FY2010 NSTX Research Forum
1 - 3 December, 2009
Macroscopic Stability
| Topical Science Group | Leader | Deputy | Theory and Modeling |
| Macroscopic Stability | Steve Sabbagh | Jon Menard | Jong-Kyu Park |
| sabbagh@pppl.gov | jmenard@pppl.gov | jpark@pppl.gov |
Macroscopic stability research in NSTX aims to understand and verify stabilization physics and develop active control methods applicable to the ST development path and to tokamaks in general, leveraged by a unique low-A, low-li, and high-beta plasma regime.
Priorities for FY2010
- Assess active and passive RWM stabilization physics for improved mode control (Milestone R10-1)
- Develop an understanding of the deleterious effects of disruptions in an ST, including halo current generation and the properties of the thermal quench
- Evaluate MHD sources of plasma viscosity and assess the impact of plasma rotation on plasma stability, including the NTM
Research Milestone R(10-1): Assess sustainable beta and disruptivity near and above the ideal no-wall limit.
Stable and sustained high beta is required for efficient fusion power production in an ST-CTF and burning plasma ST devices. It is also needed for ITER advanced operating scenarios, and future tokamak-based reactors. Results from NSTX and other advanced tokamaks have previously shown that plasma rotation and active mode control can sustain normalized beta, beta-N, near and above the ideal no-wall limit. However, disruptions due to resistive wall modes (RWM) and locked neoclassical tearing modes (NTMs) still occur. Disruptions can be triggered when beta-N approaches the ideal-wall stability limit – for example due to a transient confinement improvement, transient loss of rotation, or a transient increase in pressure-profile peaking. To more fully characterize the achievable beta sustainment and disruption avoidance in the ST, mode control improvements will be implemented which may include: (i) application of beta-N control via active control of applied neutral beam power, (ii) optimization of present mode control system parameters and RWM sensors, (iii) improvements to the RWM feedback algorithm by implementing advanced state-space control logic, and (iv) real-time feedback on measured resonant field amplification (RFA). The degree to which other instabilities, such as 2/1 NTMs, impact the disruptivity will also be characterized. Motional Stark Effect and enhanced soft X-ray diagnostics will be assessed for detection of disruption-inducing instabilities and for comparison of measured mode characteristics to theory. Codes such as DCON, IPEC, MISK, MARS-K, and VALEN will be used to calculate ideal beta limits, plasma response to 3D fields, and RWM stability and control. The control techniques, diagnostics, and simulation tools to be applied in NSTX will significantly aid in the development of a predictive capability for the sustainable plasma pressure of high-performance ST and tokamak devices.
Key Physics Topics
- Resistive wall mode physics and stabilization
- Mode-induced disruption physics and mitigation
- Non-axisymmetric field-induced plasma viscosity
- Tearing mode/NTM physics
- Dynamic error field correction
- High plasma shaping and global stability
ITPA/USBPO Participation
(areas of active participation indicated by bold text)
- MDC-2 Joint experiments on resistive wall mode physics
- MDC-4 Neoclassical tearing mode physics - aspect ratio comparison
- MDC-5 Comparison of neoclassical tearing mode avoidance by sawtooth control.
- MDC-12 Non-resonant magnetic braking
- MDC-13 Vertical stability physics/performance limits in highly elongated plasmas
- MDC-14 Rotation effects on neoclassical tearing modes
- MDC-15 Disruption database development
- MDC-16 Runaway electron generation, confinement, and loss
- MDC-17 Physics-based disruption avoidance