Analyti tic V c Veri rifica cati tion o of the P Perf rforman ance o ce of Notc tch f filter ters of of the K KST STAR AR EC ECEI EI Sy System J. Leem a , G. S. Yun a , M. Kim a , J. Lee a , W. Lee a , H. K. Park b , J. S. Kang c , N. Ito d , and A. Mase e a Pohang University of Science and Technology, Pohang, Korea b Ulsan National Institute of Science and Technology, Ulsan, Korea c Korea Research Institute of Standards and Science, Daejeon, Korea d Ube National College of Technology, Ube, Yamaguchi, Japan e KASTEC, Kyushu University, Kasuga-shi, Fukuoka, Japan KSTAR Conference 2014 Mayhills Resort, Jeongseon-gun, Gangwon-do, Korea, Feb. 24 – Feb. 26, 2014 Supported by
Detection process of the ECEI system ECEI detction system is based on “Heterodyne design” KSTAR 1 st ECEI system G. S. Yun et al., Rev. Sci. Instrum. 81, 10D930 (2010) At the 1 st mixing stage of ECEI detection process, detectors (mixer-type) could be exposed to stray power of the microwave heating sources or excessive radiation from the plasma Without protection , the detected signal can suffer froml modulation or saturation due to high power RF radiations. In the extreme case, the detector elements can be destroyed 1 st Mixing : Optical mixing (LO + ECE in the air ) 2 nd Mixing : RF mixing (LOs + IFs from 1 st mixing process in the circuit ) divided into 8 channels depending on LO frequencies ECEI detector array (developed by UC Davis) Mini lens Diode (working as a balanced mixer) Complete schematic of the ECE Imaging system C.W. Domier., http://tempest.das.ucdavis.edu/mmwave/dma.html Micro-strip dual dipole antenna for broadband (75-140 GHz) detection KSTAR Conference 2014 (Mayhills Resort, Jeongseon-gun, Gangwon-do, South Korea, Feb. 24 – Feb. 26, 2014)
Characteristics of ECEI detector MSG901 (similar to MA4E1310) ECEI dual antenna detector Specification of MA4E1310 Type : GaAs Flip Chip Schottky Barrier Diode Usage : Single and double balanced mixers through millimeter wave frequencies Operating temperature : -65 ºC ~ 125ºC Maximum LO power : “+20 dBm” Maximum RF power : “ +20 dBm” Dual dipole antenna of the ECEI system X. Kong, C.W. Domier, and N.C. Luhmann, Jr., 33rd IRMMW, 15-19, Sep, (2008) Maximum stray RF power detected by the ECEI system, When the stray RF power has normal incidence to the ECEI detector array Or, the antenna is exposed directly to the “ > 20 dB loss of antenna “ > 20 dB loss of antenna stray power of ECRH gain at incident angle > 10º ” gain at 170 GHz” Sensitivity of the mini lens-based dual dipole antenna of ECEI X. Kong, C.W. Domier, and N.C. Luhmann, Jr., 33rd IRMMW, 15-19, Sep, (2008) KSTAR Conference 2014 (Mayhills Resort, Jeongseon-gun, Gangwon-do, South Korea, Feb. 24 – Feb. 26, 2014)
KSTAR 170 GHz ECH 170 GHz ECH KSTAR 170 GHz X2 ECH/CD SYSTEM ( 1 MW /20 s) Gyrotron system • 1.11MW for 20 sec (40% efficiency) Transmission line system : ~10% loss , “70m” Launcher : ~25% loss “Direct stray power from the gyrotron system is negligible” Absorption power of 170 GHz ECH (estimated from the 2 nd ECEI & MIR ⁄ change of 𝑒𝑋 𝑞 𝑒𝑒 ) co-CD w/ 20 degree : 78 % 1 st ECEI J.H. Jeong et al.., “Recent progress of 170 GHz Gyrotron in KSTAR - 2nd harmonic heating experiment in L-mode plasma” , Japan-Korea Workshop ECE Measurement Strategy on Physics and Technology of Heating and Current Drive, 28-30, Jan, (2013) Stray microwave power from ECH heating (170GHz, 10s of MW) - Reflected ECH power is a Total reflected ECH power inside the vessel (estimation) particular hazard at plasma startup ~ 𝟐 . 𝟐𝟐𝟐𝟐 × 𝟏 . 𝟘 × 𝟏 . 𝟖𝟖 × 𝟏 . 𝟑𝟑 ~ 𝟐𝟐𝟏𝟐𝟐 Or 𝟐 . 𝟐𝟐𝟐𝟐 × 𝟏 . 𝟘 × 𝟏 . 𝟖𝟖 ~ 𝟖𝟖𝟏𝟐𝟐 ( 𝐛𝐛 𝐪𝐪𝐛𝐪𝐪𝐛 𝐪𝐛𝐛𝐭𝐛𝐭𝐪 ) D. Johnson., Status of US ITER Diagnostic Development, Web seminars of USBPO (2013) *Assume that, unabsorbed ECH power is non-uniformly distributed in the vessel. Detected power is ~ 𝐸 𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒 𝑔𝑔𝑔𝑒𝑒𝑒 × 750kW 110m3 Vessel volume ×10cm3( Volume of interest for a single antenna ) ⁄ 80𝐸 𝑛𝑋 S𝑒𝑒𝑔𝑢 𝑞𝑒𝑞𝑞𝑒 𝑒𝑒 𝑒𝑢𝑞 𝑔𝑒𝑒𝑞𝑒𝑒𝑔 × 𝑂𝑒𝑒𝑔𝑢 𝑔𝑒𝑔𝑒𝑞𝑒 𝑒𝑞𝑠𝑞𝑔𝑒𝑒𝑒𝑒 × 7 ( 5𝑒𝑒 , 𝐵𝑒𝑒𝑞𝑒𝑒𝑔 𝐻𝑔𝑒𝑒 ) < 100𝑛𝑋 ( 𝑁𝑔𝑁𝑒𝑛𝑒𝑛 𝑆𝑆 𝑞𝑒𝑞𝑞𝑒 𝑒𝑒 𝑒𝑒𝑒𝑒𝑞 ) KSTAR Conference 2014 (Mayhills Resort, Jeongseon-gun, Gangwon-do, South Korea, Feb. 24 – Feb. 26, 2014)
Frequency Selective Surface An array of periodic structure A single series circuit on a conducting sheet WAVE TRANMISSION 𝒂 𝒑 𝒂 𝒕 𝒂 𝒑 THROUGH THE STRUCTURE Structure of single-loop 𝑎 𝑡 = Impedance of the periodic grating frequency selective surface Z. Shen et al., Plasma and Fusion 𝑎 𝑝 = Impedance of the free space Research 2, S1030 (2007) Depending on the geometries of the periodic structure, FSS can work as band-stop filter or band-pass filter 2 1 R = T = 1 − R ⁄ 2 𝑎 𝑡 𝑎 𝑝 + 1 R = Reflection coefficient of the circuit T = Transmission coefficient of the circuit Examples of Frequency Selective Surface and its equivalent circuit D. Singh et al., Progress In Electromagnetics Research B, Vol. 38, 2012 KSTAR Conference 2014 (Mayhills Resort, Jeongseon-gun, Gangwon-do, South Korea, Feb. 24 – Feb. 26, 2014)
Design of the KSTAR ECEI 170GHz notch filter Square-loop Frequency Selective Surface “Different from previous work, angle insensitivity is 1. High rejection rate ( > 25 dB) a critical specification in this application . Five potential FSS structures are investigated, and the 2. Frequency insensitive to the incident angle unit cell elements are the ring, square loop, square center, Jerusalem cross and double square. FSSs with square loop and ring unit cell structures show best angle insensitivity . The square loop structure is selected as the final model because it is easier to fabricate than the ring structure.” – Protection filter development in TEXTOR Z. Shen et al., Plasma and Fusion Research 2, S1030 (2007) Measured angular performance of TEXTOR 140 GHz SL-FSS filter Z. Shen et al., Plasma and Fusion Research 2, S1030 (2007) 𝑆 𝑎 𝑝 𝑎 𝑝 𝑀 𝐷 Expected performance of KSTAR ECEI 170GHz notch filter KSTAR ECEI 170GHz notch filter and its equivalent circuit N. Ito. Short report on 170GHz Notch filter for KSTAR KSTAR Conference 2014 (Mayhills Resort, Jeongseon-gun, Gangwon-do, South Korea, Feb. 24 – Feb. 26, 2014)
Analytic verification of the notch filter (1) Equivalent circuit of 𝑎 𝑡 = 𝑆 + j 𝑞𝑀 − 1 square-loop FSS 𝑞𝐷 2 1 Calculate 𝑺 R = transmission ⁄ 2 𝑎 𝑡 𝑎 𝑝 + 1 Calculate R, L and C coefficient in 𝒂 𝒑 𝒂 𝒕 𝒂 𝒑 of the equivalent 𝒂 𝒑 𝒂 𝒑 function of 𝑴 circuit to find Z S incident beam T = 1 − R frequency 𝑫 How to calculate R, L and C of equivalent circuit of square-loop FSS? The equivalent-circuit model technique is based on the equations given by “ Marcuvitz” , who first estimated the impedance of the periodic gratings For square loop, modelling process starts with a series of infinite metallic strips (a) (b) (a)The element geometries of a series of infinite 𝑞 metallic strips. 𝑞 𝑞 (b)The element 𝑞 geometries of an 𝑒 array of square loop structure KSTAR Conference 2014 (Mayhills Resort, Jeongseon-gun, Gangwon-do, South Korea, Feb. 24 – Feb. 26, 2014)
Analytic verification of the notch filter (2) Inductive Strip Grating Low-frequency source strikes the grating - - - - - + + + + + Free electrons in the metal are free to move along the strips and continue to move in the same direction until 𝐹 𝑝 E-field reverses directions Large amount of field energy is absorbed by the strips High-frequency source strikes the grating The electrons wiggle back and forth 𝐽𝑒 𝑃𝑒𝑒 Out of phase between moving electron 𝐹 𝑝 𝑴 and E-field Small absorption of field energy - + - - - + + + - + High-pass filter Capacitive Strip Grating Low-frequency source strikes the grating The strips are remained in the former state for large + + + + + - - - - - - - periods of time, since the E-field of a long- - - - + + + + + wavelength varies slowly - - - - - + + + + + + + + + + - - - - - Only a small portion of the wave energy is 𝐹 𝑝 - - - - - + + + + + + absorbed + + + + - - - - - - - - - + + - + + + + + + + + - - - - - - - - - + + - High-frequency source strikes the grating + + + + + + + + - - - - - The strips are not remained in one state but switch - - - - - + + + + + + + + + + - - - - - rapidly between the two due to the E-field 𝑃𝑒𝑒 - - 𝐽𝑒 - - - + + + + + + + + + - + - - Electrons in the metal are constantly - - 𝑫 + oscillating + + + + - - - - - 𝐹 𝑝 - - - - - + + + + + Large energy of the incident wave is absorbed Low-pass filter KSTAR Conference 2014 (Mayhills Resort, Jeongseon-gun, Gangwon-do, South Korea, Feb. 24 – Feb. 26, 2014)
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