Workshop Working Groups and Topics

This year, the TTF Workshop will consist of:

i.) Special Plenary Topical Contributed Sessions
ii.) Working Group Sessions
iii.) Posters

Special Plenary Topical Contributed Sessions
This year we plan to hold two special interdisciplinary plenary contributed sessions. The topics of these sessions are:

P1) Transport at Finite and High Beta (W. Nevins, coord.)

This plenary session will highlight recent developments in experiment, theory, and computations with regard to transport at finite beta. Finite plasma beta couples electrostatic and magnetic perturbations in the plasma core, leading to modifications to the parallel electric field, modifications to the interaction between the microturbulence and zonal flows due to the emergence of magnetic stresses, and the possible modifications to the magnetic topology. Magnetic perturbations and breaking of magnetic surfaces also appears to be important in the plasma edge for understanding both the ELM crash and mechanisms which suppress ELMs. We will welcome submissions which explore the effects of finite beta in both the core and edge plasmas.


P2) Dynamics of Transitions to Enhanced Confinement (P. Diamond, coord.)

Understanding and predicting the dynamics of transition to and from regimes of transport barriers and/or enhanced confinement, such as the I-mode, H-mode, ITB, Hybrid modes, etc remain important issues in transport and turbulence research. Recent  interesting experimental results have highlighted new insights and new questions relevant to transition dynamics. This session will focus on experiment, theory and simulation of forward and back transitions to enhanced confinement regimes. All aspects of the problem are open to discussion, including  the effects of mean, zonal and GAM flows, magnetic resonances and shear, fueling, heating and torque profiles etc. Papers dealing with the relevant physics on all confinement devices are welcome, as are papers which elucidate the connections between the dynamics of the various phenomena.

The purpose of these sessions is to stimulate interdisciplinary discussion and interchange on themes common to the TTF as a whole, without the interference of parallel sessions. To this end, these sessions will be PLENARY. Loosely following the style of the EU-US TTF meetings, the plenary sessions will consist of brief introductory overviews, several contributed oral papers, and group discussion, with a discussion leader.

TTF meeting participants are encouraged to submit contributed papers to these two special sessions. The scope of the topics is intentionally broad, so as to accommodate a diversity of approaches. The two topics span all aspects of the TTF. Hence, novel interpretations and directions are very welcome! In the event that a submission to one of the special sessions is not selected, it can be considered for a regular working group.

Working Groups

Each working group includes both theory and experiment, with the ultimate goal being tests of theory, simulations and models against experiment. In addition, diagnostic needs and novel diagnostic ideas for a given area are also included in the scope of each working group. The reality of the ITER project provides extra impetus for work on burning plasma transport issues relevant to each of the working groups.

A. Core Transport Working Group (D. Newman, G. McKee, R. Sanchez)

The core working group covers transport issues from the center of the plasma to the top of the H-mode edge pedestal. Topics include:

     • Electron and ion thermal transport
     • Particle transport
     • Momentum transport and generation of rotation
     • Profile/transport control/modification issues (e.g. role of rotation, sources plasma shape, etc.
     • Formation, control and dynamics of Internal Transport Barriers
     • Core-edge interface (the edge as a dynamic boundary for the core)
     • Physics of transport structures (e.g. zonal flows, streamers, avalanches)
     • High performance and burning plasmas (i.e. steady state, bootstrap dominated, etc.)

This years focus areas for the Core Breakout Oral Session are:

1)  Understanding multi-channel transport. Experimental, model and inter-comparison results which can be used for determining the relationships between the Ion thermal transport, Electron thermal transport, Particle transport and momentum transport channels.  Of particular interest are Model-Experiment comparisons which can be used to qualify our understanding of the multi-channel transport physics and can be used for validation of the models.

2) Internal transport barrier initiation, evolution and control. Particularly to shed light on barriers in a select group of transport channels, and the relationship between the edge and internal barrier dynamics.

B. Edge Physics Working Group (R. Groebner, R. Maingi)

The Edge Physics group covers transport physics in the region just inside and outside the last closed flux surface, with emphasis on H-mode plasmas. Topics of interest include:

     • Physics of H-mode pedestal structure
     • Pedestal Transport, sources and sinks
     • Transport induced by ELMs and other edge MHD activity
     • Transport in the scrape-off layer
     • Mechanism for L-H transition, including transient regimes
     • Physics of hysteresis and the back-transition
     • Physics of the density limit

This years focus areas for the Edge Physics Breakout Oral Session are:

1) US DOE Joint Research Target on Pedestal Structure. The session will deal with the physics mechanisms responsible for the structure of the pedestal. Topics include comparison of observed pedestal structure with predictive models, and characterization of pedestal turbulence and comparison with models. This work contains both a theory and an experiment component.

2) Benevolent Pedestal Fluctuations, which will concentrate on a discussion of smaller-scale pedestal instabilities that regulate the density buildup in enhanced confinement modes without providing large heat loads to the PFCs. Examples of such modes include the Edge Harmonic Oscillation, the Quasi-Coherent mode and the Weakly-Coherent Modes

C. Momentum Transport and the Origins of Spontaneous Rotation

This working group was created in 2007 to increase focus on plasma rotation, which influences transport in a number of ways. Important topics for the 2009 meeting include:

     • Toroidal momentum transport, especially non-diffusive mechanism, off-diagonal
     • Cross coupling between particle transport and momentum transport
     • Influence of edge plasma properties on spontaneous rotation and momentum transport
     • Poloidal momentum transport in low collisionality plasmas
     • Integrated modeling of spontaneous rotation

This year, the oral working group session on Momentum Transport will have a special focus on the theory, experiment and simulation of CORE intrinsic rotation phenomena. This will include spontaneous flow reversals, intrinsic rotation in ITBs and other enhanced confinement states, and ECH and LH driven plasmas. Papers which address/explain the relation among these phenomena are especially welcome.

D. Fast Particle Working Group (B. Breizman, N.N. Gorelenkov, W. Heidbrink)

     • Observations and modeling of fast-particle-driven instabilities and fast particle transport
     • Assessment of fast particle effects on burning plasma performance (e.g. ITER)
     • Fast particle diagnostics and MHD spectroscopy
     • Theory and simulation of nonlinear wave-particle interactions
     • Interpretation of fast particle data from present experiments and projections for burning plasmas

The 2011 EP WG sessions will concentrate on collaboration between the two recently funded SCIDAC projects. Both groups have agreed to exchange their project descriptions prior to the TTF meeting to initiate this discussion. We will make an effort to encourage theorists and experimentalists to work together on validation issues.

1) Understanding relative roles of bursty (coherent) and turbulent (stochastic) transport mechanisms for energetic particles.

2) Transport of runaway electrons.

E. 3D (C.S.Chang, C. Hidalgo, K. Ida)

To clarify the role of non-axisymmetric effects in tokamaks, stellarators and RFPs through intrinsic or applied 3D magnetic structures. Magnetic perturbations have been found to have a strong influence in controlling ELMs through stochastization of the magnetic field, and also to control zonal flows. This year's focus areas for the 3D breakout oral session are:

1) The stochastization of the magnetic field: appearance or disappearance of a stochastic region, which has a strong impact on the transport both in the core and the edge, including the transition between stochastic and nesting magnetic fields.

2) Driving and damping mechanisms of zonal flows: amplification of zonal flows by mean radial electric fields and the role of the mean and fluctuating radial electric fields on transport self-regulation. Investigation of the interplay between mean radial electric fields and zonal flows in the transition from nesting to stochastic regions, and the role of symmetry

F. Verification and Validation Working Group (P.W. Terry, W. Nevins)

The Verification and Validation Group has been charged with examining verification and validation (V&V) as it has been defined and structured generally and in other scientific fields, and with formulating V&V procedures and practices applicable to the range of numerical modeling activities within the U.S. Fusion Program, taking into consideration the goals, expectations and desired outcomes of different modeling activities, and resource limitations that are likely to apply to verification and validation. Verification and validation were discussed at a town hall meeting in 2007 and 2008 as part of an effort to examine the state of the art of experiment/model comparison, to confront and seek solutions to particular challenges in performing validation in fusion, and to begin forging consensus about what validation in fusion should be and should accomplish. The town hall meeting was organized by a focused task group that this year seeks to broaden its base and help formulate ideas for validation campaigns involving experiment, modeling, and theory. It is hoped that these efforts will evolve into a cross-cutting working group that interacts in the other TTF working group sessions to advance validation as a common exercise in physics, and meets less frequently to handle technical issues specific to verification and validation.

The V&V group intends to solicit work that describes the development, use, and effectiveness of validation metrics.  We may not get much back this time around, but if we did, it would be appropriate to break out at some point and have a working session on how to refine and optimize metrics barriers in a select group of transport channels, and the relationship between the edge and internal barrier dynamics.