asipp asipp 1 high-resolution thomson scattering (tvts) diagnostics on ht-7 tokamak chunqiang shao,...

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High-resolution Thomson Scattering (TVTS) Diagnostics On HT-7 tokamak

Chunqiang Shao, Xiaofeng Han, Xiaoqi Xi, Junyu Zhao 2011-07-20

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ASIPPASIPPOutline

1 Thomson scattering

2 TVTS system on HT-7 tokamak

3 Improvements for this spring experiment

4 System Performance

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• Principle– laser injected into the plasma will be scattered by t

he electrons. While the velocity distribution of electrons is Maxwellian, the scattering power spectrum will be Gaussian.

– Due to the thermal motion of the electrons, the scattering spectrum is Doppler broadened: its width is proportional to the square root of the local Te.

– The number of scattered photons is proportional to the number of electrons in the scattering volume(means the ne in a fixed volume).

Thomson scattering

ee T /1

enarea

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• Hot plasma– In the relativistic, isotropic plasma, the spectrum wil

l shift to the blue side. and the shape factor of scattering power spectrum should be relativistic corrected:

Thomson scattering

])2/(sin8

exp[

])2/(sin82

71[

)2/sin()/2(2)(

220

22

220

32

0

02121

e

e

e

e

ee

kT

cm

kT

cm

mkT

cS

the relation between thespectrum's width and Te

For 1KeV electrons, there will be 10nm Drift.

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ASIPPASIPPOutline





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ASIPPASIPPTVTS system on HT-7 tokamak

Nd:YAG laser,1064nm,4.2J

reflector(99% at 523nm,very low at 1064nm)

focusing lens

collection lensfibers

HT-7

• image intensifier lens coupled with an EMCCD• a short exposure time for background light reduction • optimum SNR.

High throughput transmission grating spectrometer

~2.2Jfrequency multiplier

~1.8Jis mostly 532nm

~2.0Jefficiency of SHG>66%

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ASIPPASIPPFiber

• Superguide SPCH (From Fiberguide CO.)

90 + 10 fibers, 15m

SMA connectors 30 fibers for one spectrometer ,3m

Alignment fibers with the monitor and motorized fiber holder to avoid the optical misalignment

• Silica/hard clad, 0.8/0.83mm, NA of 0.39• buffer stripped

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ASIPPASIPPSpectrometer and I-EMCCD

• High throughput transmission grating spectrometer

An Improved CT spectrometer(transmission grating or refection grating)

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• The transmission of the trans.grating spectrometer we used

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• Image Intensifier lens coupled with an EMCCD– A short exposure time for background reduction and match up

to the pulse's width—— Image Intensifier (the switch of its power is controlled by a DG535)

– Optimum SNR ——EMCCD

I.I. : suply voltage-Gain Curve

(volt)

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• An Optimal Parameter– I.I suply voltage (4.85V, 8000times enlarge but the efficiency of the sc

reen is 0.01)– The Program binning(1*100, 3 Fibers, Corresponded to10mm)– EM Gain(24)

The Quantum efficiency curve of Andor Ixon DV885 EMCCD

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ASIPPASIPPOutline





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ASIPPASIPPImprovements

• This round:– Used the own reflectors (90% at 532 nm) and collection lens for T

V system.– Improve the efficiency of frequency multiplier to >66% with adjust

ing frequency-doubling crystal (The reflectors on EAST were coated for both 1064nm and 532nm, and the pulse we measured its energy contained both 1064nm and 532nm lights, so we didn't realize the content of the 532nm light was very low last round)

HT-7

Laser energy E (J) >1.85(532nm>99%)

Reflectors 3(for 532nm)

The peak of Transmittance of Collection Lens around 532nm

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• The Timing Sequence of system

(design a most optimal one for probing the background)

Timing Sequence

TS signal

Laser

Lens and fibers Spectrometer

Image Intensifier EMCCD

Agilent DG535

External trigger of laser

Master Controlopen gates

Acquisition time

The real TS signal time, width~15ns

get matched

Acquisition time for signal and background, width~20ns

The interval between the gates of signal and background was limited by the readout speed of EMCCD.

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ASIPPASIPPPolaroid

• The laser is linearly polarized light, so does the Thomson scattering and stray light(use Notch Filter to remove it).But the plasma background and linear radiation are Non-polarized light.

• Wire-grid polarizer– High Transmittance– High Temperature Resistance

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ASIPPASIPPPolaroid

• The test of efficiency of polaroid (reduce the background and the linearly radiation)

Use the Polaroid

linearradiation(Li)

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ASIPPASIPPOutline





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HT-7 （ Center-10mm~80mm ）

Laser energy(J) 2.2

Reflectors 3

Incident laser energy(J) 1.88

Solid angle of collection (mSr)

7.8

Scattering angle(°) 90

Scattering length(mm) 90

density(1019m-3) 2.5

Parameters

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Parameter: 4.2J(1064nm), after frequency multiplier(532nm)~2.1J, then three reflector, ~1.8J, The gate 30ns(pluse width~20ns), Spatial resolution~9mm 。

compared with

T-10 TVTS

TS signal

Use a filter to reduce the stray light

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ASIPPASIPPHow to get the TS s

pectrum

calibrate the Efficiency curve of system calibrate the Wavelength

The signal － The background

The TS signal

The detection part of system broaden the signal ( Characterized by Instrument Function )

Deconvolution

The real Spectrum of Thomson Scattering

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T7 Tokamak TVTS Efficiency curve(Sensitivity curve)

nm

a.u.

the spectrometer

lens

standard light source (Hg)

The Optical path for calibrating Efficiency curve (just the same path with the TV system)

Relative calibration

We used a known spectrum(Hg) to substitute the TS spectrum. But we didn't know the energy we collect from the standard light source.

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357.51nm761.41nm

Wavelength Calibration

the linear radiation of Lithium

Slit width was seted to 200μm to obtain a high wavelength resolution,and the notch filter was not used. Then we use the linearly radiation of Lithium to calibrate the wavelength

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the TS signal(the signal cut background)

Data Processing

the signal and background

These are the shape factor of scatterig power spectrum with red points and the fitting curve with bule line. It should be noted that the efficiency curve has been calculated here.

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Enlarge

Instrument Function(I.F.) ：use the stray light （ 532nm ） with the same factors of sys to obtain the I.F.

Instrument Function

Due to the convolution between the I.F. and the spectrum, the measured spectrum was been broadenedthe convolution formula: g(x)=s(x)*f(x) = ∫s(m)f(x-m)dm

For the both two are Gaussian functions, their convolution is still a Gaussian function, and its width has the relation:

g(x)f(x)s(x)

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21 eee gfS )( 2

1211 eee fgS

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IF broaden width ： 10.2nm(1/e high width) Filter bandwidth ： 17nm(Tavg<90% ： 37nm)

Wavelength range of Spectrometer ： 380nm-720nm

Te: ～ 50eV to ～ 5000eV

Transmission Band 1

Tavg > 90% 399 – 513 nm

Transmission Band 2

Tavg > 90% 550 – 709 nm

Notch Bandwidth

17 nm (typical)

The range of measurement

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ASIPPASIPPWith different density

The number of scattered photons is proportional to t

he local ne. We can see th

e intensity of the spectrum became stronger very clearly with the density grow up.

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~800eV ~1000eV

With and without the LHW

Green line:background time

10ms

Binning: 3 Fibers.Typical point:15th~17th fibers.Up from the center corresponded to:24mm~30mm

According to the temperature calculated we can see the effect of LHW heating. The TVTS sys. works!

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Te/eV

Z/mm

Temperature distribution

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ASIPPASIPPSummary

• We have firtly proved the high resolution Thomson Scattering (TVTS) Diagnostic System to be capable of measuring the electrons' temperature this spring HT7 experiment.

• We could give the Temperature distribution of the center of tokamak ( -10mm ~ 80mm ), and we chose 7 points have better data (0 mm ~ 60 mm, Spatial resolution~ 9mm).

•The range of temperature we can measure : 50eV ~5000eV

Acknowledgement

The TV system was started building 3 years ago by Xiaoqi Xi with the help of our tutor Junyu Zhao. They made the great contributions.

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Thank you for your attention!

asipp asipp 1 high-resolution thomson scattering (tvts) diagnostics on ht-7 tokamak chunqiang shao,...

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