Transverse Multibunch Instabilities Research Articles

Transverse multibunch instabilities for two bunch trains on separated orbits

Transverse multibunch instabilities including the resistive wall instability and ion instabilities are investigated analytically and numerically for two bunch trains on separated orbits in a storage ring. The two separated orbits' operating mode appears more stable against transverse multibunch instabilities than the conventional single orbit operating mode and may be beneficial to high current operations for colliders or synchrotron light sources.

Review of collective beam instabilities in electron-positron storage rings

The review of studies of collective beam instabilities in electron-positron storage rings is presented. The processes of excitation and suppression of the longitudinal microwave instability, transverse mode coupling instability, longitudinal and transverse multi-bunch instabilities, and instabilities induced by an interaction of a beam with ions or electron clouds are discussed. Important equations for estimation of the threshold beam currents and the rise time of instabilities, as well as the references to the major original works are given. The methods for diagnostics and suppression of instabilities are considered using specific examples.

Simple model for multibunch transverse coherent instabilities in a beam containing a gap

We use the model with exponentially decaying wakes to study transverse multibunch instabilities in a beam where a uniformly filled train of bunches is followed by the gap which is empty of bunches. Stability of both betatron and synchrobetatron modes is inspected. Contrary to cases of uniformly filled beams, the amplitudes of multibunch eigenmodes in such a beam grow towards the end of the train. This amplification of oscillation amplitudes along the beam can limit the beam performance in high-current operation of accelerators.

Landau damping via the harmonic sextupole

Multibunch instabilities of a storage ring electron beam occur due to coherent particle oscillations generated through a bunch to bunch coupling via the impedances, deteriorating the beam quality. One cure for multibunch instabilities is Landau damping, i.e., introducing a spread in the oscillation frequencies among the particles of the individual bunches in order to destroy the coherence of the coupled multibunch oscillation. Measurements at ELETTRA have shown that the harmonic sextupole provides Landau damping capable of suppressing transverse multibunch instabilities. The damping is induced by the nonlinear tune spread with amplitude among the electrons within the individual bunches.

Controlling transverse multibunch instabilities in linacs of high-energy linear colliders.

In this paper, we study multibunch beam breakup, with emphasis on theoretical methods applicable to the design of a linear collider with a center-of-mass energy near 1 TeV. One way to significantly improve the luminosity and energy transfer efficiency of such a collider is to accelerate a train of bunches rather than just a single bunch each time the linac accelerating structure is filled with a pulse of rf energy. For the required bunch charges and intensities, the transverse instability due to the wake fields produced in the accelerating structure is very severe unless measures are taken to control it. Therefore, we examine the effects of several methods of reducing this instability: (1) use of damped acceleration cavities, (2) placing the bunches near nodes of the transverse wake fields produced by preceding bunches, (3) introducing a spread (over different cells of the accelerating structure) of the individual mode frequencies in the transverse wake field, and (4) varying the strength of the transverse focusing from bunch to bunch, in such a way as to partially cancel the effects of the wake fields from preceding bunches. We present examples illustrating the effectiveness of these cures, using realistic linear-collider design parameters.

Instability Studies and Double RF-System Operation at BESSY

Longitudinal multi-bunch oscillations are observed at the BESSY storage ring even with beam currents of 1-2 mA, although stored currents up to 970 mA can be achieved. With a double rf-system the threshold currents can be increased when operating the system in the tune splitting or in the `Landau'-cavity mode. A longitudinal impedance of ?Z/n??12 ? is obtained from bunchlength measurements. No transverse multi-bunch instabilities have been observed. This may be explained by Landau damping induced by the non-linear fields of the ions trapped in the beam.