Alcator C-Mod Quarterly
Progress Report – FY08 Q1
The main activities at Alcator C-Mod during the fourth quarter of FY07 were a quick vacuum break to repair broken flux loops followed by operation of the device.
Science
Results
Two C-Mod papers are on the shortlist for the 2007 Nuclear Fusion Award. The ten shortlisted papers are judged to be those of the highest scientific standard, selected from the journal volume published two years previous to the award year. Nominations are based on citation record and recommendation by the Board of Editors. The two papers are: B LaBombard: Transport-driven scrape-off-layer flows and the boundary conditions imposed at the magnetic separatrix in a tokamak plasma (2004) Nuclear Fusion, 44 (10), pp. 1047-1066
JE Rice: Observations of anomalous momentum transport in Alcator C-Mod plasmas with no momentum input (2004) Nuclear Fusion, 44 (3), pp. 379-386
A Monte Carlo simulation of boron deposition onto the Surface Science Station's (S3) quartz microbalances (QMB) during boronization has been developed by Roman Ochoukov, a C-Mod graduate student. Simulation results are consistent with boron ionic deposition at Ti ~ 1-2 eV. Finite Larmor radius effects allow deposition on surfaces parallel to the magnetic field. Ion heating at the Upper Hybrid (UH) resonance is found to be critical to explain observed boronization results. At the highest pressures, with the largest deposition rates, the boron ions become effectively de-magnetized, and the deposition on the S3 QMBs is independent of orientation to the magnetic field. This result implies that previous deposition estimates based on QMB data and ion travel along field lines were low by as much as a factor of ten. Peak deposition rates as high as 3 nm/minute for surfaces at the UH resonance, regardless of orientation to the magnetic field, can be expected, implying an approximately 1.4 mm boron thickness after 8 hours of boronization.
Diagnostics
The data acquisition system for the 152 channel soft x-ray tomography diagnostic has been upgraded from CAMAC-based 12-bit, 100 kHz digitizers to cPCI-based 16-bit, 250 kHz digitizers. Additionally, an edge viewing aperture has been re-installed on one of the arrays so that the diagnostic is configured to have: 76 core channels, 38 channels viewing the pedestal at the outboard mid-plane and 38 channels viewing the pedestal at the top of the plasma. These pedestal arrays will be used to investigate further flux surface asymmetries in x-ray emissivity previously observed in C-Mod H-modes.
Forty-four C-Mod scientists and graduate students attended the DPP APS meeting in Orlando, Florida Nov.12-16. Four invited orals, 13 contributed orals, and 27 posters were presented on C-Mod results. Paul Bonoli gave a talk on "Lower Hybrid Current Drive Experiments on Alcator C-Mod: Comparison Between Theory and Simulation", Brian LaBombard discussed "Critical Gradients and Plasma Flows in the Edge Plasma of Alcator C-Mod", Steve Wukitch talked on "ICRF Performance with Metallic Plasma Facing Components: Revenge of the Sheath", and Valerie Izzo, University of California, San Diego, gave a talk on "MHD Simulations of Disruption Mitigation on DIII-D and Alcator C-Mod". John Rice presented a talk on "Spontaneous Rotation in Tokamak Plasmas" at the Angular Momentum Mini-Conference associated with the meeting. Jim Terry was named a Fellow of the APS during the meeting. Jim has made major contributions to the physics programs of Alcator C, C-Mod, and TFTR. His citation reads "For significant contributions in the areas of volume recombination in plasmas, plasma impurity transport, wall-conditioning with lithium, plasma transport, and plasma turbulence in magnetic fusion confinement devices."
The presentations may be found at http://www.psfc.mit.edu/research/alcator/pubs/APS/APS2007/orlando2007index.htm
There were two mentions of C-Mod results presented at the DPP APS meeting in the Jan.2008 issue of APS News, regarding disruption mitigation and edge turbulence imaging.
A new cluster, consisting of 256 processor cores in 64 nodes, each with two AMD Opteron 2214 (2.2 GHz) dual-core processors, with 1 GB memory per processor core, a head node, a spare node, 2.5 TB RAID storage, and gigabit and Infinipath networks, has been installed at the PSFC. Full-wave lower hybrid field simulations with TORIC that took 5000 cpu-hours on our old cluster can now be done in 1176 cpu-hours, or 4.25 times faster, using the same number of processors. In addition, the new cluster has more than five times the number of processors as the old cluster. The new cluster makes it possible to do nonlinear gyrokinetic turbulence simulations in-house. A well resolved, two species GS2 nonlinear simulation of electrostatic TEM turbulence completes in less than 8 hours on the new cluster. A radial profile of the maximum linear growth rate, for a C-Mod case, can be computed in about 10 minutes. The acquisition and installation were led by Ted Baker, with design requirements and testing by Darin Ernst, John Wright, and Paul Bonoli. This project is supported in roughly equal amounts by SciDAC, the PSFC, and C-Mod.
Dave Terry has returned to Palo Alto, CA, to participate with the vendor in the inspection of the #117 klystron.
Paul Bonoli and John Wright attended a Workshop held by the SWIM Prototype FSP Project at Oak Ridge National Laboratory from October 15-17, 2007. Paul Bonoli gave a talk titled "Fast MHD Physics Accomplishments and Targets: Current Ramp-Up and ICRF Heating in Alcator C-Mod". John Wright gave a talk on implementation of "The TORIC RF Component in the Integrated Plasma Simulator". John Wright attended the US-Japan Simulation Science Workshop and the International Conference on Numerical Simulations in Plasmas in Austin, TX the week of Oct 8-12th. Joshua Stillerman attended the 'International Conference on Accelerator and Large Experimental Physics Control Systems' (ICALEPCS) in Knoxville, TN last week. He co-authored two papers: "MDSplus Real-Time Data Access in RTAI" and "Remote Operation of Large-Scale Fusion Experiments".
Catherine Fiore attended the semi-annual meeting of the APS Committee on the Status of Women in Physics, held in Detroit on 10/22/07. Martin Greenwald was in Washington to attend a meeting of the Fusion Energy Sciences Advisory Committee and to deliver a panel report on long range planning. Miklos Porkolab also attended the meeting.
Bruce Lipschultz attended the 5 year review of the Physics of Plasmas at PPPL on November 20. He was part of a committee that reviewed the operation and goals of the journal over the past 5 years.
Martin Greenwald attended the Fusion Power Associates meeting in Oak Ridge to present a summary of the FESAC report "Priorities, Gaps and Opportunities: Towards A Long-Range Strategic Plan For Magnetic Fusion Energy". Miklos Porkolab also attended the annual Fusion Power Associates meeting on Dec. 4-5 in Oak Ridge, TN and made a presentation entitled "Research Highlights and Plans for Alcator C-Mod" on behalf of Earl Marmar and the entire C-Mod Team. Paul Bonoli attended a workshop on RF/MHD coupling related to the SWIM Prototype FSP Project. The workshop was held at the University of Wisconsin, Madison from December 4-5, 2007. He gave a talk at the workshop titled "Physics Issues Related to RF Models in the Ion Cyclotron and Lower Hybrid Range of Frequencies". Earl Marmar and Dennis Whyte participated in the National Research Council "Committee to Review U.S. ITER Science Participation Planning Process" in Washington DC Dec. 14-15. The review is the result of the National Academies being asked by Congress, in the Energy Policy Act of 2005, to review the DOE/BPO plan for US fusion community participation in ITER. Whyte served as a member of the review panel, and Marmar gave a presentation entitled "U.S. BPO Panel: Planning for ITER".
Jerry Hughes, Amanda Hubbard and John Rice attended meetings of the Pedestal, CBDM, and Transport Physics groups of the ITPA, in Naka, Japan, October 1-3. Jerry and Amanda primarily attended the Pedestal meeting, where Amanda presented updates on joint experiments with JET (PEP-7) and with NSTX and MAST (PEP-16), and Jerry presented preliminary C-Mod results on pedestals in varied magnetic configurations. Amanda also presented, on behalf of Joe Snipes, recent results on low density limits for L-H transitions (CDB-10), in the CDBM Threshold working group. John primarily participated in the Transport Physics group, presenting inter-machine scalings of intrinsic rotation and chairing a rotation working group session. John also presented recent spatially resolved x-ray spectroscopic measurements from C-Mod on behalf of Alex Ince-Cushman, a C-Mod graduate student.
Joe Snipes attended the 10th IAEA Technical Meeting on Energetic Particles in Kloster Seeon, Germany from 8 - 10 October and then the remainder of the 10th ITPA MHD group meeting at IPP-Garching from 10 -12 October. Bob Granetz also attended the ITPA MHD meeting from 10-12 October.
Ron Parker served on the Scientific Council reviewing the fusion program at CEA Cadarache, exclusive of ITER, on October 10,11 2007. Ron has also agreed to serve on the European Facilities Review Panel in preparation of the next 5-year plan for fusion development in Europe.
Bruce Lipschultz attended the EU task force meeting on Plasma Wall Interactions in Madrid Spain, October 29-30, 2007, held at CIEMAT. He presented a review of the US boundary physics program plans for approximately the next 5 years based on contributions from the major tokamaks and labs involved. Bruce also attended the meeting in order to foster better communication between the US and the EU, particularly with respect to BPO work. Lastly, the gathering was used to plan the agenda for the next ITPA SOL/divertor group meeting to be held in January.
Bruce Lipschultz attended the 6th meeting of the IEA Large Tokamak Workshop (W66) on Implementation of the ITPA Coordinated Research Recommendations, held at JET in Culham UK November 28-29, 2007 hosted by the EFDA staff there. He represented C-Mod in the discussions of C-Mod commitment to running collaborative experiments. He also represented the ITPA SOL/Divertor group in the discussions of the SOL/Divertor group proposals for collaborative work. Before the meeting he gave a JET seminar entitled "Characteristics of D retention in a high-Z tokamak: A new retention process?".
On November 29, Miklos attended the Annual Meeting of the Hungarian Nuclear Society in Budapest, Hungary, and gave a presentation with the title : "Plasma Physics and Controlled Nuclear Fusion Research". He was also awarded the Karoly Simmony Plaque and Prize, the newly established Hungarian prize for outstanding achievements in plasma physics and fusion research.
Paul Bonoli attended a workshop of the ITPA Steady State Operations Group in Garching, Germany on December 10-12, 2007. He gave three talks: "Simulation of High Power ICRF Wave Heating in the ITER Burning Plasma", presented on behalf of E. F. Jaeger at ORNL; "Inter-Code Comparisons of Lower Hybrid Current Drive Models in Reactor Relevant Regimes"; and "Validation of CQL3D Against LHCD Results on Alcator C-Mod". Paul also met with Professor Marco Brambilla and Dr. Roberto Bilato of IPP to discuss physics development issues with the TORIC electromagnetic field solver.
A draft schedule for the FY08 run period can be found at
http://www.psfc.mit.edu/research/alcator/facility/Operations/operation_schedule.pdf