NSTX SAS – GMS Mtg. 12/1/04

S. A. Sabbagh and J. E. Menard

NSTX RWM Active Feedback System Implementation Plan Discussion

NSTX Global Mode Stabilization Meeting

December 1st, 2004

PPPL

NSTX SAS – GMS Mtg. 12/1/04

Active RWM Stabilization Meeting Agenda

• Brief intro: applicable physics results

• Engineering update: Coil and power systems status

• Control System plan / tasks discussion

Goal: Demonstrate NSTX RWM active stabilization in 2005 !

NSTX SAS – GMS Mtg. 12/1/04

RWM stabilization system being installed for 2005 run

• RWM sensor array used in 2004 experiments

• 6 Br coils now installed on NSTX

• 3-channel switching power amplifier (SPA) on-site

• Real-time mode detection and control algorithm development in 2005 for feedback experiments

Physics design (VALEN code)

RWM coils

leads

NSTX SAS – GMS Mtg. 12/1/04

Recent RWM sensor capability essential for feedback

• Bp sensors measure unstable n=1-3 RWM mode rotation can

occur during growth growth rate, rotation

frequency ~ 1/wall• << edge > 1 kHz

what will be needed / desired in real time?

• Control system threshold / peak |Bp|

for feedback ability to track / alter

mode phase evolution focus on n=1 for initial

system (?)

growth w/o mode rotation mode rotation during growth

N

|Bp|(n=1)

(G)

(G)

(G)

|Bp|(n=2)

|Bp|(n=3)

Bp(n=1)(deg

)B

z(G) (f<40 kHz, odd-n)

n=2,3

n=1 no-wall unstable

n=1-3 no-wall unstable

0.22 0.24 0.26 0.28t(s)

-20-10010200

100200300010203001020304002040600246

0.18 0.20 0.22 0.24 0.26 0.28t(s)

-20-10010200

10020030001020010203001020300246

114147

FIG. 1

114452

moderotation

mode growth

NSTX SAS – GMS Mtg. 12/1/04

Pre-programmed current control of initial RWM stabilization coil pair adequate for CY2004 XPs

• Resonant field amplification increase at high N consistent with DIII-D Measured stable RWM damping rate 300s-1

• AC and pulsed n = 1 field (standing wave) Require traveling wave capability in 2005

• Ripple on applied pulse to be greatly reduced by new SPA supply

N

Nno-wall

Initial RWM stabilization coilsSensors

(n = 1)

0

0.2

0.4

0.6

4.0 4.5 5.0 5.5 6.0

Pla

sma

resp

/app

lied

field

plas

ma

Bp /

app

lied

Bp

NSTX SAS – GMS Mtg. 12/1/04

MHD XP Prioritization: NSTX Forum 9/22/2004 (mod2)• MHD XP Presentations requesting run time (RWM coil XPs highlighted)

Troyon Scaling at high IN, high , modified PF1A (Gates) 1.5 days(+1.5) Error field/locked-mode studies using RWM coils (Menard) 1.5 days(+.5) MHD spectroscopy of wall stabilized high plasmas (Sabbagh) 1.0 days Suppression of resonant field amplification at high N (Sabbagh) 1.5 days Active stabilization of the resistive wall mode (Sabbagh) 1.5 days(+.5) XP453: DIII-D/NSTX RWM similarity experiment (Sontag) 1.0 days XP428: Dissipation physics of the RWM (Sontag) 0.5 days(+.5) Onset and saturation characteristics of the 1/1 mode (Menard) 0.5 days Active control of rotation damping in RWM plasmas (Zhu) 1.0 days

• External kink and control of RWM (Okabayashi) (combined) XP414: Aspect ratio effects near the high p equilibrium limit (Sabbagh) 0.5 days Fishbone mode and the beam ion distribution function (Heidbrink) 0.5 days DIII-D/NSTX CAE similarity experiment (Bt = 6 kG) (Fredrickson) 0.5 days(+.5) Neoclassical tearing modes (Fredrickson) 0.5 days

• Piggy back Kinetic Instabilities – TAE/central shear/q(0) – L-mode (Fredrickson) 0.0 days

• Piggy backRun days: 19.5-20.5; (guidance: 8 days for 14 week run, 12 days for longer)

NSTX SAS – GMS Mtg. 12/1/04

Active RWM Stabilization – Discussion Topics• Engineering update: Coil and power systems status

Circuit flexibility for odd/even parity, single turn coil capability?

• Control System plan / tasks discussion Pre-programmed RWM coil capabilities

• capability for DC and AC pulses, AC frequency range, time-dependent phase

• capability of n > 1 field generation for plasma rotation damping

RWM sensor input• real-time implementation, decision of sensors to use, mode discrimination, noise filtering

Controller• desired capabilities, software needs

• control algorithm, flexibility for algorithm development, mode control vs. suppression

• noise rejection, n > 1 capability

• PCS or alternate standalone controller ?

Output to SPA• voltage / current feedback control options, ability to switch

Feedback system analysis tasks

• VALEN using present RWM coil, SPA specs, system latency, Bp sensors; other analyses

NSTX SAS – GMS Mtg. 12/1/04

Realistic time delay yields near-maximum stabilized N

• Insignificant change of maximum stabilized N over range of planned stabilization system time delay

VALEN (J. Bialek)

Crit

ical

tim

e de

lay

(ms)

NSTXexternal

coil

C (N – NNo-wall)/(Nwall – NNo-wall)

Planned NSTX systemtime delay range}

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0.0 0.2 0.4 0.6 0.8 1.0C_beta

Present PCS (FY04)

Upgraded PCS (FY05)