EAST

POINT: POlarimeter-INTerferometer

H. Q. Liu*, Y. X. Jie, Z. Y. Zou, J. P. Qian, S. B .Zhang, W.M. Li, Y. Yang, L. Zeng, T. Lan,

L.Q.Hu and B.N.Wan

Institute of Plasma Physics, Chinese Academy of Sciences

W.X. Ding, D.L. Brower

Department of Physics and Astronomy, University of California Los Angele

*Email: hqliu@ipp.ac.cnThis work is supported by the National Magnetic Confinement Fusion Program of China with contract

No.2012GB101002, No.2014GB106002 and the National Nature Science Foundation of China with contract

No.11375237. This work is also partly supported by the US D.O.E. contract DESC0010469.

1st IAEA Technical Meeting on “Fusion Data Processing, Validation and

Analysis”, 1 - 3 June, 2015, Nice, France

First Results of Polarimeter-Interferometer System for

Current Density Measurement on EAST

EAST

Outline

1. Motivation

2. Faraday effect POlarimeter-INTerferometer

(POINT) on EAST

3. First results of EAST POINT

4. Summary & Plan

EAST

Experimental Advanced Superconducting Tokamak

Mission: 1MA SSO with 20-30MW Heating & CD power.

R0 = 1.9 m

a = 0.5 m

Bt = 3 T

Ip = 1.5 MA

= 2

= 0.65

Mo (FW)+ C+ W (mono-Divertor)

EAST

Play the key role for understanding

advanced SS plasma physics.

• Fully non-inductive CD, high bootstrap

current fraction (fbs).

• Active control of ELM and steady state

heat load on divertor

Provide valuable data bases for ITER

under ATSSO condition.

ICRH 6+6 MW(25-75MHz)

LHCD 4+6 MW(2.45GHz/4.6GHz)

NBI 4+4 MW (Co/Counter, 80kV)

ECRH 2 MW (140GHz)

RMP Coils

GP(D,H) Pellet, SMBI, Lithium technology

Diagnostics key profiles and for physics understanding

EAST In-Vessel@2014

EAST entered Phase II in Jun 2014. Capabilities in 2015.

W

Mo

C

3

EAST Achievements in 2014 & Goal in next 5 years

> 100 s high beta H-

mode operation

Extension and

Optimization of High-

Performance Advanced

Tokamak and ITER-like

scenarios

PNBI = 2.3 MW, βN = 1.8

and WMHD = 200kJ• Newly installed Co-current

NBI systems have been

successfully

commissioned, maximum

power up to 2.8MW at 65KV.

• High performance ELMy H-

mode with Beta_N up to 1.8

have been achieved.

• The duty ratio of NBI

modulation has been tested

between a very broad range:

from 1:25 to 20:1.

H-mode plasma by 4.6 GHz LHCD LHCD+NBI modulation

PNBI = 1.2 MW

PLHW,2.45G = 1.0 MW

PLHW, 4.6G = 1.2 MW

ne/nG ~0.7

Vloop < 0.04 V

Td > 20S,

Small ELM

Controllable density

EASTMotivation

Current profile relaxation in a long pulse discharge (>> resistive time) is

very important to burning plasma control. Real time current profile control

requires fast measurements of current profile.

Polarimetric and interferometric measurement with high temporal, spatial

resolution on EAST provides essential tools to study >100 s high beta H-mode

operation, optimization of High-Performance Advanced Tokamak and ITER-

like scenarios.

Measurement Goals:

(1)Real-time plasma control (q profile and current density relaxation) for long-pulse

discharges:

connect plasma (diagnostics) – PCS - actuators (ICRH,LHCD) - plasma response;

(2) Extend high-performance plasma regimes to long-pulse in preparation for ITER;

(3) Investigate the role of magnetic fluctuations (tearing modes, NTMs, fast-particle

driven instabilities) on plasma equilibrium and performance.

Three wave polarimeter-interferometer techniqueEAST

Interferometry

15=2.82 10 en dl

Phase shift

Polarimetry

-13 2

F ||=2.62 10 en B dl

Faraday Rotation Angle

R L+=

2

R L-=

2

R

L

=

=

R

L

k l

k l

Developed successfully on MST,

J-TEXT, C-Mod, EAST etc.

G. Dodel and W. Kunz, Infrared Phys, 1978;

J. H. Rommers, RSI, 1997;

D. L. Brower, RSI, 2003; W.X. Ding, RSI, 2010;

W. F. Bergerson, RSI, 2012;

J. Chen, RSI, 2012.

EASTSchematic of EAST POINT

5 chords (successful operation in 2014 campaign )

11 chords (this year)

Z1=34 cm

Z2=17

Z3=0

Z4=-17

Z5=-34

POlarimeter-INTerferometer (POINT) system

for core 𝑛𝑒 , 𝑗∅, 𝑞, 𝐵𝑝 profile and 𝐽, 𝐵, 𝑛𝑒 .• 3-wave technique, Double pass,

radially viewing,

• 11 chords (8.5 cm spacing),

• up to 1ms temporal resolution,

• 432.5 mm laser [x3] from Coherent,

• VDI planar-diode mixers,

• DPD provide real-time 𝑛𝑒 , Ψ𝐹 ,• Novel Mo retro-reflectors(20 arcsecs),

• IF control system.

~ 20m double waveguides

Laser

table

EASTPOINT Layout

POINT

tower

EAST

• Laser room: Temperature & humidity

control, Electromagnetic & acoustic

shielding.

• Vibration-free laser table: >30 tons,

• POINT tower: 8m, >20 tons,

• 25 tons vibration free optical table,

• ~20m double waveguides.

EAST

#3#2

#1

Control

system

Lasers and Detectors

Three coherent SIFIR-50 lasers

•Each FIR laser works at 432.5 μm

using formic acid gas and pumped by

a CO2 laser.

Gaussian mode output measured

2m away from laser.

Virginia Diodes, Inc. planar Schottky diode

Integrated Conical Horn Fundamental Mixer

High sensitivity, low noise, the sensitivity

>750V/W, >250V/W.

EASTRetro reflectors(RRs)

Material: Molybdenum (Mirror), Stainless

Steel (Mount Base and Housing),

Size: 50mm Diameter Optical Aperture,

55mm outside Diameter Housing and

Base Mount,

Alignment Accuracy: 20 ARC seconds,

Environment Compatability: 350°C in

VV.

Novel molybdenic retro-reflectors with shutter protection have been

mounted on the inner vessel wall in EAST.

Keep from deformation, erosion,

deposition

Baking temperature up to ~ 350℃ Discharge duration more than 1000s.

Shutter will be kept closed part of

the long pulse discharge

Shutter closed during Lithium wall

coating

EASTLasers output power and IF stability

𝜹ω1=0.85MHz

𝜹ω2=1.275MHz

𝜹ω3=2.125MHz

。

Output power shift < 25% IF need be controlled to be <1%

IF feedback control：

11

With the IF

control system.

The output IF drift

is lower than 0.6%,

850kHz±5kHz.

Signals gotten by 12 Mixers

10M/s data acquisition

RT filter & FFT

RT calculation for ΨF & ne

10kS/s RT output to PCS

250kS/s RT output to data sever

Off line FFT calculating for

Faraday rotation angle and line-

integrated density（~MHz）

Data processing and RT DPD to PCSEAST

12

FPGA based RT DPD

Local 3-Wave FIR

Demodulator (DPD-

3W-05C) provide by

Palomar Scientific

Instruments

Centered at 0.850, 1.275

and 2.125 MHz with

100 kHz tolerance,

ne @0.85&2.125 MHz,

ΨF @1.275 MHz.

EAST

In-situ test result w/o plasma：Electron line-integrated density：<1 x 1016m-2 (<1o),

Faraday rotation angle：< 0.1o.

POINT calibration

polarization calibration(rotating λ/2

plate):

-180

0

180

Ch1

-180

0

180

Ch2

-180

0

180

measure

d p

hase d

iffe

rence(

)

Ch3

-180

0

180

Ch4

0 90 180 270-180

0

180

ratated angle of 1/2wave plate()

Ch5

Density profile reconstruction

14

EAST

1.4 1.6 1.8 2 2.2 2.4-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

R(m)

Z(m

)

0

0.5

1

1.5

2

2.5

3

3.5

1019m-3

Density profile reconstruction with POINT，HCN，MIR diagnostics

system by Park Matrix method

Comparison between two laser interferometers

Vertical view HCN laser system (time response 1kHz,)

Horizontal view HCOOH laser system (time response 1MHz, noise level: ~1 x 1016

m-2

EAST

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0.0

3.02.52.01.51.00.50.0

1.0

0.8

0.6

0.4

0.2

0.0

3.02.52.01.51.00.50.0

ne0

'Den HCN'Shot 46018

HCN

POINT

1.7

1.6

1.5

1.4

1.3

1.2

2.42.32.22.12.0

0.85

0.80

0.75

0.70

0.65

2.42.32.22.12.0

nep34

nep17

ne0

nen17

nen34

'Den HCN'

Shot 46018

HCN

POINT

MHD

Point system provides better quality data for plasma control experiments.

Remote operation enables the continuation of diagnostics without the access of

machine；Sawteeth events are clearly observed on density, indicating fast time

resolution of system.

Z=0 chord

Z=17 cmInverted sawteeth

16

MHD activities clearly seen on POINT

POINT system has very good phase sensitivity to study various MHD and

turbulence on EAST. MHD activities also seen on Mirnov coil and ECE.

EAST

Mirnov coilECE

EAST

52 Seconds Long Pulse Discharge

POINT provides real-time measurements without any vibration compensation,

obvious interference from powerful NBI, LH, ICRF heating sources, indicating that

system works for any heating scheme on EAST so far.

0

100

200

300

#49982

I p(k

A)

0

2

4

density(1

01

9m

-2)

0 10 20 30 40 50

-20

0

20

Fara

da r

ota

tion(

)

t(s)

ch1 Z=34cm

ch2 Z=17cm

ch3 Z=0

ch4 Z=-17cm

ch5 Z=-34cm

LHW@ 4.6GHz(1.5MW)

EASTNBI H mode discharges

Density gradient in H-Mode discharge does not impact POINT measurements.

Point system not only provides equilibrium current profile but also internal

density and magnetic fluctuations

-30

-20

-10

0

10

20

30

Fara

day e

ffect

[deg

]

86420time [s]

Y= 34 cm 17 0 -17 -34

6

4

2

0

lin

e-i

nte

gra

ted

den

sit

y [

101

9m

-2]

86420time [s]

Y = 34 cm 17 0 -17 -34

#51063 NBI H-modeelongation: 1.6

PNBI = 2.3 MW, elongation=1.6, βN = 1.8

and WMHD = 200kJ

q Profile reconstructuion with POINT data by EFIT

(simulated test) EAST

nerCi

∂ψ

∂n𝑑𝑙 = 𝐴i

neCi

𝑑𝑙 = 𝐵i

Reverse shear

monotonic

The accuracy of the q profile

can be significantly

increased by incorporating

the POINT data constraint.

-30

-20

-10

0

10

20

30

Fa

rad

ay e

ffe

ct

[de

g]

86420time [s]

Y= 34 cm 17 0 -17 -34

6

4

2

0

lin

e-i

nte

gra

ted

de

ns

ity

[1

019 m

-2]

86420time [s]

Y = 34 cm 17 0 -17 -34

#51063 NBI H-modeelongation: 1.6

EAST

3.1s 4.6s

Initial experimental results for equilibrium

current profile from EFIT with POINT data

Current profile

Density profile

0 0.2 0.4 0.6 0.8 10

1

2

3

4

5x 10

19

rho

n e(m-3

)

3.1s

4.6s

EAST

Line intergrated Faraday rotation

Line integrated density

-0.5 -0.25 0 0.25 0.50

0.5

1

1.5

2

2.5

3

3.5

4x 10

19

Z-Z0(m)

nedl(m

-2)

3.1s

3.1s

4.6s

4.6s

-0.5 -0.25 0 0.25 0.5-15

-10

-5

0

5

10

15

Z-Z0(m)

Fa

rad

ay r

ota

tio

n (

de

g)

3.1s

3.1s

4.6s

4.6s

Initial experimental results for equilibrium

current profile from EFIT with POINT data

A comprehensive method to self-consistently

reconstruct the current and profiles with

magnetic and POINT measurements by using

the equilibrium fitting code EFIT.

22

EASTReal time qmin evolution

The reconstructed q profile shows good agreement with the

inversion radius of q =1 surface observed from ECE sawtooth. The

qmin stays below one during the sawtooth period. RT qmin is

available.

min min.( )LHref

dPq q

dt

Real time control qmin by

using off-axis LHCD in

high β plasma, to avoid

the NTM.

EASTNext step --- q profile control

460

480

500

I P (

kA)

#shot 51063

3

3.5

4

n e (1

e1

9)

0

0.5

D

(a

.u.)

-0.2

0

0.2

Bt (

a.u

.)

0123

Pnb

i (M

W)

4.2 4.25 4.3 4.35 4.40

100

200

t (s)

W (

kJ)

POINT can provide a reasonably accurate determination of the current and

q profiles for the EAST. Real time EFIT for q profile control is in developing.

Current profiles are different with different ΔΦ, suggesting the possibility of

profile control.

Summary

5-chord polarimeter-interferometer system has been developed on

EAST tokamak using three-wave configuration.

EAST POINT simultaneously measures Faraday angles and

integrated density with angle resolution ~ 0.1o , density resolution

1x1016m-2, respectively.

Density sawteeth, fluctuation, MHD are observed. Equilibrium

electron density profile, current density profile, q profile are

obtained by using EFIT code.

The POINT has been upgraded to 11-chord this year.

EAST

Thank you for your attention!

EAST