A Spin-Flip Cavity for Microwave Spectroscopy of Antihydrogen

The present thesis is a contribution to the Asacusa (Atomic Spectroscopy And Collisions Using Slow Antiprotons) experiment. The aim of this experiment is to measure the ground-state hyperfine structure of antihydrogen. This is done using a Rabi-like spectrometer line consisting of an antihydrogen source, a microwave cavity, a sextupole magnet and a detector. The cavity induces spin-flip transitions in the ground-state hyperfine levels of antihydrogen whereas the sextupole magnet selects the antihydrogen atoms according to their spin state. Such a configuration allows the measurements of the hyperfine transition in antihydrogen with very high precision. A comparison with the corresponding transitions in hydrogen would thus provide a very sensitive test of the charge-parity-time (Cpt) symmetry. In the context of this thesis, the central piece of this spectrometer line, the spin flip cavity, was designed and implemented. The delicacy of this task was achieving the required field homogeneity: It needs to be better than 90% over a volume of ≈ 1000 cm3 (wavelength 21 cm) to yield reasonable experimental resolution. Furthermore, to avoid uncontrolled spin-flip transitions (Majorana spinflips), a static magnetic field superimposed to the microwave field is necessary. This static field has to fulfill similar requirements on field homogeneity as the microwave field. A suitable static field including an efficient shielding solution was implemented in the context of this thesis as well. The overall outline of the work is as follows: After a general introduction setting the global context of this thesis, the corresponding theoretical background is presented. Subsequently, the experimental setup is discussed including a more detailed overview of the single components of the spectrometer line. In the following, special emphasis is put on the design studies and the mechanical implementation of the spin-flip cavity as well as on the implementation of the static magnetic field including an efficient shielding. The thesis is concluded with a short summary and an outlook on future upgrades of the current setup.