# Presentation: 450338

## Macroscopic Stability (MHD) Physics in NSTX

_**Macroscopic Stability (MHD) Physics in NSTX**_

- Steven A. Sabbagh
*Columbia University*
- for the NSTX Research Team
**NSTX PAC Meeting 21**
- January 18th, 2007
- Princeton Plasma Physics Laboratory
- Princeton, NJ

***Culham Sci Ctr***
***U St. Andrews***
***York U***
***Chubu U***
***Fukui U***
***Hiroshima U***
***Hyogo U***
***Kyoto U***
***Kyushu U***
***Kyushu Tokai U***
***NIFS***
***Niigata U***
***U Tokyo***
***JAERI***
***Hebrew U***
***Ioffe Inst***
***RRC Kurchatov Inst***
***TRINITI***
***KBSI***
***KAIST***
***ENEA, Frascati***
***CEA, Cadarache***
***IPP, J******ü******lich***
***IPP, Garching***
***ASCR, Czech Rep***
***U Quebec***

***College W&M***
***Colorado Sch Mines***
***Columbia U***
***Comp-X***
***General Atomics***
***INEL***
***Johns Hopkins U***
***LANL***
***LLNL***
***Lodestar***
***MIT***
***Nova Photonics***
***New York U***
***Old Dominion U***
***ORNL***
***PPPL***
***PSI***
***Princeton U***
***SNL***
***Think Tank, Inc.***
***UC Davis***
***UC Irvine***
***UCLA***
***UCSD***
***U Colorado***
***U Maryland***
***U Rochester***
***U Washington***
***U Wisconsin***

- v1.4

## MHD physics research plan provides both focus and balance to address critical fusion program issues

- _Focused_ plan built from great progress
- NSTX milestones addressed
- High-level publications and invited talks in 2006
- _Balanced_ research plan addressing program needs
- 2 ITER issue cards
- 4 ITPA tasks
- Relevant physics for ITER, CTF, KSTAR

- _NSTX / ITER RWM control_

- _Advantage_: low aspect ratio, high  provide high leverage to uncover key tokamak physics (e.g. RWM control, rotation damping, high elongation)

- 0

- 1m

- 2m

## Solid Progress in MHD Research, now Addressing Advanced Goals

- Major Accomplishments
- RWM active stabilization at low rotation (ITER-relevant)	(Sabbagh, PRL **97** (2006) 045004)
- Observed plasma rotation damping by NTV physics 	(Zhu, PRL **96** (2006) 225002)
- Dynamic error field correction increases pulse length	(Menard, IAEA FEC 2006 OV/2-4)
- Unstable *n* = 1 – 3 RWM observed 	(Sabbagh, NF **46** (2006) 635)
- RWM critical rotation is a profile; depends on *q*, *A*, ***i* 	(Sontag, IAEA FEC 2006 EX/7-2Rb) 	(Reimerdes, PoP **13** (2006) 056107)	 (Sontag, PoP **12** (2005) 056112)
- Rotation + ***** effects may provide 1/1 mode saturation	(Menard, NF **45** (2005) 539)
- Stability vs. shape, *P(r)*, *l**i* studied 	 (Gates, PoP **13** (2006) 056122)	 (Sabbagh, NF **44** (2004) 560; Menard, PoP 11 (2004) 639)
*V***, flux-isotherm, MSE in equilibrium reconstructions	(Sabbagh, NF **46** (2006) 635)
- Emphasis on 2007 Milestone; preparing for 2009 Milestone

*R(07-2): “Characterize effectiveness of closed-loop RWM control & dependence on rotation using ITER-like control coils.****”***

*R(09-2): “Understand physics of RWM stabilization and control as a function of plasma rotation.****”***

## Dynamic error field correction (DEFC) sustains plasma rotation, increases pulse length
Combination of open + closed loop control yielded best result

- R (m)

- 120047

- t = 0.745s

- Bru

- Bpu

- Brl

- Bpl

- control
- coils

- Z (m)

- stabilizer plates

- Dynamic error field correction (DEFC) sustains plasma rotation, increases pulse length
- _Combination_ of open + closed loop control yielded best result

- _RWM active control system, rotation control installed_

- external
- n = 1
- Br sensor

- RWM
- sensors

- RWM
- sensors

- control off

- open-loop

- Open+closed loop

- (Menard, IAEA / APS 2006)

## RWM actively stabilized at low, ITER-relevant rotation

- First such demonstration in low A tokamak
- Long duration > 90/***RWM*
- Exceeds DCON ***N**no-wall* for *n* = 1 and *n* = 2
*n* = 2 RWM amplitude increases, mode _remains stable_ while *n* = 1 stabilized
*n* = 2 internal plasma mode seen in some cases
- Plasma rotation **** reduced by non-resonant *n* = 3 magnetic braking
- Non-resonant braking to accurately determine RWM critical rotation, ***crit*

- N

- IA (kA)

- Bpun=1 (G)

- Bpun=2 (G)

- /2 (kHz)

- 120047

- 120712

-  < crit

- 92 x (1/RWM )

- 6

- 4

- 2

- 0

- 8

- 4

- 0

- 1.5

- 1.0

- 0.5

- 0.0

- 20

- 10

- 0

- 20

- 10

- 0

- Control OFF

- Control ON

- (Sabbagh, et al., PRL **97** (2006) 04500. ; APS 2006 Invited; IAEA 2006 Post-deadline)

## Observed rotation decrease follows NTV theory

- R (m)

- TNTV (N m)

- _Observed rotation decrease follows NTV theory_

- measured
*dL**p**/dt*

- theory

- t = 0.360s

- 116931

- axis

_*n*__ = 3 applied field_
- _configuration_

- First quantitative agreement using full neoclassical toroidal viscosity theory (NTV)
- Due to plasma flow through non-axisymmetric field
- Computed using experimental equilibria
- Trapped particle effects, 3-D field spectrum important
- Viable physics for simulations of plasma rotation in future devices (ITER, CTF)
- Scales as ***B**2**(p**i**/****i**)(1/A)**1.5*
- Low collisionality, ***i*, ITER plasmas expected to have higher rotation damping

- (Zhu, et al., PRL **96** (2006) 225002.)

## Increased Ion Collisionality Leads to Decreased crit

- Plasmas with similar *v**A*
- Consistent with neoclassical viscous dissipation model
- at low **, increased ***i* leads to lower ***crit*
- ITER plasmas with lower ***i* may require higher degree of RWM active stabilization

- (K. C. Shaing, Phys. Plasmas **11** (2004) 5525.)

- 121083

- 121071

- (Sontag, et al., IAEA FEC 2006 paper EX/7-2Rb.)

*Further analysis and 2007 XPs aim*
*to uncover RWM stabilization physics*
*(FY09 Milestone)*

## Low A, high  favorable for NTM seeding / stabilization study

- Several modes (e.g. sawteeth*, RWMs**) seed low frequency MHD modes in NSTX
- Can led to soft beta limit, or plasma rotation reduction resulting in disruption
- Large *q *= 1 radius, high **, mode coupling at low-*A* makes seeding process easier
- NTM stabilization effects amplified at low-A (GGJ  ***3/2*) – NTM less deleterious
- NTM study planned 2007 - 2009
- Characterize modes: are these NTMs, TMs, or internal kinks?
- Exploit 12 channel MSE, reflectometer, fast multi-filter USXR capabilities
- Mitigate deleterious effects of modes

- n=1

- _Sawtooth excitation of n = 2_

- Sawtooth excites *n* = 2, but *n* = 2 can decrease post-crash

- *Fredrickson, et al., Bull. Am. Phys. Soc. 2004
- **Sabbagh, et al., NF **44** (2004) 560.

## Selected 2007 Experiments Address Near-Term Research Plan

- MHD ETG _Prioritized_ Experiments (from NSTX Forum – Dec 2006)
- Assessment of intrinsic error fields after TF centering	x	x
- RFA detection optimization during dynamic EF correction	x		x
- RWM active stabilization and optimization – ITER scenario	x 	x	x
- Assessment of RWM mode stiffness	x		x
- n = 3 magnetic braking w/ optimal n = 1 error field correction		x	x
- Fast Soft X-ray Camera (FSXIC) Imaging of MHD	x 		x
- Exploration of stability limits at high *I**N* with strong shaping	x		x
- B and q scaling of low-density locked-mode threshold at low-A	x	x 	x
- Measurements of plasma boundary response to applied 3D field			x
- RWM suppression physics at low aspect ratio	x 	x	x
- RWM D3D+ joint experiment – , , V() effects on crit()		x	x
- NTV dissipation physics: n = 2 perturbations and i 	x 	x	x
- Toroidal flow damping by island-induced NTV	x 	x	x
- Marginal island width of NTMs in NSTX	x 	x	x
- NTM threshold at low plasma rotation	x 	x	x

- 5
- days

- 10
- days

- physics

- ITER

- ST devel.

- (Red highlight = addresses NSTX milestone)

- (PAC charge question #1 criteria)

- {

- toroidal

## MHD Research 2007+ logically follows past results (I) 

- RWM control
- Reduced latency feedback; also artificially increase (ITER support)
- Added feedback sensors; examine/eliminate mode deformation
- Test optimized control techniques offline ‘07, implement ’09
- Plasma rotation
- Resonant damping, islands, damping mitigation for steady-state ops
- Further evaluation of NTV physics causing *v*** damping (ITER, etc.)
- Density control (ion collisionality) to support physics study
- RWM stabilization physics
- Present study shows ***crit* is profile, decreases with increasing ***i*
- Determine underlying physics of RWM stabilization (’09 milestone)
- Rotation/profile, ***i*, RWM active control beneficial (required) tools for study

- PAC request

## MHD Research 2007+ logically follows past results (II) 

- NTM
- Characterization of mode as NTM (vs. kink, or classical tearing)
- Improved diagnostics for mode determination / stability analysis
- MSE (in plan), multi-filter SXR, fast scanning profile reflectometer
- leverage low A to determine ** dependence of mode stability
- Utilize non-resonant magnetic braking for studies at low rotation
- Shaping / configuration
- Self-consistent current profile (** dependent) for steady-state ops
- real-time ** feedback; expanded MSE for stability studies
- High ** ~ 3 studies for CTF, passive plate coupling, RWM feedback
- Disruptions
- Continue low density locked mode scaling study (ITER support)
- Halo current evaluation (w/ new Rogowski coils) useful for ITER, CTF

## Proposed research plan for 2008+ addresses advanced physics understanding, ST, and ITER support

- Initial RWM active control         “optimized” RWM control
- RWM “critical rotation”         full understanding of stabilization physics
- Plasma rotation physics/initial control        full study, active control
- Initial NTM studies        full NTM characterization, mitigation studies
- NSTX config.         CTF configuration (shape, stabilizers)
- Disruption database studies        expanded disruption studies

_**Present**_

_**Planned**_

## Additional slides

## Rotation profile shape important for RWM stability

- Benchmark profile for stabilization is ***c* = ***A*/4*q*2 *
- predicted by Bondeson-Chu semi-kinetic theory**
- High rotation outside *q* = 2.5 not required for stability
- Scalar ***crit*/***A* at *q* = 2 , > 2 not a reliable criterion for stability
- consistent with distributed dissipation mechanism

- *A.C. Sontag, et al., Phys. Plasmas **12** (2005) 056112.
- **A. Bondeson, M.S. Chu, Phys. Plasmas **3** (1996) 3013.

- Sontag, IAEA FEC 2006 EX/7-2Rb