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HSX Thomson Scattering Experiment K. Zhai, F.S.B. Anderson, and D.T. Anderson HSX Plasma Laboratory University of Wisconsin-Madison, The HSX Thomson Scattering system is based upon the design of GA divertor TS system and is constructed in collaboration with the MST group. The system is capable of 10-point profile measurement and double pulse operation that can provide measurement of rapid change of plasma parameters. Large collection optics are used in the system to get enough scattered photons from the HSX plasma with a typical density of 110 12 /cm 3 . Ten identical fiber bundles with a transmission rate of 0.6 couple the collected photons to ten polychromators that disperse the collected light. Four wavelength channels in each of the ten polychromators are optimized for temperature measurement range from 10eV-2keV. A dedicated CAMAC system is used to record the data. The initial test results of the system will be presented. *Work supported by US DoE under grant DE-FG02-93ER54222
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HSX Thomson Scattering Experiment K. Zhai, F.S.B. Anderson, and D.T. Anderson HSX Plasma Laboratory University of Wisconsin-Madison, The HSX Thomson Scattering.

Dec 30, 2015

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Page 1: HSX Thomson Scattering Experiment K. Zhai, F.S.B. Anderson, and D.T. Anderson HSX Plasma Laboratory University of Wisconsin-Madison, The HSX Thomson Scattering.

HSX Thomson Scattering Experiment 

K. Zhai, F.S.B. Anderson, and D.T. AndersonHSX Plasma Laboratory

University of Wisconsin-Madison,

The HSX Thomson Scattering system is based upon the design of GA divertor TS system and is constructed in collaboration with the MST group. The system is capable of 10-point profile measurement and double pulse operation that can provide measurement of rapid change of plasma parameters. Large collection optics are used in the system to get enough scattered photons from the HSX plasma with a typical density of 11012/cm3. Ten identical fiber bundles with a transmission rate of 0.6 couple the collected photons to ten polychromators that disperse the collected light. Four wavelength channels in each of the ten polychromators are optimized for temperature measurement range from 10eV-2keV. A dedicated CAMAC system is used to record the data. The initial test results of the system will be presented.

*Work supported by US DoE under grant DE-FG02-93ER54222

Page 2: HSX Thomson Scattering Experiment K. Zhai, F.S.B. Anderson, and D.T. Anderson HSX Plasma Laboratory University of Wisconsin-Madison, The HSX Thomson Scattering.

Incoherent Thomson Scattering

• Plasma electrons get accelerated in laser field and then emit electromagnetic radiations.

-Shape of the scattered laser light spectrum: electron temperature

-Amplitude of the scattered light: density

• Small cross section, requiring a powerful monochromatic light source.

Page 3: HSX Thomson Scattering Experiment K. Zhai, F.S.B. Anderson, and D.T. Anderson HSX Plasma Laboratory University of Wisconsin-Madison, The HSX Thomson Scattering.

TS spectrum for an isotropic relativistic Maxwellian electron velocity distribution(Plasma Physics, Vol. 14, pp. 783 to 791 )

700 800 900 1000 1100 1200 1300

0.0

0.2

0.4

0.6

0.8

1.0

Nor

mal

ized

am

plitu

dewavelength(nm)

Te100eV Te300eV Te500eV Te700eV Te1keV Te2keV

Theoretical relativistic scattering spectrum for a plasma diagnosed with YAG (1060nm) with a scattering angle of 90 degree

)2(sin4

)2(sin441

/2

220

2

22

2

230

2

32

01

2

a

cY

a

cY

mKTa ee

in which, A is a constant and

Theoretical TS Spectrum

)),,,(exp(),,()2/sin(

A)( 0201

aYY

aF

Page 4: HSX Thomson Scattering Experiment K. Zhai, F.S.B. Anderson, and D.T. Anderson HSX Plasma Laboratory University of Wisconsin-Madison, The HSX Thomson Scattering.

Schematic Diagram of the HSX Thomson Scattering System

Nd:YAG laser Beam transportation HSX vessel Beam Dump

Fiber Bundles

Collection Optics

PolychromatorsAvalanche Photodiodes

Amplifier

Data AcquisitionControl System

Basic features: 10 points (20 cm radial range), double pulse (40-100us)

Page 5: HSX Thomson Scattering Experiment K. Zhai, F.S.B. Anderson, and D.T. Anderson HSX Plasma Laboratory University of Wisconsin-Madison, The HSX Thomson Scattering.

Interdependent Subsystems

• Laser system• Beam transportation and stray light control• Collection optics of the scattered light• Spectrum dispersion and detection system• Signal handling and data acquisition• Control system

Page 6: HSX Thomson Scattering Experiment K. Zhai, F.S.B. Anderson, and D.T. Anderson HSX Plasma Laboratory University of Wisconsin-Madison, The HSX Thomson Scattering.

A commercial YAG laser is used as the scattering source.

• 10ns and 1J output pulse at the fundamental wavelength of 1.06m

• Located on optical table in clean room

• Double pulse operation

Laser System

YAG Laser

trigger

F=3.05m focus lens

CCD frame grab camera

6.2m 3.05mCeramic disc

attenuator

Page 7: HSX Thomson Scattering Experiment K. Zhai, F.S.B. Anderson, and D.T. Anderson HSX Plasma Laboratory University of Wisconsin-Madison, The HSX Thomson Scattering.

Laser focus spot viewed on a ceramic disc with a CCD camera and video capture card.

Laser spot size relative to the distance with the focus (cm)

Laser Focus Spot Using a 3m Focus Lens

100 200 300 400 500 600

50

100

150

200

250

300

350

400

450

-10 0 10 20 30 400.8

0.9

1.0

1.1

1.2

1.3

x-width y-width Gaussian, 2=1mm Gaussian, 2=0.95mm

Position relative to focus (cm)S

pot w

aist

(m

m)

Page 8: HSX Thomson Scattering Experiment K. Zhai, F.S.B. Anderson, and D.T. Anderson HSX Plasma Laboratory University of Wisconsin-Madison, The HSX Thomson Scattering.

Beam Transportation and

Stray Light Control• Beam is guided by three laser mirrors and is focused to the HSX vessel

with an f=3.05m focus lens.

• A 1/2 waveplate is used to adjust the beam polarization.

• Entrance and exit tubes are specially designed with baffles to control the stray light.

• Entrance and exit windows are Brewster angle orientated fused silica windows.  

Page 9: HSX Thomson Scattering Experiment K. Zhai, F.S.B. Anderson, and D.T. Anderson HSX Plasma Laboratory University of Wisconsin-Madison, The HSX Thomson Scattering.

HSX TS Beam Transportation

YAG Laser

HW plate

mirror

focusing lens

Brewster window

Collection optics

Plasma region

dump

120cm

120cm

388cm 305cm

297cm

Total length from laser exit to focal point: 925cm

Lens focus length: 305cm

Page 10: HSX Thomson Scattering Experiment K. Zhai, F.S.B. Anderson, and D.T. Anderson HSX Plasma Laboratory University of Wisconsin-Madison, The HSX Thomson Scattering.

Entrance Tube and Exit Tube• Specially designed baffles prevent the stray light reflected from the

entrance tube wall from passing into the vessel directly. And the critical aperture will prevent the stray light originating from the entrance window from getting into the vessel.

• Fused silica windows are oriented at Brewster angle to the incident laser.

baffle

critical aperture

Page 11: HSX Thomson Scattering Experiment K. Zhai, F.S.B. Anderson, and D.T. Anderson HSX Plasma Laboratory University of Wisconsin-Madison, The HSX Thomson Scattering.

Layout of the collection optics with respect to plasma region

Observation vacuum window

Collection lens

Laser beam

Image planeof fiber bundlesurface

Gate valve

cmLcmn

Lnd

d

hf

EN

e

es

2,/101 312

0

10476,210

2ln2

2sin4

20

keVeVT

cm

kT

e

e

e

Collection Optics

• Collection solid angle: (2.9-3.1) 10-2

• Scattered photons:

Ns=(2.4-2.6)×104

• Spectrum width:

=17-246nm

Page 12: HSX Thomson Scattering Experiment K. Zhai, F.S.B. Anderson, and D.T. Anderson HSX Plasma Laboratory University of Wisconsin-Madison, The HSX Thomson Scattering.

•System Aperture: Entrance Pupil Diameter•Effective Focal Length: 16.70 cm (in image space)•Back Focal Length: 4.11 cm•Working F/#: 2.05•Image Space NA: 0.237•Object Space NA: 0.11•Paraxial Magnification: -0.459•Entrance Pupil Diameter: 10 cm•Entrance Pupil Position: 4.66 cm•Exit Pupil Diameter: 20.11cm•Exit Pupil Position: -40.03cm•Primary Wave: 1064 nm•Angular Magnification: 0.49

Optical Properties of the Collection Lens

Page 13: HSX Thomson Scattering Experiment K. Zhai, F.S.B. Anderson, and D.T. Anderson HSX Plasma Laboratory University of Wisconsin-Madison, The HSX Thomson Scattering.

Layout of the Collection Lens and Its Coupling to Fiber Bundles

40cm

45cm 11.56cm

19.01cm

Two-layer doublet: BK7 and SF1

Diameter:10cm

Page 14: HSX Thomson Scattering Experiment K. Zhai, F.S.B. Anderson, and D.T. Anderson HSX Plasma Laboratory University of Wisconsin-Madison, The HSX Thomson Scattering.

Fiber Optics

fiber length:7m

single fiber NA:0.24-0.25

Page 15: HSX Thomson Scattering Experiment K. Zhai, F.S.B. Anderson, and D.T. Anderson HSX Plasma Laboratory University of Wisconsin-Madison, The HSX Thomson Scattering.

Fiber Transmission Test

Expanded laser beam

Cylindrical lens

rectangularfiber end

circular fiber end

Viewing lens

detector

• Cylindrical lens linear focus the beam into fiber bundle at a given NA=0.24

• Viewing lens collect the transmitted lights at a given NA=0.25

Page 16: HSX Thomson Scattering Experiment K. Zhai, F.S.B. Anderson, and D.T. Anderson HSX Plasma Laboratory University of Wisconsin-Madison, The HSX Thomson Scattering.

Fiber Bundle Transmission Test Result

0 1 2 3 4 5 6 7 8 9 10 110.58

0.59

0.60

0.61

0.62

0.63

Ten fiber bundles corresponding to ten radial channels.

Tot

al tr

ansm

issi

on

• The transmission of ten fiber bundles is within the range from 0.625-0.585, comparing the ideal transmission of 0.63.

Page 17: HSX Thomson Scattering Experiment K. Zhai, F.S.B. Anderson, and D.T. Anderson HSX Plasma Laboratory University of Wisconsin-Madison, The HSX Thomson Scattering.

Coupling to Fiber Bundles

0 2 4 6 8 10-0.5

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0.5

Length unit: cm

Each square corresponds to an individual fiber bundle’s rectangular surface of 0.8mm*7mm

Las

er b

eam

imag

e on

the

fibe

r su

rfac

e

leng

th u

nit:m

m

Page 18: HSX Thomson Scattering Experiment K. Zhai, F.S.B. Anderson, and D.T. Anderson HSX Plasma Laboratory University of Wisconsin-Madison, The HSX Thomson Scattering.

• Ten identical polychromators designed and manufactured by GA.

• Four wavelength channels in each polychromator optimized for the measurement of the electron temperature range from 10eV to 2keV.

• Silicon avalanche photodiode detector ( EG&G C30956E ) and amplifier provided by GA are attached to the polychromators.

• Output from the amplifier range from 0.0 to –1.0 volt.

Spectrum Dispersion and Detection System

Page 19: HSX Thomson Scattering Experiment K. Zhai, F.S.B. Anderson, and D.T. Anderson HSX Plasma Laboratory University of Wisconsin-Madison, The HSX Thomson Scattering.

Polychromator Calibration

• The spectral calibration determines the response of the detection system to a radiation source of constant spectral emissivity.The result of spectral calibration will be used to build a look-up-table for electron temperature measurement.

Spectral calibration of each channels in a polychromator can be measured separately in the lab.

• Absolute calibration of the absolute sensitivity of the complete detection system can only be performed in site on HSX machine to get electron density measurement.

Page 20: HSX Thomson Scattering Experiment K. Zhai, F.S.B. Anderson, and D.T. Anderson HSX Plasma Laboratory University of Wisconsin-Madison, The HSX Thomson Scattering.

Experimental Setup for Spectral Calibration

Tungsten lamp

monochromator

Reference detector

Fiber opticspolychromator

Absolutely calibrated detector

DATA acquisitionComputer

control

Page 21: HSX Thomson Scattering Experiment K. Zhai, F.S.B. Anderson, and D.T. Anderson HSX Plasma Laboratory University of Wisconsin-Madison, The HSX Thomson Scattering.

850 900 950 1000 1050 1100-0.1

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

ch1 ch2 ch3 ch4 Te=50eV Te=100eV Te=200eV Te=500eV Te=1000eV te=1500eV te=2000eV

Wavelength (nm)

Spe

ctra

l res

pons

e fu

ncti

on a

ndT

S s

catt

erin

g sp

ectr

um f

or d

iffe

rent

ele

ctro

n te

mpe

ratu

re

Measured Polychromator (SN:39024-124) Spectral Response Function Together with the Scattering Form Factor S (Te, =90°)

Page 22: HSX Thomson Scattering Experiment K. Zhai, F.S.B. Anderson, and D.T. Anderson HSX Plasma Laboratory University of Wisconsin-Madison, The HSX Thomson Scattering.

0 500 1000 1500 20000

5

10

15

20

ratio ch2/ch1 ratio ch3/ch1 ratio ch4/ch1 ratio ch3/ch2 ratio ch4/ch2 ratio ch4/ch3

0 500 1000 1500 20000

20

40

60

80

100

ratio ch2/ch1 ratio ch3/ch1 ratio ch4/ch1 ratio ch3/ch2 ratio ch4/ch2 ratio ch4/ch3

Electron Temperature (eV)Rat

io o

f si

gnal

s in

dif

fere

nt s

pect

ral c

hann

els

Conversion Function Based on the Ratios of Signals in Different Spectral Channels

Page 23: HSX Thomson Scattering Experiment K. Zhai, F.S.B. Anderson, and D.T. Anderson HSX Plasma Laboratory University of Wisconsin-Madison, The HSX Thomson Scattering.

• A computer controlled CAMAC system dedicated for HSX Thomson scattering experiment.

– A GPIB crate controller from KINETICS SYSTEM is used to communicate between the CAMAC crate and the computer.

– The signal is recorded by gating Leroy Model 2250 charge integrating digitizer. These digitizers have a sensitivity of 0.5pC/count, with a range of 512 counts.

– LabView program ready.

• System synchronized with HSX timing with a NI6602 timing card and a DG535 digital pulse generator from Stanford Research Systems.

– LabView program ready.

Signal Handling DATA System and Control system

Page 24: HSX Thomson Scattering Experiment K. Zhai, F.S.B. Anderson, and D.T. Anderson HSX Plasma Laboratory University of Wisconsin-Madison, The HSX Thomson Scattering.

Overview of the Thomson Scattering Timing Sequence During HSX Discharge

Plasma time

Laser emission

Scattering light

Digitizer gating

0 500 1000~800-850 Time:s

Stray light background

HSX master trigger TS timing Laser trigger

Digital delay

Gating digitizerPersonal computer LabVIEW control

Page 25: HSX Thomson Scattering Experiment K. Zhai, F.S.B. Anderson, and D.T. Anderson HSX Plasma Laboratory University of Wisconsin-Madison, The HSX Thomson Scattering.

Acquired Signal During a Thomson Scattering Experiment

Type of signalSample

realizationSampling time

Stray light 1~300-400ms, before plasma breakdown

Scattering light 1~800-850ms, during

plasma discharge

Pedestal subtraction

Fluctuation(noise)5 After plasma

Page 26: HSX Thomson Scattering Experiment K. Zhai, F.S.B. Anderson, and D.T. Anderson HSX Plasma Laboratory University of Wisconsin-Madison, The HSX Thomson Scattering.

• Weighted average of electron Temperature and its error:

Computation of the Weighted Average Electron Temperature

2

1

2,,,

2

12

,,

1

1

qfinaleqesyste

q qestate

TTN

T

TT

,where

• Error analysis

212

,2

,2

, )( jscjstrayjbgjC

i i

j jq

C C

C CR

min max,

)()(5.0 minmax, qeqeqe RTRTT

1. Uncertainty of the scattered signal in spectral channel j,

2. Upper and lower limits of spectral channel signal ratio,

3. Electron temperature range associated with the ratio limits

systestatefinale

q qe

qe

qqe

finale

TTT

T

T

TT

,,,

2,

,

2,

,

5.05.0

)()/1(

1

Page 27: HSX Thomson Scattering Experiment K. Zhai, F.S.B. Anderson, and D.T. Anderson HSX Plasma Laboratory University of Wisconsin-Madison, The HSX Thomson Scattering.

Flow Chart of Thomson Scattering Data Processing Program

Get raw data

Separate raw data:•Get stray light•Get scattering light•Get pedestal subtraction

• Subtract pedestal• Subtract stray light• Background pedestal analysis

compute standard error of pedestal, stray light, and scattering

• Build ratios• Compute error in channel ratio

based on deviation of stray light, scattering light, and background noise

• Get Te for different channel ratios from look-up table

• Compute final Te from weighted average

• Computer error from weighted average

END

Page 28: HSX Thomson Scattering Experiment K. Zhai, F.S.B. Anderson, and D.T. Anderson HSX Plasma Laboratory University of Wisconsin-Madison, The HSX Thomson Scattering.

• 10-point, double-pulse Thomson scattering system optimized for the measurement of HSX plasma parameters of electron temperature of 10eV-2keV and electron density of 1012/cm3 or higher.

• While all the subsystem function properly, successful operation also require precise alignment of the whole system, the input optics and collection optics. One point measurement of system is expected to operate in this year.

Summary of the System and its Operation Schedule

Page 29: HSX Thomson Scattering Experiment K. Zhai, F.S.B. Anderson, and D.T. Anderson HSX Plasma Laboratory University of Wisconsin-Madison, The HSX Thomson Scattering.

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