Boyce D. McDaniel

Beam Diagnostic Instrumentation at CESR

We discribe various beam diagnostic devices in use at CESR, an 8 GeV electron-positron storage ring operating primarily in the 4.7 to 5.5 GeV beam energy range. Getting the last 20% of performance depends to some extent on empirical tuning and appropriate presentation of various parameters is very important. Several devices are most useful in machine studies and we describe their operation. The individually regulated quadrupoles in CESR provide unique opportunities for lattice measurements and calibration of beam position monitors.

A SUB-NANOSECOND TIME-OF-FLIGHT CIRCUIT UTILIZING THE INHERENT MODULATION OF A SYNCHROTRON BEAM

Abstract A relatively simple circuit having a resolution of 0.3 nsec has been built and used to separate particles of different mass generated by the Cornell 1.4 GeV electron synchrotron. The circuit has been in operation for a year and has played a central role in several experiments. The vernier chronotron principle of Cottini and Gatti is used so that no high speed electronics is required. The method utilizes the inherent radio frequency bunching of the internal electron synchrotron beam to produce a pulse modulated photon beam. The radio frequency itself is used to perform the timing. The circuit may also be used to make a direct coincidence between two counters with a resolution of 0.4 nsec.

Single Bunch Current Dependent Phenomena in CESR

Single bunch current dependent phenomena have been examined in CESR, the Cornell Electron Storage Ring. These measurements are described and their results compared with predictions using the broad band resonator model of vacuum chamber impedance. A transient anti-damping effect in the vertical plane has been observed. The influence of various machine parameters on this effect will be described and a possible mechanism suggested.

Investigation of the Mobius accelerator at CESR

We present a status report on the investigation of the Mobius scheme for producing equal-emittance round beams at CESR. An insert has been constructed with six 45/spl deg/ rotated quadrupoles which interchange horizontal and vertical betatron oscillations on each passage. We describe the single-beam dynamics and the limitations introduced by the chromaticity correcting sextupoles. We also report on our two-beam experience.

A Single Beam Multibunch Instability at CESR

A transverse coupled bunch instability has been observed in the Cornell Electron Storage Ring CESR for both positrons and electrons. This instability shows strong horizontal or vertical coherent signals but very weak longitudinal signals. Positron injection, which requires sixty-one uniformly spaced bunches in CESR, was originally restricted by the enlarged effective horizontal beam size resulting from this instability. Although several cures have been discovered, only external octupoles provide a sufficient increase in the threshold and are compatible with injection. The theory for coupled bunch motion correctly predicts the instability threshold assuming that the driving mechanism is a 1140 MHz parasitic resonance in the RF cavity. Changes in the threshold with tune and octupole field strength are also correctly predicted.

The U. S. High Energy Accelerator Projects CESR, PEP, Doubler-Tevatron, and Isabelle

I find it is a real challenge to adequately describe all four high energy physics projects that are now under construction in the U.S. It is very gratifying, however, to find so many projects under construction after the long period in which no new starts were being made. We now have a broad spectrum of devices under construction which will certainly in the near future produce results of great excitement in the world of physics. I intend to describe some of the general characteristics of each of the machines and to discuss some of the special points of interest.

Electron accelerators at the frontiers of particle physics

The importance of electron accelerators in high particle physics began with the betatron and has evolved to machines such as the electron‐positron colliders. A review of these machines and their use as tools for probing high energy scales is reviewed. (AIP)

Observation of the Beam-Beam Limit in CESR

CESR has produced e+ e- collisions for high energy physics in the very productive T region (4.7 to 5.7 GeV per beam) since the fall of 1979. The peak luminosity recorded during physics data taking over that period is shown in Fig. 1. The dramatic increase in the luminosity has resulted from the reduction of ßy* from 11 cm to 3 cm, an increase in ¿x *, and increases in the vertical aperture. Furthermore, observations of the beam-beam interaction show that the luminosity increases as the square of the beam current at low currents and linearly with current at high currents. These observations are consistent with a vertical beam size which is constant at low currents and increases linearly at high currents. A linearly increasing vertical beam size implies a constant vertical tune shift. The luminosity and the beam lifetime are limited by nongaussian tails which reach the physical aperture of CESR.

The 10‐GeV synchrotron at Cornell

ON 10 OCTOBER Cornell University and the National Science Foundation will join in the dedication of the Wilson Synchrotron Laboratory and its associated facilities. This laboratory houses the 10‐GeV election synchrotron, the fourth in a series of electron accelerators built and used by physicists at Cornell under the inspiration and leadership of Robert R. Wilson for whom the new laboratory is named. The new machine was conceived in August 1962; in March 1965, after two and a half years of design study and finance negotiations, a construction contract was signed. Two years later a beam circulated in the machine and in March 1968 we obtained full energy of 10 GeV. This is the highest energy yet attained in any electron synchrotron. The experimental‐physics program utilizing the accelerator started in November 1967, at which time the synchrotron was already operating at an energy of 7 GeV.

Present Day Electron Synchrotrons for Energies above 3 GeV

The characteristics of five accelerators designed for energies exceeding 3 GeV are discussed. The features of the Cornell 10 GeV machine are described in some detail.