Toroidal Axion Haloscope Development at CAPP Harry W Themann - - PowerPoint PPT Presentation

Toroidal Axion Haloscope Development at CAPP

Harry W Themann Center for Axion and Precision Physics Daejeon, ROK LLNL-Microwave Cavity Workshop 2017

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Why Toroid?

Axion Power 𝑄

𝑏 ∝ 𝑅𝐷𝐶2𝑊

• Larger cavities, higher field magnets, preserve Q & C
• Larger cavities -> problem at higher frequencies
• Multiple Cavities (see SW Youn)
• What about Toroids?
• No endcaps, can I get something for nothing?
• With a toroidal magnet the 𝐶 field is, at least nominally, parallel

to all conductive surfaces

• Lends itself to superconductive films?

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Toroid Modes

• No pure TM or TE modes
• Inverse toroid aspect ratio 𝜍0 =

𝑠 𝑆

• Bicycle tubes are better than

truck tubes

• 𝐹 field lines of desired mode

similar to applied B field

• No mode crossings

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Analytic Modes

• Cap and Deutsch lEEE Transactions on Microwave

Theory and Techniques Vol MTT-26,NO.7, JULY1978

• Janaki & Dasgupta IEEE Transactions on Plasma

Science, VOL. I X . NO. I . FEBRUARY 1990

• Inverse toroid aspect ratio 𝜍0 =

𝑠 𝑆

• J & D expand in 𝜍0
• 𝑈𝑁"𝑚𝑗𝑙𝑓" ∝ 𝑏=0

∞

𝑏𝑗 TM + 𝑐=0

∞

𝑐𝑗 TE

• As 𝑆 → ∞ 𝜍0 → 0 𝑈𝑁"𝑚𝑗𝑙𝑓" 𝑐𝑓𝑑𝑝𝑛𝑓𝑡 𝑈𝑁
• For the dimensions contemplated there are no

degeneracies, no crossings

• We used simulation to verify this

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r R

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• B. R. Ko; Axion Dark Matter Workshop, Stockholm

Effective Volume B2VC

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Low Fringe Fields

R = 200cm R = 50cm Bavg= 5T 9 coils

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Q Factor

• B. R. Ko; Axion Dark Matter Workshop, Stockholm

Assembly Concept

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Assembly Concept

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Assembly Concept

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First Toroid “SUB”

• Driven by a desire to be able

to mount in a cryocooler available to us

• R=4cm r=2cm 𝜍0 = 0.5
• Simulation verifies no mode

crossing

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Cappuccino “SUB”

• Early iteration of design
• Simulation
• Dimensions of SUB
• Dimensions of tune hoop
• Antenna sizes and shapes
• Antenna placement (we had them

at angles in the beginning)

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Design Challenges

• Three sections not

necessary for this model but we decided to have a learning experience

• One challenge was to exert

force to push ends together

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Photo

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CAD Pictures

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First Look

• Coupling issues, cross talk with each other with hoop, sim

vs data

• Best antenna shape/size, reality vs simulation
• Q factor
• Calculated 20 000
• Alignment issues, best 6000
• Indium “gaskets” were a failure
• Bagel cut achieved 20 000 w/o hoop
• The simulations predicted that the hoop must go

upwards but doesn’t seem to matter

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Finished Product

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Q = 10,700 CF = 8.159GHz

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• B. R. Ko; Axion Dark Matter Workshop, Stockholm

Pictures

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Future

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500mm Major Radius

• Continue to develop flanging
• Scale up tuning
• Cryogenic ready
• Packaging
• Physical placement
• Placement WRT to cooling
• Cable routing
• Actuation routing

Conclusion

• We have a working toroidal cavity
• Learned a lot but this has also made

us realize that there are some daunting challenges in front of us.

• CAPP LVP Hall is building

momentum rapidly

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BACKUP

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Assembly Concept

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Challenges

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• B. R. Ko; Axion Dark Matter Workshop, Stockholm