Electron Cloud Tests: Electron cloud trapping in quadrupole field

An open question to the electron cloud formation in particle accelerators is the possibility of additional effects from trapping of electrons in the “mirror-like” magnetic fields of quadrupoles.  Results from simulations indicate that a significant fraction of the electron cloud would be trapped with decay times that are many microseconds.  It is especially important to determine the number of trapped electrons and their lifetime for at least two reasons.  In long bunch machines, these are the electrons that interact with the beam during the entire duration of the beam pulse and can be most effective in driving two-stream instabilities.  They also contribute seed electrons to the multipacting at the very end of the bunch passage.  In multi-bunch beams it means that the trapped electrons are not lost during a sequence of “empty buckets” or gaps introduced to allow the electron cloud to dissipate between pulse trains.  As such, they reduce the effectiveness of these gaps to control ECE.

To date, there is little experimental information available concerning electron cloud activity in quadrupoles.  One exception is some recent preliminary results from CERN made using a strip detector (measures flux striking vacuum chamber wall) in an SPS quadrupole where strong electron cloud signals were observed.  In fact, a stronger signals in the quadrupole than in dipoles or drift spaces is observed.  However, experimental information on trapping in quadrupoles is still missing since the strip detector does not measure these.  Overall, we conclude that picture of the ECE is not complete without a better understanding of electron cloud generation in quadrupoles. We propose to measure the electron cloud trapping in PSR quadrupoles at LANL, by means of dedicated electron sweeper detectors.

Documentation

 

 

 

Acc. Design Responsible: R. Macek, LANL.

Collaboration: PSR, LANL in collaboration with LC Div.SLAC.                                                                     

Layout concept and design: R. Macek, M. Pivi, T. Raubenheimer

Engineering designer:

 

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