Invited Paper-Progress Report on the 500 MeV Isochronous Cyclotron Meson Factory of ETH Zurich

The goal is a continous external proton beam of the order of 100 ?A, the usable current depending mainly on extraction rate because of activation. The energy of 500 MeV is best suited to produce high fluxes of low energy or stopped mesons. The main fields of the research are planned to be: properties and interactions of mesons and nucleons, nuclear structure physics and medical and biological applications. The use of internal targets in field free regions as well as external targets should provide a great variety of beams for simultaneous experiments. The two-stage accelerator has a 70 MeV sector focussed cyclotron for injection into an isochronous ring accelerator consisting of eight spiral sector magnets. Four cavities operating at 50 MHz should provide at least 1 MeV energy gain per turn. In the course of present development the main fields of work are orbit dynamics and measurement on 1:5 scale magnets and design of a 1:1 model magnet sector. vZ is to be kept around 0.95 throughout acceleration and vr = 1.5 may be used for resonance extraction. Experiments to reach high gap voltage on a full scale cavity in vacuum are in progress (200-300 kV obtained at present). Remaining problems are some aspects of mechanical structure, in particular the vacuum chamber and schemes for quantitative extraction and secondary beam production from external targets at very high radioactivity levels. Funds of 21 Million Dollars have been approved for construction of accelerator and buildings.