L. Burnod

Observation of visible synchrotron radiation emitted by a high-energy proton beam at the edge of a magnetic field

Abstract Theoretical studies show that owing to the abrupt change of the magnetic field occurring at the magnet edges synchrotron radiation will be emitted in the visible light range, by a high-energy proton beam. Experiments have been carried out at the CERN Super Proton Synchrotron (SPS) in order to check for the validity of the theory and measure the properties of the emitted light. Special attention has been devoted to the energies and intensities of the proton beam, as profile measurement is foreseen as an immediate application.

Proton beam profile measurements with synchrotron light

Abstract In circular proton accelerators, the synchrotron radiation emitted by high energy beams at the edges of bending magnets contains an appreciable amount of visible light. This effect is used in the CERN SPS to measure by a non interceptive method the transverse proton density distribution above 200 GeV. The device consists of a telescope followed by an image sensor and electronics processing; its performances and some examples of applications are given in this paper.

The Damper for the Transverse Instabilities of the SPS

For beam intensities above 1012 protons per pulse in the SPS, collective transverse beam instabilities develop with frequencies between 15 kHz and 3 MHz because of the resistive wall effect of the vacuum chamber1). An active feedback system2) with an electrostatic deflector has been installed in the SPS for damping the resistive wall instabilities in both the vertical and horizontal planes. Measurements have been made to determine the threshold and growth rate of these instabilities. As a novel application, the damper can be used also for the excitation of small coherent betatron oscillations. A phase-locked loop tracks the beam oscillations and provides a continuous display of the betatron wavenumber Q during the cycle.

Proton Beam Profile Monitor using Synchrotron Light

Theoretical studies, followed by experiments, show that owing to the abrupt change of the magnetic field occurring at the magnet edges, synchrotron radiation is emitted in the visible light range by a high energy proton beam. The spatial photon density being proportional to that of the proton beam the analysis of the emitted ‘image’ by a dedicated camera gives an accurate representation of the beam profiles. Based on these properties a non-interceptive detector has been developed and installed at CERN SPS proton synchrotron in order to measure the profile of the circulating beam. The results show that for an energy higher than 250 GeV and a beam intensity of at least 0.7 mA (1011 p) the results are satisfactory. The spatial resolution being 100 μm many beam parameters can be evaluated with good accuracy.

The SPS Beam Instrumentation and Closed Orbit Correction

For the running-in and the operation of a large accelerator like the SPS, the beam instrumentation plays a prominent part. Though limiting the beam detectors to where they are strictly necessary, their number is still considerable, leading to a large amount of data to be treated simultaneously. To do this efficiently, hardware and software are equally important and the design of the hardware had to be done jointly with the software. The type of detectors is determined by their function, intensity, position, profile, loss, etc... whereas the type of associated electronics and acquisition systems has to be restricted to a minimum for simplicity, production cost, easy maintenance and fast data treatment. Furthermore the small number of access shafts to the accelerator (6 for 7 km SPS ring circumference) and to the beam transfer lines leads to the transport of tiny signals over long distances (several hundred metres) in a noisy and irradiated environment. This paper summarizes the performance of the main types of detectors giving some particularities of their hardware and software with some emphasis on the closed orbit measurement and correction system.

Beam Intensity, Position and Profile Measurements for Ppbar Colliders

In a ppbar collider like the CERN SPS where only three dense pbar bunches of about 2×1010 particules per bunch can be injected once a day, the beam characteristics of these rare shots must be known systematically with a high precision to better understand and improve the collider performance. This paper describes the measurements of three important beam parameters : intensity, position and transverse profiles.