Abstract
In our previous study of bunch lengthening for the planned Hefei Advanced Light Facility (HALF) storage ring, a periodic transient beam loading effect was found in the presence of passive harmonic cavities for some cases, which can dramatically affect the bunch lengthening as well as the beam stability [T. L. He et al., Bunch lengthening of the HALF storage ring in the presence of passive harmonic cavities, in Proceedings of the IPAC2021, Campinas, SP (JACoW, Campinas, SP, Brazil, 2021), pp. 2082--2085, TUPAB265]. In this paper, we continue to use HALF as an example, via both tracking simulation and semianalytical calculation, to comprehensively study the characteristics of this periodic transient effect, analyze its dependence on some relevant factors and investigate the impact of fill pattern on its periodicity. It is found that there exits a threshold current for this periodic transient effect, which can be increased by the reduction of $R/Q$ of harmonic cavity (HC) and the increase of main cavity (MC) voltage, HC detuning, momentum compaction, and energy spread, as well as the inclusion of short-range wake. In addition, the periodicity of bunch centroid oscillation can be affected by the damping time and MC beam loading, and completely interrupted due to the nonuniform fill pattern, but this is not helpful for improvement of bunch lengthening.
Highlights
The Hefei Advanced Light Facility (HALF) storage ring is designed toward a 2.2 GeV diffraction-limited storage ring (DLSR) with natural emittance of 85 pm rad and nominal beam current of 350 mA [1]
Assuming that the same super-3HC as the SLS/ELETTRA type [2] was used, we have recently studied, via tracking simulation and semianalytical calculation, the bunch lengthening driven by the fundamental mode of super-3HC for the HALF storage ring [3,4,5]
We have shown that the periodic transient beam loading effect (PTBL) effect can cause undesirable bunch lengthening performance for the HALF storage ring at the nominal beam current of 350 mA
Summary
The Hefei Advanced Light Facility (HALF) storage ring is designed toward a 2.2 GeV diffraction-limited storage ring (DLSR) with natural emittance of 85 pm rad and nominal beam current of 350 mA [1]. It is worth noting that stable (static) beam-loading transients with some of the bunches having double-bump profiles were once reported in [8,12], which were observed by reducing the detuning of HC via measurements [12] and simulations [8,12]. We found these results probably show PTBL.
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