Orbital dynamics in the Tevatron double helix

A key feature of the Tevatron upgrade is the placement of proton and antiproton bunches on the branches of a double helix which winds around the current closed orbit. Electrostatic separators will transfer the bunches on and off the double helix so that they experience head-on collisions only at the experimental areas, B0 and D0, all other encounters occurring at large transverse separation. In this way, the number of bunches and the luminosity can be increased without a proportional growth in the beam-beam tune shift. The scenario raises a number of beam dynamics (viz., stability) issues, especially (1) the consequences of sampling magnetic fields far from the magnet´s center lines and (b) the effects of the long-range beam-beam interaction. The results of (admittedly incomplete) calculations and simulations done to date are presented to explore the second issue