1. 1 Imaging X-Ray Crystal Spectrometer with Fast Detector for Fast Measurement of Profiles of Ti and Intrinsic Plasma Rotation Velocity without Perturbation by Neutral Beam Injection K. W. Hill, M. L. Bitter, S.D. Scott Princeton Plasma Physics Laboratory, Princeton, NJ C. Bush ORNL S. G. Lee NFRC, Korea Basic Science Institute, Daejeon, Korea Presented at the NSTX 5-year plan mini workshop, PPPL, February 27 2007

2. 2 Imaging XCS has high throughput capability Proof of principle demonstrated on C-Mod, TEXTOR, and NSTX (z=+/- 40 cm) Saturation of gaseous detector at ~400 kHz count rate limited time resolution to > 100 ms –Masked crystal to transmit ~ 1% of available intensity from C-Mod –mtorr-l/s Ar puff in TEXTOR does not perturb P rad –In NSTX < 10 -8 torr Ar partial pressure on RGA, not seen on spectrometers 10-ms time resolution for ~30 chords should be possible on C-Mod with new detector –Pilatus detector, with 1 MHz PER PIXEL capability, solves detector saturation problem - 0.172 mm pixel size –Pilatus significantly alleviates radiation background problem Pilatus test at 3.1 keV successful on C-Mod –Spectra agree well with those from conventional detector –Peak x-ray rate 850 counts/pixel/s in 20-ms frame –Peak background rate 19 counts/pixel/s - unshielded ~8 cm +40 cm -40 cm

3. 3 New Imaging XCS is being constructed to measure full profiles of T i and v   on C-Mod Major upgrade to C-Mod physics capability Prototype for ITER XCS 2.4:1 imaging with 0.172 mm Pilatus pixel size vs 1:1 imaging with gaseous detector (0.5 mm FWHM) 3+1 PILATUS detectors ~30% toroidal fraction Fabricationis proceeding Be window -> MIT Crystal is in hand Detectors to be delivered April 4, 2007

4. 4 Greater demagnification could allow 80 cm of NSTX plasma to be imaged onto 2 Pilatus detectors MWPC resolution: 0.5 mm FWHM Pilatus pixel size: 0.172 mm Presently R=3.88 m and M=1/2.4 With R=1.8m, M=1/5.1 => 80 cm of NSTX imaged onto 16 cm - two Pilatus detectors Lateral spread of beam from crystal to center stack (CS) ~ 28 cm for 5- cm crystal Viewing beside CS would give ~30% component of v 

5. 5 Additional Slides

6. 6 Pilatus was proven to work at 3.1-keV He-like Ar energy at C-Mod Spectral Resolution w x y z w 3.949 Å x 3.966 Å y 3.969 Å z 3.994 Å A Pilatus detector was installed on one of the poloidally viewing Hirex spectrometers on C-Mod. Typically used at 8 - 12 keV for protein crystallography experiments

7. 7 PILATUS II spectra similar to HIREX spectra Spectra are for the same discharge but with slightly different views No indication of problems in the electrically noisy C-Mod environment Raw SpectraNormalized Spectra

8. 8 Windows allow observation and access Be window

9. 9 Main Points Proof-of-Principle of new imaging x-ray crystal spectrometer (XCS) for T i - 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 detector (<400 kHz) New pixelated silicon detector with better spatial resolution and 100,000 times higher count-rate capability removes limitations New detector tested on existing C-Mod spectrometer Imaging XCS being designed to measure full radial profiles of T i and v  on C- Mod, and Imaging XCS adopted for ITER Calculations of uncertainty in T i and v  measurements predict performance of C-Mod and ITER spectrometers

10. 10 Spherical crystal images spectra in vertical direction

11. 11 Imaging XCS can measure continuous profiles of T i and rotation-velocity without NBI Proof of principle demonstrated on C-Mod and NSTX (z=+/- 40 cm) Slow detector (400 kHz) limited time resolution to > 100 ms –Masked crystal to transmit ~ 1% of available intensity from C-Mod –Ar injection in TEXTOR does not perturb P rad –Ar in NSTX not seen on spectrometers, < 10 -8 torr partial P. on RGA New detector (Pilatus) with 1 MHz PER PIXEL capability should enable 10-ms measurements with ~ 30 chords on C-Mod Successful test of Pilatus detector at 3.1 keV x-ray energy on C-Mod New spectrometer using 4 Pilatus detectors is being constructed to measure full profiles on C-Mod Imaging XCS design adopted for ITER Greater demagnification (2.7:1 -> 5:1) would enable imaging of 80 cm of NSTX onto two Pilatus detectors ~8 cm Wavelength -> +10 cm -10 cm

12. 12 C-Mod imaging XCS demonstrated proof-of-principle +10 cm -10 cm Ar XVII w x y z

13. 13 Spectra from NSTX and C-Mod have good resolution NSTX C-Mod +10 cm -10 cm +40 cm -40 cm w x y z

14. 14 Spatially resolved T e, T i inferred from NSTX Ar XVII spectra

15. 15 PILATUS detector solves count-rate and resolution issues MWPC rate limit (400 kHz) limited time resolution to > 100 ms –Delay-line readout; all pulses pass through single electronics chain –Pileup rejection in TDC and interface latency –Less than 0.5% of available Ar line intensity used on C-Mod 8-cm diameter crystal masked down to 6 mm x 2 mm aperture Mylar foils reduced x-ray transmission by factor 1/8 –Background radiation on NB-heated tokamaks can saturate electronics PILATUS detector should enable 10-ms measurements –487 x 195 pixels, each 0.172 x 0.172 mm 2 –Analog and counting electronics on each pixel –Capable of count rates up to 1 MHz PER PIXEL –Can use full intensity available from C-Mod 30 spatial channels ~ 1 MHz per channel ~8 cm

17. 17 Pilatus detector has several attractive features 487 x 195 pixels Size 0.172 x 0.172 mm 2, ~ 2.5 times smaller then for MWPC Analog and counting electronics on each pixel Count rates up to 1 MHz per pixel Modular (5 x 12 array used on SLS) Readout time 2.54 ms => 10-ms resolution with full crystal Radiation hard (10 14 n/cm 2 ) Typical n/  background radiation -> negligible effect –Each pixel receives 1/100,000 background rate of full detector Worked well in the electrically noisy C-Mod environment

18. 18 PILATUS detector solves count-rate and resolution issues 2-D array of x-ray sensitive pixels - Each module is 487 x 195 pixels - Each pixel is 0.172 x 0.172 mm 2 Modular (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) Use of available intensity should allow 10-ms measurements for 30 radial channels Readout time down to 2.54 ms Worked well in the electrically & mechanically noisy C-Mod environment No problems with radiation-induced noise; each pixel has to deal with only 1/100,000 of total detector background noise Radiation hard (tested to 10 14 n/cm 2 ) ~8 cm

19. 19 PILATUS II Ar line time history similar to stored energy Measured with 20 ms time resolution PILATUS readout time now down to 2.54 ms Ar XVII resonance line, w, measured by PILATUS II detector

20. 20 Background rate low for unshielded PILATUS detector Peak background count rate = 14 counts/pixel/s Peak neutron rate = 5.8E13 n/s Peak x-ray rate > 1000 counts/pixel/s

21. 21 He-filled chamber houses crystals and detectors crystals detectors

22. 22 Hollow emissivity profiles can be inverted

23. ITER imaging x-ray spectrometer Design options for spectrometer location - Ex-port Better access Better shielding - In-port Wider view of plasma Choice will be based on: - Neutronics modelling - Detector radiation hardness - Detector background rejection Status of ITER x-ray spectroscopy, R Barnsley, IPR, India, 8th Feb 2006.

24. 24 Conclusions New imaging x-ray spectrometer developed for T i -, T e - 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-Mod –Suggests small area crystals suitable for ITER Detector count-rate limit and position-resolution issues solved by PILATUS II detector. Radiation-background issue greatly alleviated Imaging spectrometer being designed for C-Mod. –Detectors to be delivered in March-April => data in April Numerical and statistical analyses provide basis for estimating performance of imaging XCS on C-Mod and on ITER with neutron background.