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Appendix IPFN Instituto de Plasmas Fus Nuclear

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					ITER plasma rotation and Ti profiles from high-resolution crystal spectroscopy
              R Barnsley, L-C Ingesson, A Malaquias & M O’Mullane



                                     ADAS/SANCO (Atomic data and impurity transport codes)
                                     - Evaluation of suitable impurities and ionization stages.
                                     - Simulations of line and continuum emission.
                                     - Impurity contributions to Prad and Zeff.

                                     Integration into ITER
                                     - Vertical coverage with 2-D curved crystal optics and 2-D
                                     detectors.
                                     - Two or more graphite reflectors for the region
                                     inaccessible by direct views.

                                     Instrument performance
                                     - Optimization of sensitivity.
                                     - Simulation of signal-to-noise ratios.

                                     Data reduction
                                     - Study of quasi-tomographic derivation of rotation and Ti.


                            R Barnsley, Moscow, Nov 2003.                                 1
                                ITER-98 impurity profiles

R Barnsley, Moscow, Nov 2003.                    2
ITER profiles used for SANCO          ADAS / SANCO modelled line/continuum ratios
and signal modelling                  for H- and He-like Kr:
                                      - Chord-integrated ratios.
                                      - Reference case: f-Kr = 10-5 . Ne,   Prad ~ 700 kW.




                               R Barnsley, Moscow, Nov 2003.                              3
ADAS / SANCO results for f-Kr = 10-5 . ne:
- (Left) Ionization balance.                   (Right) Radiated power components and total.
- Prad ~ 700 kW (integrated over plasma volume).
- Zeff ~ 0.01
- Kr ionization stages down to ~ Kr 26+ have x-ray lines suitable for crystal Doppler spectroscopy.
- Most of the radiated power is not in the H- and He-like stages.


                                R Barnsley, Moscow, Nov 2003.                                  4
ADAS / SANCO results for f-Kr = 10-5 . ne:
- (Left) He-like Kr 34+, 1s 2-1s2p, 0.945 Å.            (Right) H-like Kr 35+, 1s-2p, 0.923 Å.
- Line radiation: photon/cm 3.s.
- Continuum: photon/cm3.s.Å.
- For signal calculations, Deuterium continuum was multiplied by Zeff 2 (~2.22).

                            R Barnsley, Moscow, Nov 2003.                                        5
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R Barnsley, Moscow, Nov 2003.   7
             ITER-98 x-ray spectrometer array (XCS-A)




                     5 lines of sight


• Provides good neutron shielding
• Access to plasma remote areas

- Signal attenuation (10% transmission)
- Reflection from graphite implies
  narrow bandwidth (~1%)
                                 R Barnsley, Moscow, Nov 2003.   8
                               X-ray discrete multi-chord option




The new system is integrated
at eport9 (16 LOS)
and uport3 (5 LOS)

Direct viewing lines without
graphite reflectors.


Two spectral arms are used
for each viewing line:

•One for He like Ar (edge)
•One for He like Kr (core)




                                 R Barnsley, Moscow, Nov 2003.     9
                  Multi-chord X-ray spectrometer option


                     ISO views of eport9




R Barnsley, Moscow, Nov 2003.                         10
                       Core views with continuous coverage on equatorial port 9



- Upper and lower systems give
continous coverage of the plasma
core r/a <~ 0.7

- Compatible with the option of
discrete lines of sight, by
inserting/removing shield.

- Reduced number of crystals and
Be windows

- Spatial resolution ~10 mm.

- Plasma vertical position control
with soft x-ray array.

- Plasma rotation measurements
can still be performed by two
parallel views.




                                      R Barnsley, Moscow, Nov 2003.               11
Two or more graphite reflector based lines of sight will complete plasma coverage

                            R Barnsley, Moscow, Nov 2003.                           12
                                Option for equatorial port
                                - Allows continuous imaging
                                - Minimises blanket aperture




R Barnsley, Moscow, Nov 2003.                            13
X-ray Views Referred to Mid-plane Profiles




          R Barnsley, Moscow, Nov 2003.      14
                       Spherically Bent Crystal




+ Allows plasma imaging
+ Improves S/N ratio with smaller entrance aperture and smaller detector
                           f s/f m = -1/cos(2B)
- No real focus for B < 45°
f s: Sagittal focus     f m: Meridional focus            B: Bragg angle


                       R Barnsley, Moscow, Nov 2003.                       15
                                   Toroidally Bent Crystal




                    A Hauer, J D Kilkenny & O L Landen. Rev Sci Instrum 56(5), 1985.



When combined with asymmetric crystal cut, gives considerable freedom in location of foci.



                                R Barnsley, Moscow, Nov 2003.                                16
2-D bent crystal
                                    The source is deep and optically thin.
(not to scale)
                                    A toroidally-bent crystal is required, to place the
                                    spatial focus in the plasma.
                                    Raw spatial resolution depends on:

                                    - Crystal height
                                    - Chord length in plasma
                                    - Chord-weighted emission
                                    - Optical aberrations and crystal bending
                                       Requires / ~ 10-3 (cf. / ~ 10-4 for -focus)


                                    For a crystal of height h:
                                    - r(Uport) ~ h/6          ~ 1 cm
                                    - r(Eport) ~ h/3          ~ 2 cm
                                    - r/r ~ 100 (optically)




                   R Barnsley, Moscow, Nov 2003.                                  17
R Barnsley, Moscow, Nov 2003.   18
                      Factors leading to choice of Bragg angle

                                                                       Detector




                                                                                  Crystal

Low Bragg angle (~30°) :
+ Reduced dispersion:  = /tan.
            a) Smaller first-wall penetration for a given bandwidth.
            b) Smaller detector movement for tuneable spectrometer.
+ Larger crystal radius for a given crystal-detector arm - helpful with long sight-line.
+ Greater choice of crystals for short wavelengths.
+ Detector more remote from port plug.
+ Reduced effect of conical ray geometry for imaging optics.
- Shallower input angle to detector - parallax problems with gas-chamber detector.
~ Requires a toroidal crystal for imaging at B < 45°


                               R Barnsley, Moscow, Nov 2003.                                19
                 Effect of input geometry on Johann sensitivity
Johann optics allow us to trade S/N with band-pass, while
maintaining peak sensitivity at the central wavelength



                                              Detector


                           Shield “a”



                                 “a”
                                                         Crystal       Crystal filling factor 
                                                                            a                  b
                                                                   1
                            Shield “b”
                                                                   
                                                                                           c

                            Shield “c”                                 1        2            3

                               R Barnsley, Moscow, Nov 2003.                          20
                  Parameters of the upper port imaging crystal spectrometers


The upper port system consists of two spectrometers, able to observe both H- and He-like lines of
Ar and Kr.
Toroidally bent, asymmetrically cut, crystals give enough free parameters to:
            1) Place the meridional (imaging) focus in the plasma       ~6m
            2) Place the sagittal (dispersion) focus in the port plug   ~3m
            3) Keep a compact crystal-detector arm                      ~1.3m


Crystal toroidal radii:   Sagittal ~ 4m          Meridional ~ 1m
Crystal aperture:         ~25 x 25 mm2           Spatial resolution > 25mm


Ion species               B range               Crystal                2d (nm)    range (nm)
Ar XVII / XVIII           26° -28°               SiO2(1010)            0.851     0.375 - 0.400
Kr XXXV / XXXVI           26.5° - 28.5 °         Ge(440)                0.200     0.090 - 0.096


Detector: Aperture ~ 25mm x 100mm                2-D spatial resolution < 0.1mm
Candidate detectors: Advanced solid state e.g. CCD, or advanced gas detector e.g. GEM.


                                     R Barnsley, Moscow, Nov 2003.                               21
R Barnsley, Moscow, Nov 2003.   22
Outline detector specification
Total detector height (~800 mm) = observed plasma height (~4 m) x demagnification (~0.2)
Individual detector height:         ~160 mm for 5 detectors
Detector width in  direction:      ~50 mm
Vertical resolution:                ~5 mm, for >100 resolvable lines of sight
Horizontal resolution:              ~0.1 mm
QDE / Energy range:                 > 0.7,        6 – 13 keV            (Uport also 3 – 6 keV)
Average count rate density:         ~106 count/cm2.s
Peak count rate density:            ~107 count/cm2.s
n- background count density:       ~104 count/cm2.s
                                    (flux of 10 6 n-/cm2.s, 10% sensitivity. 90% shielding)



Candidate detectors
This performance is typical of detectors in use or in development for high-flux sources such as
synchrotrons.
- Gas-microstructure proportional counters.
- Solid state arrays with individual pulse processing chain for each pixel.



                                      R Barnsley, Moscow, Nov 2003.                               23
Calculated signals for reference case:
- f-Kr = 10-5 . Ne     Prad ~ 700 kW         Zeff ~ 0.01
- Vertical image binned into 35 chords.
- Poisson noise added for 100 ms integration time.

                         R Barnsley, Moscow, Nov 2003.       24
Estimated Poisson signal-to-noise ratios based on counting statistics
- SNR ~ (Integral counts in line) / sqrt(line + continuum + n-background).
- Main noise source for data reduction is continuum, not n-background.
- A wide operational space is available between 10 -7 < f-Kr < 10-4.
- Uses a modest instrument sensitivity of 1.4 . 10 -7 cm2 per chord. (10x higher is possible).


                            R Barnsley, Moscow, Nov 2003.                                   25
             Fits to the simulated noisy raw data
             - Illustrative of the raw data quality – (obviously) not
             the best method of analysis.
             - Due to the narrower profile, chord-integral effects
             are less for H-like Kr than for He-like.
             - For r/a > 0.7, lower-ionized Kr ions or lower-Z
             impurities are required.
             - Under favourable conditions, a quasi-tomographic
             deconvolution is possible (L-C Ingesson et al).


R Barnsley, Moscow, Nov 2003.                                  26

				
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