Abstract
Transverse space charge effects in the Low Energy Ion Ring (LEIR) at CERN have been shown to be a major source of particle losses, which can be mitigated with a larger RMS longitudinal emittance. However, due to electron cooling during the injection plateau, the longitudinal density is very high prior to RF capture. In addition there is an uncontrolled cycle to cycle variation in the revolution frequency of the coasting beam on the flat bottom, which degrades the beam quality at capture. In this paper we show that applying an RF frequency modulation during the capture process allows both a controlled blow-up of the longitudinal emittance and a very good reproducibility in the longitudinal distribution, which in turn improves beam transmission through the machine.
Highlights
The Low Energy Ion Ring (LEIR) is the first synchrotron in the ion injection chain for the Large Hadron Collider (LHC)
At present there is a variation on the revolution frequency of the stacked beam from cycle to cycle, which appears to be partly due to the electron cooling
As the RF frequency used for capture is the same cycle to cycle, but the beam revolution frequency is not, the phase space distribution of the captured beam becomes non-reproducible
Summary
The Low Energy Ion Ring (LEIR) is the first synchrotron in the ion injection chain for the Large Hadron Collider (LHC). By applying frequency modulation to the RF during capture both of these effects can be mitigated, whilst maintaining strong cooling on the flat bottom.
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