Beam optics distortion caused by orbit deviation at strong sextupole magnets in SuperKEKB
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Published:2024-02-01
Issue:02
Volume:19
Page:P02012
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ISSN:1748-0221
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Container-title:Journal of Instrumentation
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language:
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Short-container-title:J. Inst.
Author:
Sugimoto H.,Ohnishi Y.,Morita A.,Koiso H.
Abstract
Abstract
The SuperKEKB is an electron-positron double-ring
asymmetric-energy collider at the High Energy Accelerator Research
Organization (KEK) in Japan. It uses a novel collision method
referred to as the nano-beam scheme to avoid the so-called hourglass
effect. The highest peak luminosity achieved thus far is
4.65 × 1034 cm-2s-1, which was
reached on June 8th, 2022. Although the SuperKEKB holds
the record for the world's highest instantaneous luminosity, several
unresolved issues prevent a further increase in luminosity. One of
the major issues is inadequate stability and reproducibility of the
beam orbit and optics. This paper discusses optics distortion caused
by orbit deviation near strong sextupole magnets. Numerical
estimations indicate that a horizontal orbit deviation of a few tens
of micrometers induces a sizable distortion of the optical functions
at the interaction point. Analyses of the amount of betatron tune
feedback and orbit at sextupole magnets used for crab waist and
vertical local chromaticity correction indicate that the
beam-current dependence of the vertical tune shift is attributable
to the change of the beam orbit at the sextupoles. The orbit
fluctuation at the sextupoles causes beta-beating and makes stable
operation at high beam currents more difficult. The results show
that orbit tuning at the sextupoles improves both the injection
efficiency and the detector background level. Optics deterioration
within a few days is another urgent issue in high-beam-current
operation. A vertical orbit change of a few tens of microns at
sextupole magnets installed in arc cells is a matter of concern
according to numerical estimations.
Subject
Mathematical Physics,Instrumentation
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