M. Chanel

Overview of the recent operation of the AAC and LEAR for the low-energy antiproton physics programme

This paper reviews the recent performance of the AAC and LEAR. Activities on the AAC include the successful exploitation of a magnetic horn as an antiproton collector lens and an energy-saving mode of operation, which has been possible since 1992, when LEAR became the only client of the AAC. LEAR worked in its full momentum range between 100 MeV/c and 2 GeV/c, with performance (intensities, ejection modes and spill length) exceeding the design specifications. Improvements are described, which contributed to the quality of the beam delivered to experiments. The reliability and availability of the antiproton machines are also discussed.

A Collimation Scheme for Ions Changing Charge State in the Leir Ring

Avalanche-like pressure rise and an associated decrease of the beam life-time, caused by (i) beam loss due to charge exchange interactions with rest gas molecules, (ii) electron capture from the electron beam of the electron cooler and (iii) ion impact induced outgassing, is a potential limitation for heavy ion accelerators. The vacuum system of the LEIR ring has to be upgraded to reach the dynamical vacuum pressure in the low 10− 12 Torr range necessary to reach design performance. A collimation system to intercept lost ions by absorber blocks made of low beam-induced out-gassing material will be installed. This paper reviews the collimation scheme and simulations of beam loss patterns around the ring.

On the optimum dispersion of a storage ring for electron cooling with high space charge

Abstract With the intense electron beams used for cooling, matching of the ion and electron velocity over the largest possible fraction of the beam profile becomes important. In this situation, a finite dispersion from the ring in the cooling section can lead to an appreciable gain in the transverse cooling speed. Based on a simple model of the cooling force, an expression for the “optimum” dispersion as a function of the electron beam intensity, the momentum spread and other properties of the ion beam will be derived. This simple theory will be compared to measurements made on the low-energy ion ring (LEIR) at CERN during 1997.

Fifty years of the CERN Proton Synchrotron : Volume 2

This report sums up in two volumes the first 50 years of operation of the CERN Proton Synchrotron. After an introduction on the genesis of the machine, and a description of its magnet and powering systems, the first volume focuses on some of the many innovations in accelerator physics and instrumentation that it has pioneered, such as transition crossing, RF gymnastics, extractions, phase space tomography, or transverse emittance measurement by wire scanners. The second volume describes the other machines in the PS complex: the proton linear accelerators, the PS Booster, the LEP pre-injector, the heavy-ion linac and accumulator, and the antiproton rings.

Recent lead ion storage tests on LEAR

With the completion of the antiproton physics program, the Low Energy Antiproton Ring is now available to be used as an accumulator ring for heavy ions in the LBC injector chain. The proposed scheme for the injection of Pb ions is given, where an intensity gain of 125 is obtained by accumulating Pb ions with electron cooling in the LEAR ring. With a linac cycling at 10 Hz and cooling times faster than 100 ms, 20 pulses can be accumulated in 2 s before transfer to the PS, the next machine in the chain. A number of machine experiments have been performed and will continue this year, in order to establish the techniques required. We discuss injection line tests, ion beam lifetime and vacuum measurements and cooling time measurements.

Neutralisation of the LEAR electron-cooling beam: experimental results

The LEAR electron cooler uses dense electron beams. Because of this high density the large space-charge potential induces significant drawbacks for the cooling process itself. As a consequence a space-charge neutralisation system has been implemented on the cooler. It consists of two positively polarised pairs of electrodes, placed on the outside of the drift space, which aim to store the ionised positive ions of charge Z. The major difficulty arises in the neutralisation instabilities. This paper reports on the technological aspects, the measurement techniques and the results.

Ion cooling and accumulation

For the preparation of dense bunches of ions for the LHC it has been proposed to accumulate in a small storage ring the beam from a linac with an ECR source. The scheme involves combined transverse and longitudinal multiturn injection and strong electron cooling to free phase space for the next injection. Successful experiments to determine the optimum parameters of a low-energy ion accumulator were performed at the Low Energy Antiproton Ring (LEAR) with Pb-ions of charge state 52+ to 55+ at an energy of 4.2 MeV/u. The reported measurements include: lifetime for different charge states as a function of the electron cooler current, cooling rates with different optical settings, efficiencies of the combined multiturn injection and results of accumulation. The transformation of LEAR into an accumulator ring for a wide range of ion species will be based on these results.

Ions for LHC: Beam Physics and Engineering Challenges

The first phase of the heavy ion physics program at the LHC aims to provide lead-lead collisions at energies of 5.5 TeV per colliding nucleon pair and ion-ion luminosity of 1027cm-2s-1. The transformation of CERN’s ion injector complex (Linac3-LEIR-PS-SPS) presents a number of beam physics and engineering challenges, which are described in this paper. In the LHC itself, there are fundamental performance limitations due to various beam loss mechanisms. To study these without risk of damage there will be an initial period of operation with a reduced number of nominal intensity bunches. While reducing the work required to commission the LHC with ions in 2008, this will still enable early physics discoveries.

Ultralow momentum anti-protons in LEAR

Abstract Limitations to the antiproton beam intensities that are decelerated and stored in LEAR are examined, and expectations for machine performance in the momentum range at and below 105 MeV/c are given. These estimates are compared with the current machine performance. The various modes of beam extraction at low momentum are reviewed and some estimations are given for fast extraction efficiencies.