ON INCREASING HERA LUMINOSITY

The Luminosity of the HERA lepton proton collider is limited in part by the bunch length of the protons of 20cm. This limitation is expected to be removed by the installation of the new damper system which will control longitudinal coupled bunch instabilities of the proton beam [1] thereby avoiding the bunch lengthening by a factor of two. This opens new possibilities for increasing the luminosity in HERA since the beta functions at IP for both leptons and protons can be lowered by about 20% without noticeable reduction of the corresponding luminosity by the so called hourglass effect [2]. While the beta function of the proton ring could be reduced with the help of the quadrupoles in the low beta section only, the reduction of the beta function of the lepton ring up to this value of 20 % cannot be done by the same means without significant loss of dynamic aperture. A more intricated use of the beam-beam focussing (dynamic beta) is required in order to achieve the desired beam spot size at the IP’s. The price to pay here is an additional beam-beam beta beat as well as a distortion of the non-linear chromaticity compensation, which may lead to enhanced synchro-betatron resonances. This paper represents an overview about available margins and given constraints for more luminosity gain in HERA under the new conditions