1 Imaging X-Ray Crystal Spectrometer with Fast Detector for Fast Measurement of Profiles of Ti and...

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. ScottPrinceton Plasma Physics Laboratory, Princeton, NJ

C. BushORNL

S. G. LeeNFRC, Korea Basic Science Institute, Daejeon, Korea

Presented at the NSTX 5-year plan mini workshop, PPPL, February 27 2007

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 Prad

– 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

New Imaging XCS is being constructed to measure full profiles of Ti and von 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

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

Additional Slides

6

Pilatus was proven to work at 3.1-keV He-like Ar energy at C-Mod

Spectral Resolution

w x y z

w 3.949Å

x 3.966Å

y 3.969Å

z 3.994Å

• 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

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 Spectra Normalized Spectra

8

Windows allow observation and access

Be window

9

Main Points

• Proof-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 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 Ti and v on C-Mod, and

• Imaging XCS adopted for ITER

• Calculations of uncertainty in Ti and v measurements predict performance of C-Mod and ITER spectrometers

10

Spherical crystal images spectra in vertical direction

11

Imaging XCS can measure continuous profiles of Ti 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 Prad

– 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

C-Mod imaging XCS demonstrated proof-of-principle

+10 cm

-10 cm

Ar XVII

w x y z

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

Spatially resolved Te, Ti inferred from NSTX Ar XVII spectra

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 mm2

– 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

Pilatus detector has several attractive features

• 487 x 195 pixels • Size 0.172 x 0.172 mm2 , ~ 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 (1014 n/cm2)• 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

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 mm2

• 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 1014 n/cm2)

~8 cm

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

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

He-filled chamber houses crystals and detectors

crystalsdetectors

22

Hollow emissivity profiles can be inverted

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

Conclusions

• New 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-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.