[en] The PS synchrotron control system is explained in general terms, covering the topics of frequency control, beam transfer, damping, stability, conservation of longitudinal emittance, and second order problems

[en] We examine a few typical examples related to proton or antiproton storage rings. (orig./HSI)

[en] In the new generation of circular accelerators or colliders where the average beam currents are pushed up to their ultimate limits, the power exchanged between the RF power source and the beam becomes much larger than the losses in the RF system itself (cavity, amplifier, circulator load). This situation of high beam loading has been analyzed previously with respect to the stability of the radiofrequency system. Without any electronic loops, one obtains the well known high current Robinson stability limit, which is somewhat modified by the presence of the phase, amplitude and tuning loops. To go beyond these limits the usual recipe is to employ RF feedback around the power amplifier-cavity combination. The beam current thresholds are simply increased by the RF feedback loop gain, without changing the static RF power balance. However when transient effects are considered, the peak RF power demanded by RF feedback may dominate the static power requirements, in particular for hadron storage rings where φ_B (synchronous phase angle) equals zero. During acceleration or storage periodic transient beam loading is due to the non-uniform structure of the beam. With high RF feedback gains and therefore large equivalent cavity bandwidths this effect becomes more and more important, especially for large machines with a low revolution frequency. In addition, non-periodic transient beam loading effects occur during the filling phase of the machine, when newly injected particles are added to the already circulating beam

[en] Some properties of the waves propagating in a constant cross-section tube are recalled, in particular the phase and group velocities of the guided wave. The dispersion diagram of a periodically-loaded waveguide is then derived by considering it either as a smooth tube perturbed with obstacles or as a chain of coupled resonators. Some examples of travelling-wave structures are presented and, finally, the interaction of the structure with beam is analyzed. This includes transit-time-factor effects as well as beam loading. (author)

[en] The average luminosity of the SPS collider could be improved if the slow blow-up of transverse emittances due to beam-beam and intra beam scattering effects were to be reduced by a transverse cooling system. We shall examine the parameters of such a system and propose a technological approach which seems better suited to the case of a few bunches circulating in a large machine

[en] The average luminosity of the SPS collider could be improved if the slow blow-up of transverse emittances due to beam-beam and intrabeam scattering effects were to be reduced by a transverse cooling system. We examine the parameters of such a system and propose a technological approach which seems better suited to the case of a few bunches circulating in a large machine. (orig./HSI)

[en] The succession of RF manipulations or special features which are implemented in the CERN proton-antiproton complex will be reviewed. This description more or less follows the particle's path, starting from the handling of high intensity beams for antiproton production, up to the end of the chain where an almost noise-free RF system keeps the proton and antiproton beams bunched for many hours

[en] In the CERN SPS proton synchrotron the four accelerating cavities are of the travelling wave structure type. At the 10 GeV/c injection energy the cavities present to the beam an impedance very similar to that of a detuned RLC cavity with the result that strong dipole and quadrupole instabilities occur. The SPS accelerated beam current was limited by the combined action of these two effects to 2.5 X 10¹³ protons which resulted in capture losses increasing with the injected beam intensity. Among the solutions possible for this problem, the RF feedback, which would alleviate both transient beam loading and instability effects, looked to the authors to be the most promising. In such a system the total voltage seen by the beam is reinjected into the feedback cavity via its power amplifier. Without any delay in the system the cavity impedance seen by the beam could be greatly reduced. Unfortunately the long delay in the system severely limits the bandwidth and the RF feedback could hardly correct more than the n = O beam loading component. The authors circumvented this problem by observing that they needed a large gain only in the vicinities of the RF frequencies. Outside these bands the phase rotation due to the long delay is unimportant if the gain is made low enough. If, in addition, the total delay of the system is made exactly equal to one machine turn, the open loop phase of the feedback system is always zero for each RF frequency. The two ingredients needed to make the RF feedback work for n not too small are therefore a transfer function with comb filter shape and a total delay of one machine turn. In this paper these ingredients are derived

[en] The radiofrequency system of the Tau Charm Factory accelerating 10¹¹ particles per bunch and a circulating current of 0.5 A is presented. In order to produce the very short bunches required, the RF system of TCF must provide a large RF voltage (8 MV) at a frequency in the neighbourhood of 400-500 MHz. It appears very attractive to produce the high voltage required with superconducting cavities, for which wall losses are negligible. A comparison between the sc RF system proposed and a possible copper system run at an average 1 MV/m, shows the clear advantage of sc cavities for TCF. (R.P.). 2 figs,. 1 tab

[en] The Large Electron Positron Collider (LEP), the largest accelerator i the world, is equipped with a superconducting RF system designed at CERN and constructed by European industry. The energy radiated by the circulating beams via synchrotron radiation is replenished by the RF system, which provides a total accelerating voltage of about 3 GV. Very large continuous RF power is thus transferred to the beam; in routine operation it amounts to more than 13 MW at a total beam current mA. The cryogenic installation, one of the largest in the accelerator world, delivers 48 kW at 4.5 K to keep the cavities superconducting. The overall RF system is described, highlighting design choices and the problems encountered during their implementation. The operational experience with this system are also reported showing that its reliability and performance has enabled LEP to largely exceed the goals set a few years ago. (author)