Abstract
Coupling impedances and wakefields are fundamental quantities to characterize the electromagnetic interaction of a particle beam with the surrounding environment. In particular, collective effects, triggered by these self-induced fields, may play an important role in beam stability and machine performance. Within the framework of the LHC Injectors Upgrade project, since a significantly higher beam intensity is planned for the CERN Proton Synchrotron, wakefields are expected to increase their influence on the beam dynamics, and their evaluation is becoming important. In this paper we present the results of recent measurements of the longitudinal broadband coupling impedance by means of the incoherent quadrupole synchrotron frequency shift as a function of beam intensity. A detailed evaluation of the contribution of several machine installations to the total impedance budget is also presented and compared with the measurements.
Highlights
INTRODUCTIONThe longitudinal broadband impedance is an important parameter to characterize the electromagnetic coupling of a particle beam with the surrounding elements like kickers, radio-frequency (rf) cavities, diameter changes of the beam pipe, bellows, and many other installations close to the beam
The longitudinal broadband impedance is an important parameter to characterize the electromagnetic coupling of a particle beam with the surrounding elements like kickers, radio-frequency cavities, diameter changes of the beam pipe, bellows, and many other installations close to the beam
Based on the measurements presented in this paper, it will be possible to assess their impact on the broadband impedance
Summary
The longitudinal broadband impedance is an important parameter to characterize the electromagnetic coupling of a particle beam with the surrounding elements like kickers, radio-frequency (rf) cavities, diameter changes of the beam pipe, bellows, and many other installations close to the beam. The first estimations of the coupling impedance in the PS date back to the late 1970s These measurements, based on longitudinal stability during debunching and on quadrupole beam transfer functions [2,3], were already indicating an impedance in the range of ZðpÞ=p ’ 25 [4]. Similar longitudinal broadband impedance measurement campaigns in the CERN Super Proton Synchrotron (SPS) were regularly performed but by injecting a mismatched bunch and observing its quadrupole oscillations [6] instead of exciting the beam with noise.
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