# Presentation: 223677

## The NSTX ResearchProgram Plan for 2004 – 2008MHD Research

- Presented by J.E. Menard, PPPL
- for the NSTX Research Team
*NSTX Five Year Plan Feedback Forum*
*December 12 – 13, 2002*

## Overview of presentation

- MHD of highest  and P (long-pulse) discharges
- Relevant to IPPA 5 and 10 year goals
- Overview research plans
- Motivated by recent results
- Global modes, NTM, ELM, fast ion MHD, RWM, etc.
- Summarize with integrated timeline
- Discuss yearly progression of research goals
- Discuss tools for achieving those goals

_**MHD Goal**_** ******** Provide MHD understanding and **
**diagnostics for development of control tools **
**needed to achieve long-pulse, high-******** discharges**

## Achieved T=35%, N = 6.4, N=4.5

-  6 achieved for   Ip/aBt0 = 2 to 6.5 MA/mT
-  increased 50-100%     from previous year

******T**** ******** 2********0********p******** / B****t0****2**

****** ******** ****2********0********p******** / ********B****2******

- Recent computations show     ***ideal*** ***no-wall limit*** **is ********N******** ******** 3-3.5** independent of R0/a for q* > 1.7
**Many shots have now clearly exceeded this limit **

**2002 data**
**2001 data**

******T**
**(%)**

****
**(%)**

## Highest T discharges limited by 1/1 modes

- Core becomes n=1 kink unstable
- 1/1 mode degrades  & rotation, slows, locks  disruption
- Neoclassical drive possible, but...
- Modes can decay as  rises
**Rotation evolution may dominate:**

**10-15kHz n=1**

**108101**
**108103**

******T****= 25%**

**5MW**

**1MA, 3kG**

******T****= 31%**

**q(0) ******** 1**

******P ****= 0.6-0.7**

**Central rotation drops**

**108103**

- SXR

- CHERS

**EFIT w/o MSE**

- Very large q=1 radius  fast disruption

## MHD events in long-pulse discharges:

- 	 early n=1, transient at high BT
- long-lived n=2 mode in flat-top, NTM?
**fast n=1 internal mode disrupts ******
- residual n=1,2 rotating modes, **NTMs?**

******T ****= 16%**

******N****= 6**

******P****= 1.3**

**5MW**

******CR**

- Prior to internal collapses,
- SXR shows only edge 2/1 or 3/1

## H-mode profiles increased  & P limits

- Decreased pressure peaking observed to increase N
- Expected for n=1 kink limit

***EFIT p(******************) loosely constrained by ***
***electron pressure profile shape ***
***to capture variation in pressure peaking***

- Reached ******P**** = **1.4 (** 2.5 higher)**
**Reduced mode-locking of 2/1 tearing modes in H-mode**

## High  obtained with high  and 

-  N increases with increasing elongation
-  N degraded for  > 1.8 in previous run year

**2002 data**
**2001 data**

** ********N**** weak function of ******** for ******** > 0.4**

**High ******** ******** higher I****p****/aB****t0 ****& ********T**

******N**

******N**

******T**
**(%)**

## High N achieved at low internal inductance

-  N >> 4 li
-  N increasing with lower li for li > 0.6
- Will this trend hold at even lower li?
**NSTX design target has ********N**** = 8.5, l****i**** = 0.25**
- N also >> 4 li
- Need more data at lower li to define limit
***lower l******i****** achievable with increased *********

******N**

******N******

## Influence of shape and profiles on global stability 

- FY2003
- Further optimize  and  in LSN and DND discharges to maximize T and N
- Find optimum shape for highest global stability limit compatible with long-pulse
- FY2004
- First MSE constrained reconstructions early during discharge ramp-up
- Assess N limits as a function of ***controllably*** low internal inductance
- Develop and assess stability for q(0) > 2 plasmas if not already naturally occurring
- Assess low-A and kinetic effects on ballooning stability
- FY2005
- Characterize J(r) evolution, compare to TSC (and other) models, and benchmark
- Aid in design controllers for heating and current drive actuators
- FY2006
- MSE-constrained rtEFITs, first attempts at real-time J(r) control using HHFW, EBW
- FY2003-future
- Work to develop real-time predictive capability for stability, operate just below limits.

## 3/2 NTMs often observed in FY2001,

- SXR data indicates odd-parity mode with inversion radius = 3/2 mode rational surface from EFIT
- Simulated eigenfunction agrees

- P limit increased significantly in 2002 (from 0.5 to 1.5)

## Neoclassical tearing modes: FY03-05

-  FY2003
- Prepare neoclassical tearing mode codes to more routinely assess mode stability once q() profile information is becomes available, important for H-mode shots.
- Implement more accurate wall shape model for wall-stabilized TM stability studies, and begin implementation of simulated Mirnov sensor responses.
- FY2004
- Measure poloidal mode numbers magnetically utilizing new poloidal Mirnov array.
- Assess seeding mechanisms for NTMs in various NSTX operating regimes.
- Investigate non-linear coupling of NTMs of different helicities.
- Work with MAST NTM experts on NTM similarity experiments
- FY2005
- Correlate magnetically inferred *m/n* data to island position measurements from SXR and possibly EBW radiometer.
- Determine if modes are excited “spontaneously” via proximity to an ideal limit or if seeded directly from other observable MHD modes.
- Infer island widths from measurements and improved modeling to assess CD needs for EBW CD feedback stabilization of the NTM.

## Neoclassical tearing modes: FY06-07

- FY2006
- Perform preliminary assessment of changes in NTM stability due to global changes in current profile resulting from EBW current drive and electron heating.
- Assess EBW power requirements for NTM stabilization based on initial measurements of CD efficiency and required CD for mode stabilization.
- FY2007
- Demonstrate direct NTM suppression with pre-programmed control of launcher and plasma conditions.
- Verify CD requirements with island suppression measurements and modeling of NTM stabilization physics.
- FY2008
- Incorporate EBW launcher control into PCS and demonstrate first active feedback suppression of the NTM.

## ELM stability sensitive to shape, fueling

- Long pulse H-modes optimized empirically
- LSN shaping increased while retaining small-ELM edge
- Edge density, collisionality likely impacting edge JBS
- Hypothesize that access to ballooning second stability impacts *n*-number and amplitude/width of ELM

- 135 Hz

- LSN

- LSN

- DN

- W/W0: 5-25%

- W/W0: 1-4%

- 0.0

- 0.2

- 0.4

- 0.6

- Time (s)

- 2

- 1

- 0

- 1

- 1

- 0

- 0

**D******** (arb.)**

- Higher
- Fueling

- Lower
- Fueling

##  Edge localized modes 

- FY2003
- Continue to perform experiments to assess impact of divertor configuration, shaping, collisionality, and plasma-wall gaps on ELM stability properties.
- Characterize pedestal energy loss in various ELMing regimes and secondary destabilization of NTMs and other modes due to ELMs.
- FY2004
- Commission very high-n array for measurement of ELM toroidal mode numbers.
- Correlate measured mode numbers with ELM type.
- FY2005
- Use reflectometer or other high resolution near-edge profile diagnostic to perform preliminary measurements of ELM structure.
- FY2006-2008
- Using kinetic EFITs with MSE and all available profile information, reconstruct discharges from controlled experiments designed to excite different types of ELMs.
- Compare ELM stability threshold, mode structure, and toroidal mode numbers to predictions from ELM stability codes such as ELITE, DCON, GATO, or PEST.

## Neutrons are beam-target;  - S nfi
Instabilities are TAE and "fishbones"
TAE bursts cause initial, fast drop, fishbones later, slower drop.
Correlation of f.b. and TAE bursts suggests coupling.
In L-mode, sometimes correlated with D drops.
Loss also seen in iFLIP

- Instabilities are TAE and "fishbones"
- TAE bursts cause initial, fast drop, fishbones later, slower drop.
- Correlation of f.b. and TAE bursts suggests coupling.
- In L-mode, sometimes correlated with D drops.
- Loss also seen in iFLIP

- Fishbone & TAE can cause fast ion losses

## DIII-D/NSTX TAE Similarity Experiments

- TAEs chirp routinely on NSTX, not true on DIII-D
- Assess differences in gap or q shear

## Fast ion MHD

- FY2003
- Perform CAE (and more TAE) similarity experiments on NSTX and DIII-D
- Assess role of toroidicity on characteristic frequencies, thresholds, growth rates, etc.
- Assess if fast ion-driven modes play a role in high P NSTX internal disruptions
- Investigate low frequency modes such as fishbone or rTAE (f=20-40kHz)
- FY2004
- Perform first measurements of CAE and TAE poloidal amplitude distribution and poloidal wavelength with full outboard poloidal Mirnov array
- Assess role of q profile in determining gap structure for TAE modes (need MSE).
- Quantitatively correlate fast ion losses (using FLIP) with MHD characteristics
- Determine the energy of ions preferentially lost.
- Infer region of distribution function driving instability.

## Fast ion MHD (continued)

- FY2005
- Utilize internal diagnostics including reflectometer, EBW spectrometer, or upgraded bandwidth SXR to measure internal structure of TAE, CAE, and GAE modes.
- Utilize fluctuation signatures and frequencies to distinguish between modes.
- Compare to theory and modeling with NOVA, HINST, and HYM (need MSE).
- Assess if "pitch-angle anisotropy model" can explain drive for instabilities and thus how much energy is available to drive modes.
- FY2004-future
- Develop beam ion profile diagnostic to determine fast ion pressure profile.
- Use profile shape in ideal stability calculations, fast ion MHD instability drive
- Assess influence of fast ion MHD on fast ion population properties
- neutron rate, power deposition, fast ion angular momentum, etc.
- Techniques to be considered:
- neutron collimator (leading candidate)
- an array of active neutral particle detectors
- D-alpha light from re-neutralized beam ions.

## Fast rotation can modify equilibrium, stability

- Local thermal MA v/vA as high as 0.3
-  Maximum density at R > Raxis
-     At axis, R[dlog(ne)/dR]=2MA2 / local *(includes thermal and fast ions)*

- Toroidal flow-shear computed to reduce internal kink growth   rates up to factor of 3
- 2-fluid effects & hot particles also stabilizing
- Contributing to saturation of  1/1 modes at high-?

**M3D Simulations:**

**107540 at t=318ms**

**Thermal**

## Influence of rotation on equilibrium and stability 

- FY2003
- Begin to include rotation effects in equilibrium reconstructions (EFIT).
- Assess change in inferred stored energy due to inclusion of v.
- Continue to assess shear flow stabilization of core kink modes (M3D).
- First use of **FLOW** equilibrium code for interpreting experimental data
- FY2004-future
- Compare fast ion centrifugal force to thermal, and possibly use changes in central gradient to infer changes in fast ion population due to MHD
- Cross check against beam ion profile diagnostics if available, NPA, FLIP
- Develop linear stability code based on **FLOW**** **including anisotropy

## Reduced error-field  reduced mode locking

- Vertical field coils found to generate large n=1 Br
**Coils subsequently re-shaped**
- Vacuum island widths now** *****reduced to < 1cm*** (from 5cm)

*(NSTX operates with m > 0 resonant)*

**q(0) =2**

**800kA Ohmic**
**B****T**** = 4.5kG**

**EFIT w/o MSE**

**q(0) =1**

- wvac
-   a

**4 Gauss locked-mode**

**2x10****19****m****-3**

**2002 PF5 coil**
**2001 PF5 coil**

**2002**

**2001**

## Error fields and locked modes 

- FY2003
- Commission internal RWM/EF sensor array electronics.
- Gather engineering data on primary passive plate positions
- Calibrate sensors including effects of non-axisymmetric positions.
- Begin assessment of sources of residual error field such as PF coils, PF coil leads, or passive plate eddy currents.
- Begin experiments using low density locked modes and beam pulses to determine locking threshold as a function of density, rotation, and proximity to no-wall limit, to check threshold against inferred error field sources.
- Use locking position to aid inference of error field sources.
- FY2004
- After utilizing internal sensor measurements to infer sources of error field, correct error fields directly where possible through re-alignment.
- Include findings in RWM power supply current requirements as needed.

## Stability analysisfinds > no-wall for many E, wall

- n=1 no-wall limit N = 3.5 to 4.5 clearly exceeded
- With-wall limit sensitive to p & q profile shapes:
**Limit lowered by monotonic q(********) with q=2 in plasma**
**Limit lowered with increased p(********) profile peaking**

## RWM physics, passive stabilization 

- FY2003
- Perform NSTX/DIII-D/MAST similarity experiments designed to investigate aspect ratio dependence of RWM stability physics and no-wall stability boundaries
- Investigate role of finite amplitude unstable RWMs in modifying rotation
- Using MARS code, perform preliminary theoretical assessment of expected critical rotation frequency for RWM stabilization in NSTX and associated scalings with beta, safety factor profile, and shaping
- FY2004
- Use equilibria with MSE to assess role of q() in RWM stability, rotation damping
- Begin benchmarking codes against measurements
_**Example**_:  In regimes where RWM is passively unstable above the no-wall limit, benchmark codes such as DCON+VALEN and/or MARS+VACUUM used in predicting RWM structure, growth-rate, and frequency, against measurements from the internal RWM/EF magnetic sensor set.
- FY2005-future
- Using experimental results and comparison to theory, assess rotation required for stabilization of RWM in long-pulse high- operating regimes.
- Use knowledge gained to test active feedback stabilization physics in regimes with low rotation speed and to project to future ST devices.

## Full toroidal coverage
24 B and 24 BP 
Each 12 above, 12 below 
B measured by single turn loop 
Embedded in tiles
Centered in plate
BP measured at ends of primary plates 
Glass insulated Cu wire wound on macor forms
SS304 shields

- 24 B and 24 BP
- Each 12 above, 12 below
- B measured by single turn loop
- Embedded in tiles
- Centered in plate
- BP measured at ends of primary plates
- Glass insulated Cu wire wound on macor forms
- SS304 shields

- Each primary plate will measure B and BP

- Thermocouple connectors allow easy installation and upgrade potential (PnP)

## Active RWM stabilization: FY03-05

- FY2003
- Finalize designs of “strawman” active coil sets using DCON+VALEN analysis.
- Decide on either internal or external coil set, and design it.
- Initiate procurement of power supplies
- Should simultaneously correct error fields and provide fast feedback for RWM control.
- FY2004
- Procure, install, and commission active coil set.
- Specify, procure, and commission active coil supplies.
- Purchase and install DAQ for PCS
- FY2005
- Complete interface of supply controls to PCS.
- First use of active feedback on RWM and EF, algorithm optimization

*See next talk by S. Sabbagh for more details: physics &  feedback system*

## Active RWM stabilization: FY06-08

- FY2006
- In regimes where RWM is passively unstable above the no-wall limit, develop feedback algorithms to stabilize the RWM up to the ideal-wall limit.
- Develop techniques to control rotation speed independent of beam heating power to decouple rotation from .
- Flow damping from non-resonant error field excitation using active coils and/or controlled error field amplification of the RWM are possible means.
- Use non-resonant error fields to modify NTM island formation.
- FY2007-future
- Utilize RWM/EF feedback to operate close to ideal-wall limit in optimized long-pulse discharges.
- Generate stochastic divertor boundary with non-axisymmetric coils
- Assess impact on edge profiles and divertor heat flux in long-pulse

## MHD-stable, high- 

- EBW, 5 MW

- MSE CIF; polarimetry

- MSE LIF (J, Er, P)

- Magnetics (including fast), SXR

- Spec and Install RWM Supplies

- Passive plate mods

- Control system optimize

- 1 MW EBW (NTM and CD)

- EBW 3 MW

- 7 MW NBI, 6 MW HHFW

- 7 MW NBI, 3 MW HHFW

*MHD tools*

- rtEFIT

- Locked mode coils

- RWM coil install/commission

- Reflectometry

- Magnetics upgrades

- Internal RWM sensors

- Core MHD fluctuation
- diagnostics

- Fast ion profile diagnostics

- RWM control coil design

*MHD physics*

- Characterize NTM, island widths

- Include v in reconstruction

- Stablility vs. J(r), P(r), shape

- ELM type vs. shape, regime

- TAE & CAE similarity expts.

- Assess CD required for NTM stabilization

- Measure ELM structure

- Compare ELM data to theory

- Gap structure vs. A and q profile

- Error fields, rotation damping physics

- 21 weeks/year

***IPPA: 5 year***

***IPPA: 10 yr***

- Effects of  v shear on  limits

- RWM/wall interactions

- Stablility vs. shape, P(r), li

_**SUMMARY GOAL:**_**  Provide MHD understanding and diagnostics for development of feedback on shape, ********, J(r), RWM, EF, & NTM, using rtEFIT, heating, RWM coils, and CD to achieve high-beta, long-pulse operation with good MHD stability properties.**

- NTM suppression

- Comparison to theory

- RWM & EF active control, rotation control

- MHD-stable, high-
- long-pulse operation