Cavities at higher and lower frequencies

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1 Cavities at higher and lower frequencies C. Hagmann, J. Hoskins, I. Stern, A.A. Chisholm, P. Sikivie, N.S. Sullivan, and D.B. Tanner University of Florida

2 Basic cavity is a right circular cylinder Or: For, r = 21 cm f = 550 MHz L = 100 cm

3 Lower frequency 30 m diameter, 3 T magnets have been built for energy storage base frequency = 8 MHz Capacitor for LC resonator Hz to MHz Each pair of plates must be in a grounded cage to avoid -> <- -> <- 0 form factor

4 Signal strength Power from the cavity is Q L ~ 70000(GHz/f) 2/3 (ASE) and Q a ~10 6 g γ ~ 0.97 (KSVZ); g γ ~ 0.36 (DFSZ)

5 Length cannot get too long The longer the cavity, the more TE modes there are in the tuning range. With metal tuning rod, there are also TEM modes at ~ integer*c/2l ~ 150 MHz for 1 m L Typical values L ~ 5r = 2.5*diameter Modes for r = 3.6 cm, L = 15.2 cm cavity. d is the distance the metal rod is from the center. (Divide frequencies by 6 for.)

6 Power will decrease with frequency Single cylinder: Power decreases because the volume decreases as f -3, the Q decreases as f -2/3 while the mass increases as f. Can use multiple cavities, tuned together and added in phase

7 Cavities must operate at the same frequency

8 operated a 4 cavity array Did not fill the cavity volume well

9 Segmented resonator Partitions reduce scale, increase frequency Efficient use of magnetic volume compared to, e.g., 4 parallel cylinders. Tune by moving rods from corner to center in each partition

10 Segmented Resonator ~¼ scale prototype TM010 frequency = 2.7 GHz Q! 25,000 (300K) V! 5 liters Scaled to, would have f = 850 MHz 4 segment resonator would have f = 1.1 GHz

11 Segmented Resonator ~¼ scale prototype TM010 frequency = 2.7 GHz Q 25,000 (300K) V m 3 3D model Comsol Single rod gives TM 010 frequency range = GHz

12 Segmented Resonator ~¼ scale prototype TM010 frequency = 2.7 GHz Q 25,000 (300K) V m 3 3D model Comsol Single rod gives TM 010 frequency range = GHz

13 Segmented Resonator ~¼ scale prototype TM010 frequency = 2.7 GHz Q 25,000 (300K) V m 3 3D model Comsol Single rod gives TM 010 frequency range = GHz

Segmented Resonator ~¼ scale prototype TM010 frequency = 2.7 GHz Q 25,000 (300K) V 0.

14 Segmented Resonator ~¼ scale prototype TM010 frequency = 2.7 GHz Q 25,000 (300K) V m 3 3D model Comsol Single rod gives TM 010 frequency range = GHz Corresponds to MHz for

15 Need up to 32 cavities Covers about 1 decade in axion mass

16 Cavities must be added in phase

17 Pound Drever-Hall (pdh) reflection locking Cavity reflects (promptly) waves that are not on resonance Reflection dip at resonance, along with phase change

18 Phase-modulated light

19 As cavity tunes, phase of reflected carrier shifts

20 Each cavity can be driven to resonance at the carrier 5 GHz oscillator φ N-way splitter 200 khz sine Directional couplers Amplifier Mixer Cavities Tuning rod actuator

21 Above a few GHz

22 Detecting higher axion masses Higher frequency resonant structures f res ~ 10 x f 0 ~ 3 GHz

23 Can be tuned For -HF; frequencies in would be 1.5 to 1.66 GHz

24 C 2 Q varies with tune

25 Approching 1 mev Synthesize static magnetic field with q = q γ Current varies along z

26 Conceptual design Dimensions ~ 3 m x 3 m x 6 m Wire spacing ~ 2 mm Number of wires ~ 4 x 10 6 (but only ~3000 planes) Currents ~ 200 A

27 Summary To go beyond the basic right circular cylinder tuning range and to retain the basic sensitivity at higher frequencies is not easy Mode crossings must be accounted for (Ed Daw has 3 slides) Good ideas are needed

28 THE END

arxiv: v1 [hep-ex] 27 Sep 2017

arxiv: v1 [hep-ex] 27 Sep 2017 First Axion Dark Matter Search with Toroidal Geometry arxiv:1709.09437v1 [hep-ex] 27 Sep 2017 Byeong Rok Ko Center for Axion and Precision Physics Research (CAPP), Institute for Basic Science (IBS), Daejeon