IN-SITU TRACKING OF OIL FROM THE DEEPWATER HORIZON OIL SPILL USING SPECTRAL FLUORESCENCE
An in-situ spectral calibration method of Thomson ... Meeting... · An in-situ spectral calibration...
Transcript of An in-situ spectral calibration method of Thomson ... Meeting... · An in-situ spectral calibration...
An in-situ spectral calibration method of Thomson scattering diagnostics for severe radiation circumstances
1H. Tojo, 2I. Yamada, 2R. Yasuhara, 3A. Ejiri, 1J. Hiratsuka, 3H. Togashi, 3T. Yamaguchi, 1E.Yatsuka, 1T. Hatae, 2H. Funaba, 2H. Hayashi, 3Y. Takase, and 1K. Itami 1Japan Atomic Energy Agency, 801-1, Mukoyama, Naka 311-0193, Japan 2National Institute for Fusion Science, 322-6 Oroshi-cho, Toki 509-5292, Japan 3Graduate School of Frontier Sciences, The University of Tokyo, Kashiwa 277-8561, Japan
1st IAEA Technical Meeting on Fusion Data Processing, Validation and Analysis 1st of June - 3rd of June 2015, Nice, France 1
Data validations and analysis are essential for diagnostic developments
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accessible ! inaccessible !
lens
Experimental data are correct with enough calibrations.
Experimental data become incorrect.
So far In near future
Use of some special techniques (data acquisition and/or analysis) enables validating data.
This talk focuses on a novel calibration method (data validation) for Thomson scattering diagnostics
Contents
l Thomson scattering diagnostic and significance of calibrations
l Techniques of calibration method l Experimental demonstrations in TST-2 and LHD l Expected performance for JT-60SA, ITER, and
DEMO l Summary
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Measurements of board spectra are required in Thomson scattering (TS) diagnostic
Board spectrum in high Te
l Thomson scattering system providing electron temperature (Te) and density (ne) profile
l Scattered spectra at various Te
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blue shift
One of fundamental diagnostic for plasma control and study about plasma instabilities
Degradations in optical components have been reported in various tests and experiments
Increase in transmissivity loss
l Change in fiber transmissivity (neutron irradiation test)
[T. Kakuta et al., J. Nucl. Mater. 1277 307 (2002).]
l Change due to thin films on the vacuum window surface
[H. Yoshida et al., RSI 68, 256 (1997)]
T=T0exp[-α(λ)t] Decay constant α
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Transmissivity losses cause underestimation in Te
l Scattered spectra generated from YAG laser
Unknown degraded transmissivity causes underestimations of Te
scattering angle(θ)=125°
Degraded spectrum at 6 keV is close to 5 keV
Developments of calibration methods are necessary for such severe conditions
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Contents
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l Thomson scattering diagnostic and significance of calibrations
l Techniques of calibration method l Experimental demonstrations in TST-2 and LHD l Expected performance for JT-60SA, ITER, and
DEMO l Summary
To correct unexpected transmissivity loss, measurements using a standard light source is a good way
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l Standard light source in the measured position generates known spectrum
Adjustments of sensitivities between the wavelength channels are possible.
However, this method cannot be used under severe radiation condition, requiring some techniques.
[V1, V2, V3, … , V5] polychromator Output signals
transmissivities
I(λ)
known human access is needed!
The known spectrum from wavelength channels are measured.
5 wavelength channels
Principle of a double-pass scattering system
l Measurement using a double-pass scattering system
Scatteings must be measured separately.
Two spectra at the same Te can be evaluated.
l Two scattered spectra from the both scatterings
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1st pass
2nd pass
1st pass 2nd pass
6080
100120
Out
put [
mV
]
0 50 100 150 200Time [ns]
CH5 (1006-1030 nm)
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Data analysis: Signal ratios provide correct Te without knowing transmissivities
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l Measured photon counts at a spectral channel j
the ratio of remains.
Laser energy
Contribution from the spectrum
to be minimized
Measured ratio Theoretical ratio Unknown parameters
Transmissivity(assumed as a constant)
bandpass width scattering length
Te and E2Ls,2/E1Ls,1 are obtained without calibrations.
(No transmissivities !)
When taking ratio of Nm,j between θ = θ1 (first pass) and θ = θ2 (second pass),
Data analysis: Relative transmissivities can be derived using the obtained Te
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Measured photon counts at j
k=1(first scattering ) 2(second scattering)
l Chi-squared to infer relative transmissivities (neηjΔλj)
unknown
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Cj
can be written by a simple expression
Photon counts from a single pass
showing relative transmissivity between the wavelength channels (j=1,2,3…)
Previous work: Multiple laser method provides Te without knowing transmissivities
l Measurement using two lasers
l Two scattered spectra from YAG and RUBY
Two spectra at the same Te can be measured.
500 600 700 800 900 1000 11000.00.51.01.52.02.53.0
Spe
ctra
l den
sity
Wavelength [nm]
RUBY YAGTe = 5 keV, θ = 140°
[O.R.P. Smith et al., RSI 68, 725 (1996).]
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Scattered light must be separately measured.
The double-pass scattering system provide overlapped spectra at any Te
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l Double pass scattering l Multiple (two) lasers
Two spectra can be overlapped at any Te
Two spectra are far from each other. à Te range is limited.
Contents
l Thomson scattering diagnostic and significance of calibrations
l Techniques of calibration method l Experimental demonstrations in TST-2 and LHD l Expected performance for JT-60SA, ITER, and
DEMO l Summary
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TST-2 and Thomson scattering system
Laser system: YAG laser, 1064 nm, 1.6J Spectrometer: polychromator with 6 wavelength channels
・Plasma current:Ip ~ 100 kA ・Discharge duration: Δt ~ 40 ms ・ ne ~ 1019 m-3 ・Te < 400 eV
Position of Collection mirror
TST-‐2
Laser mirror
<Typical plasma parameters> R (major radius): < 0.38 m, a (minor radius):0.25 m, Bt (toroidal field)< 0.2 T,
optical delay
Measured signal ratio provides correct Te
l Signal ratio between the two passes
SN89151, R = 389 mm
960 980 1000 1020 1040 1060Wavelength [nm]
0
1
2
3
4
5
Ratio
of in
tegr
ated
sign
als
fitted line:Te,c = 196 ± 16 eV
0 50 100 150 200 250Time [ns]
CH5, signal
CH1
CH2
CH3
CH4
CH5CH6
CH4 and CH5 dominate Te determination
Conventional method Te = 205 ± 13 eV
single pass
The fundamental principle of this method was demonstrated.
LHD device and Thomson scattering diagnostic
first pass
second pass
delay optics to measure two scatterings separately
• Path length ~ 30 m • Temporal delay ~ 100 ns
LHD experiments already developed a double-pass scattering system to measure high Te and anisotropy in Te
l Purpose of these experiments Confirm the validity of this method for a higher Te range
I. Yamada et al., Journal of Instrumentation 7 C05007 (2012). K. Narihara et al., Review of Scientific Instruments 72 1122 (2001).
Te range < 2keV
Typical signals from the double-pass scatterings in LHD
l Typical signals Integrated area for Te calculations
No signal in the second pass (forward scattering) à not used
l Measured ratios and fitting results
Te = 746 eV
CH1
CH4
CH1 CH3
CH4 CH5
Te and the relative transmissivity measurements for a wide Te range have been demonstrated at LHD and TST-2
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LHD (NIFS)
TST-2 (Univ. of Tokyo)
Conventional method
Dou
ble-
pass
sig
nal-r
atio
met
hod
l Te measurements l Relative transmissivity measurements (LHD)
#116036, t=4500s
measured from standard light source Good agreements between the two
method for a wide Te range (two orders)
derived
Rel
ativ
e tr
ansm
issi
vity
(std
=CH
3)
H. Tojo et al., 23rd International Toki conference, Toki, Japan, 18th – 21st Nov. 2013
Cj/C
3
submitted to Fusion Engineering and Design.
Contents
l Thomson scattering diagnostic and significance of calibrations
l Techniques of calibration method l Experimental demonstrations in TST-2 and LHD l Expected performance for JT-60SA, ITER, and
DEMO l Summary
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JT-60SA device
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Toroidal Field Coils
Cryostat
Divertor
Central Solenoid Coils
Equilibrium Field Coils
Vacuum Vessel
NBI
Plasma Current Ip 5.5MA Toroidal Field Bt 2.25T Major Radius Rp 2.97m Minor Radius ap 1.18m Elongation κx 1.93 Triangularity δx 0.5 Safety Factor q95 3 Plasma Volume Vp 133m3 Flat Top 100 s
Total heating power (NB+ECH): 41MW
JT-60SA utilizes super conducting toroidal / poloidal coils, new vacuum vessel and new cryostat.
The double-pass scattering diagnostic will be utilized in JT-60SA
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Target spec. core edge
Radial spatial resolution
2 – 3 cm ~ 1 cm
Dynamic range 0.1 – 30 keV 0.01 – 10 keV
l port-P2 collection optics (core)
l port-P5 collection optics (high field side, edge)
Equatorial plane of JT-60SA
l ❑ port-P1 collection optics (low field side, edge)
Plasma
H. Tojo et al., RSI 81 10D539 (2010).
YAG laser
Spatial channel at the core (θ = 125°) was used to evaluate accuracy
Systematic errors in Te can be negligible with this new method
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l Procedure to evaluate calibration accuracy
Nm,1 = Ns,1 + Random No. (-σj,k – +σj,k )
Nm,2 = Ns,2 + Random No. (-σj,k – +σj,k )
Calculation of Te and Cj for 1000 times
Ideal scattered photon counts
Fiber w/o irradiation (standard)
irradiated fiber (measured in JT-60U)
l Assumption: unknown degradation occurs
unknown change
50
100
150200
Cou
nts
TRUE:10.00keV
GaussianCenter: 8.76keVSig (%): 2.08
8.0 8.5 9.0 9.5 10.0 10.5Electron temperature [keV]
050
100
150C
ount
sGaussianCenter: 10.00keVSig (%): 2.82
l Histograms of calculated
Conventional method
Double-pass (Signal ratio)
Data validity is confirmed.
Relative transmissivity losses can be determined with enough accuracy
Rel
ativ
e er
ror i
n C
j
1062.5–1065.5nm
Low signal intensity
500 – 660 nm
C4/1019
Cou
nts
Wavelength channel
l Distribution of relative transmissivity
Error
In JT-60SA, we are now planning to use this method for not only correct Te determination but also monitoring trasmissivity change.
Use of one port is a realistic design of Thomson scattering diagnostics in ITER and DEMO
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l Geometry of TS system using one port
Laser and collection optics are closed each other.
Calibrations using a double-pass scattering system in such wide scattering angle and high Te have not been considered.
few spaces for diagnostics
One port !!
Reflection mirror is necessary but need various analysis. (EMF, heat load, and oscillations)
high Te plasma
Optimization of wavelength channels are essential to measure both spectra.
400 600 800 1000Wavelength [nm]
0
1
2
3
4
Spec
tral d
ensi
ty
Forward (θ = 180°-160° = 40°)
Backward (θ = 160°)
Te = 40 keV
• The number of wavelength channels • Measured wavelength range
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(1) Optimize wavelength channels considering both scatterings
to find the best configuration for good accuracy
(2) Estimate Te and Cj accuracies using the optimized conditions
l Scattered spectra at wide scattering angle (θ1=160° and θ2=40°)
l Accuracy evaluations are performed by the following two steps
Configuration of wavelength channels must be carefully selected.
Calibration methods of ITER Thomson scattering system and parameters used in this study
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l Core measurements l Edge measurements
Calibration method G.S. Kursliev et al., Nuclear Fusion 55 053024 (2015).
E. Yatsuka et al., J. Plasma Fusion Res. SERIES 9 12 (2010).
Two or three lasers Two lasers
Accuracy
Scattering angle
Te range
θ < 160° θ < 140°
< 10 keV < 40 keV
Te cannot be evaluated in some Te range (2 lasers)
Low Te cannot be evaluated.
ß In this study, parameters for the core measurements are used to evaluate accuracies.
Scattering length (Ls) 63 mm
Scattering angle (θ) 160° Solid angle (Ωs) 2.72 msr Transmissivity except for polychromator (Topt)
35%
Target normalized radius ((R-R0)/a)
-0.1
Use of border enable finding good segments of wavelength channels
Err.(λ1,λ2,λ3) =σ Te
Te
Segment
averaged error over the Te range
# of channels (Nch): 5
The minimizations were performed by the simulated annealing method [2]. W. Press et al., Numerical Recipes in Fortran, second edition, Cambridge University Press (1992).
l Locations of the wavelength channels
l Error calculation
Optimizing to find the minimum error
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O. Naito et al., Rev. Sci. Instrum. 70 (1999) 3780.
0.01 0.10 1.00 10.00 100.00Te [keV]
0.01
0.10
Aver
age
rela
tive
erro
r
Optimized wavelength channels provide good accuracy (<10%) for Te = 0.5 – 40 keV , same level as three laser method
[λ1, λ2, λ3, λ4, λ5] = [921, 995, 1034, 1049, 1057 nm]
σ Te
Te= 5.3%
l Averaged relative errors in Te at Nch = 7
θ = 160°
l Scan over the No. of wavelength channels
Minimum error at Nch =7
(Nch)
No clear change for Nch > 5 is attributed to internal transmissivity losses in polychromators
3 4 5 6 7 8# of wavelgnth channels
0.000.050.100.150.20
Aver
age
rela
tive
erro
r R
elat
ive
erro
r in
T e
G.S. Kursliev et al., Nuclear Fusion 55 053024 (2015).
l ITER core TS
Two lasers
Three lasers
Rel
ativ
e er
ror i
n T e
0.1 1.0 10
0.1
1
Te [keV]
Relative transmissivities (calibration factors) can be measured
All wavelength channels can be measured in Te = 1 keV measurements. àpossible to monitor degradation even during experiments
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l Cj with expected error bars at Te= 1keV
l Relative errors of Cj at Te= 0.1, 1, 40 keV
Contents
l Thomson scattering diagnostic and significance of calibrations
l Techniques to overcome radiation conditions l Experimental demonstrations in TST-2 and LHD
l Applicability in JT-60SA l Expected performance for ITER and DEMO l Summary
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Summary
l An in-situ calibration method using a double-pass scattering system has been developed as a data validation technique. • Measurements of two overlapped spectra enable providing Te without
knowing the transmissivities. l Te and relative transmissivities have been successfully measured in
TST-2 and LHD (0.1 – 2 keV). l JT-60SA will utilize a double-pass scattering system
• The data validation is confirmed by numerical analysis showing the method suppresses a systematic error in Te.
l This method can be used in new type of Thomson scattering
diagnostic with a wide scattering angle and high Te. • Wavelength channels considering the forward and backward scattering
are optimized to provide high accuracy in Te. • Good accuracies (<10%) for a wide Te range are expected.
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