Alcator C-Mod Quarterly Progress Report – FY10 Q1

 
The main activity at Alcator C-Mod during the first quarter of FY10 was operation of the machine. There were 27.4 research days and 6.9 research weeks.
 
 
 
 
 

Physics
 
ICRF MCFD
 
Several runs have been devoted to a parameter study of ICRF Mode Conversion Flow Drive. Scans of several relevant parameters, including He3 concentration, toroidal field, electron density, plasma current and antenna phasing, were carried out. The existence of an optimum He3 concentration for flow drive efficiency was confirmed. The field scan indicated that the most efficient flow drive appears when the Mode Conversion and Ion Cyclotron layer are close to the axis. Dipole and +90 degree antenna phasing resulted in similar rotations, while -90 degree phasing generated slower rotation, but still in the co-current direction. Preliminary analysis of the current scan data indicates more efficient flow drive at the higher current, but more data are required to confirm this result. The observed rotation, unlike the intrinsic rotation results, appears to be proportional to the injected power and inversely proportional to the electron density. The drive mechanism also appears to be more efficient at higher electron temperature. A regression analysis of the observed rotation with plasma parameters is shown in Figure 1.
 
 

 
 Figure 1
 
 
 
 
 
 
Impurity transport in I-mode
 
Recently, a laser blowoff system has been commissioned for the study of impurity transport. An example of two CaF2 injections into an I-mode discharge is shown in Figure 2. As can been from the He-like calcium signal, the impurity confinement times were relatively short, of order 30 ms.
 

 
 Figure 2
 
 
At the same time, the energy confinement was similar to H-mode, as can be seen in Figure 3. These are the important features of I-mode which make it an attractive operational scenario: good energy confinement with poor particle confinement.
 

 
 Figure 3
 
 
 

 
 
Publications

Overview of the Alcator C-Mod Research Program

E. Marmar et al 2009 Nucl. Fusion 49 104014

Lower hybrid heating and current drive on the Alcator C-Mod tokamak

J.R. Wilson et al 2009 Nucl. Fusion 49 115015

Dimensionless pedestal identity plasmas on Alcator C-Mod and JET

G.P. Maddison et al 2009 Nucl. Fusion 49 125004

 
 
 
 
Meetings
 
 

Quarterly Review

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We held the FY2009 Q4 C-Mod quarterly review by teleconference with

DoE. Attendees included Rostom Dagazian, John Mandrekas, John Sauter, Sharon

Stevens, Curt Bolton and Ed Synakowski (OFES), Earl Marmar, Bob Granetz, Jim

Irby, Steve Wukitch, Dennis Whyte, Brian LaBombard, John Rice, Ian Hutchinson,

Miklos Porkolab, Jerry Hughes, Steve Wolfe and Yijun Lin (MIT), Bill Rowan

(U. Texas) and Steve Scott (PPPL). Presentations from the review can be found at

www.psfc.mit.edu/research/alcator/pubs/quarterlies.html

APS

Most members of the C-Mod national team were in Atlanta the week of Nov.2 for the 51^st APS-DPP meeting. Presentations made by the team can be viewed on the web at

http://www.psfc.mit.edu/research/alcator/pubs/APS/APS2009/atlanta2009index.htm

and include 5 invited talks, 1 invited tutorial, 15 contributed orals, and 31 contributed poster presentations.

Data Acquisition and Computation

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Fifteen new Linux workstations have been put into service in the C-Mod control room. These computers are replacements for obsolete workstations purchased more than 6 years ago.

Lower Hybrid System

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All components required for installation of the new lower hybrid launcher are now in-house, and assembly of both the LH couplers and the waveguide interconnection system (jungle gym) are in process. The assembly of the LH II couplers, which includes the WR187 waveguides plus the 4-way-splitter, is proceeding. The link below is a picture of the launcher showing the coupler grill on the left and the interface to the vacuum flange on the right.

http://www.psfc.mit.edu/research/alcator/photos//POWER_SYSTEMS/RF/lower_hybrid/LH%20Second%20Launcher/New%20LH%20Launcher_20091204_001.JPG

The LH-SOL reflectometer vacuum waveguide run manufacturing and cross calibration were completed. This system is now ready for fit-up into the LH launcher assembly.

Assembly of the jungle gym is taking place in the C-Mod cell. All support bars, brackets and clamps have been fabricated for the initial fit up of waveguides from the alignment plate to the jungle gym, and these waveguides are in place. The first two of the split directional couplers and DC blocks were installed for fit up. The link below shows the current status of the launcher support stand and jungle gym. The launcher will attach to the stand on the left where an alignment plate is currently being used to position the waveguides.

http://www.psfc.mit.edu/research/alcator/photos//POWER_SYSTEMS/RF/lower_hybrid/LH%20Second%20Launcher/P1010482.JPG

 
Collaborations
 

MP#589, which is designed to address the question "Does the quasi-coherent mode limit pedestal gradients?", was recently given run time. Rich Groebner (GA) served as co-Session Leader for this experiment, which parallels research carried out on DIII-D for the kinetic ballooning mode. This experiment explored time-dependent aspects of H-mode pedestal formation, in particular the evolution of edge profiles and the establishment of the quasi-coherent mode (QCM). In contrast to typical pedestal studies, which tend to focus on steady H-mode phases, this experiment concentrated mainly on the initial 50--100ms following the L-H transition. To maximize data collection, several discharges were run at each target condition, with 3--4 H-modes triggered in each discharge. At each of three target currents (0.65, 0.8 and 1.0MA), a thorough data set of pedestal profiles from Thomson scattering was collected, as were fluctuation measurements from PCI, reflectometry, gas puff imaging, and fast magnetics. By assembling ensemble data sets from groups of identical H-modes, we intend to relate the onset and evolution of the QCM, and perhaps other turbulence characteristics, to critical values of pedestal gradients. Detailed analysis of the data set is to be completed, but preliminary observations indicate that the measurable onset of the QCM is roughly contemporaneous with the roll-over in the pedestal pressure gradient.

Run time was also given to MP#587a, an investigation of "The Parallel Structure and Dynamics of Blob/Filaments". Olaf Grulke (IPP-Greifswald) served as co-Session Leader for this experiment using remote participation tools. The goal of these experiments was to obtain cross-correlations between the outer midplane Gas Puff Imaging (GPI) array with probe-based fluctuation diagnostics (F-port Scanning Probe (FSP) and fixed divertor probes). Magnetic mapping between the GPI array and the probe locations was successfully established by tuning the plasma current and equilibrium in a series of ohmic discharges over a range of densities corresponding to 0.2< n/n_Greenwald < 0.5. The analysis of the time-delayed cross-correlations is underway.

ITER-like plasma experiments on C-Mod are supporting the benchmarking and verification of simulations used to project the performance of ITER discharges.  The emphasis so far has been on the current rampup and rampdown phases of the discharge.  C-Mod has verified that ICRF heating can preserve volt-seconds in the rampup phase as was predicted with time-dependent free-boundary simulations with the Tokamak Simulations Code (TSC) for ITER.  C-Mod has also shown that the current profile is not changed by the presence of ICRF heating, and this is being investigated through simulations of the experiments with TSC.  The rampdown experiments in C-Mod have demonstrated the Ohmic coil over-current, which was predicted by simulations of ITER, at the H to L mode transition.  The experiments indicate that maintaining the H-mode sufficiently long into the rampdown or ramping down the current sufficiently fast can mitigate this issue.  The rampdown experiments in C-Mod also clearly show a reduction in pedestal parameters (temperature and density) as the plasma current is reduced which will provide direct guidance in the future modeling of ITER's rampdown phase.

Domestic Travel

Jerry Hughes and John Rice attended the joint meeting of the ITPA Topical Groups on Pedestals and Transport & Confinement, held at PPPL October 5--7. Jerry presented highlights of recent L-H threshold, pedestal and ELM research on C-Mod, as well as a summary of progress and plans of TC-3, which is an ITPA multi-machine joint experiment addressing the low-density limit for H-mode access. Finally, he presented an update on plans for implementation of an expanded L-H transition database to be hosted at MIT, and led a working discussion with tokamak database experts and device representatives about the detailed implementation of this database. John presented summaries of the status and plans of Joint Experiments TC-9 (Scaling of intrinsic rotation with no external momentum input) and TC-14 (RF-driven rotation).

Catherine Fiore participated in an APS CSWP (Committee on the Status of Women in Physics) at Brown University on Oct.15.

Martin Greenwald traveled to Washington the week or Oct.12 to participate in a briefing of OFES staff on the Fusion Simulation Project.

Andy Pfeiffer and Alan Binus visited UCLA the week of Oct. 12 to prepare UCLA's FMIT transmitter for transport back to MIT. This equipment will be used for ICRF related research.

Jim Irby served on the Fusion Facility Operation Committee (FFOC) at a meeting held at the DIII-D facility in San Diego on 10/19 and 10/20. This time was used to discuss machine operations, planning and budgeting for major projects and upgrades, and safety concerns common to all facilities. Peter Petersen represented DIII-D on the committee and organized the meeting, and Al Von Halle represented the NSTX facility. Also attending the meeting were Arnie Kellman and Joe Tooky, both of DIII-D. Mark Foster represented DoE at the meeting. On 10/21 Jim visited the Jet Propulsion Laboratory in Pasadena, CA, meeting with Peter Siegel. They discussed the development of FIR detectors and mixers, laser systems, and optical components.

Monday November 16th Catherine Fiore spoke at the Women in Science and

Engineering Workshop that was held at Jefferson Laboratory in Newport News,

Virginia. Her talk was titled "Report from the CSWP Gender Equity Conference."

Amanda Hubbard, Earl Marmar, and Miklos Porkolab attended the Fusion Power Associates meeting in Washington, DC the week of Nov.30. Amanda presented a talk entitled "U.S. Burning Plasma Organization: Supporting U.S. Scientific Contributions to ITER" on behalf of the BPO. Earl presented an "Overview of the Alcator C-Mod Program and Recent Results", and Miklos presented a more general talk on "Plasma Physics and Fusion Energy".

Martin Greenwald traveled to Washington to brief William Brinkman and Pat Dehmer of the Department of Energy on the Fusion Simulation Program.

Martin Greenwald traveled to PPPL for a meeting of the Fusion Simulation Program (FSP) management team.

Bruce Lipschultz and Brian LaBombard attended the ITPA SOL/DIV meeting in San Diego (chaired by Lipschultz) Dec. 14-17. Brian subsequently participated in a meeting of the international program committee for the 19th Conference on Plasma-Surface Interactions, which will be held in San Diego, May 2010. He also met with Rajesh Maingi (NSTX) and Tony Leonard (GA) to discuss plans for the FY2010 joint facility experiments on boundary layer heat transport.

International Travel

Matt Reinke attended the ADAS Workshop from October 4th-7th at Schloss Ringberg in Germany where he presented an overview of C-Mod spectroscopy and impurity transport studies. He discussed low-energy charge exchange modeling with collaborators from Madrid that should enable better understanding of C-Mod thermal C-X results.

Robert Granetz attended an ITPA/IEA MHD meeting in Culham the week of Oct.4. The sessions concentrated on disruption issues, including toroidal and poloidal asymmetries of radiated power during gas jet mitigated disruptions, as well as disruption-generated runaway electrons. C-Mod recently had two run days devoted to studying the asymmetry characteristics, and the results were presented at the ITPA meeting.

The week of Oct 4th, John Wright traveled to Lisbon to attend the 21^st International Numerical Simulation of Plasmas conference (ICNSP'09). He gave an invited talk titled, "Challenges in self-consistent full wave simulations of lower hybrid waves." In addition, a poster by Leonardo Patacchini titled,"Ion collection by a sphere in ExB fields", was presented by John. Conference proceedings will be published in IEEE Transactions on Plasma Science on Numerical Simulation of Plasmas early next year.

Matt Reinke attended the 2009 ADAS-EU Tutorial at IPP-Garching from Oct 8th-16th. Members from the ADAS team instructed a small group on the use of the Atomic Data and Analysis Structure (ADAS) software as well the underlying atomic physics modeling. Also while at IPP he discussed experiments and diagnostics with a number of ASDEX-U researchers, including recent impurity seeded H-modes studies on C-Mod.

Josh Stillerman attended the ICALEPS 2009 Conference in Kobe, Japan, and presented a paper on the timing verification system.

Amanda Hubbard, Paul Bonoli and Chuck Kessel attended the Integrated Operational Scenarios ITPA meeting in Frascati, Italy. Hubbard presented an overview of C-Mod research in support of ITER scenarios and Kessel presented a report on C-Mod ITER-like ramp-up and ramp-down experiments. Bonoli presented an "Update on Static (time) Scenario 4 studies for ITER using ACCOME", and also presented a report on behalf of F. Jaeger entitled "ICRF heating scenarios for the reduced magnetic field, non-nuclear phase of ITER".

Steve Wukitch participated in ASDEX Upgrade Programme Seminar (Tegernsee, Germany) the last week in Oct.

Josh Stillerman visited NIFS (Toki, Japan) on a three week JSPS fellowship, working with Dr. Nakanishi on remote data system performance. In addition he provided MDSplus support to Dr. Takashi from the CHS experiment, and presented talks on the C-Mod data acquisition and control systems.

John Rice was in Lausanne serving on the committee for a thesis defense on Nov. 24. He also attended the First International Conference on Frontiers in Diagnostic Technologies in Frascati Nov. 25-27, where he gave an invited talk on the spatial imaging high resolution x-ray spectrometer system.

Bob Granetz participated in the ITER Control System Workshop in Cadarache, France the week of Dec.8.

Bruce Lipschultz attended the FOM/Rijnhuizen Scientific Advisory committee meeting December 8-9. He then traveled to IPP-Garching primarily to discuss the construction of SLR-lens based spectrographs. Ralph Dux and Thomas Putterich have constructed several such spectrographs for CXRS and impurity influx measurements. The intent is for several such instruments to be built at C-Mod. While at the IPP Dec. 10-11 Bruce Lipschultz also discussed with H. Zohm and A. Kallenbach the plans for T. Putterich to visit C-Mod, had discussions with J. Roth on the summary report of the July 2008 meeting on analysis of retention data for ITER, and discussed with M. Wischmeier the

modeling of divertor physics.

Earl Marmar attended the 8th IEA Large Tokamak Workshop on Implementation of the ITPA Coordinated Research Recommendations, a joint workshop of the IEA Large Tokamak, Poloidal Divertor and TEXTOR Implementing Agreements. The meeting was held at the KSTAR Research Center, in Daejeon, Korea, on December 15 and 16. The agenda included reports of 2009 ITPA joint experiments, plans for joint experiments in 2010, and status and plans for the world's major tokamaks. The workshop concluded with executive committee meetings of the Large Tokamak and Poloidal Divertor IEA Agreements, including discussions of the near term plans to combine these two agreements, and the completion of formal procedures to add Korea as a member of the Poloidal Divertor Agreement.