27 th EPS Conference on ControlledFusion and Plasma Physics

BUDAPEST, HUNGARY, 12-16 JUNE 2000

MULTIPOINT ND THOMSON MULTIPOINT ND THOMSON

SCATTERING ON HT-7SCATTERING ON HT-7

J. Mao, J.Zhao, Y.D.Li, A. Xie, Z. Fang,V.Sannikov* A. Gorshkov*

Institute of plasma Physics, Academia Sinica, Hefei, Anhui, 230031, P.R.China.* PRC Kurchatov Institute, Moscow 123182. RUSSIA

ABSTRACTABSTRACT

A compact, low cost, multipoint Thomson scattering diagnostic for HT-7 Super

conducting Tokamak has been in operation. Its capability of measuring electron te

mperatures is 200ev to 2kev at densities of a few times 1012 cm-3, a spatial resolutio

n of 2.4cm for 5 spatial points and a temporal resolution of 1ms-1s for 8 time point

s. The major components consist of 20-25J Nd:glass laser with 35ns width (8 pulses

per burst), KDPdoubling unit; Spherical mirrors of multipass input optical system

; wide-angle collection objective, bandpass glass filter for reducing the stray light t

o zero; f/2.5 polychromator, the fiberglass collimator, the photomultiplier’s box wi

th electronic preamplifier, high gain and high signal/ noise ratio, CAMAC data ac

quisition and so on. The multipass optical system has been successful for increasin

g the quantity of scattered photons by laser beam passes 10 times through plasma.

The HT-7 Thomson scattering diagnostic has provided successfully the informatio

n on two dimensional electron temperature in the plasma of HT-7 tokamak with L

HCD and IBW heating.

Layouts of HT-7 T.S.Layouts of HT-7 T.S.

KDPfilter

CALIB

PLCRO.

PMTCAMAC

2250

HT-7HT-7HT-7HT-7

KDP

FIBERBAND FILTER

PRISM FILTER OSILLATORAMPLIFIER POWER SUPPLY

PARAMETERS of HT-7 T.S.PARAMETERS of HT-7 T.S.

Te~0.2-2keV; Nelim > 2 1012 cm-3

Spatial resolution : 2.4cm for 5 spatial points

(0, 4cm,8cm,12cm,16cm)

Temporal resolution : 1ms-1s for 8 points

Nd Laser: Nd:glass laser, 20-25J1.06,4J0.53

(KDP doubling), width 35ns 1 or8 pulses.

lens

spherical mirrors

spherical mirrors

Laser

Prism

Filter

PMTPMT

FIBER COLLECTOR

COMPONENTCOMPONENT

Nd LaserOptical systemPolychromator and PMTFibelglass collimatorData Acquisition,CAMACFilter and MultipassCalibration System

Nd:glass Laser SystemNd:glass Laser System

Oscillator ; an Amplifier; KDP crystal; Energy meter;Glass filter to cut off light of 1.06Laser room

OSCILLATOROSCILLATOR

* Ring resonator very stable* LiF crystal with colored,Qswitch* 50mJ, 40 nsec., line width<0.01Å Operate in a TEMoo*Two opration model. 1Hz repetition1 or 8 pulses

* Dove prism with Brester’s angles.Light beam is rotated inside the resonator along the optical axisreduce the thermal stress which are accumulated during the operation

AMPLIFIERAMPLIFIER

* Telescopic resonator 7 passes

* LiF-2 plate with corored for Q switch,width 35nsfor protecting the master oscillator from back-emission* Increasing laser power density by KDP’s nonlinear process.

POLYCHROMATORPOLYCHROMATOR

PMTPMT

GRATINGOBJECTIVEFIBER

COLLECTOR

* Wide-angle collection objective (F=200mm)* f=1/2.5

* Transmission about 0.7-0.8* Diffraction grating 600 L/mm, 1515cm2

PHOTODETECTORSPHOTODETECTORS

* 25 Pieces ( 5 x 5 )

* S-20 PHOTOCATHODE

* Quantum Efficiency (5300Å ) ,

10%-12% (6943Å~3%)

* 12 Dynodes

Dnode dark Current ~ 10-8

* High Gain

* Preamplifiers: 50times,

Bandpass: 0.15-35MHz

S20

BANDPASS GLASS FILTERBANDPASS GLASS FILTER

* Two pieces installed frond of the input fiberglass guides

* Reduce the stray light to zero

* Special glass filter used cut off of laser radiation(1.06μ)

* High damage resistant for high power laser

MULTIPASS OPTICALMULTIPASS OPTICAL

E=E0(1+R+R2+R3+....R9)==9.8EO

Two spherical mirrors R>>D 2R=3.2m, D=0.052m* Two pieces installed frond of the input fiberglass guides Reduce the stray light to zero Success for Lager Device firstly

FM

Lh

EN ne

0

lens

spherical mirrors

spherical mirrors

Laser

Prism

Filter

CALIBRATION SYSTEMCALIBRATION SYSTEM

Optical Path Alignment (HeNe and Laser) Energy Calib. (Energy Meter) Spectral Calib. (Hg lamp) Spatial position Calib. (movable target) Sensitivity of 25 Channel (Tungsten Lamp)

Tungsten Lamp

lenslens chopper

fiber

Photodiode

To CAMAC

FLOW CHART OF THOMSON SCATTERING SYSTEM

Profile of Te(r)Profile of Te(r)

-2 0 2 4 6 8 10 12 14 16 18 20 22 24 26 280

200

400

600

800

1000

1200 T.S.shot No. 28886 at 150ms

Te (

ev)

r (cm)

High THigh Te0e0 ~ 1KeV during LHCD ~ 1KeV during LHCD Te by T.S compare with Te by ECETe by T.S compare with Te by ECE

IBW250kw LHCD420kwIBW250kw LHCD420kw

-2 0 2 4 6 8 10 12 14 16 18 20 22 24 26 280

100200300400500600700800900

100011001200130014001500

36806 with IBW36759 Ohm

Te (

eV)

r (cm)

-2 0 2 4 6 8 10 12 14 16 18 20 22 24 26 280

100

200

300

400

500

600

700

800

900

1000

1100

1200

32840

32838

Te (e

v)

r (cm)

Profile of Te(r)Profile of Te(r)

Ip=130KA, Ne~1.5Ip=130KA, Ne~1.510101313/cm/cm33

with with IBW 150kwIBW 150kw

-2 0 2 4 6 8 10 12 14 16 18 20 22 24 26 280

200

400

600

800

1000

1200 33051 33055 33056

Te (e

v)

r (cm)

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

0.34

0.36

0.38

0.40

0.42

0.44

0.46

0.48

0.50

0.52

33065 33066

Te

(ke

V)

Time(s)

600ms

Te by SXSTe by SXS

Te by T.S.Te by T.S.

450ms33051

600ms3305533055

SUMMARYSUMMARY

• The multipass optical system has been successful for increasing the quantity of scattered photons.

• The HT-7 Thomson scattering diagnostic has provided successfully the information on two dimensional electron temperature and density profiles in the plasma of HT-7 tokamak with LHCD and IBW heating.

SUMMARYSUMMARY

• The multipoint Thomson scattering diagnostic for HT-7 Tokamak has been in operation.

• Nd Laser: Nd:glass laser, 20-25J1.06,4J0.53;

1 or 8 pulses. Optical system is very stable.

• System stray light was reduced to near zero by Two pieces of glass filter.

• The ratio of noise to signal is < 5%.