Function-process links Conclusions of the electron transport working group.
Cavities and Magnets Working Group
-
Upload
angelica-jimenez -
Category
Documents
-
view
27 -
download
5
description
Transcript of Cavities and Magnets Working Group
Cavities and Magnets Working Group
Darin Kinion (LLNL)4/26/2012
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
G. Rybka Vistas in Axion Physics 2012 3
Axion Search Big PictureSource: T. Dafni, PATRAS 2010 (modified)
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)
Power from Axion-Photon Conversion
• B = Magnetic Field Strength• V = Volume of cavity(ies)• Q = min{QL,Qa}
• Cmn = Form factor
mnS
QCT
VBP
2
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
VBP
2
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
QCT
VBP
2
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
VBP
2
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
VBP
2
Push to higher frequency
For ADMX, r = 21 cmf = 550 MHz
L = 100 cm
Or:
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.)
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)
ADMX operated a 4 cavity array
Did not fill the cavity volume well
Cavities must operate at the same frequency
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
Need up to 32 cavitiesCovers about 1 decade in axion mass
Detecting higher axion massesHigher frequency resonant structures fres ~ 10 x f0 ~ 3 GHz
Yale experiment- single small cavity• Cu resonant cavity at 34 GHz, cooled to T=4 K, tunable,
TE011 mode.
18Vistas in Axion Physics 2012
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