Presentation on theme: "K. W. Hill, M. L. Bitter, S.D. Scott S. G. Lee"— Presentation transcript:
1 K. W. Hill, M. L. Bitter, S.D. Scott S. G. Lee Development of a High Resolution X-Ray Imaging Crystal Spectrometer for Measurement of Ion-Temperature and Rotation-Velocity Profiles in Fusion Energy Research PlasmasK. W. Hill, M. L. Bitter, S.D. ScottPrinceton Plasma Physics Laboratory, Princeton, NJS. G. LeeNFRC, Korea Basic Science Institute, Daejeon, KoreaA. Ince-Cushman, J. E. RiceMIT Plasma Science and Fusion Center, Cambridge, MACh. Broennimann, E. F. EikenberrySLS, Paul Scherrer Institute, Villigen, SwitzerlandR. BarnsleyQueen’s University Belfast and EFDA/JETVisiting researcher at ITER International Team, Cadarache, FrancePresented at the 16th International Toki Conference: Advanced Imaging and Plasma Diagnostics, December 5-8, 2006, Toki, Japan
2 Abstract * Supported by U.S. DoE Contract No. DE-AC02-76-CHO-3073 A high resolution imaging x-ray crystal spectrometer (XICS) is being developed for Doppler measurement of radial profiles of ion temperature, Ti, and toroidal rotation velocity on Alcator C-mod. The XICS consists of a spherically bent crystal and a 2D position sensitive x-ray detector, and provides x-ray spectra from highly charged ions from multiple sightlines through the plasma. The proof of principle of the IXCS was demonstrated by measurement of Ar XVII Ka spectral images at from +/- 8 cm of the plasma height in Alcator C-Mod and +/- 40 cm in NSTX. However, the time resolution was limited to values >100 ms by the ~ 400 kHz count-rate limit of the available 2D detector. A new silicon pixel array detector, the PILATUS II, with a count-rate capability of 1 MHz PER PIXEL, has been tested on C-Mod by recording spectra of Ar XVII at 3.1 keV, and should enable XICS measurements with time resolution < 10 ms. The detector test results and C-Mod XICS design and expected performance will be presented.* Supported by U.S. DoE Contract No. DE-AC02-76-CHO-3073
3 Main PointsProof-of-Principle of new imaging x-ray crystal spectrometer (XCS) for Ti- and rotation-profile (v) measurement previously demonstrated on NSTX, Alcator C-Mod, and TEXTOR; temporal and spectral resolution limited by the available 2d x-ray detectorNew pixelated silicon detector with better spatial resolution and 100,000 times higher count-rate capability removes limitations; detector tested on existing C-Mod spectrometerImaging XCS being designed to measure full radial profiles of Ti and v on C-Mod, and imaging XCS adopted for ITERCalculations of uncertainty in Ti and v measurements predict performance of C-Mod and ITER spectrometers
4 Imaging x-ray crystal spectrometer is versatile Measure time dependent profilesIon and electron temperaturePlasma rotationImpurity charge-state distributionAll plasma typesNeutral-beam injection not requiredSimple design, constructionSingle spectrometer measures full profileSpherically bent crystalTwo-dimensional imaging x-ray detectorASIC-based electronics and PC data acquisition
5 Spherical crystal images spectra in vertical direction
6 Spectra from NSTX and C-Mod have good resolution
7 Spatially resolved Te, Ti inferred from NSTX Ar XVII spectra
8 Lessons learned from operation of spectrometer on C-MOD and NSTX Initial Ar spectra with modestly high resolution obtained ( )MWPC detector resolution not quite adequate for Ti measurementHigher resolution detector now available will enable Ti measurementHigh signal and background count rates mitigated8-cm diameter crystal masked down to 6 x 2 mm2 areaGraded x-ray attenuators ~equalize count rate across radial profile; another factor of 1/8 reduction in count rateLimited shielding against hard x rays or gamma rays addedScattered x rays from crystal and holder reduced by aperturesSignificant count-rate limitation observed with MWPC kHzInherent detector count-rate limitPileup rejection in Time-To-Digital converter (TDC)Throughput limitation in electronic interfaceSolved by Pilatus II detector with count rate capability of 1 MHz PER PIXEL
9 PILATUS detector solves count-rate and resolution issues ~8.5cm2-D array of x-ray sensitive pixels- Each module is 487 x 195 pixels- Each pixel is x mm2Modular (build array of any size)Each pixel can handle a count rate of 1MHz- total count rate of previous 10 cm x 30 cm MWPC was 400 kHz (Factor of 100,000 increase)Readout time down to 2.54 msWorked well in the electrically &mechanically noisy C-Mod environmentRadiation hard (tested to 1014 n/cm2)
10 Shot-integrated He-like Ar spectrum from Pilatus detector shows excellent spectral resolution The Pilatus detector was installed on one of the poloidally viewing Hirex spectrometers.w x y zw3.949Åx3.966Åy3.969Åz3.994ÅSpectral Resolution
11 PILATUS II spectra similar to HIREX spectra Spectra are for the same discharge but with slightly different viewsNo indication of problems in the electrically noisy C-Mod environmentRaw SpectraNormalized Spectra
12 PILATUS II Ar spectra track stored energy Measured with 20 ms time resolutionPILATUS readout time now down to 2.54 msAr XVII resonance line, w, measured by PILATUS II detector
14 Imaging XCS configuration selected for C-Mod and ITER Because of the successful demonstration of the imaging XCS and the PILATUS II detector, an imaging XCS is being designed to measure full profiles of Ti and v on C-Mod, and the imaging XCS design has been selected for ITER.On ITER the background from neutron and radiation will increase the uncertainty in measurement of the line position and width.
15 C-Mod Imaging XCS is being designed for Ti, v profiles crystalsdetectors
16 Full plasma radial view and toroidal component planned for C-Mod 2:1 imaging3 PILATUS detectors~30% toroidal fraction
17 ITER imaging x-ray spectrometer Design options for spectrometer locationEx-portBetter accessBetter shieldingIn-portWider view of plasmaChoice will be based on:- Neutronics modellingDetector radiation hardnessDetector background rejectionStatus of ITER x-ray spectroscopy, R Barnsley, IPR, India, 8th Feb 2006.
18 Neutron shielding is a major factor in the design Horizontal cross-section of 40deg. SectorNeutron transport modelled by Atilla codeFlux at first wall ~ 1014 n/cm2.sStatus of ITER x-ray spectroscopy, R Barnsley, IPR, India, 8th Feb 2006.
19 Modeled neutron levels for the ITER upper port imaging crystal spectrometer. Status of ITER x-ray spectroscopy, R Barnsley, IPR, India, 8th Feb 2006.
20 Estimates of performance of C-Mod and ITER spectrometers Estimates of uncertainty in Ti measurement and minimum resolvable toroidal rotation velocity were made for C-Mod imaging spectrometer.On ITER, both x-ray continuum and fusion-neutron background will increase uncertainties in measurement of Ti and vtor. Numerical and analytic statistical analyses were made to quantify these increased uncertainties.
21 Numerical line position and width agree with equations N = counts in GaussianNexp = 5000No background = pixelsI = pixelss = pixelsI / sqrt(N) = pixelss = pixelsI / sqrt(2N) = pixelsGenerate normal dist with RANDOMNBin onto detector pixels with HISTFit Gaussian with GAUSSFITRecord line position and widthDo “experiment” “Nexp” timesCalculate moments for and
22 Statistical contributions to vtor and Ti error can be small C-Mod spectrometer2000 to counts in 10 msBackground not included1-3 km/s resolvable1 - 3% error in Ti
23 Position and width uncertainties increase with background approximately as expected Uncertainty for P/B=1 increases2x for position3x for widthSimulated Gaussian plus backgrounda=2.13, b=7.67, c=1.24, d=2.92Equations from I. H. Hutchinson,“Statistical Uncertainty in Line Shift andWidth Interpretation”PositionWidth
24 ConclusionsNew imaging x-ray spectrometer developed for Ti -, Te - and rotation-profile measurement on NSTX and Alcator C-Mod.Imaging concept verified on C-Mod, NSTX, and TEXTOR.Very small crystal area provided high count rates from C-ModSuggests small area crystals suitable for ITERDetector count-rate limit and position-resolution issues solved by PILATUS II detector.Imaging spectrometer being designed for C-Mod.Numerical and statistical analyses provide basis for estimating performance of imaging XCS on C-Mod and on ITER with neutron background.
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