Landau cavities at MAX II

Harmonic cavities have been used in storage rings to lengthen bunches and increase beam lifetimes dominated by Touschek scattering. Transient beam loading in the harmonic cavities generated by asymmetries in the fill pattern causes significant variation of the bunch synchronous phase and bunch length along the bunch train when the longitudinal restoring force has been reduced. This results in a significant reduction in the mean bunch lengthening and potential lifetime increase. We describe how beam current modulations give rise to transient effects much larger than expected from the linear model of the beam cavity interaction. We also develop a tracking simulation to predict results and apply this simulation to an analysis of the beam loading transients for the case of passive and active normal and superconducting third harmonic rf systems using Advanced Light Source parameters.

Section: Introductionmentioning

confidence: 99%

Transient beam loading effects in harmonic rf systems for light sources

Byrd

Santis

Jacob

et al. 2002

“…A radio frequency cavity with resonant frequency near a harmonic of the fundamental rf cavity may increase Landau damping of synchrotron oscillations and lengthen the bunch, thereby suppressing coupled-bunch instabilities and increasing the Touschek lifetime [1][2][3][4][5][6][7][8][9]. A Landau cavity may be operated in passive mode, where its voltage is induced by the beam current, or active mode, where its voltage is maintained by an rf power supply and feedback.…”

Section: Introductionmentioning

confidence: 99%

“…(8), the integration should be taken over an interval in t that greatly exceeds s t , but is smaller than the confining rf bucket. Equation (8) gives, for a quadratic synchrotron potential ͓U͑t͒ at 2 ͔, s t a͑s E ͞E͒͞v s , and, for a quartic synchrotron potential ͓U͑t͒ ct 4 ͔,…”

mentioning

confidence: 99%

Robinson instabilities with a higher-harmonic cavity

Bosch

Kleman

Bisognano

2001

A radio frequency system with a fourth-harmonic "Landau" cavity suppresses coupled-bunch instabilities and increases the beam lifetime of the Aladdin electron storage ring. When the storage ring is operated with a small momentum compaction, instabilities limit the utility of the Landau cavity. Analytical modeling of instability frequencies and growth rates, simulations, and experiments suggest that the observed instabilities result from coupling between dipole and quadrupole Robinson modes.

“…Harmonic cavities have been successfully used for many years in second and third generation light sources in both active [9] as well as passive [10][11][12][13][14] configurations. The basic theory is described in [15] and beam instability analyses under the presence of harmonic cavities have been carried out by several authors (e.g.…”

Section: Introductionmentioning

confidence: 99%

Equilibrium bunch density distribution with passive harmonic cavities in a storage ring

Tavares

Andersson

Hansson

et al. 2014

The MAX IV storage rings, currently under construction in Lund, Sweden, will use third harmonic cavities operated passively to lengthen the bunches and alleviate collective instabilities. These cavities are an essential ingredient in the MAX IV design concept and are required for achieving the final design goals in terms of stored current, beam emittance, and beam lifetime-such performance challenges are in fact common to all recent ultralow emittance storage ring designs and harmonic cavities are currently under consideration in several laboratories. In this paper, we report on parametric studies comparing different harmonic cavity settings in terms of the resulting bunch length, peak bunch density, and incoherent synchrotron frequency spread for the MAX IV 3 GeV ring. The equilibrium longitudinal bunch density distribution was calculated by establishing a self-consistent equation for the bunch form factor, describing the bunch shape. The calculations are fully self-consistent in the sense that not only the amplitude but also the phase of the waves excited by the beam in the harmonic cavity were assumed to be a function of the bunch shape, which allowed us to explore a wide parameter range not restricted to the region close to the conditions for which the first and second derivatives of the total rf voltage are zero at the synchronous phase. Our results indicate that up to a factor 5 increase in rms bunch length is achievable with a purely passive system for the MAX IV 3 GeV ring while keeping a relatively large harmonic cavity detuning, thus limiting the unavoidable Robinson antidamping rate from the fundamental mode of a passively operated harmonic cavity to values below the synchrotron radiation damping rate. The paper is complemented by results of measurements performed in the MAX III storage ring, which showed good agreement with calculations following the fully self-consistent approach.