Design for a practical laboratory detector for solar axions

We present a practical design for a detector sensitive to axions and other light particles with a two-photon interaction vertex. Such particles would be produced in the solar interior by Primakoff conversion of blackbody photons and could be detected by their reconversion into x rays (average energy about 4 keV) in a strong laboratory magnetic field. An existing large superconducting magnet would be suitable for this purpose. The transition rate is enhanced by filling the conversion region with a buffer gas (H₂ or He). This induces an effective photon mass (plasma frequency) which can be adjusted to equal the axion mass being searched for. Axion-photon conversion is then coherent throughout the detector volume for all axion energies. Axions with mass in the range 0.1 eV{}mₐ{}5 eV can be detected using gas pressures of 0.1--300 atm. Axions with the standard coupling strength to photons would give counting rates of 10^-5--10 sec^-1 over this mass range. The search would definitively test one of the only two regions of axion parameters not excluded by astrophysical constraints.