Optical Notch Filter for the Stochastic Cooling System of COSY

Two cooling methods are installed in the cooler synchrotron COSY. The electron cooler is used for stacking and cooling of proton beams with energies between 45 MeV and 180 MeV. After last year’s commissioning the stochastic cooling system became a standard tool for beam cooling in the momentum range of 1.5-3.3 GeV/c. The stochastic cooling pickups also serve for precision measurements of the chromaticity [6]. One advantage of COSY is the possibility to set up different machine settings in a ‘supercycle’. Internal experiments can take data below, close at and far above the threshold in one supercycle. The transversal stochastic cooling system was updated using the COSY software timing system to allow cooling in all three experiments. For longitudinal cooling a new notch-filter was fabricated. The delay-line of the notch-filter was substituted by an optical delay line. We will present the characteristics of the optical notch filter and the enhancement of the beam quality for an internal gas target using the longitudinal cooling system with the new notch-filter. In order to use the longitudinal cooling in a ‘supercycle’ the optical delay line has been further improved. A part of the optical signal path is carried free through an air section. This section is adjusted according to the beam travelling time with the aid of a motor-driven prism.