# Presentation: 951067

## Overview of PPPL Field Work Proposal Opportunities in Macroscopic Stability

**J. Menard**
**for the MHD Science Focus Group**
**Tuesday, November 22, 2005**

## ITPA, ITER, and PPPL research in MHD - overview

- Overview of near-term high priority MHD research for ITPA/ITER
- Possible contributions of NSTX, Theory, and off-site research to international MHD efforts
- Longer-term MHD research opportunities for PPPL beyond ITPA near-term priorities

## High Priority Research Areas for 2005/6 proposed by the MHD ITPA Topical Group (1)

| For NTMs complete 2/1 * scaling studies, validate ECCD control models against data (including modulation), develop sawtooth seed island control to high beta and high fast particle regimes, initiate development of a 3D MHD model (including seeding) and specify diagnostics for NTM detection.

For RWMs understand mode damping through cross-machine experiments.  Study n≠1 RWMs.  Benchmark theory models for RWM feedback and experimentally study feedback control at low rotation.  Study coil systems for RWM control in ITER and specify diagnostics. Specify high beta error field criterion.

Construct new disruption DB including conventional and advanced scenarios to initially study fast Ip quenches and then runaway electrons. |
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## High Priority Research Areas for 2005/6 proposed by the MHD ITPA Topical Group (2)

| Develop disruption mitigation techniques particularly at high performance and by noble gas injection and understand influence of MHD on gas penetration. Validate DINA and/or TSC on gas injection. Develop reliable disruption prediction methods.

Understand intermediate-n AEs ; redistribution of fast particles from AEs; and perform theory-data comparisons on damping and stability.

Specify for ITER the low frequency noise in the diagnostic signals used in feedback loops (for both RWM and vertical control). |
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## Potential contributions of NSTX and Theory to High Priority ITPA Research Areas in MHD

- NTM
- NSTX
- Use MSE + low-A to test NTM threshold theory - perform NSTX/DIII-D cross machine NTM experiments
- Utilize PEST-3 and M.R. equation to explore NTM seeding physics – still poorly understood
- Theory
- Development of NC viscosity models in M3D for NTM potentially very useful
- Sawtooth modeling in M3D important for seeding physics
- RWM
- NSTX
- Extensive experiments on critical rotation physics and MHD spectroscopy  + role of error fields
- For ITER - Perform RWM feedback experiments in low-rotation plasmas to test feedback control physics/modeling
- Theory
- M3D modeling of RWM needs better dissipation model and control coils + controller
- MARS-F analysis of n > 1 critical rotation started – will extend to feedback modeling

## Potential contributions of NSTX and Theory to High Priority ITPA Research Areas in MHD

- Disruption database
- NSTX to contribute data, but may need help with software interface to database
- Theory
- Extensive M3D modeling of VDE + high-beta disruptions already performed
- Study gas jet penetration (via MHD modes) physics for disruption mitigation – currently studied with NIMROD
- AE modes
- NSTX
- Unique ability to study modes at ITER-relevant vfast/vA AND measure q-profile
- Studying role of q-profile on modes + impact of modes on FI confinement and NBI driven current
- Theory
- Nonlinear treatment of single TAE in reasonable agreement with experiment
- Working on alpha transport in ITER from multiple AE modes – enhancing damping physics in M3D

## Possible burning plasma MHD research opportunities for PPPL beyond ITPA near-term priorities

- Usage of 3D fields for ELM control
- ELM control critical for protecting ITER divertor and PFCs
- How 3D externally applied fields impact edge stability and transport is poorly understood
- Can we better leverage 3D tools from stellarator to model 3D perturbed tokamaks and test against NSTX and DIII-D?
- Possible role for M3D also?
- Error fields – angular momentum transport and island formation
- Error field amplification not well understood (leverage same codes above?)
- How does the 3D field impact toroidal “viscosity”/rotation and transport?
- How does the amplification scale with beta?
- What is the structure of the amplified field?
- Locked island formation concern during ITER low-density Ip ramp-up phase
- ITPA performing locked-mode identity experiments to develop scaling law that will supposedly apply ITER
- First principles 2-fluid theory needed to understand physics of island shielding & formation + predict mode “natural” frequency and therefore locking threshold

## MHD SFG input to FWP – discussion (1)

- NSTX Macroscopic Stability Milestones through 2007
- R2(06-2) Characterize the effectiveness of active feedback control of resonant error fields using closed-loop control of currents in ex-vessel correction coils.
- R2(07-2) Characterize the effectiveness of active feedback control of wall-coupled, pressure-limiting global modes, using closed-loop control of currents in ex-vessel correction coils.
- DIII-D collaboration future accomplishments
- 2006 research
- develop realistic VACUUM code model of feedback circuit
- Establish active feedback in low rotation target plasmas
- 2007 research
- Sustained operation above no-wall limit and sustained N = 4 utilizing active feedback at low rotation + high-delta divertor configuration

## MHD SFG input to FWP – discussion (2)

- Proposed Theory Activities for FY06
- Continue study of Resistive Wall Modes & ELMs in tokamaks.
- Develop a predictive model of neoclassical tearing modes in tokamaks/STs.
- Identify mechanisms for disruptions in tokamaks, STs, and stellarators.
- Perform physics studies involving collisional effects on hybrid model.
- Proposed Theory Activities for FY07
- Continue study of resistive wall modes and Elms.
- Continue to identify mechanisms for disruptions in tokamaks, STs, and stellarators.
- Continue to develop a predictive model of neoclassical tearing modes in tokamaks and STs.
- Further improvements in the real-time equilibrium reconstruction algorithms towards the goal of real-time forecasting of tokamak discharges.
- Begin study of new physics introduced when the majority population is represented kinetically.

## MHD SFG input to FWP – discussion (x)

- Interests in DIII-D, ITER, future modeling
- Sawtooth control for ITER
- Modeling for ECCD near q=1
- Understanding of *AE modes
- Proposed Theory Activities for FY07
- Continue study of resistive wall modes and Elms.
- Continue to identify mechanisms for disruptions in tokamaks, STs, and stellarators.
- Continue to develop a predictive model of neoclassical tearing modes in tokamaks and STs.
- Further improvements in the real-time equilibrium reconstruction algorithms towards the goal of real-time forecasting of tokamak discharges.
- Begin study of new physics introduced when the majority population is represented kinetically.

## Leverage 3D physics capabilities of stellarator research to contribute to tokamaks, ST, BP

- 3D equilibrium
- 3D stability
- Suppression of large ELMs critical for ITER
- Recent ELM mitigation results not well understood – need
- Ergodization of near-edge region, increased transport (PIES)
- 3D shaping may modify peeling-ballooning stability (Terpsichore)
- 3D shaping may modify turbulent transport and profiles (see below)
- Test on DIII-D and NSTX
- 3D turbulence
- Compute linear stability (FULL code) for ITG in weakly 3D system
- NC ripple may damp GAM/Zonal flow, allowing higher turbulence levels and transport
- Can this be tested in simulations and experiments?

## NTM research opportunities

- Presented by D. A. Gates
- At the MHD SFG meeting
- August 25, 2005

## Motivation

- Neoclassical tearing modes are recognized as potentially performance limiting for ITER
- ITER Physics Basis, Chapter 3.2 Nucl. Fusion **39** (1999) 2251-2389
- 2/1 NTMs have can lock and cause disruptions
- 3/2 NTMs degrade confinement.
- There is not a demonstrated ability to predict mode onset from first a first principles theory
- Most existing analysis is based on high aspect ratio circular cross-section theory (even for STs!)

## NTM modeling developments

- Real geometry
- Rosenberg, AL,  Gates, DA,  Pletzer, A,  et al.   **Modeling of neoclassical tearing mode stability for generalized toroidal geometry **PHYS PLASMAS 9 (11): 4567-4572 NOV 2002
- Also see work by D. Brennan
- Onset criteria
- Calculate ’
- Evaluate threshold models (e.g. ion polarization current model and *****/ ****||* model)

## New research opportunities

- Include effects of rotation (and shear) on stability
- Non-linear effects
- FIR (Frequently interrupted regime) (S. Gunther, et al.)
- effect of NTMs on confinement
- Effect of island size on rotation
- Mode coupling
- Kinetic models for mode onset

## JET-ITER collaboration

- The arbitrary geometry code developed by Adam Rosenberg would be a useful contribution to JET-ITER
- This would require ~1 man-year of effort to develop the code as a more robust tool