998 research outputs found
Beam-beam compensation studies in the Tevatron with electron lenses
At the Fermilab Tevatron collider, we studied the feasibility of suppressing
the antiproton head-on beam-beam tune spread using a magnetically confined
5-keV electron beam with Gaussian transverse profile overlapping with the
circulating beam. When electron cooling of antiprotons was applied in regular
Tevatron operations, the nonlinear head-on beam-beam effect on antiprotons was
small. Therefore, we first focused on the operational aspects, such as beam
alignment and stability, and on fundamental observations of tune shifts, tune
spreads, lifetimes, and emittances. We also attempted two special collider
stores with only 3 proton bunches colliding with 3 antiproton bunches, to
suppress long-range forces and enhance head-on effects. We present here the
results of this study and a comparison between numerical simulations and
observations. These results contributed to the application of this compensation
concept to RHIC at Brookhaven.Comment: 5 pages, 6 figures. Submitted to the Proceedings of the ICFA
Mini-Workshop on Beam-beam Effects in Hadron Colliders (BB2013), Geneva,
Switzerland, 18-22 March 201
Bunch-by-bunch measurement of transverse coherent beam-beam modes in the Fermilab Tevatron collider
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 offline 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 1.6e-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.Comment: 21 pages, 13 figures, 1 tabl
Electron Lens as Beam-Beam Wire Compensator in HL-LHC
Current wires are considered for compensation of long-range beam-beam
interactions for the High Luminosity upgrade (HL-LHC) of the Large Hadron
Collider at CERN. In this note, we demonstrate the advantage of using Electron
Lens for this purpose instead of a conventional current-bearing wire
Effect of pulsed hollow electron-lens operation on the proton beam core in LHC
Collimation with hollow electron beams is currently one of the most promising
concepts for active halo control in the HL-LHC. In order to further increase
the diffusion rates for a fast halo removal as e.g. desired before the squeeze,
the electron lens (e-lens) can be operated in pulsed mode. In case of profile
imperfections in the electron beam the pulsing of the e-lens induces noise on
the proton beam which can, depending on the frequency content and strength,
lead to emittance growth. In order to study the sensitivity to the pulsing
pattern and the amplitude, a beam study (machine development MD) at the LHC has
been proposed for August 2016 and we present in this note the preparatory
simulations and estimates
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