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Abstract. The Mainz Microtron MAMI is a cascade of three racetrack microtrons, delivering since 1991 a high-quality 855 MeV, 100 µA cw-electron beam for nuclear, hadron and radiation physics experiments. An energy upgrade of this facility to 1.5 GeV by adding a Harmonic Double-Sided Microtron (HDSM) as a fourth stage is well underway and first beam is expected during the first half of 2006. A detailed description of the multiple recirculation scheme with normal conducting accelerator structures, the basis for the reliable operation of MAMI, is given and the historical development from MAMI A to MAMI B is described. The natural advancement to MAMI C by realizing a polytron of the next higher order, the HDSM, is covered in the last section and a first glimpse into the future of MAMI is given. PACS

In the quest for detailed spectroscopic insight into the electronic structure at solid surfaces in a large momentum range, we have developed an advanced experimental approach. It combines the 3D detection scheme of a time-of-flight momentum microscope with an optimized filling pattern of the BESSY II storage ring. Here, comprehensive data sets covering the full surface Brillouin zone have been used to study faint substrate-film hybridization effects in the electronic structure of graphene on Ir(111), revealed by a pronounced linear dichroism in angular distribution. The method paves the way to 3D electronic bandmapping with unprecedented data recording efficiency.

High quantum efficiency photocathodes are mandatory for the operation of photoinjector driven electron accelerators with high average current and high brightness beams. Photocathodes based on bi-alkali antimonides, e.g., CsK 2 Sb, exhibit high quantum efficiencies for visible light and can be operated close to the photoemission threshold, thus they are suitable candidates to provide high current and low emittance electron beams. In this paper, a codeposition procedure of K and Cs on Sb resulting in high quantum efficiency photocathodes is presented and compared to the sequential growth procedure that was established for photomultiplier and accelerator applications. In-situ x-ray photoelectron spectroscopy is applied to gain insights into the reaction pathway of antimony with alkali metals, and to optimize the growth process of CsK 2 Sb on Mo. It has been found that the average stoichiometry of the samples is similar after both procedures. The study also presents the behavior of the photocurrent at cryogenic temperatures, the influence of cooling and warmup cycles on the photocathode lifetime and our experience with storage and transport. This work demonstrates that our codeposition growth procedure reproducibly delivers high quantum efficiency photocathodes, and that their quantum efficiency, when excited with green photons, is not influenced by cryogenic temperatures.

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