Microwave imaging reflectometry Microwave imaging reflectometry for - PowerPoint PPT Presentation

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. Kim 1 , C. W. Domier 2 , and N. C. Luhmann, Jr. 2 POSTECH, 1) KNU, 2) UC Davis 1 st APTWG International Conference NIFS, Toki-city, Gifu, Japan June 14 - 17, 2011

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 overcome deficiencies of the conventional 1-D reflectometry used for density fluctuation measurement measurement. X. Garbet et al., NF 47 , 1206 (2007) APTWG2011 International Conference (NIFS, Toki-City, Japan, June 14-17, 2011) 2

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 ε ε ~ ~ ( ( ) ) c r r o ∫ ∫ φ = k dr ε ( ) r 0 o where k 0 is probe beam wave number, ~ ε = ε + ε is plasma permittivity. ( ) ( ) ( ) r r r o 1-D fluctuation uctuat o • The interpretation is straightforward in 1-D Th i t t ti i t i htf d i 1 D fluctuation but complicated in 2-D fluctuation due to interference. => requires imaging reflectometry 2-D fluctuation APTWG2011 International Conference (NIFS, Toki-City, Japan, June 14-17, 2011) 3

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 detector array, reducing inference t d i i f effects. • Th The MIR system can detect density MIR t d t t d it fluctuations in the larger amplitude and shorter wavelength owing to the i imaging optics. i ti APTWG2011 International Conference (NIFS, Toki-City, Japan, June 14-17, 2011) 4

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): T. Munsat et al., PPCF 45 , 469 (2003) − size, wavelength, and flow velocity of fluctuation or 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 section APTWG2011 International Conference (NIFS, Toki-City, Japan, June 14-17, 2011) 5

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

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 Radial position of X-mode cut-off layer (r/a): 0.4 ~ 0.8 R di l iti f X d t ff l ( / ) 0 4 0 8 Radius of curvature: 700 ~ 1000 mm. APTWG2011 International Conference (NIFS, Toki-City, Japan, June 14-17, 2011) 7

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 μ s (4 MS/s digitizer) time resolution: 0 25 μ s (4 MS/s digitizer) – maximum detectable frequency: 2 MHz APTWG2011 International Conference (NIFS, Toki-City, Japan, June 14-17, 2011) 8

Detectable wave number range • Maximum wave number (a): (a) π π π 2 2 4 12 . 56 = = = = - 1 ~ 2 . 1 cm k θ λ λ ( ( / / 2 2 ) ) 6 6 cm cm a a a a • Minimum wave number in case (b): π π π π π π 2 2 2 2 3 3 . 14 14 = = = = - 1 ~ 0 . 52 cm k θ λ ( 2 ) 6 cm a a (b) ≤ ≤ k ≤ ≤ -1 -1 0 0 . 52 52 cm cm 2 2 . 1 1 cm cm k θ • Ion gyro radius for B = 3 T is ρ = = 0 0 . 13 13 ~ 0 0 . 47 47 cm (f (for 0 0 . 3 3 ~ 3 3 keV) k V) T T i i k ρ = 0 . 07 ~ 0 . 91 at r/a = 0.57 θ i k ρ = 0 . 08 ~ 0 . 96 at r/a = 0.8 θ i APTWG2011 International Conference (NIFS, Toki-City, Japan, June 14-17, 2011) 9

Cut-off layer fluctuation due to density fluctuation δ = + → δ cutoff = δ = + → δ cutoff = / 5 % 8 . 4 mm / 5 % 5 . 3 mm n n R n n R e e e e APTWG2011 International Conference (NIFS, Toki-City, Japan, June 14-17, 2011) 10

Cut-off layer fluctuation vs. density fluctuation r/a ~ 0.57 r/a ~ 0.8 Measured phase Cut-off layer Electron density fluctuation fluctuation fluctuation fluctuation fluctuation fluctuation • δ R = 1.7 mm ( δ phase = 2 π ) is equivalent to δ n/n ~ 0.9 % at r/a ~ 0.57 • δ R = 1.7 mm ( δ phase = 2 π ) is equivalent to δ n/n ~ 1.5 % at r/a ~ 0.8 APTWG2011 International Conference (NIFS, Toki-City, Japan, June 14-17, 2011) 11

ECEI and MIR Systems at G- & H-port G-port H-port MIR and 2 nd ECEI system 1 st ECEI system APTWG2011 International Conference (NIFS, Toki-City, Japan, June 14-17, 2011) 12

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

Launching and receiving optics ECEI zoom lenses Launching lens Launching optics S bt Subtrait lens it l Detector array Receiving optics Receiving lens APTWG2011 International Conference (NIFS, Toki-City, Japan, June 14-17, 2011) 14

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

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

Laboratory test setup of prototype MIR system APTWG2011 International Conference (NIFS, Toki-City, Japan, June 14-17, 2011) 17

Corrugation phase measurement of reflecting wheel Corrugated reflecting wheel: Corrugation wavelength ~ 50 mm Corr depth ~ 1 9 radian ~ 0 6 π Corr. depth ~ 1.9 radian ~ 0.6 π ~ 0.3 λ 0 ( λ 0 =3.4 mm) APTWG2011 International Conference (NIFS, Toki-City, Japan, June 14-17, 2011) 18

Reflected beam from corrugated wheel Corr. depth vs circumference measured by dial gauge . l (mm) ( ) depth [mm] 860 1.67 max 865 1.82 870 1.72 875 1.45 880 880 1 08 1.08 885 0.88 890 0.78 min 895 0.89 900 1.18 905 1.48 910 1.72 max 915 1.82 920 1.72 925 1.47 930 1.17 935 935 0 91 0.91 min 940 0.79 945 0.80 950 1.08 • corr depth = max – min = 1 04 mm corr. depth max min 1.04 mm • corr. wavelength = 50 mm APTWG2011 International Conference (NIFS, Toki-City, Japan, June 14-17, 2011) 19

Reflected beam from corrugated wheel • probe beam = cos( ω RF t) ( ω RF =88 or 92.5 GHz) • LO beam = cos( ω LO t ) ( ω RF =89 GHz) • wheel corrugation phase = φ _corr = 0.6 π cos( ω wheel t) ( ← corrugation depth = 1.2 π ) • beam path length phase = φ _path = 2 π /(3.4 mm) L [mm] = 1.85 L [mm] • reflected beam = cos[ ω RF t + φ _corr + φ _path] ↓ (first stage: array) ↓ ( g y) • IF_detection (by array) = cos[( ω RF - ω LO )t + φ _corr + φ _path] • IF_reference (by mixer) = cos[( ω RF - ω LO )t ] ↓ (second stage: IQ demodulator) • I signal (by IQ box) = cos( φ _corr + φ _path) = cos[0.6 π cos( ω wheel t) + 1.85L] • • Q signal (by IQ box) = sin( φ corr + φ path) = sin[0 6 π cos( ω Q signal (by IQ box) = sin( φ _corr + φ _path) = sin[0.6 π cos( ω wheel t) + 1.85L] t) + 1 85L] APTWG2011 International Conference (NIFS, Toki-City, Japan, June 14-17, 2011) 20

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

Test of IQ system Ideal case Test result of the IQ system APTWG2011 International Conference (NIFS, Toki-City, Japan, June 14-17, 2011) 22