zcotton-mouton polarimeter on chs - 核融合科学研究所 · 15 m hcn laser 2.45 10 11 3 2 ......
TRANSCRIPT
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“Advanced Imaging and Plasma Diagnostics”
Advanced Laser Diagnostics for Electron Density Measurements
K. Kawahata, T. Akiyama, R. Pavlichenko, K. TanakaK. Nakayama, S. Okajima1), S. Tsuji-Iio
National Institute for Fusion Science, Chubu University1)
IntroductionIntroductionCottonCotton--Mouton Mouton polarimeterpolarimeter on CHSon CHSTwo color laser interferometerTwo color laser interferometer
16th International Toki ConferenceCeratopia Toki, Toki, JAPAN
December 5 - 8, 2006
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Optimization of probe beam wavelength
LHD
Pneumatic
Windows
2.0
m
3.9 m 7.8 m
Waveguide
FIR LaserInterferometer
Isolator
Housing
Helical Coil
ReflectorsRetro-
Frame
6.0
m
CO2 LaserInterferometerHousing
10.6
m
Poloidal Coil
7.3 m
Proposed Polarimeter system for ITER
FIR Laser Interferometer installed on the LHD
On LHD, a 13-channel 119-μm CH3OH far infrared laser interferometer has been routinely operated for the precise measurements of the electron density profile .
The maximum densities of over 4 x 1020 m-3
were achieved by using pellet fueling and LID pumping.
Need of a short wavelength laser
λ:~ 50 μmA poloidal polarimeter system has been designed for
the measurements of current density profile in ITER.Proposed laser oscillation line is 119-μm CH3OH, but
the beam bending effect due to plasma density gradientis large.
Laser oscillation lines around 50μm are considered to be suitable from the consideration of the beam refraction and signal-to-noise ratio.
3/14
Choice of probe beam wavelength• The optimum wavelength suitable for
interferometry/palarimetry can be selected from the following considerationsPhase shift: Cutoff frequency: Beam bending effect:
(Example: Zo = 3.8 m, ne(0) = 1x1020/m3 leads to λ< 330 μm)
Mechanical vibration:
Faraday rotation:
Cotton-Mouton effect:
2161 1097.8)(sin λα oc
o
c
om n
nn
nn −− ×=≅=
2/12/1 )(2)(2πλ
απλ o
moo Z
ZZ
d ≤→=
mnZ oo3/1210 )(1016.1 −×≤λ
D. Veron
1
2
152.82 10 ( )z
zn z dzϕ λ−= × ∫
15 2 -3c 0 1.11 10 / (m )
n λ= ×
12 Lλφ π −ΔΔ =2
1
13 22.62 10z
znB dzλ−Ω = × ∫
11 3 22.45 10 eB n zε λ− Δ= ×
0
0.3
0.6
0.9
1.2
0
1
2
3
4
-1 -0.5 0 0.5 1
sh64359-1136-b120-a2020
n / no
Te(eV)
n /
no Te (keV)
ρ
n(0) = 4.2x1020m-3
T(0) = 0.87 keVβ(0) = 4.2 %
at B = 2.64 T
~50μm
k B
k B⊥
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Selection of Wavelength for ITER DiagnosticsDependence of phase difference by
CM effect on wavelength of laser
∫ ⊥−×=
−=
]m[]T[]m[]mm[104.2
]rad.[23-320
XOCM
dlBneλ
φφφO
X
Linearly Polarized Beam
Elliptically Polarized Beam B
Plasma
101 10210-2
10-1
100
101
102
103
104
Wavelength (μm)
Cott
on-M
outo
nP
has
e S
hift
(deg.
)
10.6 μm57 μm
119 μm
337 μm
52
5.7
Ne=1x1020m-3, B0=5.3T, L=4m
5/14
101 10210-1
100
101
102
103
Wavelength (μm)
Far
aday
Rota
tion (deg.
)
14
60
101 10210-2
10-1
100
101
102
Wavelength (μm)
Dis
plac
em
ent
(mm
)
4
0.9
101 102100
101
102
Wavelength (μm)
Phas
e S
hift
(Fringe
)
4320
4 mm0.9 mmDisplacement
52 deg.5.7 deg.Cotton-Mouton
60 deg.14 deg.Rotation
43 fringes20 fringesPhase
Measurement119 μm57 μm
Selection of Wavelength (continue)
∫ ⊥ dlBne23λ
02nλ
∫ dlBne2λ
∫ dlneλ
Ne=1019+1x(1-ρ2)1020m-3, B0=5.3T, L=4m, Ip=15MA
Ne=1x1020m-3, B0=5.3T, L=4m Ne=1019+2x(1-ρ2)1020m-3,
B0=5.3T, L=4m
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HCN laserCHS
SRG
Optics for multi-channel
Frame Laser light
CHS plasma
Optics for detection Basement
Acrylic resin pipe for waveguide
5950
CottonCotton--Mouton Mouton PolarimeterPolarimeter for Electron Density for Electron Density Measurement with HCN laser on CHSMeasurement with HCN laser on CHS
• Path length from the laser to optical frame is about 15 m.• Dielectric waveguide (φ 47 ID) made of acrylic resin is used to transmit laser beams.
The transmission efficiency is totally about 80%. • Detectors are schottky barrier diodes.
Upper part of optical frame
Optics box
15 m
HCN laser11 3 22.45 10 eB n zε λ− Δ= ×
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ω
ω ωb+O-mode
X-modePlasma Polarizer
π/4Detector
sin{( )t+ }ω ω φb o+
sin( t+ )ω φx
B
Measurement Method of CM effect
Phase difference due to Cotton-Mouton effect can be measured as a phase difference between probe and reference signal.
Free from amplitude variations due to oscillation instabilities of laser and beam deviation.
{ }[ ]{ } Const.)(cos
)sin()(sin
XOb
2XObprobe
+−+∝
++++=
φφω
φωφωω
t
ttIProbe signal:
Const.)cos( bref +∝ tI ωReference signal:CMφ=
S.E. Segre, Phys. Plasma 2 2908 (1995)
8/14
Optical Setup of CM Polarimeter with Int.
HCN
SRG
WaveguideBS
Wire Grid BS
CHS Plasma
BS
BS
λ/2 plate
ω
Polarizer
ω+ωb (1 MHz)
Detector
Reference
Interferometer
CM polarimeter
preamplifierBandpass Filter
Phase Counter(Interferometer)
ADC
sinωbt
sin(ωbt+φint.)
sin(ωbt+φCM)
• Beat signal of 1 MHz• Simultaneous measurement system of an interferometer
and a CM polarimeter with the same plasma center chord inorder to check the absolute value of CM phase difference.
This is almost same as the system proposed on W7-X.
9/14
0 50 100 1500
10
Time (ms)
n e, n
eCM
(1019
m-3
)
Response Time = 1 ms CM Polarimeter Interferometer
-
#126371Bt=1.76 T
NBI ECH Gas Puff
-Measurement Results
Phase difference due to Cotton-Mouton effect can be measured successfully.
The result of the polarimeter is almost consistent with that of theinterferometer except initial phase of the discharge. Amplitude of phase variations is within ±0.5 deg. with time constant of 1.0 ms.Interferometer shows fringe jump errors twice (t=135,144ms)
After improvement of cross and back talks
Cf. JET CM Measurement
CM 1deg.with 10t msδφ = Δ =
10/14
Development of a new two color FIR laser diagnostics
The Highest Output Power
CO2 Laser
FIR LaserStark Cell
0
2
4
6
8
10
00:00 05:00 10:00 15:00 20:00 25:00
Time (min.)
Las
er
outp
ut
(arb
it. unit)
CO2 laserCavity length: 3 mDischarge length: 1.25 x2Output coupler:ZnSe, 20 m radius curvatureGrating: 150 g/mm, blazed at 10.6 μm
FIR LaserCavity length: 2.9 mLaser tube: 25 mm inner diameterInput coupler: gold-coated copper M.Output coupler: Silicon hybrid coupler
57 μm laser output
cw FIR laser system
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Plasma
Two color FIR laser Interferometer
2
1
2
1
15
( )
2.82 10 ( )
z
ezc
z
ez
n z dzn
n z dz
πφλ
λ−
Δ =
= ×
∫
∫
57.2 μm is optimum value to avoid refractive effects in high density operation of LHD and future fusion devices.Both laser beams pass the same optical path in the interferometer without any optical path difference. One detector simultaneously detects the beat signals of both laser oscillation lines.
1E⊥2E
1E⊥2E⊥
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10 dBm, 500 kHz/divTwo color beat signals detected by Ge:Ga photoconductor.
Beat frequency;
0.6 MHz for 57 µm
1.2 MHz for 48 µm
The frequency of the beat signals can be changed with the cavity length and pressure of the FIR laser.
Detection of two-color beat signals
Ge:Ga DetectorYAG Laser
He-Ne Laser
FIR Laser
C.C.M.Monitor
48 μm 57 μm
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Demonstration of Two color FIR laser Interferometer
One detector simultaneously detects the beat signals of both oscillation lines, and each interference signal can be separated electrically – the 57.2 μm at 0.6 MHz and the 47.6 μm at 1.6 MHz.Two color FIR laser interferometer work was successful in demonstration of mechanical vibration compensation.
57 μmbeat signal
48 μmbeat signal
57 μmbeat signal48 μmbeat signal
57 μmbeat signal48 μmbeat signal
Detector (I)
Detector (II)
57-μm LaserInterferometer
48-μm LaserInterferometer
Optical path length was modulated by using a piezo-electric transducer.
PhaseCounter
Pie
zo D
rive
Vol
tage
(a.u
.)
0 100 200
-100
0
100
48 μm 57 μm 48-57 μm
Vib
ratio
nal
Dis
plac
emen
t (μm
)
Time (ms)
±20 μm
14
SUMMARY
(1) A Cotton-Mouton polarimeter has been developed on CHS, combining with an interferometer.
(2) The measurement results of the (2) The measurement results of the polarimeterpolarimeter showshowa good agreement with the interferometer.a good agreement with the interferometer.
(3) A two color FIR laser interferometer is under development for high density plasmas on LHD. Simultaneous operation at 57.2μm and 47.7μm is confirmed.
(4) (4) Two color beat signals are simultaneously detected by using a Ge:Ga photoconductive detector.
(5)(5) Two color FIR laser work was successful in Two color FIR laser work was successful in demonstration of mechanical vibration compensation.demonstration of mechanical vibration compensation.