DORIS at 2 x 5 GeV

During the last year the e-e+-storage ring DORIS was changed from a 2 x 3,5 GeV double ring with 2 x 480 bunches circulating to a single ring single bunch machine with a maximum energy of 2 x 5.1 GeV. The modifications in the magnet structure and of the rf system are described. The main problems at higher energies were due to magnet saturation and insufficient sextupole strength. To overcome transverse instabilities, a feedback system had to be used. Experimental data in the c.m. energy range of 9.5 to 10.1 GeV were taken successfully with luminosities up to 25 nb-1 per day.