Photoelectron trapping in quadrupole and sextupole magnetic fields

An e ÿ p instability has been observed in some proton rings. The instability, which causes beam loss, limits the performance of the ring. The instability may be serious for 3 and 50 GeV proton storage rings in the Japan Proton Accelerator Research Complex (J-PARC). We study the e ÿ p instability in several high intensity proton storage rings operated in the world. This work informs J-PARC of the necessity to cure the instability, for example, by applying a TiN coating on the chamber surface.

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“…The result may depend on the model. It may be possible that there is some special mechanism to trap [19] or to amplify electrons.…”

Section: Simulation Of Electron Cloud Formationmentioning

confidence: 99%

Electron cloud instability in high intensity proton rings

Ohmi

Toyama

Ohmori

2002

Phys. Rev. ST Accel. Beams

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“…12 [16]. The photoelectron density is almost constant during the train gap in these two fields, which implies a long electron lifetime.…”

Section: Trapping In Quadrupole and Sextupole Magnetsmentioning

confidence: 97%

Numerical study of the photoelectron cloud in KEKB Low Energy Ring with a three-dimensional particle in cell method

Wang

Fukuma

Ohmi

et al. 2002

Phys. Rev. ST Accel. Beams

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A three-dimensional particle in cell simulation code has been developed to study the photoelectron cloud instabilities in KEKB LER. In this report, the program is described in detail. In particular, typical simulation results are presented for the photoelectron motion in various kinds of magnetic fields. The simulation shows that a solenoid is very effective in confining the photoelectrons to the vicinity of the vacuum chamber wall and in creating a region free of photoelectrons at the vacuum pipe center. The more uniform the solenoid field is, the more effectively does it suppress the electron-cloud buildup. Multipacting can occur both in a drift region and in a dipole magnet, and the heat load deposited on the chamber wall due to the lost electrons is important in these two cases. Electron trapping by the beam field as well as by various magnetic fields is an important phenomenon, especially inside quadrupole and sextupole magnets. Our numerical results qualitatively agree with the experimental studies.

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“…Quadrupole and sextuple magnet fields are mirror fields that may trap electrons via the mirror-field trap mechanism. However, mirror-field trapping requires that the bunch length is shorter than the period of gyration [42]. Therefore, electrons emitted from the chamber's surface cannot be trapped due to the long bunch length.…”

Section: Dipole Magnetic Field and Other Fieldsmentioning

confidence: 98%

Mechanism of electron multipacting with a long-bunch proton beam

et al. 2004

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The energy gain and motion of electrons can quantitatively describe the mechanism of electron multipacting in a long-bunched proton machine. Strong multipacting usually happens around the bunches' tails due to the high energy of electrons when they hit the chamber surface. We investigated several important parameters of electron multipacting, proving that it is sensitive to the beam's intensity, the shape of its longitudinal profile, its transverse size, the secondary emission yield, and the energy at peak secondary emission yield. Our analyses, simulations, and experiments are all in agreement.

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Photoelectron trapping in quadrupole and sextupole magnetic fields

Cited by 11 publications

References 1 publication

Electron cloud instability in high intensity proton rings

Electron cloud instability in high intensity proton rings

Numerical study of the photoelectron cloud in KEKB Low Energy Ring with a three-dimensional particle in cell method

Mechanism of electron multipacting with a long-bunch proton beam

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