Axion Dark Matter Experiment
Encyclopedia
The Axion Dark Matter eXperiment (ADMX) is an ongoing experimental search for axion
s in our galaxy's dark matter
halo.
is a good dark matter
candidate. The only known way to detect a very light axion is with an axion haloscope. The haloscope is a resonant cavity
with a large axial magnetic field
. Axions in our galaxy's dark matter halo convert in the magnetic field into photons, generating a tiny amount of radio frequency
power.
demonstrated the practicality of the axion haloscope, ADMX was constructed at Lawrence Livermore National Laboratory
in 1995. From 2006 to 2008 ADMX was upgraded to use very low noise SQUID
amplifiers. In 2010 it has been decommissioned for transfer to the University of Washington
. There it will be upgraded with a dilution refrigerator
.
. The amplified signal is mixed down to audio frequency and digitally sampled. ADMX is sensitive to a yactowatt (10−24 watts) of axion power. In order to limit thermal noise, the SQUID and the cavity are maintained at about 2 Kelvin by pumping on liquid helium.
Axion
The axion is a hypothetical elementary particle postulated by the Peccei-Quinn theory in 1977 to resolve the strong CP problem in quantum chromodynamics...
s in our galaxy's dark matter
Dark matter
In astronomy and cosmology, dark matter is matter that neither emits nor scatters light or other electromagnetic radiation, and so cannot be directly detected via optical or radio astronomy...
halo.
Background
The very light axionAxion
The axion is a hypothetical elementary particle postulated by the Peccei-Quinn theory in 1977 to resolve the strong CP problem in quantum chromodynamics...
is a good dark matter
Dark matter
In astronomy and cosmology, dark matter is matter that neither emits nor scatters light or other electromagnetic radiation, and so cannot be directly detected via optical or radio astronomy...
candidate. The only known way to detect a very light axion is with an axion haloscope. The haloscope is a resonant cavity
Microwave cavity
A microwave cavity is a closed metal structure that confines electromagnetic fields in the microwave region of the spectrum. Such cavities act as resonant circuits with extremely low loss at their frequency of operation...
with a large axial magnetic field
Magnetic field
A magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;...
. Axions in our galaxy's dark matter halo convert in the magnetic field into photons, generating a tiny amount of radio frequency
Radio frequency
Radio frequency is a rate of oscillation in the range of about 3 kHz to 300 GHz, which corresponds to the frequency of radio waves, and the alternating currents which carry radio signals...
power.
History
Pierre Sikivie invented the axion haloscope in 1983. After smaller scale experiments at the University of FloridaUniversity of Florida
The University of Florida is an American public land-grant, sea-grant, and space-grant research university located on a campus in Gainesville, Florida. The university traces its historical origins to 1853, and has operated continuously on its present Gainesville campus since September 1906...
demonstrated the practicality of the axion haloscope, ADMX was constructed at Lawrence Livermore National Laboratory
Lawrence Livermore National Laboratory
The Lawrence Livermore National Laboratory , just outside Livermore, California, is a Federally Funded Research and Development Center founded by the University of California in 1952...
in 1995. From 2006 to 2008 ADMX was upgraded to use very low noise SQUID
SQUID
A SQUID is a very sensitive magnetometer used to measure extremely weak magnetic fields, based on superconducting loops containing Josephson junctions....
amplifiers. In 2010 it has been decommissioned for transfer to the University of Washington
University of Washington
University of Washington is a public research university, founded in 1861 in Seattle, Washington, United States. The UW is the largest university in the Northwest and the oldest public university on the West Coast. The university has three campuses, with its largest campus in the University...
. There it will be upgraded with a dilution refrigerator
Dilution refrigerator
A dilution refrigerator is a cryogenic device first proposed by Heinz London. Its refrigeration process uses a mixture of two isotopes of helium: helium-3 and helium-4...
.
Hardware
The core of ADMX is an 8.5 Tesla superconducting magnet in a liquid helium bath. Inside the magnet's bore is a tunable microwave cavity . Power from the cavity is amplified with a SQUIDSQUID
A SQUID is a very sensitive magnetometer used to measure extremely weak magnetic fields, based on superconducting loops containing Josephson junctions....
. The amplified signal is mixed down to audio frequency and digitally sampled. ADMX is sensitive to a yactowatt (10−24 watts) of axion power. In order to limit thermal noise, the SQUID and the cavity are maintained at about 2 Kelvin by pumping on liquid helium.