The dynamics of electron cloud buildup, saturation, and dissipation represent a complex
interaction between beam and accelerator parameters. The dynamics of electron clouds
in scenarios with short, high-frequency bunches with low bunch charge are different
than that where beams have long, lower-frequency and higher bunch charges. We present
simluations of electrons clouds for different beam parameterizations and compare
electron cloud dynamics between JLEIC and PIP-II accelerators.
where electron cloud buildup has been observed,
have a good probability of being accelerated to the opposite wall of the beam pipe before
the next bunch crossing.
In this scenario, electrons near
a beam pipe wall experience the electrostatic potential of a passing beam bunch, and are
accelerated towards the center of the beam pipe. After the bunch passes, the electrons drift
to the opposite wall of the beam pipe, with sufficient energy to produce secondary electrons.
Since the time to drift across the beam pipe is less than the time to the next bunch crossing,
the cloud density can build up rapidly under this scenario.
In high-frequency accelerators, with lower bunch charges and shorter bunches, electrons will not
have time to drift across the beam pipe before the next bunch crosses. In this case, the
dynamics are different, because the electrons in the
cloud receive a series of many small, rapid kicks instead of fewer, larger interactions with
the beam. The onset of electron cloud buildup could be delayed in this scenario. However, once a cloud
does form, it could be expected that the cloud would be more dense near the beam, which may
lead to more rapid emittance growth and instability formation.
In this paper, we report simulation results for modeling of electron cloud buildup and dynamics
in high-frequency accelerators. We model parameters relevant to the JLab Electron-Ion Collider
(JLEIC) that is currently being designed. We consider beam frequencies up to 476 MHz for a
variety of different ions, from protons up to Pb (82+), and with bunch charges ranging from
4.2e9 to 0.05e9 ions/bunch, and ion energies from 100 - 40 GeV/u for protons to
lead ions respectively. We
compare simulations of electron cloud buildup and dynamics for these different cases, and
contrast with similar simulations of proton-driven electron cloud buildup in the Fermilab
recycler under the PIP-II upgrade scenario, with a frequency of 52.8 MHz, bunch charge
of 80e9 p/bunch, and energies ranging from 8 - 20 GeV.
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