Abstract

Several simulation codes have been adapted so as to model the single-bunch electron-cloud instability including a realistic variation of the optical functions with longitudinal position. In addition, the electron cloud is typically not uniformly distributed around the ring, as frequently assumed, but it is mainly concentrated in certain regions with specific features, e.g., regions which give rise to strong multipacting or suffer from large synchrotron radiation flux. Particularly, electrons in a dipole magnet are forced to follow the vertical field lines and, depending on the bunch intensity, they may populate two vertical stripes, symmetrically located on either side of the beam. In this paper, we present simulation results for the CERN SPS and LHC, which can be compared with measurements or analytical predictions.

Highlights

  • INTRODUCTIONMany past studies of electron-cloud instabilities were performed considering a uniform electron distribution without magnetic field and a constant focusing lattice

  • Many past studies of electron-cloud instabilities were performed considering a uniform electron distribution without magnetic field and a constant focusing lattice.about 80% of the CERN SPS circumference is filled with bending magnets where the electron multipacting is higher than in field free regions

  • About 80% of the CERN SPS circumference is filled with bending magnets where the electron multipacting is higher than in field free regions

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Summary

INTRODUCTION

Many past studies of electron-cloud instabilities were performed considering a uniform electron distribution without magnetic field and a constant focusing lattice. A great limitation is the excessive computing time needed when considering a large number of beam-electron interactions per turn For this reason, simulations with HEADTAIL can presently only be performed using a weak-strong model for the interaction between the cloud and the bunch [3]. In the latter case, the initial electron distribution is uniform. For ρe = 6×1011 m−3, we notice a small growth over 40 ms, while without magnetic field a fast TMCI-like instability develops This difference can partly be explained by the presence of the stripes, which depletes the electron density at the center of the pipe.

BETA FUNCTION VARIATION
TOWARDS A REAL LATTICE
Findings
CONCLUSION AND FUTURE WORK
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