Cavities and Magnets Working Group

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Cavities and Magnets Working Group Darin Kinion (LLNL) 4/26/2012

description

Cavities and Magnets Working Group. Darin Kinion (LLNL) 4/26/2012. Cavity Axion Searches. Asztalos et al. PRL 104, 041301 (2009). ADMX experiment. Cavity experiments are sensitive to axions in the range 1 μ ev – 100 μ eV. a. γ. B. Axion Search Big Picture. - PowerPoint PPT Presentation

Transcript of Cavities and Magnets Working Group

Page 1: Cavities and Magnets Working Group

Cavities and Magnets Working Group

Darin Kinion (LLNL)4/26/2012

Page 2: Cavities and Magnets Working Group

G. Rybka Vistas in Axion Physics 2012 2

Cavity Axion Searches

Asztalos et al. PRL 104, 041301 (2009)

Cavity experiments are sensitive to axions in the range1 μev – 100 μeV

ADMX experiment

a

B

γ

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G. Rybka Vistas in Axion Physics 2012 3

Axion Search Big PictureSource: T. Dafni, PATRAS 2010 (modified)

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Big Questions:

• Should we still be looking for axions?– Yes!

• Should we be using microwave cavities to search for axions?– Yes!

• What mass (frequency) range should be to goal?– No overwhelming theoretical consensus– Stick to “natural” range for existing cavity amplifier

technology (100 MHz – 40 GHz)

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Power from Axion-Photon Conversion

• B = Magnetic Field Strength• V = Volume of cavity(ies)• Q = min{QL,Qa}

• Cmn = Form factor

mnS

QCT

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Stored Energy (B2V)

• NHMFL – very interesting array of large volume, high-field magnets

• Built magnets could possibly be utilized, but no natural fits for ADMX

• New magnets – very expensive ($7M-$50M)• Retrofit, renovation of existing magnet could be

problematic

mnS

QCT

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Cavity Q

• ADMX-HF exploring the idea of using superconducting thin films to reduce losses in cavity walls and tuning rods

• Requires homogenous B field to reduce radial component

• Factor of 6 improvement possible

mnS

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System noise temperature

• Combination of physical temperature and first amplifier (mostly) noise temperature

• Superconducting amplifiers provide near quantum limited performance up to ~ 8-10 GHz

• HFETs above 8-10 GHz, pending future amplifier developments

• Quantum Noise ~ hf/kb – above 6 GHz reduce need for dilution refrigerators (He3 systems)

mnS

QCT

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Cavity form factor

• Drives choice of mode typically TM010 for the right-circular cavity

• Higher modes provide path to higher frequencies, as well as in situ testbed for new amplifiers

• Extensive use of Finite Element software

mnS

QCT

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Push to higher frequency

For ADMX, r = 21 cmf = 550 MHz

L = 100 cm

Or:

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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.)

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Push to higher frequencies

• As the cavity(ies) get smaller the question becomes what to fill the remaining magnet volume with– Multiple cavities– Small cavities with TM010-like modes– More magnet wire (increase B0 as volume shrinks)

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ADMX operated a 4 cavity array

Did not fill the cavity volume well

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Cavities must operate at the same frequency

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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

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Need up to 32 cavitiesCovers about 1 decade in axion mass

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Detecting higher axion massesHigher frequency resonant structures fres ~ 10 x f0 ~ 3 GHz

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Yale experiment- single small cavity• Cu resonant cavity at 34 GHz, cooled to T=4 K, tunable,

TE011 mode.

18Vistas in Axion Physics 2012

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Summary

• Current searches are underway– ADMX & ADMX-HF– Yale search at 30+GHz

• Incremental improvement possible in B,V but very expensive

• Factor of 6 possible in Q• Strategy for covering higher frequencies is a

real issue