• 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.

• F. Caspers, S. Federmann, E. Mahner, P.C. Pinto, D. Seebacher, M. Taborelli
  CERN, Geneva
• B. Salvant
  EPFL, Lausanne
• C. Yin Vallgren
  Chalmers University of Technology, Chalmers Tekniska Högskola, Gothenburg

Electron cloud is a limitation to increasing the beam current in the CERN SPS in the frame of an intensity upgrade of the LHC complex. Coating the vacuum chamber with a thin amorphous carbon layer is expected to reduce the electron cloud build-up. Three SPS straight sections have been coated to study the performance of this carbon coating. The microwave transmission method is one possible way to monitor electron cloud and hence to test the effect of the coating. In this paper the evolution of the experimental setup for measurements of the electron cloud using LHC type beams with different bunch spacing will be described. Due to the low revolution frequency of about 43 kHz serious electromagnetic compatibility problems and intermodulation have been found. These effects and their mitigation are described. Finally we present the measurement results illustrating the possible reduction due to the carbon coating.