R. Meller

CESR status and performance

Machine performance for the running period is reviewed with an emphasis on phenomena associated with the large number of parasitic crossings peculiar to a single ring collider with multi-bunch beams.

Beam-beam interaction with a horizontal crossing angle

Abstract We report measurements of the dependence of luminosity and beam-beam tune-shift parameter on horizontal crossing angle at a single interaction point in the Cornell Electron Storage Ring. The report is based on data collected between September 1991 and January 1992 at CESR. For head-on collisions (zero crossing angle) the achieved tune-shift parameter is ξ v = 0.03 ± 0.002 at 11 mA/bunch. For a crossing half-angle of θ c = ± 2.4 mrad, we achieve ξ v = 0.024 ± 0.002 at similar bunch currents. The data suggest some degradation of performance if the trajectory through the interaction region is distorted magnetically even while head-on collisions are preserved. Therefore at least some of the observed dependence of tune-shift parameter on crossing angle may be due to the associated large displacement of the beam trajectories in the interaction region optics. Furthermore, with the introduction of the crossing angle, the algorithm for optimizing luminosity is significantly complicated due to linear optical errors and the solenoid compensation. We interpret the measured tune-shift parameter at θ c = 2.4 mrad as a lower limit to what can ultimately be achieved.

Performance of the beam stabilizing feedback systems at CESR

The operation of CESR as an electron-positron collider using trains of bunches requires, the use of beam stabilizing feedback systems at routine operating currents. These systems operate on the longitudinal and both transverse modes of dipole oscillation. The experience in routine operations and feedback system performance will be presented.

Improvements to the CESR injector and injection process

It is essential that the storage-ring beam injection time be minimized at an e/sup +/e/sup -/ collider factory in order to maximize the integrated luminosity output of the facility. We describe a program of improvements to the CESR injector chain and injection process which have resulted in a reduction in the CESR fill time of /spl sim/40%. This has in turn allowed shorter high-energy-physics run lengths so that a higher average luminosity is maintained. Shorter fill times have resulted from increased linac beam intensity, stability and reliability, improved synchrotron transmission, faster machine condition switching time, improved CESR injection efficiency and a change to the CESR filling cycle in which both the positron and electron beam currents are topped up at the end of a run.

Precision timing control system

Operation of the CESR storage ring with complex bunch patterns has made necessary more flexible timing controls. Multiple trains of bunches based on a fundamental spacing of 14 ns are used in both the injector and the storage ring. Hence, a generally programmable trigger pattern is needed for electron gun pulsing, beam detection, beam feedback gating, and RF phase control. To achieve this, an upgrade of the previous CESR timing system using small-feature CMOS logic has been built. The new system has a time delay resolution of 10 ps and RMS jitter of 14 ps. The delay transfer function is linear to within 30 ps, and is monotonic over 32 bits of range. The use of programmable large-scale integrated circuits and the VME packaging system results in a system that is contained in 4 crates and occupies a fifth of the volume of its predecessor.

Resolution of a high performance cavity beam position monitor system

International Linear Collider (ILC) interaction region beam sizes and component position stability requirements will be as small as a few nanometers. It is important to the ILC design effort to demonstrate that these tolerances can be achieved - ideally using beam-based stability measurements. It has been estimated that RF cavity beam position monitors (BPMs) could provide position measurement resolutions of less than one nanometer and could form the basis of the desired beam-based stability measurement. We have developed a high resolution RF cavity BPM system. A triplet of these BPMs has been installed in the extraction line of the KEK Accelerator Test Facility (ATF) for testing with its ultra-low emittance beam. A metrology system for the three BPMs was recently installed. This system employed optical encoders to measure each BPMs position and orientation relative to a zero-coefficient of thermal expansion carbon fiber frame and has demonstrated that the three BPMs behave as a rigid-body to less than 5 nm. To date, we have demonstrated a BPM resolution of less than 20 nm over a dynamic range of +/- 20 microns.