# Presentation: 845064

## XP452: RWM physics with initial global mode stabilization coil operation 

- Goals
- Alter toroidal rotation / examine critical rotation frequency
- Examine effect of applied DC error field
- Greater control in timing to reach critical rotation frequency
- Examine resonant field amplification (RFA)
- Determine RFA amplitude  / phase vs. N/Nno-wall
- Determine stable RWM mode damping
- Investigate MHD spectroscopy / possible dynamic stabilization
- Determine RFA amplitude / phase dependence on frequency
- Compute RWM damping rate and mode rotation frequency
- Apply modulation at 1/wall ~ 50 – 100 Hz to attempt stabilization

## Initial GMS coil XP targets have analogs in DIII-D MPs

- _Critical rotation frequency_

- _Resonant field amplification_

- A.M. Garofalo, *et al.*, *Nucl. Fusion* **42 (2002) 1335.**** **

- A.M. Garofalo, *et al.*, *Phys. Plasmas* **9 (2002) 1997.**** **

## DIII-D/JET RFA Similiarity XP recently conducted

- H. Reimerdes, *et al.*, *EPS Meeting 2004***.**** **

- _JET (error field coil and sensors)_

- Coil similar to NSTX
- RFA data yields
- amplitude / phase
- stable RWM damping rate
- mode rotation frequency

## XP452: RWM Physics with initial GMS coil - Run plan

- _	__Task__	__	__	__	__	__	__Number of Shots_
- 1) Critical rotation study / toroidal rotation alteration
- 	A) Vary DC applied current, phase 0 degrees:
- 	   (i) 2.5 or 3 NBI sources, longest possible pulse with ***N* / ***Nno-wall* > 1		1
- 	   (ii) Apply GMS coil current in four steps up to maximum allowed		4
- 	   (iii) 1or 2 NBI sources (***N* / ***Nno-wall* < 1) in above with high *V*** damping		1     sub
- 	B) Repeat above with phase 180 degrees				5     (11)
- 2) RFA study
- 	A) Vary ***N*, GMS DC coil current minimizing Vf damping + GMS coil current pulse:
- 	   (Apply 0.1s pulse during a period of approximately constant ***N*)
- 	   (i) Vary ***N* by using 1.5, 2, 2.5, 3 NBI sources				4
-                       (apply two GMS coil pulses per shot if discharge duration is long enough)
- 	   (ii) Repeat with one other GMS DC coil current conditions to vary *V*** 		4
- 	   (iii) Vacuum field shots (to eliminate eddy current effects of pulse)		4     (12)
- 3) MHD spectroscopy / dynamic stabilization
- 	A) Vary applied field modulation over DC GMS coil current minimizing *V*** damping:
- 	   (Apply modulation early (***N* / ***Nno-wall* < 1) through planned end of discharge)
- 	   (i)  3 NBI sources, vary applied field frequency 40, 30, 20, 12, 7 Hz		5
- 	   (ii) 2 NBI sources, vary applied field frequency				3
- 	B) 1 NBI source at GMS frequency that produced maximum RFA amplitude		1
- 	C) Apply modulation to DC offset that destabilizes RWM: three frequencies		3
- 	D) Vacuum field shots for each frequency used (if necessary)			5     (17)
- _4) (Optional) repeat the most successful trials above with an even parity perturbation   (optional 20)__	_
- 							         Total: 40

## Schematic Waveforms for GMS coil – XP452

- Aspect ratio in 110184 increased in time – vary A in similar way

- 6

- 0

- 0.1

- 0.2

- 0.3

- 0.4

- 0.5

- 0

- 0.5

- 1.0

- X10

- Amps

- 2

- 4

- 6

- (arb)

- Time (Seconds)

- Source B

- Source C – timing varies with Ip

- _Default NBI timing_

- Plasma current

- 0

- 0.1

- 0.2

- 0.3

- 0.4

- 0.5

- 0

- Source A

- 0.6

- 0.7

- 0.6

- 0.7

- GMS coil current

- 0

- 5

- -5

- x106

- 1

- 2

- (vary N, constant pulse)

- 3

- (vary frequency, constant N)

- Bt = 3kG plan

## Duration and Required / Desired Diagnostics

- XP could be completed in 1.5 run days
- Overlap with DIII-D/NSTX RWM Similarity experiment
- Required
- Magnetics for equilibrium reconstruction
- Internal RWM sensors
- CHERS toroidal rotation measurement
- Thomson scattering
- Diamagnetic loop
- Desired
- USXR diagnostic at two toroidal positions
- Toroidal Mirnov array
- MSE