1. Vistas in Axion Physics April 2012 ADMX 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. Vistas in Axion Physics April 2012 ADMX Basic cavity is a right circular cylinder For ADMX, r = 21 cm  f = 550 MHz L = 100 cm Or:

3. Vistas in Axion Physics April 2012 ADMX 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. Vistas in Axion Physics April 2012 ADMX 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. Vistas in Axion Physics April 2012 ADMX 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 ADMX.)

6. Vistas in Axion Physics April 2012 ADMX Power will decrease with frequency 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 Single cylinder:

7. Vistas in Axion Physics April 2012 ADMX Cavities must operate at the same frequency

8. Vistas in Axion Physics April 2012 ADMX ADMX operated a 4 cavity array Did not fill the cavity volume well

9. Vistas in Axion Physics April 2012 ADMX 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. Vistas in Axion Physics April 2012 ADMX Segmented Resonator ~¼ scale prototype –TM010 frequency = 2.7 GHz –Q  25,000 (300K) –V  5 liters Scaled to ADMX, would have f = 850 MHz 4 segment resonator would have f = 1.1 GHz

11. Vistas in Axion Physics April 2012 ADMX Segmented Resonator ~¼ scale prototype –TM010 frequency = 2.7 GHz –Q  25,000 (300K) –V  0.005 m 3 3D model –Comsol –Single rod gives TM 010 frequency range = 2.7 – 3.4 GHz

12. Vistas in Axion Physics April 2012 ADMX Segmented Resonator ~¼ scale prototype –TM010 frequency = 2.7 GHz –Q  25,000 (300K) –V  0.005 m 3 3D model –Comsol –Single rod gives TM 010 frequency range = 2.7 – 3.4 GHz

13. Vistas in Axion Physics April 2012 ADMX Segmented Resonator ~¼ scale prototype –TM010 frequency = 2.7 GHz –Q  25,000 (300K) –V  0.005 m 3 3D model –Comsol –Single rod gives TM 010 frequency range = 2.7 – 3.4 GHz

14. Vistas in Axion Physics April 2012 ADMX Segmented Resonator ~¼ scale prototype –TM010 frequency = 2.7 GHz –Q  25,000 (300K) –V  0.005 m 3 3D model –Comsol –Single rod gives TM 010 frequency range = 2.7– 3.4 GHz –Corresponds to 870 – 1100 MHz for ADMX

15. Vistas in Axion Physics April 2012 ADMX Need up to 32 cavities Covers about 1 decade in axion mass

16. Vistas in Axion Physics April 2012 ADMX Cavities must be added in phase

17. Vistas in Axion Physics April 2012 ADMX Pound Drever-Hall (pdh) reflection locking Cavity reflects (promptly) waves that are not on resonance Reflection dip at resonance, along with phase change

18. Vistas in Axion Physics April 2012 ADMX Phase-modulated light

19. Vistas in Axion Physics April 2012 ADMX As cavity tunes, phase of reflected carrier shifts

20. Vistas in Axion Physics April 2012 ADMX Each cavity can be driven to resonance at the carrier  5 GHz oscillator 200 kHz sine N-way splitter Directional couplers Cavities Mixer Amplifier Tuning rod actuator

21. Vistas in Axion Physics April 2012 ADMX Above a few GHz

22. Vistas in Axion Physics April 2012 ADMX Detecting higher axion masses Higher frequency resonant structures f res ~ 10 x f 0 ~ 3 GHz

23. Vistas in Axion Physics April 2012 ADMX Can be tuned For ADMX-HF; frequencies in ADMX would be 1.5 to 1.66 GHz

24. Vistas in Axion Physics April 2012 ADMX C 2 Q varies with tune

25. Vistas in Axion Physics April 2012 ADMX Approching 1 meV Synthesize static magnetic field with q = q  Current varies along z

26. Vistas in Axion Physics April 2012 ADMX 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. Vistas in Axion Physics April 2012 ADMX 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. Vistas in Axion Physics April 2012 ADMX THE END