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Investigation of MHD Phenomena in NSTX Using a Fast Soft X-ray Imaging Camera

ORNL PPPL. Investigation of MHD Phenomena in NSTX Using a Fast Soft X-ray Imaging Camera. C. E. Bush (ORNL), B. C. Stratton, S. von Goeler, J. Robinson, L. E. Zakharov, E. Fredrickson (PPPL) D. Stutman and K. Tritz (JHU) and the NSTX Team 17th Topical Meeting on the

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Investigation of MHD Phenomena in NSTX Using a Fast Soft X-ray Imaging Camera

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  1. ORNL PPPL Investigation of MHD Phenomena in NSTX Using a Fast Soft X-ray Imaging Camera C. E. Bush (ORNL), B. C. Stratton, S. von Goeler, J. Robinson, L. E. Zakharov, E. Fredrickson (PPPL) D. Stutman and K. Tritz (JHU) and the NSTX Team 17th Topical Meeting on the Technology of Fusion Energy November 12-16, 2006 Albuquerque, New Mexico

  2. Goal, Motivation and Outline • Goal: MHD physics studies on NSTX using fast soft x-ray camera imaging. • Knowledge of fast particle behavior important in NSTX and ITER • SXR camera obtains a snapshot of mode and structure of MHD • Rich variety of MHD observed on NSTX: EPMs, NTMs and ELMs. • Important to ITER and future STs • Tools are available for effective data analysis and physics modeling.

  3. The Camera System is Optimized for Time and Spatially Resolved Observation of MHD • State of the Art PSI5 CCD Camera. • 300 frames of 64x64 pixel at up to 500 kHz • Image allows fast ID of mode and structure Important for NSTX, future STs and ITER. • Fast conversion of 1-5 keV soft X-ray to visible light • Uses P47 phosphor (plus signal gain) • Electrostatic image intensifier and lenses • demagnify image by 6:1; couples light to CCD • Pinhole camera for wide-angle tangential view • Remotely selectable pinholes: 1-5 mm dia • Remotely selectable beryllium foils.

  4. The Horizontal Field-of-View of the Camera Includes Nearly the Full Minor Cross-Section of Plasma Remotely Selectable Size: 1-5 mm • Optical axis inclined at 9º downward angle with respect to midplane • Full spatial structure of MHD Mode captured in each frame.

  5. System Installed on NSTX CCD camera NSTX bay K port Image intensifier inside magnetic shield Pinholes and Be foils

  6. Example of SXR Images of m/n=1/1 Mode • Camera frame • rate= 100 kHz • Mode frequency: • ~2.5 kHz • Images show 4 • times during one • mode period • m/n=1/1 mode • character clearly • seen • Shot #113778 t0+90 ms t0=175.060 ms t0+180 ms t0+270 ms

  7. SXR Diode Traces for a m/n = 1/1 mode Shot 113778 600 Ip(kA) 400 200 Shot 113778 0 20 Wtot(kJ) 10 0 1000 ISXR-center(arb) 0 ISXR-above-mid(arb) 0 0 0.1 0.2 0.3 0.4 Time (s)

  8. SXR Diode Traces for a Tearing Mode 600 400 3 ms Time of FSXIC Camera Ip(kA) 200 0 1200 800 ISXR-center(arb) 400 ISXR-below-mid(arb) 1200 800 400 800 ISXR-above-mid(arb) 400 0.173 0.175 0.177 0.179 Time (s)

  9. Camera Images Clearly Show m/n = 1/1 Modefor Shot 113778 • Camera frame rate: 100 kHz (for 3 ms)

  10. Singular Value Decomposition (SVD) of the Camera Data Separates Coherent Fluctuations in Space and Timefrom Background Noise • SVD identifies major components • 300 frames are recorded per shot, N = 300 • Matrix A(MxN) of N time series of M frames is decomposed into 3 matrices • A(MxN) = UWVT • Where: • U(MxN) - columns are spatial vectors (topos) • V(NxN) - columns are temporal vectors (chronos) • W(NxN)- a diagonal matrix (of weights)

  11. SVD for a m/n = 1/1 mode 107 The Singular Value Decomposition (SVD) yields the coherent fluctuaions in space “topos” U0-U4 and time “chronos” V0-V4 within a background of noise. U0, V0 => global time evolution of the Plasma Ref. S. Ohdachi et al. Rev. Sci. Instrum., 74 2136 (2003) 113778 U0 105 103 U1 V0 U2 V1 V2 U3 V3 U4 V4 0.175 0.176 0.177 0.178 Time (s)

  12. Time Evolution of m/n=1/1 Mode from SoftX-ray Diode Shows Mode Slowing Down SXR Signal Time (s) • Signal from conventional soft x-ray diode with radial midplane view • shows time evolution of m/n=1/1 mode (Shot 113355). • Later, will show of reconstruction of a camera image late in • the evolution of the mode (247.0 ms).

  13. Shot 113355: Tearing Mode • Camera frame rate: 10 kHz

  14. SVD Shows the m/n = 1/1 mode 107 The Singular Value Decomposition (SVD) yields the coherent fluctuaions in space “topos” U0-U4 and time “chronos” V0-V4 within a background of noise. U0, V0 => global time evolution of the Plasma Ref. S. Ohdachi et al. Rev. Sci. Instrum., 74 2136 (2003) 113355 U0 105 103 V0 U1 V1 U2 V2 U3 V3 U4 V4 0.22 0.23 0.24 0.26 Time (s)

  15. SXR Camera Image and Reconstruction at t=247.0 ms (shot=113355) using Cbbst Code Reconstruction Camera Image

  16. 072 122 139 244 232 227 Example: Multi-Mode (shot 113384)

  17. Summary • A state of the art fast soft X-ray imaging camera has been successfully used for MHD physics on NSTX • 300 frames at up to 500 kHz • Full cross sectional structure with excellent time resolution • Several MHD phenomena have been observed and studied • tearing mode, fishbones, sawteeth • m/n = 1:1 and higher observed • Tools for analysis and physics modeling are providing consistent results • Plan to use thicker foils for hotter NSTX Plasmas • Plan to study more complex MHD phenomena This work was supported by the US DOE, Contract No. DE-AC02-76-CHO-3073.

  18. EXTRAS

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