Thomson scattering system using ruby lasers

Spatial profile measurement of electron temperature (Te) and density (ne) of JT-60U plasma with high precision, resolution (8~22 mm), repetition (time interval: 0.002 to 2 second) and reliability.

[Detectors, Diagnostic Method]
Thomson scattering light of multiple ruby lasers obtained through collection optics, fiber optics and spectrometers is detected by 20x12 photodiode array (PDA) for high temperature core plasma and 144 photomultiplier tubes (PMTs) for low temperature edge plasma. Te and ne can be estimated through a non-linear least square fit of fully relativistic Thomson scattering spectrum to measured one reconstructed with the detector signals and calibration data.


(1) Parameters of ruby lasers, beam combiner, and beam optics

- Ruby Laser1
(PDS4, Lumonics)
Ruby Laser 2
(PDS2s, Lumonics)
Ruby Lasers
energy (J) 2.5, 5, 10, 2010
pulse interval (sec) 1, 2, 4, single4
pulse width (nsec) 3030
divergence (mrad) less than 300less than 300
polarization PS
diameter (mm) 2622
Beam Combiner
polarizer plate transmissionreflection
Faraday rotation angle 90 degreenone
total energy loss less than 5%less than 2%
Faraday rod
dimension (mm) 45f x 40length -
Verdet const. (min./Oe/cm) -0.242 at 632.8 nm-
solenoid coil
dimension (mm) 64f x 197length -
coil current (A) ~750-
number of turns 150-
minimum time delay against PDS4 (ms) -2
Beam Optics
number of bending mirrors 8, including three computer-controlled mirror gimbals for adjusting a single beam path line
focusing lens f/9.75m (beam diameter in vessel : 3~7 mm)
beam dump colored filter glass
energy monitor
components integrating sphere with ND filter and Fresnel lens, optical fiber PIN photodiode,
and gated ADC/memory
location just after beam combiner (input side) and just after beam dump (output side)

(2) Parameters of vacuum hardware, collection optics, fiber optics, and alignment system.

- Edge Plasma Measurement Core Plasma Measurement
Vacuum Hardware
window size (mm) 260f x 20t 260f x 30t
remote controlled shutter yesyes
viewing dumpfine ditched graphite fine ditched graphite
Collection Optics
type double Gaussian type lens Cassegrain type reflection mirror
effective field of view 18 degree46 degree
span of measurement (m) ~0.7~1.4
spatial resolution (mm) 8, 1622
F number 2.1-
focal length (mm) 340225.57
magnification -0.22-0.16
transmission 90%75%
solid angle (sr) 0.00650.0055
Fiber Optics
core/clad diameter ( mm)
180/200, quartz180/200, quartz
I/O bundle size (mm) 1.73hx1.59w and 0.80h x3.50w
3.50hx1.42w and 1.50h x3.40w
3.50hx1.07w and 1.60h x2.40w
NA ~0.3~0.3
length (m) 104104
transmission (He-Ne) 45~50%45~50%
measurement bundles 3030
alignment bundles 4(2x2)4(2x2)
Alignment System
for object field of collection fiber optics
parallel correction (Bt direction) -6.5 mm to +6.5 mm (0.001mm step) -5.5 mm to +5.5 mm (0.001mm step)
rotation correction on optical axis -6.5 degree to +6.5 degree (0.001 degree step) -3.5 degree to +3.5 degree (0.001 degree step)
function of regular monitor and
auto-recovery through direct and
quantitative procedure
for beam optics
remote correction through the following procedure:
(1) monitoring beam position on target screen detected by CCD cameras
(2) adjusting beam line to prescribed path through three computer-controled mirror gimbals

(3) Parameters of spectrometers and coupling optics

- Edge Plasma MeasurementCore Plasma Measurement
type Littrow x 1 (for PMT system) Littrow x 2 (for PMT & PDA systems)
F number 2.92.9
focal length (mm) 275275
grating (1/mm) 1200600
grating size (mm) 97x10097x100
output image size (mm)
60.0hx51.3w 60.0hx51.3w
spectral resolution of PMT 4~56
spectral resolution of PDA - 12
spectral range (nm) 550~688403~683
Fiber Bundles from Spectrometer to PMTs
core glassglass
clad diameter ( mm)
NA 0.570.57
length ( m) ~2.3~2.5
transmission 50~60%50~60%
number of bundles 130 ch [spatially 30 and spectrally (4~5) ] 60 ch [spatially 10 and spectrally 6 ]
Wavelength Cutoff Glass for Core Plasma Measurement by PDA System
width in dispersion direction- 4.0 mm for Ruby (694.3 nm)
4.0 mm for Ha /Da emission
3.8 mm for Hb /Db emission
Coupling Lens for Core Plasma Measurement by PDA System
field lens & collimator lens - achromat lens (made to order)
focusing lens - Noct Nikkor 58mm/F1.2S

(4) Parameters of PDA/PMT detector systems.

- PMT System for Edge &
Core Plasma Measurement
PDA System for
Core Plasma Measurement
Detectors photomultiplier tube
(R943/R1387, Hamamatsu Photonics)
2-D photodiode array (PDA) with
proximity focused type image intensifier
photocathode size(mm) 10 x 10 (GaAs)
34f (S-20) partially used for core measurement
25f (S-20, multialkali)
photodiode size (mm) - 17.42 x 13.84
quantum efficiency
photocathode 0.13(400~700 nm) for GaAs
0.16 (400 nm), 0.09 (540 nm) for S-20
0.16 at 400 nm, 0.03 at 694.3 nm
photodiode - 0.93 at 400 nm (peak wavelength of P-47)
phosphor decay time (nsec) - 210 (P-47), up to 5% residual intensity
ADC gate width (nsec) 125 (ADC)125 (Photocathode - MCP)
A/D conversion bits ( 11 in LeCroy 4301B) 12
A/D conversion time ( msec)(~10 in LeCroy 4301B) max. 3
data transfer time ( msec)- 480 (signal 240 ch + background 240ch)
number of elements
for edge measurement 130 PMTs = spatially 30 x spectrally (4~5) -
for core measurement 60 PMTs = spatially 10 x spectrally 6 240 ch /unit = spatially 20 x spectrally 12
dynamic range more than 105~103

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