successfully operated at up to 800kW net power into the plasma during last week's operation. Long-pulse Diagnostic Neutral Beam System ------------------------------------------ The DNB anode flange water leak repair was completed this week. The source was assembled on Monday, and successfully leak checked. After a brief (30 minute) warm-up period, the cathode heater was brought back to its nominal current of 110A. Beam conditioning was started and proceeded well. The beam is currently operational at 50kV and 6 Amperes. Some additional conditioning is expected to be required, but overall performance is good. Travel and Visitors ------------------- Gabriele Manduchi from Consorzio RFX in Padova visited to discuss long pulse and real time extensions to MDSplus. He met with Martin Greenwald, Tom Fredian and Josh Stillerman. Randy Wilson, David Mikkelsen, Gerrit Kramer, and Chuck Kessel (all of PPPL) were at MIT last week to participate in C-Mod experiments. Meetings -------- Abstracts for a total of 32 contributed posters, 11 contributed orals, and 3 invited talks based in whole or in part on C-Mod research were submitted for the APS Division of Plasma Physics Meeting (DPP-06) in Philadelphia. _______________________________________________ Cmod_weekly mailing list Cmod_weekly@lists.psfc.mit.edu http://lists.psfc.mit.edu/mailman/listinfo/cmod_weekly