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Draft:Haloscope

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A haloscope is an experimental apparatus designed to detect axions, a theoretical elementary particle proposed as a candidate for dark matter in our galactic halo. Hence the name haloscope. The idea behind haloscopes arises from the axion's ability to convert into photons under the influence of a strong magnetic field. Haloscopes aim to observe this photon conversion and, in doing so, provide direct evidence for the existence of axions. These experiments are particularly focused on axions within the mass range of a few microelectronvolts (μeV) to a few millielectronvolts (meV), aligning with predictions from certain theoretical models.

History

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Working Principle

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The detection mechanism of a haloscope hinges on axions' theoretical property of converting into photons in the presence of a strong magnetic field. This phenomenon, known as the Primakoff effect, occurs when axions couple with electromagnetic fields. A haloscope typically consists of a powerful superconducting magnet, often arranged in a solenoidal configuration, surrounded by a highly sensitive microwave cavity.

Key Components:
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  1. Superconducting Magnet: The haloscope requires an extremely strong magnetic field, typically several teslas in strength. This magnet serves as the medium for axion-photon conversion by facilitating the interaction between hypothetical axions and photons.
  2. Microwave Cavity: The cavity, which is usually made from materials with low loss rates, is used to resonate at specific frequencies. The frequency is tunable over a range, as different axion masses (which correspond to photon frequencies) need to be probed. This cavity is held at cryogenic temperatures (near absolute zero) to minimize thermal noise.
  3. Cryogenic Cooling: The entire apparatus must be maintained at cryogenic temperatures to reduce thermal noise and increase the sensitivity of the photon detection process.
  4. Low-Noise Amplifiers: Any signal produced by axion-photon conversion is expected to be extremely weak. Specialized amplifiers, such as quantum-limited amplifiers, are used to boost the signal while maintaining its fidelity.

Operation

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The haloscope is tuned to scan for specific axion masses by adjusting the microwave cavity to different resonant frequencies. When axions pass through the strong magnetic field within the haloscope, they may convert into detectable photons at a frequency that matches their mass-energy. These photons would then resonate within the microwave cavity, and the resulting signal is amplified and recorded.

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ADMX (Axion Dark Matter eXperiment )

HAYSTAC (Haloscope at Yale Sensitive to Axion Cold Dark Matter)

CAPP (Center for Axion and Precision Physics Research) in South Korea



References

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