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Multi-energy SXR imaging for magnetically confined fusion studies

NSTX. Supported by. Multi-energy SXR imaging for magnetically confined fusion studies. College W&M Colorado Sch Mines Columbia U CompX General Atomics INEL Johns Hopkins U LANL LLNL Lodestar MIT Nova Photonics New York U Old Dominion U ORNL PPPL PSI Princeton U Purdue U SNL

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Multi-energy SXR imaging for magnetically confined fusion studies

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  1. NSTX Supported by Multi-energy SXR imaging for magnetically confined fusion studies College W&M Colorado Sch Mines Columbia U CompX General Atomics INEL Johns Hopkins U LANL LLNL Lodestar MIT Nova Photonics New York U Old Dominion U ORNL PPPL PSI Princeton U Purdue U SNL Think Tank, Inc. UC Davis UC Irvine UCLA UCSD U Colorado U Illinois U Maryland U Rochester U Washington U Wisconsin Culham Sci Ctr U St. Andrews York U Chubu U Fukui U Hiroshima U Hyogo U Kyoto U Kyushu U Kyushu Tokai U NIFS Niigata U U Tokyo JAEA Hebrew U Ioffe Inst RRC Kurchatov Inst TRINITI KBSI KAIST POSTECH ASIPP ENEA, Frascati CEA, Cadarache IPP, Jülich IPP, Garching ASCR, Czech Rep U Quebec Luis F. Delgado-Aparicio Princeton Plasma Physics Laboratory APS – April meeting, Washington, DC, USA February, 12-17, 2010

  2. In collaboration with… K. Tritz, D. Stutman, M. Finkenthal and D. Kumar Plasma Spectroscopy Group (PSG) The Johns Hopkins University (JHU) M. Bitter and K. Hill Princeton University Plasma Physics Laboratory (PPPL)

  3. Outline Introduction and motivation Main diagnostic and multi-energy technique Applications Diagnostic improvements and development of new edge and core systems Summary

  4. Magnetic fusion schemes = harsh environment Tokamak (toroidalnayakamera– magnitnayakatushka) Plasma measurements in harsh environment are quite a challenge Hot plasma temperatures Fast charged particles Strong plasma currents High magnetic fields & EM-noise 100’s keV – MeV ions MeV neutrons Gamma rays

  5. Motivation for the development of Multi-Energy Soft X-ray (ME-SXR) systems The motivation for the construction of ME-SXR arrays is the development of versatile diagnostics which can serve a wide range of MCF experiments for a number of critical simultaneous profile measurements. Useful in a wide variety of applications. Compared to magnetic measurements at the wall, the ME-SXR technique has advantages for low-f MHD detection, such as spatial localizationand insensitivity to stray magnetic fields. Evaluate discrepanciesbetween Thomson Scattering and Electron Cyclotron Emission diagnostics for electron temperature measurements

  6. Outline Introduction and motivation Main diagnostic and multi-energy technique Applications Diagnostic improvements and development of new edge and core systems Summary

  7. 1st prototype: multi-energy “optical” SXR array NSTX Top view Magnetic axis (core) L. Delgado-Aparicio, et al., RSI, 75, 4020, (2004). JAP, 102, 073304 (2007). PPCF, 49, 1245 (2007). NF, 49, 085028, (2009).

  8. “Description” of multi-energy/multi-color technique Synthetic X-ray Spectrum Probe the slope of the continuum:

  9. 1st prototype: multi-energy “optical” SXR array NSTX Top view Magnetic axis (core) L. Delgado-Aparicio, et al., RSI, 75, 4020, (2004). JAP, 102, 073304 (2007). PPCF, 49, 1245 (2007). NF, 49, 085028, (2009).

  10. Principle of the “optical” soft x-ray (OSXR) array Conversion of XUV emission to visible light X-rays from NSTX plasma (vacuum side) Fiber optic vacuum 20 mm CsI:Tl deposition window (FOW) Visible light system (airside) l=550 nm To discrete channels and light detectors (PMT, APD, Image intensifier) + (RC/TIA) amplifiers It’s a system that uses a fast (~1 s) and efficient scintillator (CsI:Tl) in order to convert soft x-ray photons(0.1<Eph<10 keV) to visible green light(~550 nm).

  11. Outline Introduction and motivation Main diagnostic and multi-energy technique Applications Diagnostic improvements and development of new edge and core systems Summary

  12. a) Plasma heating using RF waves • Laser-based TS system probes • the plasma every • ~ 16 ms. • Three ME-SXR emissivities appear to be different (different sensitivity to neand Te). • Fill in between Thomson scattering measurements!

  13. Te0~4keV in between Thomson Scattering time slices • Fill in between Thomson scattering measurements! • Error bars: 50-80 eV • Application to RF heating heat deposition studies. L. Delgado-Aparicio, et al., JAP, 102, 073304 (2007). L. Delgado-Aparicio, et al., PPCF, 49, 1245 (2007).

  14. b) Impurity transport is one of the challenges facing the current fusion research ITER tungsten walls For instance: Tungsten, is an attractive candidate as fusion wall material due to its very high melting point and high thermal conductivity. Nevertheless it can melt within one millisecond when in direct contact with the plasma.

  15. Adding an extrinsic impurity for transport studies

  16. Example: ion-gyroradiusscan at fixed q-profile Ne puff Ne puff Ne puff L. Delgado-Aparicio, et al., PPCF, 49, 1245 (2007).

  17. Reproducible properties in subsequent plasmas Plasma current, NBI heating and q-profile Controlled experiment reproduced elongation and triangularity

  18. Example of experimental and simulated SXR profiles L. Delgado-Aparicio, et al., Nucl. Fusion, 49, 085028, (2009).

  19. Penetration of impurities changed at high fields L. Delgado-Aparicio, et al., Nucl. Fusion, 49, 085028, (2009).

  20. Experimental diffusivity in good agreement with theoretical models Note large increase in Dneo and Dexp at r/a>0.8 L. Delgado-Aparicio, et al., Nucl. Fusion, 49, 085028, (2009).

  21. Convective velocity changes sign with BT VZ<0 at r/a>0.5 at low-field is anomalous ⇒ instabilities? L. Delgado-Aparicio, et al., Nucl. Fusion, 49, 085028, (2009).

  22. c) Resistive Wall Mode (RWM) research in NSTX RWM Sensors (Br) • RWM is an external kink modified by presence of resistive wall. • RWM Characteristics: • slow growth: G≲ 1/twall • slow rotation: fRWM≲ 1/2ptwall • twall~5-10 ms • stabilized by rotation & dissipation • High toroidal rotation passively stabilizes RWM at high-q. • RWM can affect both the outer and inner plasma. • Long-pulse, high-bN requires stabilization. Passive plates RWM Sensors (Bp) RWM active stabilization coils (exterior view) (interior view) S. A. Sabbagh, et al., NF, 46, 635, (2006).

  23. Actively-stabilized RWM plasmas show n=1 mode

  24. ME-SXR reconstructions indicate n=1 stable mode Fast SXR-based Te(R,t) measurements L. Delgado-Aparicio, et al., to be submitted, NF (2010).

  25. d) Pressure (b) -collapse and plasma recovery • Three ME-SXR emissivities have different sensitivity to ne and Te. • All arrays are sensitive to the peripheral and core Tecrash.

  26. Fast Te(R,t) estimate for b-collapse • 0th order approx. since b collapse is not axysimmetric. • Te,core~200 eV , Te,mid-radius~600 eV and Te,edge~300 eV. L. Delgado-Aparicio, et al., to be submitted, NF (2010).

  27. Outline Introduction and motivation Main diagnostic and multi-energy technique Applications Diagnostic improvements and development of new edge and core systems Summary

  28. Room for “desirable” improvement Increase spatial resolution (from present 4 cm to 1 cm) Particle transport at the edge: D~q2 Resolve edge plasma profiles Observe cooling of NTM O-points. Increase spectral resolution (# of SXR filters) Better constraint for Te(R,t) measurements. Thinner filters will allow measurements/imaging of pedestal & gradient region using continuum & line emission. Increase number of ME-SXR cameras for study of non-axisymmetric perturbations (3D-effects).

  29. Edge optical-based ME-SXR system under construction for NSTX (2010 run) • Benefits of optical-based SXR array • High spatial resolution (~1 cm) • Spatial oversampling • Filter/energy band versatility • Simple design and components K. Tritz (JHU)

  30. Alternative: edge diode-based fast (>10 kHz) system • Benefits of diode-based SXR array • High dynamic range • High bandwidth • Modular components • Compact detector and electronics K. Tritz (JHU)

  31. Core diode-based system for C-mod & NSTX Pilatus pixelated photon-counting detectors enable new diagnostics ~8cm • Pilatus: PIxelated Large Area detector. • Dectris - Pilatus 100k Module (~100k pixels) • 1. Sensor: Silicon (320 m) diode array. • 2. Pixels: 172x172m2(487x195) • 3. Parameters are adjustable on a per-pixel basis • Amplifier, shaper and lower level discriminator • Energy Range: 2.5 - 20 keV • Area: 8.4 x 3.4 cm2 • Count Rate/pixel: < 2x106 x-rays/s • Min readout time 2.54 ms • Latest version of Pilatus, called “EIGER” has 75 mm pixel size and ~24 kHz framing rate capability with only 1 ms dead time between frames. K. Hill & M. Bitter (PPPL)

  32. Pilatus “pinhole camera” can measure spatially resolved broad-band soft x-ray spectra, 2-20 keV Concept: • Energy resolution ~500 eV FWHM • Example: Emin= 2 keV, 2.5, 3, 3.5, 4, 5, 7, 10 and 14 keV. • Few columns (5) at low-energy, where count rate is high and many columns (50) at high-energy where count rate is lower. • Sum 487 rows vertically to form 49 spatial sightlines and improve statistics. Aplications: • Poloidal tomographic reconstructions. • Model Max. continuum + lines emission. • 2D picture of Te, Zeff, nmetals. • Electron thermal and impurity transport. • Easy to adapt to different tokamak sizes. K. Hill & M. Bitter (PPPL)

  33. Summary The motivation for the construction of ME-SXR arrays is the development of versatile diagnostics which can serve a wide range of MCF experiments for a number of critical simultaneous profile measurements. Useful in a wide variety of applications: a) RF heating, b) particle transport, c) thermal transport and d) a variety of MHD events. Compared to magnetic measurements, the ME-SXR technique has advantages for low-f MHD detection, such as spatial localization and insensitivity to stray magnetic fields. The use of thinner filters will allow imaging and measurements of pedestal & gradient regions using continuum and impurity line-emission. Recommend the use of few ME-SXR cameras (tangential/poloidal views) in multiple toroidal locations for study of non-axisymmetric perturbations.

  34. Acknowledgements (I) The Johns Hopkins University (JHU) Plasma Spectroscopy Group (PSG) K. Tritz, D. Stutman, M. Finkenthal and D. Kumar Princeton University Plasma Physics Laboratory (PPPL) R. Bell, M. Bitter, W. Blanchard, E. Fredickson, S. P. Gerhard, K. Hill, J. Hosea, R. Kaita, S. Kaye, B. LeBlanc, J. Manickam, J. Menard, C. K. Phillips, L. Roquemore, W. Solomon and B. Stratton Columbia University (CU) S. A. Sabbagh, J. Berkekey, J. Bialek and J. Levesque Oak Ridge National Laboratory (ORNL) R. Maingi, J.M. Canik and A.C. Sontag Nova Photonics H. Yuh University of Wisconsin-Madison F. Volpe

  35. Acknowledgements (II) • The Johns Hopkins University: Gaib Morris, Scott Spangler, Steve Patterson, Russ Pelton and Joe Ondorff. • Princeton Plasma Physics Laboratory: Bill Blanchard, Patti Bruno, Thomas Czeizinger, John Desandro, Russ Feder, Jerry Gething, Scott Gifford, Bob Hitchner, James Kukon, Doug Labrie, Steve Langish, Jim Taylor, Sylvester Vinson, Doug Voorhes and Joe Winston (NSTX). • This work was supported by The Department of Energy (DOE) grant No. DE-FG02-86ER52314ATDOE

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