Alcator C-Mod Quarterly Progress Report – FY09 Q4

The main activity at Alcator C-Mod during the fourth quarter of FY09 was operation of the machine.

Milestones

C-Mod has now completed 9.1 weeks of research operation, satisfying our portion of the OFES Joint Facilities Operation milestone for FY09.

The 3rd Quarter FY09 Joint Facility Milestone on particle control and hydrogenic fuel retention was successfully completed and reported to the DOE Office of Fusion Energy Science.  The Milestone report, coordinated by Dennis Whyte at Alcator C-Mod with key contributions from Steve Allen (DIII-D) and Charles Skinner (NSTX), included new experimental and modeling results from all of the three facilities.

Physics

The improved L-mode or “I-mode” plasma confinement regime potentially offers both an attractive operating regime and new insights into transport barrier physics.   The regime occurs on Alcator C-Mod in the ‘unfavorable’ magnetic configuration, with the ion B×ÑB drift pointing away from the active x-point when, as is well known, the power threshold for the L-H mode transition is higher than in the ‘favorable’ configuration with drifts toward the x-point.    At intermediate powers, in many cases edge temperatures gradients steepen, to levels approaching those in H-mode, indicating a clear energy transport barrier.  Unlike the classic L-H transition, however, the change is gradual, apparently not a bifurcation, and does not exhibit the usual sharp drops in fluctuations, D_a etc. [see Figure 1].    A mode less coherent than the QC mode is apparent. Density gradients remain low as in typical L-modes, indicating little reduction in edge particle transport, and indicating an atypical decoupling of the energy and particle transport channels [see Figure 2].   This is perhaps the most attractive feature of the regime. In recent C-Mod experiments, the improved L-mode regime has been extended from transient periods to a quasi-steady operational regime, with energy confinement approaching that in H-modes.  This and the addition of new diagnostics, in particular Charge Exchange Recombination Spectroscopy, have enabled more complete measurements of barrier profiles and fluctuations.  Notably, it is found that an E_rwell develops in the Improved L-mode, but that it is shallower and has lower shear than that in H-modes, which exhibit both a particle and energy transport barrier.

Figure 1

                                                          Figure 2

Publications

An assessment of full wave effects on the propagation and absorption of lower hybrid waves,  J. C. Wright, P. T. Bonoli, A. E. Schmidt, C. K. Phillips, E. J. Valeo, R. W. Harvey, and M. A. Brambilla, Phys. Plasmas 16, 072502 (2009)

Comparison of scrape-off layer turbulence in Alcator C-Mod with three dimensional gyrofluid computations, S. J. Zweben, B. D. Scott, J. L. Terry, B. LaBombard, J. W. Hughes, and D. P. Stotler, Phys. Plasmas 16, 082505 (2009)

Full wave simulation of lower hybrid waves in Maxwellian plasma based on the finite element method, O. Meneghini, S. Shiraiwa, and R. Parker, Phys. Plasmas 16, 090701 (2009)

Meetings

Catherine Fiore, Amanda Hubbard, Jerry Hughes, and John Rice participated in the H-mode Workshop at PPPL Sept.30-Oct.2. Their presentations were:

Fiore:   Rotation and Transport in Alcator C-Mod ITB Plasmas

Hubbard: Improved L-mode plasmas with decoupled energy and particle barriers

           in Alcator C-Mod

Hughes:  H-mode pedestal regulation experiments on Alcator C-Mod

Rice:    Recent Progress in Rotation and Momentum Transport by the ITPA

           Transport and Confinement Group

Domestic Travel

Martin Greenwald traveled to PPPL the week of July 16 for the kick-off meeting of the FSP (Fusion Simulation Program).

Paul Bonoli and Robert Granetz attended the APS-DPP sorters meeting on July 23-24 at the APS headquarters in Maryland.  Paul Bonoli is on the MFE theory sub-committee and Robert Granetz is chair of the MFE experiment sub-committee.

Greg Wallace visited PPPL on July 28-29. He presented a seminar "Observations of Lower Hybrid Wave Interactions in the Scrape-Off-Layer of a Diverted Tokamak".

Jim Terry spent Aug 19-Aug 21 in Washington DC as part of the "Committee of Visitors" charged by FESAC and OFES to assess processes used by OFES to select and monitor their funded programs, as well as the effect of those processes on the resulting portfolios.  Jim was chairman of one of the sub-committees within that committee.

Paul Bonoli, John Wright, Steve Richardson, and Jungpyo Lee attended the annual Workshop of the SciDAC Center for the Simulation of Wave-Plasma Interactions. The workshop was held at Oak Ridge National Laboratory from September 9-11, 2009. For about one and half days, the workshop focused on summarizing Center accomplishments from the past year. During the last full day of the workshop detailed discussions occurred on future directions for the Center.

Syun'ichi Shiraiwa and Orso Meneghini visited GA the week of Sept. 9 to present their work on full wave RF modeling and discuss collaboration with GA colleagues in coupling it to a Fokker-Planck code and the RF-particle following code ORBITRF.

Martin Greenwald spent the week of Sept. 15 at PPPL for a meeting of the FSP (Fusion

Simulation Program) management team, culminating in presentations at the first PAC meeting.  Earl Marmar served as a member of the PAC at the meeting.

Paul Bonoli attended a Tutorial Workshop on using the Integrated Plasma Simulator (IPS) that was held at Oak Ridge National Laboratory on September 29, 2009. The IPS is a framework that has been developed by the SWIM Prototype Fusion Simulation Project (FSP) that allows multiple physics components such as the transport code TSC, the Monte Carlo neutral beam code NuBeam, full-wave ion cyclotron solvers such as AORSA and TORIC, and Fokker Planck codes such as CQL3D to be run concurrently on massively parallel computing platforms such as the Franklin computer at NERSC.

Paul Bonoli, John Wright, and Jesus Ramos also attended a meeting of the SWIM FSP Project that was held at ORNL from September 30 - October 2, 2009.  Paul and Jesus attended the meeting in person and John attended the meeting remotely from MIT. John Wright gave a talk related to work he has been doing on XML applications for data input to simulation codes. Paul gave talks on plans and progress for using the IPS to perform simulations of current profile control experiments in Alcator C-Mod using lower hybrid and ion cyclotron mode conversion current drive. Jesus gave a talk on work he has done on a closed fluid and drift-kinetic electron formulation for slow MHD.

Ian Hutchinson attended the Fission-Fusion Hybrid ReNeW workshop in Gaithersburg Maryland. He was the spokesman for the skeptics panel.

International Travel

Bruce Lipschultz traveled to Cadarache, France, for a 2 day meeting (July 15-16) of the ITPA Coordinating committee. As chairman of the SOL/Divertor committee he presented a summary of work occurring over the past year and plans for the coming year. The information presented included both aspects of research done and development of R&D plans to address ITER high priority needs.

Ian Hutchinson and Amanda Hubbard were invited lecturers the week of Aug.12 at the Plasma Physics Summer School organized by the International Center for Theoretical Physics in Trieste, Italy.

Yijun Lin was at JET the week of Aug.12 to participate in the ICRF mode conversion flow drive experiment. The experiment was successful, with clear effects observed from mode conversion.  Preliminary analysis shows that, unlike that on C-Mod, the rotation was driven in the counter-current direction.