Abstract
A system for bunch-by-bunch detection of transverse proton and antiproton coherent oscillations in the Tevatron is described. It is based on the signal from a single beam-position monitor located in a region of the ring with large amplitude functions. The signal is digitized over a large number of turns and Fourier analyzed off-line with a dedicated algorithm. To enhance the signal, band-limited noise is applied to the beam for about 1 s. This excitation does not adversely affect the circulating beams even at high luminosities. The device has a response time of a few seconds, a frequency resolution of $1.6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$ in fractional tune, and it is sensitive to oscillation amplitudes of 60 nm. It complements Schottky detectors as a diagnostic tool for tunes, tune spreads, and beam-beam effects. Measurements of coherent mode spectra are presented to show the effects of betatron tunes, beam-beam parameter, and collision pattern, and to provide an experimental basis for beam-beam numerical codes. Comparisons with a simplified model of beam-beam oscillations are also described.
Highlights
In particle colliders, each beam experiences nonlinear forces when colliding with the opposing beam
A manifestation of these forces is a vibration of the bunch centroids around the closed orbit. These coherent beam-beam oscillation modes were observed in several lepton machines, including PETRA, TRISTAN, LEP, and VEPP-2M [1,2,3,4]. Their observation in hadron machines is made more challenging by the lack of strong damping mechanisms to counter external excitations, they were seen both at the ISR and at RHIC [5,6,7,8,9]
One motivation for the study of coherent beam-beam modes was the realization that their frequencies may lie outside the incoherent tune distribution, with a consequent loss of Landau damping [10]
Summary
Each beam experiences nonlinear forces when colliding with the opposing beam. A manifestation of these forces is a vibration of the bunch centroids around the closed orbit. These coherent beam-beam oscillation modes were observed in several lepton machines, including PETRA, TRISTAN, LEP, and VEPP-2M [1,2,3,4]. Their observation in hadron machines is made more challenging by the lack of strong damping mechanisms to counter external excitations, they were seen both at the ISR and at RHIC [5,6,7,8,9]. The goal of the present research is to develop a new diagnostic tool to estimate bunch-by-bunch tune distributions, to assess the effects of Gaussian electron lenses for beam-beam compensation [11,12,13,14], and to provide an experimental basis for the development of beam-beam numerical codes
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