Fundamental science by high-power microwaves - Millimeter-wave spectroscopy of positronium hyperfine structure and further ( Prof. Dr. Akira Miyazaki)

This frequency range has been used for astrophysics applications, which need to detect very low power (<<1W) microwaves coming from the universe. On the other hand, since positronium has limited lifetime (142 ns), this study requires 203 GHz (wavelength 1.5mm) waves of more than 10 kW equivalent power. Such a unique technical requirement was fulfilled by use of a novel microwave source gyrotron, originally developed for plasma heating in the nuclear fusion application. The hyperfine structure of positronium was directly measured by the gyrotron with an externally attached Fabry-Perot cavity designed for this frequency.

Using a similar setup, research on direct search for extra U(1) gauge boson called hidden photon is being prepared. The search range of the experiment is limited by low quality factor of cavities and low sensitivity of sensors, and would not be comparable to optical laser experiment without state-of-the-art superconducting technology. The core technology for the ultimately high quality factor and sensors is superconducting radio frequency (<10 GHz). At the end of the seminar, some recent activities on superconducting cavities will be presented.