A five-year program to increase CESR luminosity by a factor of 5 to 10 was begun in Fall 1993. The program is staged in two parts which are referred to as ``Phase 2'' and ``Phase 3.''
Phase 2 operation is planned for the period from mid-1994 until
installation of the CLEO III detector components in 1997. In this phase we
will use bunch trains with a small horizontal crossing angle to store beam
currents up to the limit of the 5-cell RF cavities (approximately 300
mA/beam). Nine trains of 3 bunches each will be used. The IR quad
configuration will be modified to provide the larger horizontal aperture
required for the separate electron and positron orbits. The peak
luminosity for this operation will be around
.
Phase 3 equipment will be installed in CESR at the same time as the
installation of the CLEO III detector described in this report.
Replacement of the four 5-cell RF cavities with four superconducting 1-cell
cavities and modification of the IR to allow more closely spaced bunches
will permit increasing the beam currents. This configuration will allow
us to reach the limits of the ring vacuum chamber (gas desorption and
available pumping rate) using 9 trains of 5 bunches each. The proposed IR
layout will accommodate values of to 1 cm,
making further increases in
luminosity possible if the bunch length can be shortened comparably. The
expected peak luminosity in the Phase 3 configuration is 1 to
.
The IR quad arrangement must be modified from its present configuration to provide greater effective horizontal aperture for crossing angle orbits. The crossing angle operation requires additional aperture in the horizontally focussing quads. This may be achieved by exchanging the two electromagnetic quads on each side (Q1 and Q2) and lengthening the permanent magnet quad using spare sections from the former North area permanent magnet quads. Energy flexibility (4.7 to 5.6 GeV) is possible by moving the Q1 quadrupole longitudinally.
As the bunch spacing is decreased to 14 ns in Phase 3 operation, the
first parasitic crossing point moves from 4.2 to 2.1 m away from the
interaction point. The combination of small separation and large
with
the Phase 2 optics results in an excessive long range beam-beam tune
shift. A high gradient (40 Tesla/m) superconducting quad focuses the beam
vertically in the Phase 3 configuration to minimize the tune shift at the
parasitic crossing. A 30 cm long stepped permanent magnet quad provides
additional focussing as well as shielding of background.