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Supported by Microwave imaging reflectometry Microwave imaging reflectometry for transport study on KSTAR W. Lee, I. Hong, M. Kim, J. Leem, Y. Nam, G. S. Yun, H. K. Park, Y G Kim 1 K W Kim 1 C W Domier 2 and N C Luhmann Jr 2 Y. G. Kim 1 , K. W.

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SLIDE 1

Supported by

Microwave imaging reflectometry Microwave imaging reflectometry for transport study on KSTAR

  • W. Lee, I. Hong, M. Kim, J. Leem, Y. Nam, G. S. Yun, H. K. Park,

Y G Kim1 K W Kim1 C W Domier2 and N C Luhmann Jr 2

  • Y. G. Kim1, K. W. Kim1, C. W. Domier2, and N. C. Luhmann, Jr.2

POSTECH, 1)KNU, 2)UC Davis

1st APTWG International Conference NIFS, Toki-city, Gifu, Japan June 14 - 17, 2011

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SLIDE 2

Density Fluctuation Measurement for Turbulence Study

  • Accurate measurement of plasma density and

electron temperature fluctuations is critical to electron temperature fluctuations is critical to understand the mechanism of anomalous transport based on turbulence.

  • 2-D microwave imaging reflectometry (MIR) can
  • vercome deficiencies of the conventional 1-D

reflectometry used for density fluctuation measurement measurement.

APTWG2011 International Conference (NIFS, Toki-City, Japan, June 14-17, 2011)

  • X. Garbet et al., NF 47, 1206 (2007)

2

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SLIDE 3

Microwave Reflectometry

  • Incoming wave is reflected at the cut-off layer.
  • Reflected waves contain information of the

shape of the cut-off layers.

  • Fluctuating phase of the reflected signal is

r

c

r

∫

) ( ~ ~ ε

where k0 is probe beam wave number,

dr r r k

  • ∫

= ) ( ) ( ~ ε ε φ

is plasma permittivity. Th i t t ti i t i htf d i 1 D

) ( ~ ) ( ) ( r r r

  • ε

ε ε + =

1-D fluctuation

  • The interpretation is straightforward in 1-D

fluctuation but complicated in 2-D fluctuation due to interference.

uctuat o

APTWG2011 International Conference (NIFS, Toki-City, Japan, June 14-17, 2011)

2-D fluctuation

=> requires imaging reflectometry

3

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SLIDE 4

Microwave Imaging Reflectometry (MIR)

  • Probing beam illuminates extended

region of cutoff layer. The beam front curvature is matched

  • The beam front curvature is matched

to that of cutoff surface (toroidal and poloidal) for optical robustness.

  • The cutoff layer is imaged onto the

d t t d i i f detector array, reducing inference effects. Th MIR t d t t d it

  • The MIR system can detect density

fluctuations in the larger amplitude and shorter wavelength owing to the i i ti

APTWG2011 International Conference (NIFS, Toki-City, Japan, June 14-17, 2011)

imaging optics.

4

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SLIDE 5

Multi-Frequency MIR system

Multi-frequency conventional reflectometry (1-D): − size (correlation length), wavelength, and flow velocity of fluctuation or wave in radial direction − only detect fluctuations in small amplitude and long wavelength (or wave number) Single frequency MIR system (1-D): − size, wavelength, and flow velocity of fluctuation or

  • T. Munsat et al., PPCF 45, 469 (2003)

wave in poloidal direction − enhanced detecting capabilities in the fluctuating amplitude and wavelength Multi-frequency MIR system (2-D): − size, wavelength, and flow velocity in poloidal cross

APTWG2011 International Conference (NIFS, Toki-City, Japan, June 14-17, 2011)

section

5

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SLIDE 6

Design of Design of the KSTAR MIR system the KSTAR MIR system

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SLIDE 7

X-mode Cut-off Layer

Bt = 2.0 T Bt = 2.5 T Bt = 3.0 T Bt = 3.5 T

88 GHz cut-off layer 92 GHz 92 GHz cut-off layer

R di l iti f X d t ff l ( / ) 0 4 0 8

APTWG2011 International Conference (NIFS, Toki-City, Japan, June 14-17, 2011)

Radial position of X-mode cut-off layer (r/a): 0.4 ~ 0.8 Radius of curvature: 700 ~ 1000 mm.

7

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SLIDE 8

KSTAR MIR System

  • Design parameters:

– probe beam frequencies: 88±1 and 92±1 GHz (ultimately 5 frequencies) – detection channel: poloidal 16 and radial 2 (ultimately 5) (ultimately 5) – spatial resolution: poloidally ~0.8 cm and radially ~ 5 cm – maximum detectable wave number: poloidally 2 cm-1 and radially 0.3 cm-1 time resolution: 0 25 μs (4 MS/s digitizer) – time resolution: 0.25 μs (4 MS/s digitizer) – maximum detectable frequency: 2 MHz

APTWG2011 International Conference (NIFS, Toki-City, Japan, June 14-17, 2011) 8

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SLIDE 9

Detectable wave number range

  • Maximum wave number (a):

(a)

1

  • cm

1 . 2 ~ cm 6 56 . 12 4 ) 2 / ( 2 2 = = = = a a k π π λ π

θ

  • Minimum wave number in case (b):

cm 6 ) 2 / ( a a λ 14 3 2 2 π π π

1

  • cm

52 . ~ cm 6 14 . 3 ) 2 ( 2 2 = = = = a a k π π λ π

θ

(b)

  • 1
  • 1

cm 1 2 cm 52 ≤ ≤ k

  • Ion gyro radius for B = 3 T is

cm 1 . 2 cm 52 . ≤ ≤

θ

k

k V) 3 3 (f 47 13 T

at r/a = 0.57

keV) 3 ~ 3 . (for cm 47 . ~ 13 . = =

i i

T ρ

91 . ~ 07 . =

i

k ρ

θ

at r/a = 0.8

APTWG2011 International Conference (NIFS, Toki-City, Japan, June 14-17, 2011)

96 . ~ 08 . =

i

k ρ

θ

9

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SLIDE 10

Cut-off layer fluctuation due to density fluctuation

mm 4 . 8 % 5 /

cutoff =

→ + = R n n

e e

δ δ mm 3 . 5 % 5 /

cutoff =

→ + = R n n

e e

δ δ

APTWG2011 International Conference (NIFS, Toki-City, Japan, June 14-17, 2011) 10

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SLIDE 11

Cut-off layer fluctuation vs. density fluctuation

r/a ~ 0.57 r/a ~ 0.8 Measured phase fluctuation Cut-off layer fluctuation Electron density fluctuation

  • δR = 1.7 mm (δ phase = 2 π) is equivalent to δn/n ~ 0.9 % at r/a ~ 0.57

fluctuation fluctuation fluctuation

  • δR = 1.7 mm (δ phase = 2 π) is equivalent to δn/n ~ 1.5 % at r/a ~ 0.8

APTWG2011 International Conference (NIFS, Toki-City, Japan, June 14-17, 2011) 11

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SLIDE 12

ECEI and MIR Systems at G- & H-port

H-port G-port MIR and 2nd ECEI system 1st ECEI system

APTWG2011 International Conference (NIFS, Toki-City, Japan, June 14-17, 2011) 12

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SLIDE 13

Design of MIR System

  • The MIR and ECEI system share the zoom lenses.
  • The dichroic plate, a kind of high pass filter, will be used to separate the MIR and ECEI

signals signals

APTWG2011 International Conference (NIFS, Toki-City, Japan, June 14-17, 2011) 13

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SLIDE 14

Launching and receiving optics

ECEI zoom lenses Launching lens

Launching optics

S bt it l Subtrait lens

Receiving optics

Detector array Receiving lens

APTWG2011 International Conference (NIFS, Toki-City, Japan, June 14-17, 2011) 14

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SLIDE 15

Schematic of Hardware System

APTWG2011 International Conference (NIFS, Toki-City, Japan, June 14-17, 2011) 15

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SLIDE 16

L b T f h li i Laboratory Test of the preliminary

  • ptics and electronics
  • ptics and electronics
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SLIDE 17

Laboratory test setup of prototype MIR system

APTWG2011 International Conference (NIFS, Toki-City, Japan, June 14-17, 2011) 17

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SLIDE 18

Corrugation phase measurement of reflecting wheel

Corrugated reflecting wheel: Corrugation wavelength ~ 50 mm Corr depth ~ 1 9 radian ~ 0 6 π

APTWG2011 International Conference (NIFS, Toki-City, Japan, June 14-17, 2011)

  • Corr. depth ~ 1.9 radian ~ 0.6 π

~ 0.3 λ0 (λ0 =3.4 mm)

18

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SLIDE 19

Reflected beam from corrugated wheel

( )

  • Corr. depth vs circumference

measured by dial gauge.

l (mm) depth [mm] 860 1.67 865 1.82 870 1.72 875 1.45 880 1 08

max

880 1.08 885 0.88 890 0.78 895 0.89 900 1.18 905 1.48

min

910 1.72 915 1.82 920 1.72 925 1.47 930 1.17 935 0 91

max

935 0.91 940 0.79 945 0.80 950 1.08

  • corr depth = max – min = 1 04 mm

min APTWG2011 International Conference (NIFS, Toki-City, Japan, June 14-17, 2011)

  • corr. depth max

min 1.04 mm

  • corr. wavelength = 50 mm

19

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SLIDE 20

Reflected beam from corrugated wheel

  • probe beam = cos(ωRF t)

(ωRF =88 or 92.5 GHz)

  • LO beam = cos(ωLO t )

(ωRF =89 GHz)

  • wheel corrugation phase = φ_corr = 0.6π cos(ωwheel t)

(← corrugation depth = 1.2 π)

  • beam path length phase = φ_path = 2π/(3.4 mm) L [mm] = 1.85 L [mm]
  • reflected beam = cos[ωRF t + φ_corr + φ_path]

↓ (first stage: array) ↓ ( g y)

  • IF_detection (by array) = cos[(ωRF - ωLO)t + φ_corr + φ_path]
  • IF_reference (by mixer) = cos[(ωRF - ωLO)t ]

↓ (second stage: IQ demodulator)

  • I signal (by IQ box) = cos(φ_corr + φ_path) = cos[0.6π cos(ωwheel t) + 1.85L]
  • Q signal (by IQ box) = sin(φ corr + φ path) = sin[0 6π cos(ω

t) + 1 85L]

APTWG2011 International Conference (NIFS, Toki-City, Japan, June 14-17, 2011)

  • Q signal (by IQ box) = sin(φ_corr + φ_path) = sin[0.6π cos(ωwheel t) + 1.85L]

20

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SLIDE 21

Comparison btw experimental data and analytic calculation

  • I signal = amp * cos(φ_corr + φ_path) * amplitude modulation + offset_I
  • Q signal = (amp*elongation) * sin(φ_corr + φ_path) * amplitude modulation + offset_Q
  • amplitude modulation = [1 + amp_mod * cos(ωmodulation t)]

APTWG2011 International Conference (NIFS, Toki-City, Japan, June 14-17, 2011) 21

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SLIDE 22

Test of IQ system

Ideal case Test result of the IQ system

APTWG2011 International Conference (NIFS, Toki-City, Japan, June 14-17, 2011) 22

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SLIDE 23

Summary

  • A microwave imaging reflectometry (MIR) system is being developed for

transport study in KSTAR plasma and will be installed in late this year.

– detection channel: poloidal 16 and radial 2 (upgraded to 5 in 2013) – spatial resolution: poloidally ~0.8 cm and radially ~ 5 cm – time resolution: 0.25 μs – maximum detectable wave number: poloidally 2 cm-1 and radially 0.3 cm-1

  • Preliminary design of the imaging optics and electronics has been finished and

Preliminary design of the imaging optics and electronics has been finished and prototypes of them is being tested.

  • Numerical simulation study together with the laboratory experiment is being

conducted for characterization of the imaging optics and analysis of measured data.

APTWG2011 International Conference (NIFS, Toki-City, Japan, June 14-17, 2011) 23