Supported by Imaging the Pedestal Island Structure during the Application of 3D Magnetic Perturbations Office of Science D.J. Battaglia 1*, M.W. Shafer

Supported by

Imaging the Pedestal Island Structure during Imaging the Pedestal Island Structure during the Application of 3D Magnetic Perturbationsthe Application of 3D Magnetic Perturbations

Office ofScience

D.J. Battaglia1*, M.W. Shafer1,

E.A. Unterberg1, T.E. Evans2, D.L. Hillis1, R. Maingi1, J. Canik1, L. Roquemore3, F. Scotti3, B. Stratton3

1 Oak Ridge National Laboratory, Oak Ridge, TN2 General Atomics, San Diego, CA

3 Princeton Plasma Physics Laboratory, Princeton, NJ

* Participant in the U.S. DOE Fusion Energy Postdoctoral Research Program administered by ORISE & ORAU

NSTX / CMOD Pedestal WorkshopPPPL

September 8, 2010

NSTX / CMOD Pedestal WorkshopSeptember 8, 2010 2 / 13

Vacuum field calculations predict 3D magnetic perturbations open up resonant islands

• Stochastic edge region due to overlap of resonant islands– Believed to modify transport in the

H-mode pedestal, altering ELM stability

• Intact islands deeper into plasma– Islands are largest near x-point

due to flux expansion– Vacuum calculation: Islands are

typically 1 - 20 cm wide

• The vacuum model is sufficient only if the plasma response is negligible

T.E. Evans, et. al., Nuc. Fusion 48 (2008) 024002


Image the pedestal island structure during the Image the pedestal island structure during the application of 3D magnetic perturbationsapplication of 3D magnetic perturbations

• Motivation: How do 3D magnetic perturbations penetrate into a tokamak plasma (shielded or amplified)?– What mechanisms lead to the modification of ELM stability in the presence of

3D magnetic perturbations?

• Proposal: Measure position and width of any induced edge islands using SXR imaging and compare to models– Passive emission: can measure islands near X-point

• Flux expansion increases size of islands– Islands are stationary

• Cannot use temporal filters (FFT, SVD, etc.) • Need a large measurement area (islands won’t rotate into field of view)• Measurement can be slow (10s – 100s ms)

– VUV or SXR wavelengths to image islands inside the H-mode pedestal (Te > 1 keV) with acceptable signal-to-noise


Coordinated effort on NSTX and DIII-D to image the edge island structure

• SXR edge imaging diagnostics are planned for both NSTX and DIII-D– Planned diagnostics image SXR emission using

pinhole and scintillator conversion to visible– Projects share modeling and analysis resources

• Diagnostics motivated by results from TEXTOR-DED and NSTX– SXR pinhole cameras measure

spatial and temporal characteristics of rotating core MHD

– Sufficient sensitivity for frame rates up to 20 kHz


Present SXR camera system on NSTX measures large-scale core 3D structures

PRINCETON SCIENTIFIC INSTRUMENTSULTRA-FAST FRAMING CCD CAMERA

RELAY LENS

IMAGE INTENSIFIER TUBE

FIBER OPTIC WINDOWAND PHOSPHOR (P47)

INTERCHANGEABLE APERTURES AND BERYLLIUM ATTENUATION FOILS

BELLOWS, ELECTRIC BREAK AND GATE VALVE

NSTX BAY-K

The NSTX fast tangential soft x-ray camera


Data from SXR camera used to benchmark simple SXR emission model

115840(2007)

ModelComparison of CCD image and model (same

color scale)

NSTXL-mode 900 kA3 mm pinhole

20 kHz fps7.6 μm Be filter

Model is used to to optimize viewing geometry and estimate signal levels for new diagnostics

D. Battaglia, et al., RSI (2010), accepted


CMOS camera upgrade provides full-shot data record, aids potential edge-island measurements

PSI5 (CCD) Phantom 4 (CMOS) Phantom 7 (CMOS)

Max Frame Rate 500 kHz (64 x 64) 58 kHz (64 x 64) 121 kHz (64 x 64)

Exposure Fixed by fps Selectable Selectable

Max frames 300 65k 200k

Readout noise 20e RMS Probably larger Probably larger

Quan Eff (540 nm) 50% 22% 35%

Raw data SVD component SVD component 1 & 2 (x8)

Shot 140110 (Aug, 2010) 910 – 988 ms Phantom 4 at 37kHz


Focus for next year: Use existing NSTX system to test analysis and attempt edge measurements

• Optimize core imaging system for edge measurements– Thin filter and small pinhole– Take data during upcoming 2010 XPs that apply intermittent 3D fields

• Test analysis (i.e., inversions) on core data– Rotating islands are large, in region of low shear with excellent contrast

• Take data during 2011 campaign with dedicated XP for edge island imaging– Use modeling to optimize q95, plasma boundary, and 3D field phase to

increase probability of resolving any islands

• Design new SXR divertor imaging system for NSTX-U (2012)

NSTX / CMOD Pedestal WorkshopSeptember 8, 2010 9 / 13NSTX / CMOD Pedestal WorkshopSeptember 8, 2010 9 / 13


M.W. Shafer, et al., RSI (2010), acceptedNSTX / CMOD Pedestal WorkshopSeptember 8, 2010 10 / 13

NSTX / CMOD Pedestal WorkshopSeptember 8, 2010 11 / 13NSTX / CMOD Pedestal WorkshopSeptember 8, 2010 11 / 13


√



Summary of coordinated effort to measure edge islands on NSTX and DIII-D

• Determining existence, position and size of induced islands important for extrapolating RMP theory to ITER and beyond– Image 0.75 < ψN < 0.98 in X-point region

– Need flexible diagnostic that can measure islands in wide range of plasmas

• Coordinated SXR imaging effort on DIII-D and NSTX – Implement similar diagnostics in order to test models over a range of plasma

parameters

– SXR emission model used to optimize design and characterize measurement capabilities

– NSTX has existing core imaging system that will support analysis and may provide initial edge imaging data

– NSTX system installed soon after NSTX upgrade (2012 – 2013)

– DIII-D diagnostic design underway – first data Fall 2011

Documents

Supported by Imaging the Pedestal Island Structure during the Application of 3D Magnetic Perturbations Office of Science D.J. Battaglia 1*, M.W. Shafer