HERA Accelerator Studies 2000

The HERA accelerator study periods during 2000 were mainly concerned with issues of the luminosity upgrade project. These studies have been described in detail in [1] and will be summarized in this report. The luminosity upgrade was already an important subjects during the accelerator studies of December 1998 [2] and during the year 1999 [3]. Part of these studies have also been reported in [4, 5, 6, 7].It is planned to reduce the horizontal electron emittance from the current 41$\pi$nm to 22$\pi$nm during the luminosity upgrade by increasing th RF frequency by about 250Hz and by using a 72$\circ$ optics. While the luminosity in such an optics was initially too small, luminosity scans indicated that a too large vertical electron beam size limited the luminosity. Decoupling by a vertical closed orbit bump through sextupoles and a minimization of the vertical dispersion then lead to improved luminosity scans and to a satisfactory luminosity for the 72$\circ$ optics. To estimate the effect of the increased beam-beam forces on the electron beam after the luminosity upgrade, several optics with 72$\circ$ degrees phase advance per FODO cell but with different beta functions at the interaction points were used to establish luminosity. These studies indicated that the beam-beam force will not diminish the luminosity for the luminosity upgrade parameters. While increasing the luminosity by the mentioned emittance reduction schemes, the electron beam polarization should not be reduced. Therefore the change of polarization with an RF shift was investigated and a spin matched 72$\circ$ optics was used to store a polarized beam with up to 65% polarization