Interferometers and Thomson Scattering Diagnostic on KSTAR

K.C. Lee, J.H. Lee, Y.U. Nam, and KSTAR team

-2-

I. Millimeter Wave Interferometer

II. FIR Interferometer

III.Thomson Scattering

IV.Summary

Outline

Mm-wave Interferometer System

• KSTAR mm-wave interferometer system has been installed with horizontally placed single channel of triangular shape.

• Measured line-integrated density is doubled and slightly lower than in case of line placed on the center of plasma.

• Line density value is more stable on vertical plasma motion than radial motion.

Inner-wall Reflector Microwave Parts

Power Supply Phase Comparator

Cassette & Beam Focusing Module

Fringe-jump Compensation

In case of abrupt density change (top), high frequency noise (middle), and signal degradation due to DC voltage drift (bottom).

Line density of up to 1020 m-2 has been successfully measured.

• A phase variation due to an electron density itself is hard to be distinguished from the variation due to a fringe-jump in some plasma shot with abrupt density change such as a H-mode event.

• A correlation between a phase variation and resulted voltage signal can be distorted. When a plasma density is extremely high, a wave propagating within plasma can be refracted and deviates from receiving antenna. This results low incoming power to the circuit and results low output voltage accordingly. Same phenomena can be caused by a shift of source frequency due to a noise on the power supply for oscillators.

• An accuracy of the compensated signal should be improved with detailed analysis on the correlation between two raw output signals.

Real-time Density Measurements

Optical converter system for connecting with PCS system.

Input signals to the interferometer system, post-processed line-density, input signals to the PCS system and real-time processed line-density (from top to bottom)

• A density feedback control system is required to maintain a stable plasma condition. For this purpose, output signals from phase comparator circuit have been connected to PCS system. An optical converter system was included to reduce electrical noise and to prevent ground loops.

• Measured raw data was converted to line-integrated electron density data using a real-time fringe-jump correction algorithm. With these scheme, real-time control experiments of electron density have been successfully performed.

-6- 6

NBI source1 : #9237: [ 1.15MW ]

NBI source2 : #9238: [ 1.23MW ]

Source 1&2 : #9239: [ 1.38MW ] NBI heating power :

density feedback

fueling was lower for

later shots to keep the

density same

Density Feedback Control by MM Wave Interferometer

MM wave system

limited by cut off

~ 1020/m3

Far Infrared (FIR) Interferometer System

x 2.81015 n( x )d x o

x

KSTAR 2013 Campaign : vertical 1-Channel system at G-port

Radius of beam position : 180 cm

Methanol (CH3OH) LASERs (λ=118.8µm, f=2.52THz)

Modification of beam path for 2013 KSTAR

Improvement of IF signal level

First result of FIR Interferometer system (vertical 1-channel in 2013 campaign )

Clear opposite peaks at the ELM clashes indicating density flow from mid-plane to diverter

Comparison of ELM clash measurement by FIR & MM

finished

Upgrade for 4 channel system

-13-

2010 Installed Thomson system in the KSTAR

1mm dia. Optical fiber 5ea., commercial Nd:YAG Laser 2J, 10Hz

Collection optics shutter problems!

2011 Bundle Optical fiber 17ea., commercial Nd:YAG Laser 2J, 10Hz

Got a small signal!

2012 Bundle Optical fiber 17ea., Prototype ITER Edge Thomson Laser Nd:YAG 2J, 100Hz

Got a larger signal / measured L-H transition

2013 Bundle Optical fiber 17ea., Prototype ITER Edge Thomson Laser Nd:YAG 2J~5J, 100Hz

Data is comparing with other profile diagnostics

Collaborate with JAEA & NIFS.

History of Thomson Scattering on KSTAR

-14-

KSTAR Thomson scattering system(2012)

- Te : 10eV~1.5keV (edge), 500eV~20keV (core)

- ne : 3Х1012~2 Х1014 ㎝-3

- 17spatial points (core 6, edge 11 points, 2012) final

(core 5, edge 12 points, 2013) 52 points

- Spatial Resolution : < 10 cm (core), < 3 cm (edge)

- 1 cm , ~0.4

- Polychromator 17ea

(core 5ea by NFRI, edge 12ea by NIFS)

-ADC channel : Signal 85ch.+Back Ground 85ch. Total 170ch.

- Time resolution 100Hz

-Laser : 2J (~5J, 2013), 100Hz Nd:YAG Laser, 1064nm

(collaboration with JAEA)

Specification of KSTAR Thomson scattering system

-15-

Port allocation of KSTAR Thomson

scattering system

N S

B-port : Beam Dump

Laser Input port L-Port

Collection optics N-port

Beam dump B-port

Laser travel length ~ 40m

Guiding Mirror 9ea.

Tangential Thomson scattering system

N-port : collection optics

Tangential Beam

Nd:YAG (1064 nm)

AB

C

O

M

N

L

D

E

F

P

G

H

IJ

K

Optic system &

Cassette

Beam dump system

Laser input system

Tangential Beam

Nd:YAG (1064 nm)

AB

C

O

M

N

L

D

E

F

P

G

H

IJ

K

Optic system &

Cassette

Beam dump system

Laser input system

L-port : Laser Input

-16-

The proto type ITER Edge Thomson scattering Nd:YAG laser system transferred to NFRI from JAEA in 2012.

5J, 100Hz, 1064nm Double laser line

A-line

B-line

2.5J, 100Hz

2.5J, 100Hz

* LASER system rented from JAEA

=1064nm, pulse width ~20nsec

A B

18mm

Laser & dump system

2012

2011

Laser operation

‘12 : Used only B-line, 2J, 100Hz

‘13 : Used A-line, A+B line,

2.5~5J, 100Hz

Dump system

-17-

‘12

‘13

Core 6 points Edge 11 points

Core 5 points Edge 12 points

Measuring Positions in 2012 & 2013

Plasma center

1700 1800 1900 2000 2100 2200 2300

R(mm)

-18-

Polychromator filter combinations

Center/FWHM wav

elength (nm) Channel 1 Channel 2 Channel 3 Channel 4 Channel 5

Core 870/100 967/90 1028 / 34 1053/15 1064/4

Edge 1064 / 4 940 / 100 1010 / 40 1040 / 20 1055/10

Sig. Bg.

100Hz

80nsec 100nsec Time

Polychromator Invertor Amplifier

DAQ system(signal, Background) KSTAR MDS+

Scattered light from Tokamak

Core Lens Edge Lens

Data flow

Collection Optics 3.5 mm Х

1.8 mm, 17ea bundle optical fiber

3.5mm 1.8

mm

3.5 mm Х 1.8 mm, 17ea

bundle optical fibers

Gate integration type DAQ system

Polychromator / DAQ / Optics

collaborat with NIFS

-19-

Calibrated Tungsten light source

Polychromator

Motorized Monochromator

Computer

Data Acquisition System

Schematic for Wavelength calibration & light Intensity Calibration system with W light

Relative (Polychromator) calibration & Absolute(Rayleigh) calibration

0 200 400 600 800 1000 1200 1400

0.0

0.5

1.0

1.5

2.0

I(A

.U.)

Te(eV)

ch1

ch2

ch3

ch4

ch5

Edge #1

600 700 800 900 1000 1100

0.0

2.0x105

4.0x105

6.0x105

8.0x105

1.0x106

1.2x106

1.4x106

Re

sp

on

se

[co

un

t/W

]

wavelength [nm]

ch 1

ch 2

ch 3

ch 4

ch 5

Core #1

600 700 800 900 1000 1100

0.0

2.0x105

4.0x105

6.0x105

8.0x105

1.0x106

1.2x106

1.4x106

Re

sp

on

se

[co

un

t/W

]

wavelength [nm]

ch 1

ch 2

ch 3

ch 4

ch 5

Edge #1

0 5000 10000 15000 20000

0.0

0.4

0.8

1.2

1.6

2.0

I(A

.U.)

Te(eV)

ch1

ch2

ch3

ch4

ch5

Core #1

Core polychromator #1 Edge polychromator #1

Lookup tables for polychromators

Response curve of polychromators Core polychromator #1 Edge polychromator #1

0 5 10 15 20

400

600

800

1000

1200

1400

Edge Polychromator #1

Linear Fit

Sig

na

l (a

.u.)

N2 Pressure (mbar)

Rayleigh calibration with N2 gas

-20-

-1 0 1 2 3 4 5 6 7 8

200

220

240

260

280

300

320

340

360

380

400

Inte

nsity(a

.u.)

Time(sec)

Ch4

Ch5

#4274 raw data

‘10 data : 1mm diameter

optical fiber, commercial Nd:YAGLaser (2J, 10Hz )

1800 1900 2000 2100 2200 23000

1

2

3

4

5

Radial position [mm]

Ele

ctro

n T

empe

ratu

re [k

eV]

1800 1900 2000 2100 2200 23000.0

0.5

1.0

1.5

2.0

2.5

3.0

Rel

ativ

e E

lect

ron

dens

ity (

a.u.

)

Radial position [mm]

H-mode@ 6.3sec

‘11 data : optical fiber bundles, Commercial

Nd:YAGLaser(2J, 10Hz )

DATA & RESULT

-21-

1800 1900 2000 2100 2200 2300

0.0

0.5

1.0

1.5

2.0

2.5

3.0

1.6 sec

2.9 sec

L-mode

ne(1

01

3/c

m3)

R(mm)

H-mode

1800 1900 2000 2100 2200 2300

0.0

0.5

1.0

1.5

2.0

2.5

L-mode

H-mode

R(mm)

Te

(ke

V)

1.6 sec

2.9 sec

KSTAR Shot #7082(Ip=636kA)

‘12 data : optical fiber bundles, ITER Nd:YAG Laser(2J, 100Hz)

𝐹 =𝑎2 − 𝑎4

2𝑚𝑡𝑎𝑛ℎ

𝑎0 − 𝑥

2𝑎1, 𝑎3 + 1 + 𝑎4 Where, 𝑚𝑡𝑎𝑛ℎ 𝑥, 𝑏 =

1+𝑏𝑥 exp 𝑥 −exp(−𝑥)

exp 𝑥 +exp(−𝑥)

* Ref. 1

2012 data

a0: position of pedestal, 4a1: width of pedestal, a2: height of pedestal, a3: linear core slope, a4: SOL value

Modified tangent hyperbolic function

1.6sec 2.9sec

Int. 𝒏

Ip NBI ECH

D

-22-

1800 1900 2000 2100 2200 2300

0

1

2

3

ne(1

01

3/c

m3)

R(mm)

Time(sec)

6.00

6.10

6.20

6.29

6.30

6.31

6.32

6.33

6.34

6.35

6.36

6.37

6.38

6.39

6.40

KSTAR Shot #7102

KSTAR Shot #7102 (Ip=629.4kA)

* H-L transition

* profile changes (100Hz resolution)

* Pedestal Height changes

6.0 6.1 6.2 6.3 6.4

0.6

0.8

1.0

I(A

.U.)

Time(sec)

D

* Pedestal width Width @ 6.0~6.29sec t : 6.0~6.29sec

1800 1900 2000 2100 2200 2300

0.0

0.5

1.0

1.5

2.0

2.5

3.0

R(mm)

ne(1

01

3/c

m3)

Width

-23-

2160 2180 2200 2220 2240 2260 2280 2300

0.00E+000

2.00E+012

4.00E+012

6.00E+012

8.00E+012

1.00E+013

1.20E+013

1.40E+013

1.60E+013

ne

(cm

-3)

R(mm)

2.5

Fit

2.3

Fit

2.1

Fit

2160 2180 2200 2220 2240 2260 2280 2300

0

20

40

60

80

100

120

140

160

180

V [km

/s]

R [mm]

t=2.5 sec

t=2.3 sec

t=2.1 sec

2160 2180 2200 2220 2240 2260 2280 2300

0

100

200

300

400

500

600

700Shot #9422

Te

(eV

)

R(mm)

2.5

Fit

2.3

Fit

2.1

Fit

2160 2180 2200 2220 2240 2260 2280 2300

0

200

400

600

800

1000

1200

1400

Ti [e

V]

R [mm]

t=2.5 sec

t=2.3 sec

t=2.1 sec

Shot #9422

2013 data

Pedestal structure both in Thomson & CES for H-mode T=2.1 s : L-mode T=2.3 s : transition T=2.5 s : H-mode

*Not an absolute density in Thomson data (only relative change must be considered)

Da

𝒏

NBI

(further comparison is on-going)

-24-

2160 2180 2200 2220 2240 2260 2280 2300

0

100

200

300

400

500

600

700Shot #9422

Te

(eV

)

R(mm)

2.5

Fit

2.3

Fit

2.1

Fit

2.16 2.18 2.2 2.22 2.24 2.26 2.28

0

0.2

0.4

0.6

0.8

1

1.2

R (m)

Te

(ke

V)

Shot 9422 : Te Profile @ ITF

=26.00 kA [tave

=20 ms]

t = 2.500 s

t = 2.300 s

t = 2.100 s

Value of Te,ped are in good agreement

2160 2180 2200 2220 2240 2260 2280 2300 2320

0

200

400

600

800

1000

1200

Te

(eV

)

R(mm)

Thomson

ECE

Shot #9062, 6.4sec

Thomson & ECE

(further comparison is on-going)

-25-

Summary

Mm wave interferometer is working routinely with

capability of density feedback control

FIR interferometer of KSTAR produced first

measurement in 2013 through various modification

KSTAR Thomson scattering system is developed

including ITER Nd:YAG laser and data are compared

with other profile diagnostics

FIR to be 4 channel system and polarimeter is in design

Various modification is under way for TS data improvement

In future…