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Investigating Edge Island Structures in Tokamaks Under 3D Magnetic Perturbations

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13 diapositives · 263 Views · Sep 16, 2014

This study focuses on the impact of 3D magnetic perturbations on the pedestal island structure in tokamaks. Our goal is to understand how these perturbations penetrate the plasma and affect ELM stability. We utilize SXR imaging to measure the position and width of induced islands, particularly near the X-point where they are expected to be largest. This coordinated effort on NSTX and DIII-D aims to provide valuable insights into the behavior of edge islands, which is crucial for optimizing plasma confinement and preparing for future ITER applications.

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Investigating Edge Island Structures in Tokamaks Under 3D Magnetic Perturbations
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  1. Supported by Office of Science Imaging the Pedestal Island Structure during the Application of 3D Magnetic Perturbations 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, TN 2 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 Workshop PPPL September 8, 2010

  2. Vacuum field calculations predict 3D magnetic perturbations open up resonant islands T.E. Evans, et. al., Nuc. Fusion 48 (2008) 024002 • 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

  3. Image the pedestal island structure during the application 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

  4. 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

  5. Present SXR camera system on NSTX measures large-scale core 3D structures The NSTX fast tangential soft x-ray camera PRINCETON SCIENTIFIC INSTRUMENTS ULTRA-FAST FRAMING CCD CAMERA RELAY LENS NSTX BAY-K IMAGE INTENSIFIER TUBE FIBER OPTIC WINDOW AND PHOSPHOR (P47) BELLOWS, ELECTRIC BREAK AND GATE VALVE INTERCHANGEABLE APERTURES AND BERYLLIUM ATTENUATION FOILS

  6. Data from SXR camera used to benchmark simple SXR emission model Comparison of CCD image and model (same color scale) NSTX L-mode 900 kA 3 mm pinhole 20 kHz fps 7.6 μm Be filter 115840 (2007) Model Model is used to to optimize viewing geometry and estimate signal levels for new diagnostics D. Battaglia, et al., RSI (2010), accepted

  7. CMOS camera upgrade provides full-shot data record, aids potential edge-island measurements Raw data SVD component SVD component 1 & 2 (x8) Shot 140110 (Aug, 2010) 910 – 988 ms Phantom 4 at 37kHz

  8. 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)

  9. September 8, 2010 NSTX / CMOD Pedestal Workshop 9 / 13

  10. M.W. Shafer, et al., RSI (2010), accepted September 8, 2010 NSTX / CMOD Pedestal Workshop 10 / 13

  11. September 8, 2010 NSTX / CMOD Pedestal Workshop 11 / 13

  12. √ September 8, 2010 NSTX / CMOD Pedestal Workshop 12 / 13

  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