Abstract
The buildup of low energy electrons in an accelerator, known as electron cloud, can be severely detrimental to machine performance. Under certain beam conditions, the beam can become resonant with the cloud dynamics, accelerating the buildup of electrons. This paper will examine two such effects: multipacting resonances, in which the cloud development time is resonant with the bunch spacing, and cyclotron resonances, in which the cyclotron period of electrons in a magnetic field is a multiple of bunch spacing. Both resonances have been studied directly in dipole fields using retarding field analyzers installed in the Cornell Electron Storage Ring (CESR). These measurements are supported by both analytical models and computer simulations.
Highlights
As a part of the CesrTA program at Cornell [1], the Cornell Electron Storage Ring (CESR) was instrumented with several retarding field analyzers (RFAs) [2], to study the buildup of low energy electrons in an accelerator vacuum chamber
A retarding field analyzer consists of three main components [2]: holes drilled in the beam pipe to allow electrons to enter the device; a retarding grid, to which a voltage can be applied, rejecting electrons with less than a certain energy; and a positively biased collector, to capture any electrons which make it past the grid
Electron cloud buildup has been investigated in dipole field regions throughout CESR
Summary
As a part of the CesrTA program at Cornell [1], the Cornell Electron Storage Ring (CESR) was instrumented with several retarding field analyzers (RFAs) [2], to study the buildup of low energy electrons in an accelerator vacuum chamber. This effect, known as electron cloud [3,4], has been observed in a number of machines [5,6,7,8,9,10,11], and is known to cause emittance growth and beam instabilities [12].
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