Transverse Schottky and beam transfer function measurements in space charge affected coasting ion beams

Abstract

Transverse Schottky spectra and beam transfer functions (BTFs) of coasting ion beams were measured in the heavy ion synchrotron SIS-18 in order to study the impact of space charge on the transverse beam dynamics. The particle number in the beam was varied to investigate the intensity dependence of the space-charge effect. No cooling was applied to the beams throughout the experiment. The expected deformation of the Schottky spectra and BTFs is observed. An analytic model with linear space charge is employed to describe the deformed Schottky and BTF signals. In this model, the incoherent space-charge force and the coherent forces due to impedances are treated separately. Using the model, the space-charge induced tune shift is evaluated both from the position and the form of the signals. The data are well described by the model, only in the high-intensity BTFs deviations are observed. The stability diagrams are shifted according to the space-charge parameter obtained from the BTFs. In addition, the tune shift is estimated by virtue of measured beam profiles and particle numbers. The estimated tune shift is of the same order of magnitude but smaller than the measured one. Possible explanations for deviations between the measurements, the model, and the estimation are discussed.

Transverse decoherence and coherent spectra in long bunches with space charge

“…The particle number and the bunch length could be measured with a reasonable accuracy. The transverse beam radius, which enters the space charge tune shift as squared (" y ¼ a 2 y Q 0y =R, a y is the vertical rms radius) and is thus especially important, could not be determined with a satisfactory precision, as it was also the case in the previous coasting-beam measurements [17] at SIS18. 13.…”

Microbunch dynamics and multistream instability in a heavy-ion synchrotron

“…The later measurement was preformed as part of the work presented in Ref. [16]. The solid line corresponds to the momentum loss obtained from Eq.…”

Transverse Schottky noise spectrum for bunches with space charge

“…For high intensity beams at medium energies, such as in the SIS-18 synchrotron at GSI and in the projected FAIR synchrotrons [2], it is important to understand the effect of space charge on the Schottky spectrum. In coasting beams the transverse Schottky bands, centered at the betatron sidebands, are deformed in a characteristic way [3][4][5]. The deformation provides important information on collective beam properties, such as the space charge tune shift or the Landau damping rate.…”