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The Axion Dark Matter eXperiment (ADMX)

The Axion Dark Matter eXperiment (ADMX) uses a resonant microwave cavity within in a large superconducting magnet to search for cold dark matter axions in the local galactic dark matter halo. Sited at the Center for Experimental Physics and Astrophysics at the University of Washington, ADMX is a large collaborative effort with researchers from universities and laboratories around the world. ADMX will soon implement its dilution refrigerator and begin the Gen 2 data schedule. The experimental insert, seen right, within the magnet showing (top to bottom) the thermal shielding, liquid helium reservoir and microwave cavity.

Read about the Side Car RF Cavity

ADMX Sidecar is a higher frequency pathfinder experiment that uses a miniature resonant cavity to search for axions in the 2 GHz - 10 GHz frequency range.

Detecting Axions

The Axion Dark Matter eXperiment (ADMX) detects the very weak conversion of dark matter axions into microwave photons (as seen above). Axion conversion into photons is stimulated by an apparatus consisting of an 8 tesla magnet and a cryogenically cooled high-Q tunable microwave cavity (shown at the upper right). When the cavity's resonant frequency is tuned to the axion mass, the interaction between nearby axions in the Milky Way halo and ADMX's magnetic field is enhanced. This results in the deposit of a very tiny amount of power (less than a yoctowatt) into the cavity.

An extraordinarily sensitive microwave receiver allows the very weak axion signal to be extracted from the noise. The experiment receiver features quantum-limited noise delivered by an exotic Superconducting QUantum Interference Device (SQUID) amplifier and lower temperatures from a 3He refrigerator.

ADMX is the first experiment sensitive to realistic dark-matter axion masses and couplings and the improved detector allows an even more sensitive search.

The Experiment

The microwave cavity within the magnet bore is at the heart of ADMX. It is a circular cylinder, 1 meter long and 0.5 meter diameter. We search for axions by slowly scanning the cavity resonant frequency by adjusting positions of two tuning rods within the cavity. A signal appears when the cavity resonant frequency matches the axion mass
The ultra-low noise microwave receiver makes the experiment possible. The dominant background is thermal noise arising from the cavity and the receiver electronics. Signals from the cavity are amplified by an exotic cryogenic Superconducting QUantum Interference Device (SQUID) amplifier followed by ultralow noise cryogenic HFET amplifiers. The receiver then downconverts mirowave cavity frequencies to a a lower frequency that can be easily digitized and saved.

Sensitivity Map for Axions


"The Definitive Search for Dark Matter Axions"

General Info

Contact Leslie Rosenberg at:
Email: ljrosenberg@phys.washington.edu
Phone:(206) 221-5856
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