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
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