ECEI, MIR, RF Spectrometer in KSTAR – Advanced mm-wave and RF diagnostics

Gunsu S. Yun*, W. Lee, J. Lee, M.J. Choi, J. Lee, M. Kim, J. Leem, Y.B. Nam, G.H. Choe (POSTECH)Hyeon K. Park (UNIST)

H. Park, D.S. Kim, K.W. Kim (KNU)C.W. Domier, N.C. Luhmann, Jr. (UC Davis), N. Ito, A. Mase (Kyushu Univ.)S.G. Lee, S.W. Yoon, Y.S. Bae , KSTAR Team (NFRI)

Collaborators:

ITPA Diagnostics TG meetingMay 19 - 22, 2014, POSTECH, Pohang, Korea

* Work supported by NRF Korea

(2) MIRFast imaging system for nefluctuations

(1) Two ECEI systemsFast & high-resolution imaging system

for Te fluctuations

(3) Fast RF Spectrometerfor plasma waves (ion cyclotron,

Alfven, whistler, etc)

Outline

2

ECEI-1(year 2010)Dual arrays

I. KSTAR 2D ECE Imaging (ECEI)

• Space resolution ~ 1x1—2x3 cm2

• Te resolution (real-time), 𝛿𝛿𝑇𝑇𝑒𝑒/ 𝑇𝑇𝑒𝑒 ≈ 2%• Time resolution ~ 2 µs

~6 m

Lens

Detector

Simultaneous Imaging of Core and Edge Study of interaction

btw instabilities* Internal Kink

(CORE)

ELM(Edge)

3

Appendix0. Array of heterodyne detectorsSeparate Compartments for amplifiers and diode arrays for better noise shielding‡

(Side view)

Schottky diode on a patch antenna†

Isoview

Top view

†P. Zhang, RSI 2008 ‡ Yun, LAPD (2013) 4

Heterodyne Detector Arrays

Triplet for vertical zoom

1. Lens System for Imaging • Lens material: HDPE• Lens configuration: Cooke

triplet or doublet for flexible zooming (vertical zoom factor ~ 1—3)

Focus lenses

LFS

HFS

Focus Lenses

~4m

Cooke Tripletfor Vertical Zoom

(top view)

Measured beam profile at the image plane

Image Position (mm)

Source Position (mm)

Zoom factor measurement

5

2. Wide-Band Beamsplitter

Beamsplitter

• Thin Tempered Glass(borofloat33, t=1.1mm, Dk = 4.6)

170 GHz notch filter

Detector ARRAY box

3. Notch-filter

• Array of copper squares- Copper Thickness : 9 um- Pattern dimension = 476~512 um

• Dielectric Thickness : 254 um• Dielectric Constant : 2.20• Dissipation Factor : 0.0007

Deep and symmetric notching

6

4. High-pass filters for single-sided mixing

Tran

smitt

ance

(dB)

Input frequency (GHz)

Full transmission ~ 17 GHz wide

– measured – calculation

Dichroic high-pass filters

ARRAY BOX

5. Half-wave plate for O1 mode operation at high B

X2 freq, too high

O1 freq

X2 cutoff

O1 cutoff

Bt = 3 TGrooved HDPE plate ~ meta-

material

-50 0 50

50

100

150

200

250

300

350

400

Beam

Pow

er[m

V]

without half wave platewith half wave plate

Rotation Angle (deg)

7

𝛿𝛿𝑇𝑇𝑒𝑒/�𝑇𝑇𝑒𝑒

Dual flux tubes (DFTs) †(#6022)

𝑞𝑞 ≈ 1

Crescent tube (#4004)

Triple flux tubes(#5422)

* Choe, KSTAR Conf. (2013)Yun, PRL 109 (2012)Bierwage, to be submitted

Sawtooth structures modified by ECRH*

8

Tearing modes*

m/n=2/1 mode

*M. Choi, NF (2014), accepted.

m/n=3/2 mode

𝛿𝛿𝑇𝑇e𝑇𝑇e

𝛿𝛿𝑇𝑇e𝑇𝑇e

Shot 6304t = 4.322s

Shot 6123t = 6.788s

9

Alteration of ELM structure by n=1 magnetic perturbations (MP)*

* Yun, PoP (2012)Jeon, PRL (2012)J. Lee, KSTAR Conf. 2013

𝛿𝛿𝑇𝑇ECE𝑇𝑇ECE

0.10.05

0-0.05

(shot#6123)

15

10

5

0

-5

-10

-15

205 210 215 220 225 230

No MP

~𝟏𝟏𝒌𝒌𝒌𝒌

/𝒔𝒔

z(c𝑚𝑚

)

R(c𝑚𝑚)

n~10

Non-resonant MP

~𝟏𝟏𝟏𝟏

𝒌𝒌𝒌𝒌/𝒔𝒔

n=5

First simultaneous observation of outboard and inboard ELM filaments†

Edge localized modes (ELMs)

Outboard

R [cm]

z [c

m]

140 160 180 200 220 240

-100

-50

0

50

100Inboard

KSTAR #9380 (t = 5.569 s)

Δ𝑇𝑇𝐸𝐸𝐸𝐸𝐸𝐸𝑇𝑇𝐸𝐸𝐸𝐸𝐸𝐸

TV image with EFIT

ECEIECEI

† J. Lee, KSTAR Conf. 2013; Yun, ITPA MHD 2014

10

~6 m

Lens

Detector

KSTAR 3D ECEI

ECEI-1(year 2010)Dual arrays

ECEI-2(year 2012)Combined with MIR

22.5°

Quasi 3D (year 2012)

(shot#7328, t=7.917s)

o Exact determination of Toroidal mode number *

o Toroidal asymmetry of ELM dynamics

*J. Lee, submitted to RSI. 11

R(cm)

Dual flux tubes† in 3D(Modified Sawtooth by ECH)

NOT A SIMULATION

z(cm)

𝑞𝑞 = 1surface

o The observed flux tubes are approximately aligned with the model flux tubes of m/n=1/1.

o Naturally explains the changes of the sawtooth period.

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II. Microwave Imaging Reflectometry†

Imaging of 2D density fluctuationsDispersion of turbulent fluctuations

Specifications• Tunable probing frequencies from 78 to 92 GHz • Frequency spacing = 2 or 4 GHz• Channels: poloidal 16 and radial 2 • Spatial resolution: 1.6 cm (1/e2 width poloidal)• Channel spacing: 0.6 cm (poloidal), 1 ~ 17 cm (radial)• Detection limit of wave number: kθ = up to 3 cm-1

• Time resolution: 1 or 2 μs normal (0.5 μs min)

1~17 cm

0.6 cm

†W. Lee, NF (2014)

13

Source, array, and electronicsUpgraded to 4 frequencies in 2014

14

Imaging optics

Normalized response of each detector ∼1.6 cm 1/e2 width.

15

Spectral change of turbulent density fluctuations

r/a ~ 0.6 r/a ~ 0.7

* ECH r/a ~ 0.3

16

Lab-frame poloidal flow (𝑽𝑽𝜽𝜽∗ ) of density fluctuations

r/a ~ 0.6 (NBI-only)

Cross-coherence, 𝛾𝛾𝑥𝑥𝑥𝑥2 𝑓𝑓 = �𝐺𝐺𝑥𝑥𝑥𝑥 𝑓𝑓 2 𝐺𝐺𝑥𝑥𝑥𝑥 𝑓𝑓 𝐺𝐺𝑥𝑥𝑥𝑥(𝑓𝑓)

Cross-power, 𝐺𝐺𝑥𝑥𝑥𝑥 𝑓𝑓 = 𝑥𝑥∗ 𝑓𝑓 ⋅ 𝑦𝑦 𝑓𝑓 time

r/a ~ 0.7 (NBI-only)

17

Time evolution of 𝑽𝑽𝜽𝜽∗ during L-H transition†

†W. Lee, LAPD16, Madison, WI, 2013 18

Pow

er [M

W]

Te[k

eV]

ne [1

019m

-2]

Wto

t[kJ

]Hα

arb]

Splitter(8 way)

BandpassFilter

Detector

III. Fast RF spectroscopic system†

A prototype 8-channel RF spectrometer† has been developed in 2011 to detect RF emissionsduring MHD events such as sawtooth crashes and edge-localized mode (ELM) crashes.

A wide-band antenna was installed outside the vessel near the ECEI system (next slide).

1st ECEI2nd ECEI

Antenna

Wide-band bow-tie antenna0.2 ~ 2GHzVSWR < 2

Amp(~30dB)

†J. Leem, JINST 2012 19

Fast digitizer Wide-band

antenna

Three-axis loop antenna

Upgrade planned for fine-resolution full-band measurement and polarization measurement for the 2014 KSTAR campaign.

Similar filter-bank RF spectrometer is installed at LHD for comparative study (collaboration w/ T. Akiyama)

20

Example of RF burst at the ELM crashes

Dα

�̇�𝐵 [T/s]

RF@200 MHz@300 MHz

�̇�𝐵 [T/s]

Time [s]

(1) The RF captures the exact timing of ELM crash.

𝛿𝛿𝛿𝛿𝑒𝑒𝑒𝑒𝑒𝑒𝛿𝛿𝑒𝑒𝑒𝑒𝑒𝑒

10𝜇𝜇𝜇𝜇

LCFS

1

2

1

Dα

H-mode discharge𝐵𝐵0 = 2.3 T, 𝐼𝐼𝑃𝑃 = 550 kA,𝑛𝑛e0~2e19 m−3,Wtot = 220 kJ, NBI = 2.7 MW

RF@200 MHz@300 MHz

21

RF level change during the inter-crash period

�̇�𝐵 [T/s]

(2) Rapid enhancement and saturation of the RF emission level (around 200 MHz) is commonly observed during the inter-crash period. Modulation in the RF emission level is also often observed.

2

Dα

Dα

�̇�𝐵 [T/s]

RF@200 MHz@300 MHz

1

2RF @200 MHz @300 MHz

Possible mechanism: Mode conversion of ion cyclotron harmonic waves to compressional (fast) waves through the lower hybrid resonance

A useful diagnostic for pedestal evolution

22

Summary

Visualization is an essential tool for complex MHD and turbulence physics.

Achieved quasi-3D ECE imaging at the KSTAR tokamak through technological innovations

Realized MIR; measured the wave dispersion of density fluctuations

Fast RF diagnostic proved to be very useful for studying MHD crash dynamics, plasma waves, etc.

Work supported by NRF Korea, Japan-Korea Collaboration program and US DoE.

24

𝑛𝑛𝑒𝑒0 = 5 × 1013 cm−3

𝑇𝑇𝑒𝑒0 = 3 keV2fce

fce

fpe

fcutoff(x2)

ECEI window of operation

25

ECE downshift

Near the pedestal foot and outside, ECE signals come mostly from inside, a well-known phenomenon called downshift.

ECE downshift(not localized) Localized ECE

E. de la Luna et al., 34th EPS (2007)

JET H-mode pedestal

neTe

R (cm)

τ(µW/cm3/GHz)

26