Abstract
The ongoing trend towards synchrotron light storage rings with ultralow emittance lattices leads to greater challenges to achieve beam stability, sufficient Touschek lifetime, low heating of machine components, and conservation of the emittance at high bunch charge. One solution to meet these challenges is to lengthen the electron bunches with harmonic cavities. Many upgrade proposals therefore include harmonic cavities to enhance the machine performance. This is also the case for the MAX IV 3 GeV storage ring, which employs passive third harmonic cavities to achieve up to five times bunch lengthening. Unfortunately, the performance of the harmonic cavities is reduced if a gap in the fill pattern is required. In this paper, the effect on synchronous phase and bunch length due to a gap in the fill pattern for rings with passive harmonic cavities is calculated in a self-consistent way including the bunch form factor. The aim is to achieve faster simulation of various schemes for compensating a gap compared to multiparticle tracking. A new semianalytical method based on an iterative matrix formulation is presented, as well as a single-particle tracking code including the bunch form factor. The results from these methods are compared to both results from a multiparticle tracking code and measurements at the MAX IV 3 GeV storage ring. The importance of including the bunch form factor in simulations is evaluated and discussed.
Highlights
In new and planned upgrades of synchrotron light storage rings around the world, there is a trend towards lattices that achieve ultralow horizontal emittance, pushing the limit for diffraction-limited light up to keV x-ray energies [1]
For medium-energy rings, low transverse emittance at high bunch charge gives rise to strong intrabeam scattering (IBS) that blows up the emittance [4]
This paper focuses on simulations of steady-state transient beam loading effects for rings operating with passive harmonic cavities, but the same considerations are important for schemes with active harmonic cavities, such as the one employed in the BESSY-VSR upgrade [18], if highbrilliance and timing users are to be served simultaneously
Summary
In new and planned upgrades of synchrotron light storage rings around the world, there is a trend towards lattices that achieve ultralow horizontal emittance, pushing the limit for diffraction-limited light up to keV x-ray energies [1]. The effect on synchronous phase and bunch length due to a gap in the fill pattern for rings with passive harmonic cavities is calculated in a self-consistent way including the effect from the bunch profiles by introducing a bunch form factor for every bunch. The paper presents a new semianalytical method based on an iterative matrix formulation, as well as a single-particle tracking code that includes self-consistent calculation of the bunch form factor. The results from these methods are compared to results from a multiparticle tracking code and measurements at the MAX IV 3 GeV storage ring. The importance of including the bunch form factor in simulations is evaluated and discussed
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