ITER Urgent Needs and Cross-Cutting
|Leader - Experiment||Deputy - Experiment||Leader - Theory and Modeling|
|Jon Menard||Rajesh Maingi||Allen Boozer|
The purpose of the ITER/CC TSG is to coordinate/lead research on issues urgent to ITER design and operation that cross-cut multiple NSTX TSGs. The ITER/CC TSG will also coordinate/lead research on cross-cutting issues critical to NSTX, NSTX Upgrade, and ST development.
The primary organizing principle for the ITER/CC TSG for the FY2011-12 run is to utilize and understand various particle transport control methods to optimize integrated plasma performance.
- Investigate H-mode pedestal transport, turbulence, and stability response to 3D fields - especially the influence of 3D fields on main-ion and impurity particle transport
- Investigate combinations of active techniques for reducing core impurity accumulation - especially in ELM-free H-mode plasmas. Example techniques include: ELM triggering with 3D fields and vertical jogs, core electron heating with HHFW, variations in magnetic balance and I-mode exploration, reduced divertor C influx via increased flux expansion and/or divertor gas-puffing
- Explore the accessibility of reduced lithium evaporation scenarios with high plasma performance and intrinsic small ELMs for particle control
- Organize experiments and analysis in support of cryo-pump design for NSTX Upgrade
- Oversee ELM research to ensure a coherent research program and minimize experimental overlap
R(11-4): H-mode pedestal transport, turbulence, and stability response to 3D fields
Responsible TSGs: ITER/CC, Transport & Turbulence, Boundary Physics, Macroscopic Stability
"The use of three-dimensional (3D) magnetic fields is proposed to control the H-mode pedestal to suppress ELMs in ITER. However, the mechanisms for particle and thermal transport modification by 3D fields are not well understood. On NSTX, 3D fields are observed to trigger ELMs in ELM-free discharges and this triggering has been exploited to reduce impurity and radiated power buildup. The mechanisms for this triggering are also not well understood. As observed on other experiments, the plasma response to 3D fields in NSTX is sensitive to the edge q value – in particular, the threshold for triggering ELMs with applied n=3 fields varies non-monotonically with q95. To better understand these findings, this milestone will explore possible mechanisms for modifying particle transport, thermal transport, and the resultant modifications to the pedestal kinetic profiles and ELM stability. Example possible mechanisms include: zonal flow damping, stochastic-field-induced E×B convective transport, and banana diffusion or ripple loss. Pedestal turbulence trends as a function of applied field will be measured with BES, high-k scattering, and gas-puff imaging. Edge particle transport will be measured using improved Thomson scattering, impurity injection, and edge SXR. If available, more flexible 3D field control will be used to vary the applied spectrum. The underlying 3D equilibrium is also a very important determinant of the 3D edge transport, and the transport and turbulence measurements combined with other edge measurements will be utilized to help infer whether the edge plasma response is predominantly ideal or resistive/stochastic in nature. These measurements and comparisons to theory will contribute to improved understanding of the transport and stability response of the pedestal to 3D fields for ITER."