Download Design of a spectrograph system for temperature

Spectrometric Diagnosis Group
in Plasma Chemistry and Physics
박영동1, 오수기2
1Department of Chemistry,
2Department of Physics,
Ajou University, Suwon 443-749, Korea
Vision/Mission
High Resolution Spectroscopy/Optical Diagnosis Group
Chemistry
Laser Spectroscopy
Molecular Beam Spectroscopy
Photoionization Spectroscopy
Physics
Interferometry Optics
Fabry-Perot
Atomic and Plasma Physics
Stength/Capacity
Chemistry
Molecular Spectroscopy
Theoretical Spectroscopy
Physics
Optics – Fourier optics, interferometry
Plasma Physics
Tokamak Plasma
The magnetic field lines inside the tokamak
chamber are divided into two groups:
the magnetic
separatrix surface
One forming nested closed
surfaces in the main
chamber without touching
the material wall
the “core” region
hot and dense
the other leading
to the divertor
chamber
the “scrape-off” region
cold and diluted
The heating effect of the electric current, joule-heating, is less than 50 million
degrees.
The need for additional heating has led to neutral beam heating.
CXS is an appropriate tool to measure the effect of neutral beam heating.
The Charge Exchange Recombination Spectroscopy (CXRS)
ion temperature
Doppler
broadening
poloidal and
toroidal
rotation speed
Doppler shift
impurity density
total intensity
H0 + C6+ → H+ + [C5+]*
charge exchange between neutrals in the
neutral beams and ions in the plasma
CXRS system in JT-60U
Doppler Broadened Data
Fabry-Perot interferometer
Mirrors
Photon counter
Piezo actuator
Design of a spectrograph system for temperature
measurement in Fusion Reactor using Doppler Broadening
Fabry-Perot interferometer system
Advantages
can achieve very high spectroscopic resolution
Disadvantages
1. Need very sharp filter to separate photones
outside of free spectral range
2. input beam should be stable during scan
period.
3. hard to employ large aperture system
McPherson Model 2062 2-meter focal
length f/14.1 Monochromator, $200,000
McPn CXRS
Grating
Groove Density (g/mm) 1200
Resolution** (nm)
0.005
Dispersion (nm/mm)
0.4
AJOU CXRS
50 cm
C
C
D
Focusing
Mirror
Grating 2
1800
gr/mm
1st order
Grating 1
1200
gr/mm
-1st order
Light
Source
Collimating
Mirror
Entrance
Slit
50000
Grating
Groove Density (g/mm)
1200+1800
Resolution** (nm)
0.007
Dispersion (nm/mm)
0.7
Intensity(a.u.)
40000
0.07 A FWHM fitted
experimental data
30000
20000
10000
0
531.95
532.00
Wavelength(nm)
532.05
AJOU CXRS
AJOU CXRS
AJOU CXRS
Ne I =529.8189 nm
Ne I =530.4758 nm
Ne I =528.0085 nm
FIG. 4. The measured Ne I spectrum lines by the two-grating
spectrometer equipped with the PhotonMax 512B CCD camera.
AJOU CXRS
Conventional
(80 ms, 1760
McPherson
spectrometer(80
ms)mm)
Ajou
two-grating
ms)
Two-grating
(96spectrometer(46
ms, 1720 mm)
Intensity (a. u.)
200
McPn CXRS
150
The Ajou system
is ~10 times better
in S/N for a
fraction of the cost
for ‘old’ system.
100
50
0
528.5
529.0
529.5
530.0
Wavelength (nm)
FIG. 5. The spectrum signals are obtained with the two-grating
spectrometer (triangle) and conventional spectrometer (square) for the
KSTAR plasma. It is shown that the S/N ratio of the two-grating
spectrometer is much larger than that of the conventional spectrometer.
1.6
(a)
Ti (keV)
1.2
0.8
Ajou
0.4
Conventional (1.70 s)
Two-grating (1.75)
0.0
1.7
1.8
1.9
2.0
2.1
2.2
2.3
McPherson
exposure(ms) 46
80
intervals(ms) 50
100
140
(b)
Vt (km/s)
105
70
Conventional (1.70 s)
Two-grating (1.75 s)
35
0
1.7
1.8
1.9
2.0
2.1
2.2
2.3
Major radius (m)
FIG. 6.(a) The ion temperature profiles and (b) toroidal rotation velocity
measured with both spectrometers for the KSTAR plasma shot number of
4364are compared.
ITER CXRS
optical fiber bundle
the viewing lines
diagnostic neutral beam
spectrometers
The Charge Exchange Recombination Spectroscopy (CXRS) system in an upper port plug for ITER.
Figure from http://www.rijnhuizen.nl/annual_report/2007/02_the_research_at_rijnhuizen/2_2.html
What’s Next?
JT-60U
Number of channels
Spatial resolution
toroidal : 23
toroidal : 5 cm
Time resolution
16.7 ms
poloidal : 36
poloidal : 0.8/1.5 cm
K-STAR
Number of channels
The more, the better
Time resolution
16.7 ms
1.
2.
3.
4.
target
128 channels
20 ms
Increase S/N by a factor of 3 or greater.
Needs a CCD detector at Ajou.
Design multilayer spectrometer systems.
A few researchers.(Grads, Post doc.)
올해도 복스러운 해가 되기를 기원합니다
[Spectroscopic principle for CXRS]
Neutral atom (H0) and impurity ion (Aq+) undergo a charge transfer that leaves the product
ion in an excited state.
H0 + Aq+ → H+ + [A(q-1)+]*
Aq+ = C6+. carbon is one of intrinsic impurities and they are fully stripped throughout the
plasma volume. Emissions are excited at wavelengths long enough for making accurate
Doppler broadening and shift measurements.
[Diagnostic Method]
One of heating beams NB #14 is used for this measurement (see figures). Due to the above
reaction, carbon ions near the neutral beam emit green light (529.2 nm at n=8-7 transition).
Doppler broadening (→ temperature), Doppler shift (→ rotation velocity) and its area (→
impurity density). According to the ionization balance, there are C5+ ions in the edge
region, which can emit at the same transition due to direct excitation by electrons (not by
neutral beams). Therefore it is important to separate the spectrum by beam excitation from
that by electron excitation. In order for this, CXRS system in JT-60U has an exclusive
optics for the background spectrum.
From Y. Koide, A. Sakasai, Y. Sakamoto, H. Kubo and T. Sugie, Rev. Sci. Instrum. 72, 119 (2001)