Directional Microwave Antenna Structures for the Detection of Dark Matter Axions

Present detectors for dark matter axions in the microwave range use lower-order cavity modes which inherently suer from low directivity and a small detection volume for higher axion masses. We discuss here an alternative type of axion antenna structure in the microwave range. It consists of a rectangular waveguide, shorted at its ends, representing a TE 10n-resonator. It is placed in the bore of a wiggler or undulator magnet. The magnetic eld strength is sinusoidal along the magnet length which is exploited to work around the disadvantages of a lower-order mode cavity. Movable dielectric slabs at the side of the structure provide a straightforward way to scan over a range of axion masses in the order of 10%.