• S. Federmann, F. Caspers, E. Mahner
  CERN, Geneva
• B. Juhasz, E. Widmann
  SMI, Vienna

The hy­per­fine tran­si­tion fre­quen­cy of hy­dro­gen is known to a very high pre­ci­sion and there­fore the mea­sure­ment of this tran­si­tion fre­quen­cy in an­ti­hy­dro­gen is of­fer­ing one of the most ac­cu­rate tests of CPT sym­me­try. The ASACUSA col­lab­o­ra­tion will run an ex­per­i­ment de­signed to pro­duce ground state an­ti­hy­dro­gen atoms in a CUSP trap. These an­ti­hy­dro­gen atoms will pass with a low rate in the order of 1 per sec­ond through a spin-flip cav­i­ty where they get ex­cit­ed de­pend­ing on their po­lar­iza­tion by a 1.42 GHz mag­net­ic field. Due to the small amount of an­ti­hy­dro­gen atoms that will be avail­able the re­quire­ment of good field ho­mo­gene­ity is im­posed in order to ob­tain an in­ter­ac­tion with as many an­ti­hy­dro­gen atoms as pos­si­ble. This leads to a re­quire­ment of an RF field de­vi­a­tion of less than ± 10 % trans­verse to the beam di­rec­tion over a beam aper­ture with 100 mm di­am­e­ter. All de­sign as­pects of this new spin-flip cav­i­ty, in­clud­ing the re­quired field ho­mo­gene­ity and vac­u­um as­pects, are dis­cussed.