Multiple-Cavity Detector for Axion Search Workshop on Microwave - PowerPoint PPT Presentation

Multiple-Cavity Detector for Axion Search Workshop on Microwave Cavities and Detectors for Axion Research 2017. 01. 10 ~ 13, Livermore, CA SungWoo YOUN Young Scientist Fellow Center for Axion and Precision Physics Research (CAPP) Institute for Basic Science (IBS) Republic of Korea

2 SungWoo YOUN Multiple-Cavity Detector Introduction : Magnet bore : Cavity Larger Higher Volume frequency f TM 010 = 11.5 GHz R [ cm ] ! Single large cavity Single small cavity Multiple small cavities a → γγ ∼ B 2 VQC P ! • Multiple-cavity detector • Increases experimental sensitivity for axion searches in higher frequency regions • Requires signal combination in phase: phase-matching

3 SungWoo YOUN Multiple-Cavity Detector Configurations 1 2 3 Schematic N complete N amplifiers 1 amplifier Characteristic readout chains 1 combiner 1 combiner

4 SungWoo YOUN Multiple-Cavity Detector Configurations 1 2 3 Schematic N complete N amplifiers 1 amplifier Characteristic readout chains 1 combiner 1 combiner Sensitivity* ! N ⋅ SNR sngl !N ⋅ SNR sngl ! N ⋅ SNR sngl ** (SNR) SNR sngl = SNR of single cavity SNR sngl = P ( G ⋅ S ) 2 V out = G ⋅ ( S + N C ) + N A ⇒ = S S ( G ⋅ N C + N A ) 2 P N N C G, N A * Correlated signal and uncorrelated noise ** N.F. comb = 0

5 SungWoo YOUN Multiple-Cavity Detector Configurations 1 2 3 Schematic N complete N amplifiers 1 amplifier Characteristic readout chains 1 combiner 1 combiner Sensitivity ! N ⋅ SNR sngl N ⋅ SNR sngl N ⋅ SNR sngl (SNR) Pros. Individual access Higher sensitivity Simpler design Lowest sensitivity N complete readout Cons. N amplifiers SNR 3 < SNR 2 * chains * In reality, N.F. comb ≠ 0 ex) G=12, N.F. amp =6, N.F. comb =0.5 => SNR 3 is lower than SNR 2 by 10%

6 SungWoo YOUN Multiple-Cavity Detector Configurations 1 2 3 Schematic N complete N amplifiers 1 amplifier Characteristic readout chains 1 combiner 1 combiner Sensitivity ! N ⋅ SNR sngl N ⋅ SNR sngl N ⋅ SNR sngl (SNR) Pros. Individual access Higher sensitivity Simpler design Lowest sensitivity N complete readout Cons. N amplifiers SNR 3 < SNR 2 chains

7 SungWoo YOUN Multiple-Cavity Detector Multiple-Cavity Detector • Introduced in 1990 and exploited by ADMX • KSVZ with 3.3639 < m a [µeV] < 3.3642 excluded with 90% C.L. • Phase-matching mechanism is challenging • Failure reduces signal power and degrades SNR • Broadens the bandwidth of power spectrum • Decreases the cavity quality factor • 5 year IBS Young Scientist program is devoted to develop the system at CAPP/IBS

8 SungWoo YOUN Multiple-Cavity Detector Design of a Multiple-Cavity System • Array of N identical cavities • Same dimension and same tuning mechanism S.A. Cryostat Amplifier • N-way power combiner Combiner • Before the first stage of amplification • Remaining RF components are identical with a single-cavity experiment • A quadruple-cavity detector • For a magnet bore (D) of 10 cm • Maximum cavity radius (R) of 1.7 cm R • Cavity wall thickness of 4 mm • 46% volume usage D • TM 010 frequency: 6.75 GHz

9 SungWoo YOUN Multiple-Cavity Detector Simulation Study (COMSOL) Resonant frequency 6.80E+09 Cu cavity Δ f ~ 20% 6.60E+09 (R=1.7cm,L=10cm*) δ f/ δθ ~ 5 MHz/deg 6.40E+09 6.20E+09 Tuning system (Dielectric rotational rod) 6.00E+09 ( ε =10, r/R=0.1*) 5.80E+09 5.60E+09 5.40E+09 0 0.2 0.4 0.6 0.8 1 Quality factor Form factor 25000 0.8 0.7 20000 0.6 0.5 15000 0.4 ! ! 2 ∫ d 3 x B 0 ⋅ E ( x ) 10000 0.3 Δ Q ~ 30% C = 0.2 ! 2 δ Q/ δθ ~ 0.15%/deg 5000 ∫ 2 V d 3 x ε ( x ) B 0 E ( x ) 0.1 0 0 0 0.2 0.4 0.6 0.8 1 0 0.2 0.4 0.6 0.8 1

10 SungWoo YOUN Multiple-Cavity Detector Conversion Power and Scan Rate • A quadruple-cavity system • 4 cavities with R = 1.7 cm and L = 10.0 cm => V = 0.35 L • Conversion power ⎛ ⎞ ⎛ ⎞ ⎛ ⎞ g a γγ ρ a f a a → γγ = 1.8 × 10 − 22 W P ⎜ ⎟ ⎜ ⎟ ⎜ ⎟ 0.97 0.45 GeV cc 6 GHz ⎝ ⎠ ⎝ ⎠ ⎝ ⎠ 2 ⎛ ⎞ ⎛ ⎞ ⎛ ⎞ ⎛ ⎞ B 0 Q l V C × ⎜ ⎟ ⎜ ⎟ ⎜ ⎟ ⎜ ⎟ 8 T ⎝ 0.35 L ⎠ ⎝ 0.5 ⎠ Q a ⎝ ⎠ ⎝ ⎠ • Scan rate 4 2 2 2 ⎛ ⎞ ⎛ ⎞ ⎛ ⎞ g a γγ ⎛ ⎞ ρ a f a df dt = 16.3 MHz 4 ⎜ ⎟ ⎜ ⎟ ⎜ ⎟ ⎜ ⎟ year ⎝ SNR ⎠ 0.97 0.45 GeV cc 6 GHz ⎝ ⎠ ⎝ ⎠ ⎝ ⎠ 2 4.5 K 2 4 2 ⎛ ⎞ ⎛ ⎞ ⎛ ⎞ ⎛ ⎞ ⎛ ⎞ B 0 Q l V C × ⎜ ⎟ ⎜ ⎟ ⎜ ⎟ ⎜ ⎟ ⎜ ⎟ 8 T ⎝ 0.35 L ⎠ ⎝ 0.5 ⎠ T sys Q a ⎝ ⎠ ⎝ ⎠ ⎝ ⎠

11 SungWoo YOUN Multiple-Cavity Detector Phase (Frequency) Matching • Source of frequency mismatch • Machining tolerance in cavity fabrication • 50 µm => 25 MHz for a 6 GHz cavity • Ideal frequency matching is not possible! • Typical step size ≠ 0°: 0.1 m° => 0.5 kHz • Realistic approach: Frequency mismatch! • Up to a certain level where a reduction in the FMT “combined” power is not significant • Frequency Matching Tolerance, FMT f 0 f f 0 : target frequency

12 SungWoo YOUN Multiple-Cavity Detector Phase (Frequency) Matching • Source of frequency mismatch • Machining tolerance in cavity fabrication • 50 µm => 25 MHz for a 6 GHz cavity • Ideal frequency matching is not possible! Ideal • Typical step size ≠ 0°: 0.1 m° => 0.5 kHz • Realistic approach: Frequency mismatch! Combined • Up to a certain level where a reduction in the FMT “combined” power is not significant • Frequency Matching Tolerance, FMT • Criteria : P comb > 0.95 P ideal f 0 f f 0 : target frequency

13 SungWoo YOUN Multiple-Cavity Detector Frequency Matching Tolerance – I • Pseudo-experiment study • 4-cavity detector, Q u = 10 5 , f 0 = 6 GHz • Tolerance Under Test (TUT) = (0,) 10, 20 ,30, 60, 100, 200 kHz • Combined power spectra • 1000 pseudo-experiments => averaged power spectra Combined power spectra (60 kHz) Averaged combined power spectra Power Spectra ( 60kHz ) Relative Amplitude 4 4 TUT = 0 kHz TUT = 0 kHz TUT = 60 kHz 10 kHz 20 kHz 3 3 Arbitrary Unit Arbitrary Unit 30 kHz 60 kHz 100 kHz 2 2 200 kHz 1 1 0 0 5.9996 × 10 9 5.9998 × 10 9 6.0000 × 10 9 6.0002 × 10 9 6.0004 × 10 9 5.9996 × 10 9 5.9998 × 10 9 6.0000 × 10 9 6.0002 × 10 9 6.0004 × 10 9 Frequency ( Hz ) Frequency ( Hz ) Power amplitude from each cavity is normalized to 1.

14 SungWoo YOUN Multiple-Cavity Detector Frequency Matching Tolerance – II Relative Power and Width Averaged power amplitude and width TUT Power Scan Q u SNR 1.2 (kHz) Amp. Rate 20.00 0 1.00 1.00 1.00 1.00 1.0 Relative Power 18.00 Width ( kHz ) 16.00 0.8 10 0.99 0.99 0.99 0.96 14.00 12.00 0.6 20 0.96 0.95 0.94 0.85 10.00 8.00 0.4 30 0.93 0.91 0.88 0.71 6.00 4.00 0.2 60 0.78 0.73 0.67 0.31 0.0 100 0.60 0.55 0.45 0.11 0 5000 10000 15000 20000 Tolerance Under Test ( Hz ) • For 6.0 GHz axion signal, 4-cavity detector with Q u =10 5 • 20 kHz is the FMT for the system • In general, FMT = 2 GHz / Q u • For Q u =10 6 , FMT = 2 kHz • cf. typical step size of 0.1 m° => frequency step: 0.5 kHz

15 SungWoo YOUN Multiple-Cavity Detector Tuning Mechanism – I • Basic principle of coupling – critical coupling • Minimizing the reflection coefficient ( Γ ) in S parameter spectrum • Forming a circle passing through the center of the smith chart • For a single cavity • Γ is minimized when • System is critically coupled Γ = Z L − Z 0 Z L + Z 0 • For a multiple-cavity system • Combined Γ is minimized when • Frequency matching is successful • Entire system is critically coupled

16 SungWoo YOUN Multiple-Cavity Detector Tuning Mechanism – II • Frequency matching & critical coupling Linear piezo 3) • Consisting of three steps 1) simultaneous operation of the tuning systems • To shift target frequency 2) finer operation of the individual tuning … systems • To achieve frequency matching 3) global operation of the couplers • To achieve critical coupling Rotational piezos • At the sacrifice of sensitivity loss of <0.5%* 1) 2) * Machining tolerance of 50 µm and uncertainty on surface conductivity of 2%

17 SungWoo YOUN Multiple-Cavity Detector Experimental Demonstration Couplers • Double-cavity • O.D.= 5.08 cm Linear Positioner • I.D. = 3.88 cm • f TM010 = 5.92 GHz Coupler holder • Q L = 9,000 at RT • Tuning system • Dielectric rods (95% alumina) • f TM010 = 4.54 GHz at center • Q L = 2,500 at RT • Two rotators (ANR240) Rotators • Frequency tuning • One linear positioner (ANPz101eXT12) • Global operation of two couplers

18 SungWoo YOUN Multiple-Cavity Detector Sequence of Demonstration • Using a double-cavity system with a combiner • Calibrate the system up to the two antennas • Critical coupling of each cavity separately at slightly different resonant frequencies • Measure the initial Q (and S 11 ) values • Assembly of the full system • Two (small) reflection peaks and double (small) circles