NSTX IAEA FEC 2006 PD: S.A. Sabbagh 1 Supported by Office of Science S.A. Sabbagh 1, R. E. Bell 2, J.E. Menard 2, D.A. Gates 2, A.C. Sontag 1, J.M. Bialek.

NSTX IAEA FEC 2006 PD: S.A. Sabbagh 1

Supported byOffice ofScience

S.A. Sabbagh1, R. E. Bell2, J.E. Menard2, D.A. Gates2, A.C. Sontag1, J.M. Bialek1, B.P. LeBlanc2, F. Levinton3, K. Tritz4, H.

Yu3, and the NSTX Research Team

Resistive Wall Mode Active Stabilization in High Beta, Low Rotation Plasmas

Columbia UComp-X

General AtomicsINEL

Johns Hopkins ULANLLLNL

LodestarMIT

Nova PhotonicsNYU

ORNLPPPL

PSISNL

UC DavisUC Irvine

UCLAUCSD

U MarylandU New Mexico

U RochesterU Washington

U WisconsinCulham Sci Ctr

Hiroshima UHIST

Kyushu Tokai UNiigata U

Tsukuba UU Tokyo

JAERIIoffe Inst

TRINITIKBSI

KAISTENEA, Frascati

CEA, CadaracheIPP, Jülich

IPP, GarchingU Quebec

21st IAEA Fusion Energy Conference

16 – 21 October, 2006Chengdu, China

1Department of Applied Physics, Columbia University, New York, NY, USA2Plasma Physics Laboratory, Princeton University, Princeton, NJ, USA

3Nova Photonics, Inc., Princeton, NJ, USA4Johns Hopkins University, Baltimore, MD, USA

v1.0


Experiments in 2006 examined RWM physics and stabilization at ITER-relevant rotation

RWM active stabilization New control system installed RWM control demonstrated RWM actively stabilized in

slowly rotating plasmas

Plasma rotation control Sustained rotation by real-

time reduction of amplified error field

Reduced rotation by non-resonant magnetic braking

Passive plates Blanket modules PortControl Coils

Control Coils

ITER vessel

ITERplasma

boundary

0 1 2R(m)

Z(m

)

0

-1

-2

1

2

NSTX / ITER RWM control

Advantage: low aspect ratio, high provides high leverage to uncover key tokamak physics for ITER (e.g. RWM control, momentum dissipation)


2.01.51.00.50.0R (m)

-2

-1

0

1

2

120047t = 0.745s

Bru

Bpu

Br ext

n = 1

Brl

Bpl

controlcoils

Z (

m)

stabilizer plates Stabilizer plates for kink

mode stabilization

External midplane control coil closely coupled to vacuum vessel Similar to ITER port plug

designs

Internal sensors can detect n = 1 – 3 RWM Unstable n = 1 – 3 RWMs

already observed in NSTX (Sabbagh, et al., NF 46 (2006) 635.)

n > 1 RWM studied during n = 1active stabilization

RWM Active Feedback System Installed on NSTX


Dynamic error field correction (DEFC) increases pulse length in strongly rotating plasmas

No-wall limit

Rotating mode onset

control offopen-loop

Open+closed loop

Open-loop control of error field amplified by stable RWM yields higher rotation yields longer pulse

Combination of open + closed loop control yielded best result Rotation increase or

saturation at long pulse lengths - first time in NSTX

see OV/2-4 Menard


RWM stabilized at ITER-relevant rotation for ~ 90/RWM

First such demonstration in low A tokamak Exceeds DCON N

no-wall for n = 1 and n = 2

n = 2 RWM amplitude increases, mode remains stable while n = 1 stabilized

• Multi-mode research – connection to RWM stabilization in RFPs

(Sabbagh, et al., PRL 97 (2006) 045004.)0.40 0.50 0.60 0.70 0.80 0.90

t(s)

0.00.51.01.52.0

05

10152005

1015200.00.51.01.5

02468

Shot 120047

0

2

4

6

N

IA (kA)

Bpun=1 (G)

Bpun=2 (G)

/2 (kHz)

N > N (n=1)no-wall

120047

120712

< crit

92 x (1/RWM )

6420840

1.51.00.50.02010

02010

0

t(s)0.4 0.5 0.6 0.7 0.8 0.9







n = 2 internal plasma mode seen in some cases

(Sabbagh, et al., PRL 97 (2006) 045004.)

t(s)0.4 0.5 0.6 0.7 0.8 0.9

0.40 0.50 0.60 0.70 0.80 0.90t(s)

0.00.51.01.52.0

05

10152005

1015200.00.51.01.5

02468

Shot 120047

0

2

4

6

N

IA (kA)

Bpun=1 (G)

Bpun=2 (G)

/2 (kHz)

N > N (n=1)no-wall

120047120712

< crit

92 x (1/RWM )

1207176420840

1.51.00.50.02010

02010

0







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

(Sabbagh, et al., PRL 97 (2006) 045004.)

t(s)0.4 0.5 0.6 0.7 0.8 0.9

0.40 0.50 0.60 0.70 0.80 0.90t(s)

0.00.51.01.52.0

05

10152005

1015200.00.51.01.5

02468

Shot 120047

0

2

4

6

N

IA (kA)

Bpun=1 (G)

Bpun=2 (G)

/2 (kHz)

N > N (n=1)no-wall

120047120712

< crit

92 x (1/RWM )

1207176420840

1.51.00.50.02010

02010

0


0.9 1.0 1.1 1.2 1.3 1.4 1.50.0

0.1

0.2

0.3

0.4

Dotted curve: 120038, t = 0.535s

/

A

passively stabilized by rotation(120038, t = 0.535s)

experimental critical rotation profile

(120712, t = 0.575s)

activelystabilized

(120047t = 0.825s)

R (m)

crit/A

(axis)

(q=2)

Rotation reduced far below RWM critical rotation profile

Rotation typically fast and sufficient for RWM passive stabilization Reached /A = 0.48|axis

Non-resonant n = 3 magnetic braking used to slow entire profile The /crit = 0.2|q = 2

The /crit = 0.3|axis

Less than ½ of ITER Advanced Scenario 4 /crit (Liu, et al., NF 45 (2005) 1131.)

Rotation profile responsible for passive stabilization, not just single radial location see paper EX/7-2Rb Sontag

(120717, t = 0.915s)


0.9 1.1 1.3 1.5R (m)

TN

TV (

N m

)Observed rotation decrease follows NTV theory

3

4

2

1

0

measured

theoryt = 0.360s116931

axis

n = 3 applied fieldconfiguration

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, KSTAR) Scales as B2(Ti/i)(1/A)1.5 Low i ITER plasmas will have

higher rotation damping(Zhu, et al., PRL 96 (2006) 225002.)

see EX/7-2Rb Sontag


0.40 0.50 0.60 0.70 0.80 0.90t(s)

0

10

20

30

400

2

4

6

8

100

2

4

6

Shot 119755

45o (119761)

315o (119755) 290o (119764)

225o (119770)

negativefeedbackresponse

f

6

4

2

086420

30

20

100

N

/2 (kHz)

Bpun=1 (G)

0.50.4 0.6 0.7 0.8 0.9t (s)

feedback on RWM active feedback on n = 1 Control current relative

phase, f

Phase scan shows superior settings for negative feedback Pulse length increases Internal plasma mode seen

at f = 225, damped feedback system response

Gain scan also performed Sufficiently high gain

showed feedback loop instability

Varying relative phase shows positive/negative feedback


Poloidal n =1 RWM field decreases to near zero Radial RWM field increasing

Subsequent growth of poloidal RWM field Asymmetric above/below

midplane

Midplane radial sensor shows RWM bulging Upper/lower radial sensors show

decrease, while midplane sensor increases

Theory: may be due to stable ideal n = 1 modes becoming less stable (e.g. q evolution)

RWM may change form and grow during active control

0.55 0.59 0.63 0.67 0.71 0.75t(s)

02

4

6802468

10120

10

20

300

2

4

6

Shot 120048

0

2

4

6

Bp n = 1 lower

Br n = 1 lower

Shot 120048

0.590.55 0.63 0.67 0.71 0.75t (s)

6420

840

2010

0

420

6420

N

/2 (kHz)Bpu,l

n=1 (G)

Bru,ln=1 (G)

Br extn=1 (G)

N collapse

120048bulge

Future research will assess usingcombined sensors for optimization

= crit


Clear differences between RWM and internal plasma modeNo active stabilization

(RWM disrupts plasma)Active stabilization

(fast N drop, plasma recovers)

0.56 0.60 0.64 0.68

20

40

0

t(s)

0.5

1.0

1.5

0.0

Bp

n=

1 (

G)

20

40

0

Bp

n=

1 (

G)

US

XR

(a

rb)

edge

core 0.5

1.0

1.5

0.0

US

XR

(a

rb)

edge

core0.7240 0.7241 0.72420.7239

t(s)

0.66 0.70 0.74 0.78t(s)

Internal mode ~ 25 kHz Plasma rotation ~ 12 kHz (n = 2)

5 ms

20 s

120717

negativefeedbackresponse

120705

(USXR: K. Tritz JHU)

mode strongest at edge

0.56 0.60 0.64 0.68t(s)

0100

200

300

Shot 120705

010

20

3040

0.66 0.70 0.74 0.78t(s)

0100

200

300

Shot 120717

010

20

3040

0.56 0.60 0.64 0.68t(s)

0100

200

300

Shot 120705

010

20

3040

0.66 0.70 0.74 0.78t(s)

0100

200

300

Shot 120717

010

20

3040

n = 2

RWM n = 1

n = 1n = 2

n = 2 internalmode

for toroidal mode number:

0.2 0.4 0.6 0.8 1.0Time (s)

0

20

40

60

80

100

Freq

uen

cy (

kH

z)Shot 120717B() spectrum

1 2 3 4 5

0.6 0.8

20

40

0t(s)

(kHz)

n = 1n = 2


NSTX begins RWM active stabilization research relevant to ITER and beyond

First demonstration of RWM active stabilization in high , low A tokamak plasmas with significantly less than crit

In the predicted range of ITER Plasma response to feedback control demonstrated

Stability of n = 2 RWM demonstrated during n = 1 RWM stabilization n = 1,2 plasma mode sometimes observed; fast collapse, recovery

Plasma rotation reduction by non-resonant applied field; follows NTV theory Full NTV calculation yielding quantitative agreement to experiment Key component of RWM stability physics and dynamics; general

momentum transport relevance


Additional slides for poster follow


Work slides follow


NSTX begins RWM active stabilization research relevant to ITER, KSTAR, CTF

Passive stabilizers

(IVCC) (top)Passive stabilizers Blanket modules Port

Control Coils

Control Coils

ITER vessel

ITERplasma

boundary

0 1 2R(m)

Z(m

)

0

-1

-2

1

2

NSTX ITER KSTAR

KSTAR physics design supported by past design studies, present experiments in NSTX, DIII-D

In-Vessel Control Coils


Close connection to present experiments in NSTX impacts the KSTAR stability physics study

RWM active stabilization demonstrated in low rotation (ITER-relevant) plasmas (Sabbagh, et al., PRL 97 (2006) 045004)

KSTAR with co-NBI should have rotation control for experiments Precise plasma rotation control through neoclassical

toroidal viscosity (Zhu, et al., PRL 96 (2006) 225002)

n = 2 non-resonant magnetic braking possible rotation control option for KSTAR

Unstable resistive wall mode with toroidal mode number n > 1 observed (Sabbagh, et al., NF 46 (2006) 635)

May need to address n > 1 unstable modes in KSTAR at the highest beta or for certain equilibrium profile shapes

RWM critical rotation speed (H. Reimerdes, et al., PoP 13 (2006) 056107)

Dependence on aspect ratio, Alfven speed, ion collisionality – key research topic

NSTX IAEA FEC 2006 PD: S.A. Sabbagh 1 Supported by Office of Science S.A. Sabbagh 1, R. E. Bell 2, J.E. Menard 2, D.A. Gates 2, A.C. Sontag 1, J.M. Bialek.

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