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Amongst all the modifications of the PS Complex to produce the LHC ion beams, the conversion of the old Low Energy Antiproton Ring (LEAR) into the Low Energy Ion Ring (LEIR) is a major issue. The accumulation in LEIR of 9*10 8 Lead ions in normalized transverse emittances of 0.7 µm allows the production of 4 of the 592 bunches needed in one LHC ring, in one LEIR cycle. Then, it will take around 10 min to fill one LHC ring. The requested luminosity of 10 27 cm -2 s -1 for lead ion collisions is reachable and is ~1000 times more that the actual chain (Linac3, PSB) can do. The production of Lead ion beams is described, with particular attention to electron cooling, the injection system and the beam lifetime. 1 OVERALL DESCRIPTION OF THE LEAD ION FILLING SCHEME OF LHC To reach the desired luminosity for the lead experiments in LHC, the required number of ions is 0.7x10 8 /bunch at 2.7 TeV/u within normalised emittances (βγ σ 2 /βh,v) smaller than 1.5 µm. The upper number of lead ions per bunch in LHC is determined by both the quench limit (interactions at collision points) and the saturation of the Alice central detector. The corresponding lower limits are given by the beam orbit observation system and by the minimum acceptable luminosity in Alice. The emittance budget has been set to 1.2 µm at the exit of the SPS, 1 µm at the end of the stripper in the TT2 line, and 0.7 µm at the exit of LEIR. To fulfil this requirement, it has been proposed [1] to add an accumulator ring LEIR. An improved ECR ion source (from 100 µA to 200 µA of Pb

Two types of cooling (electronic and stochastic) are used in the AD (antiproton decelerator) for efficient deceleration and to provide the required parameters of the antiproton beam. In the not too distant future electronic cooling will be used in LEIR (low-energy ion ring) to accumulate ions in the LHC (large hadron collider). Both cooling systems are described.

To prepare dense bunches of lead ions for the LHC it has been proposed to accumulate the 4.2 MeV/u linac beam in a storage ring with electron cooling. A series of experiments is being performed in the low-energy ring LEAR to test this technique. First results were already reported at the Beam Crystallisation Workshop in Erice in November 1995. Two more recent runs to complement these investigations were concerned with: further study of the beam lifetime; the dependence of the cooling time on optical settings of the storage ring and on neutralization of the electron beam; and tests in view of multiturn injection. New results obtained in these two runs in December 1995 and in April 1996 will be discussed in this contribution.

In view of a future antihydrogen programme at CERN, the options for producing MeV antiprotons are revisited. The current limitations, operational performances and foreseen improvements are detailed. An alternative scheme using a dedicated machine for production and deceleration is also discussed.

An experiment was proposed to study Λ Λ - CP violation at LEAR. The feasibility of LEAR for this experiment is studied. The limitations and the beam characteristics are reviewed. The necessary LEAR upgrading are Indicated.

Space-charge effects have been identified as the most serious intensity limitation in the CERN PS and PS Booster, on the way towards ultimate LHC performance and beyond. We here explore the application of several previously proposed space-charge compensation methods to the two LHC pre-injector rings, and the challenges which need to be overcome. The methods considered include the reduction of tune shift and resonance strengths via octupoles, pole-face windings, electron lenses, or neutralisation.

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 1027 cm-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.

Cooling down time measurements carried out at LEAR with 4.2 MeV/nucleon Pb54+ ions and various combinations of lattice functions led to unexpected results. Notably, a finite dispersion was found to decrease strongly the horizontal cooling down times. Furthermore, intermediate betatron functions yielded shorter cooling down times than large ones and an increase of the cooler length by a factor 2 did not lead to the expected increase in the cooling rate. The aim of this report is to explain, at least qualitatively, the experimental observations.

O/sup 8+/ and O/sup 6+/ ions were stored in the CERN Low-Energy Antiproton Ring (LEAR) during a machine experiment session. The aim was to obtain some hints on the lifetime of heavy ion beams in a good cooling ring vacuum and to test cooling and stacking of ions. Stochastic cooling was used to compensate the beam decay due to multiple scattering on the residual gas, which is the most important effect on lifetime. An equilibrium momentum spread of less than 5*10/sup -4/ was measured, thus proving the efficiency of stochastic cooling for multiply charged ions. With the vacuum conditions of LEAR (2.6*10/sup -12/ torr gauge reading with a residual gas of 90% H/sub 2/), measured beam lifetimes are 25 min for O/sup 6+/ at 7.2 MeV/u and 600 min for O/sup 8+/ at 11.5 MeV/u. These numbers set favorable limits for low-energy ion storage rings. >

Beam transfer functions (BTF), giving the frequency domain response of the beam to an external excitation, are widely used to measure the impedance of the beam environment, to analyse stability conditions and to determine the true momentum distribution in spite of strong signal shielding in dense, cooled beams. A problem encountered in low-intensity (antiproton and rare ion) storage rings is the unwanted noise on the BTF signal. We have developed a method of noise suppression which may be viewed as gating in time domain: Transforming (by software) the BTF into time domain, cutting off the tail after the response decayed and going back into frequency space we obtain a significantly cleaner signal. The tail of the time response contains information on beam and system noise which can be treated separately. Results obtained on the low energy antiproton ring LEAR are discussed. >

At the CERN Low Energy Antiproton Ring (LEAR), high-density beams are obtained with electron and stochastic cooling. The authors have tried to determine the characteristics of the beam and its environment in a regime where the cooling force is present and where the impedance is space-charge-dominated. Methods used include beam-transfer function (BTF) measurements and Schottky scans. It is shown that, when the beam is strongly cooled, Landau damping is lost. A powerful active feedback is necessary to recover beam stability and increase the possible circulating current. It is noted that transverse BTFs are a convenient tool for adjusting and monitoring the action of the damper. By a combination of longitudinal BTF and Schottky measurements, the momentum distribution of very cold beams can be determined despite the strong signal distortion, and the beam coupling impedance can be estimated. >

The fast-growing "Ring 4" instability occurring at intensities above 6.5/spl times/10/sup 12/ protons in the top one of the four rings of the CERN PS Booster (PSB) is finally explained by an asymmetry in the 40 vacuum pump manifolds common to all rings. Measurements (by wire method) and calculations show a sharp resonant peak (Q/spl sim/2000) at 1100 MHz and shunt impedances two times higher for the Ring 4 ports as compared to the other rings. This factor is sufficient to explain that the threshold of the instability falls below the maximum intensity only in Ring 4. A final, but labor-intensive and expensive, cure consists of inserting short-circuiting sleeves into all 160 beam ports. Results of beam and impedance measurements and the planned cure will be presented and discussed.

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.

In preparation for the heavy ion program of the LHC, accumulation and cooling tests with lead ion beams have been performed in the LEAR storage ring. These tests have revealed that due to the unexpected, large outgassing of the vacuum system, the dynamic pressure of the ring could not be maintained low enough to reach the required beam intensities. To determine the actions necessary to lower the dynamic pressure rise, an experimental program has been initiated for measuring the molecular desorption yields of stainless steel vacuum chambers by the impact of 4.2 MeV/u lead ions with the charge states +27 and +53. The test chambers were exposed either at grazing or at perpendicular incidence. Different surface treatments are reported in terms of the molecular desorption yields for H/sub 2/, CH/sub 4/, CO and CO/sub 2/. Unexpected large values of molecular yields per incident ion up to 1.5 /spl times/ 10/sup 4/ molecules/ion have been observed. The implications of these results for the vacuum system of the future ion accumulator ring (LEIR) and possible remedies to reduce the vacuum degradation are discussed.

New methods to create hollow distributions in longitudinal phase space based on manipulations with a double harmonic RF system at high energy are presented with application to the PS Booster synchrotron (PSB). Whereas the first tenatative to create hollow bunches at the PSB aimed to improve the performance of the PSB itself, these new methods are expected to reduce the limitations due to direct space charge forces in the receiving PS (where no double harmonic RF system is available) after transfer. One method aims to introduce empty phase space in the centre of the phase space by recombination of the beam in one bucket with another empty bucket. The second method is based on redistribution of phase space surfaces during the transfer of the beam from one second harmonic sub-bucket to another. During that process, phase space surfaces are exchanged and low density from the periphery ends up in the centre, whereas the high density surfaces from the centre are transferred to the periphery. Both methods have been simulated by particle tracking. The second method has been applied in practice at the PSB. The set-up turned out to be simple and fast, and to yield hollow distributions with good reproducibility.

The CERN baseline scenario for a Neutrino Factory comprises accumulation and compression of the beam delivered by a 2.2 GeV kinetic energy H− linac, to provide the time structure needed on the target. Originally, accumulation and bunch compression in one single ring was envisaged. To limit the RF voltage necessary for bunch rotation, quasi‐isochronous lattices were studied. The low transition energy together with the long circumference, either leads to large dispersion or necessitates the addition of bending magnets with negative deflection angle. Several solutions for quasi‐isochronous lattices were investigated. Finally, the quasi‐isochronous lattices were abandoned, and a solution has been chosen with two separate rings, one for accumulation and the other for bunch‐compression, and conventional lattices working far below transition.

Because of their high density together with extremely small spreads in betatron frequency and momentum, cooled beams are very vulnerable to incoherent and coherent space-charge effects and instabilities. Moreover, the cooling system itself, i.e. the electron beam in the case of e-cooling, presents large linear and non-linear “impedances” to the circulating ion beam, in addition to the usual beam-environment coupling impedances of the storage ring. Beam blow-up and losses, attributed to such effects, have been observed in virtually all the existing electron cooling rings. The adverse effects seem to be more pronounced in those rings, like CELSIUS, that are equipped with a cooler capable of reaching the presently highest energy (100–300 keV electrons corresponding to 180–560 MeV protons). The stability conditions will be revisited with emphasis on the experience gained at LEAR. It will be argued that for all present coolers, three conditions are necessary (although probably not sufficient) for the stability of intense cold beams: (i) operation below transition energy, (ii) active damping to counteract coherent instability, and (iii) careful control of the e-beam neutralisation. An extrapolation to the future “medium energy coolers”, planned to work for (anti)protons of several GeV, will also be attempted.

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.

To reach the design luminosity for lead-ions in the LHC, the present Low-Energy Antiproton Ring (LEAR) has to be converted into a Low-Energy Ion Ring (LEIR). Since the present ECR lead-ion source does not provide sufficient intensity, the main goal of LEIR is to act as a low-energy (4.2 MeV/u) accumulator where the ion beam is stacked and cooled (with the help of an electron-cooler) to reach the required intensity and emittances. An experimental program has been carried out at LEAR in recent years in order to test the cooling and stacking process with the present electron-cooler. A variety of results have been reported at previous conferences. This paper will focus on the electron-cooling aspects resulting from the afore mentioned experiments. Taking into account the experience gained, some guidelines will be given concerning the future LEIR machine and the electron-cooling device(s) that will be needed to produce cold dense electron beams.

The specific diagnostics systems used in cooler rings will be reviewed. The hardware used and the ways in which the physical characteristics of the beam are accessed will be described. It will also be shown how to evaluate the forces that are exerted on the beam during cooling.

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.

The LEAR machine is foreseen to be used as a lead ion accumulator in the injector chain for the LHC. Therefore, to test the principle of Pb54+ ion accumulation in LEAR, at 4.2 MeV/u, a number of studies and experiments have been made aimed at determining the improvements and modifications necessary to fulfill the LHC requirements. Amongst subjects studied we have investigated: a) The ion production and the injection line matching, b) The linac energy ramping in view of accumulation through combined longitudinal-transverse multi-turn injection, c) The ion beam lifetime and recombination processes, and finally d) The electron cooling time, as a function of the lattice parameters at the cooler. Recent experiments and measurements will be reported and commented in this paper. Also mentioned are some particular diagnostic methods.

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 perform-ance (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.

By measuring the lifetime of stored beams, the recombination of the ions with cooling electrons was investigated. Rates found are larger than expected for radiative electron capture and significantly higher for Pb53+ than for Pb54+ and Pb52+. These results are important for the design of the lead ion injection system for the Large Hadron Collider and for recombination theories.

The major modifications made to the LEAR (Low Energy Antiproton Ring) electron cooler for its reliable and effective use in everyday operations are described. The transverse feedback system used to counteract the coherent instabilities observed with the dense beams obtained with electron cooling is also discussed. Experience gained while using the cooler in a semi-operational manner has made it possible to redesign the critical components. Supplemented by the active feedback system, electron cooling can now be used consistently between decelerating ramps to obtain beams of ultralow momenta with an appreciable gain in duty cycle and beam quality as compared to previous modes of operation. >

The first results are presented of electron cooling experiments in the Low-Energy Antiproton Ring (LEAR) at CERN, performed with a proton beam of about 50 and 21 MeV. The number of stored protons ranged from 107 to 3 × 109. Cooling times of the order 1 s and proton drag rates of up to 0.7 MeV/s were obtained. The capture of cooling electrons by protons producing hydrogen atoms was used to derive an effective electron temperature (0.25 eV). From the angular profile of the neutral hydrogen beam an upper limit of 3π mm.mrad could be deduced for the horizontal equilibrium proton-beam emittance. The lowest equilibrium momentum spread was 2 × 105 (FWHM), as derived from the analysis of the longitudinal Schottky signal. This Schottky signal exhibited an unusual behaviour with beam intensity and under certain conditions showed a doublepeak structure which was associated with collective beam noise. For very cold beams transverse instabilities were observed, which resulted in a rapid spill-off of protons and a stabilization at lower intensities. The threshold of these instabilities was raised by heating the proton or the electron beam. The cooling of a bunched proton beam was investigated. The reduction of the proton momentum spread led to bunch lengths of about 2 m, containing 3 × 108 protons.

The LEAR control system and its current status are described briefly. The system consists today of two interconnected PDP 11 73' s and one microVAX in an Ethernet-like local area network. For real-time requirements, CAMAC-based microprocessor systems are used. The main point of the paper is the description of an evolutive data base architecture where the emphasis is on access to accelerator physics parameters rather than to power supply parameters.

The CERN PS Booster (PSB) has been connected to the new computer control system (NORD-CAMAC) during the four months' shutdown in summer and autumn 1980. Subsequently the PSB had to furnish beams of high quality, particularly for the Antiproton Accumulator (AA). To make the change-over efficient and possible within the time and manpower limitations, local autonomous microcomputer-aided test facilities were used for more than a year. These were designed (i) for the development of process equipment including its electronics, (ii) for equipment commissioning, (iii) for fault diagnosis and (iv) for the improvement of the future machine performances. The specifications, the detailed implementation and the results are reported.

First electron cooling experiments were performed with 10 7 to 2×10 9 stored antiprotons of 50, 21 and 6 MeV at the Low Energy Antiproton Ring (LEAR) at CERN. Most effort was put into the study of the longitudinal cooling. Schottky pick-up signals were used to measure the equilibrium momentum spread and the longitudinal cooling time. From the equilibrium between stochastic heating and electron cooling the longitudinal friction force in the low 10 3 m/s relative velocity range could be deduced. This method was used also to increase the cooling force by improving the alignment between the antiproton and the electron beam. Some of the experimental data are compared with results of a simulation program for electron cooling (SPEC).

Future requests for protons from the physics community at CERN, especially after the start-up of the CNGS experiments in 2006, can only be satisfied by a substantial increase in the SPS beam intensity per pulse. In September 2004 a three-week beam run was dedicated to high intensity; all accelerators in the chain were pushed to their limits to study intensity restrictions and find possible solutions. New record intensities were obtained in the accelerators of the PS & SPS Complex with this type of beam which is different from the nominal LHC beam. The challenges in producing this high-intensity beam are described, together with the measures needed to make it fully operational.