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Presently the most popular way to prepare high quality polarized antiproton beams is the so called spin filter method. The feasibility of the method has been proven for a proton beam and measurements of the spin dependent interaction of antiprotons have been proposed by the PAX collaboration. Another well known source for polarized antiprotons is the \(\bar{\Lambda}\) decay which was used at FERMILAB in the only experiment performed so far with polarized antiprotons. An alternative approach for polarized antiproton beams may be the production process itself. If the produced antiprotons show polarization it would be rather simple to handle a polarized antiproton beam in the existing antiproton collector and cooler at CERN just like in the unpolarized case.

A simplified scheme for the provision of antiprotons at 100 MeV/c based on fast extraction is described. The scheme uses the existing p~ production target area and the modified Antiproton Collector Ring in their current location. The physics programme is largely based on capturing and storing antiprotons in Penning traps for the production and spectroscopy of antihydrogen. The machine modifications necessary to deliver batches of 1/spl times/10/sup 7/ p~/min at 100 MeV/c are described. Details of the machine layout and the experimental area in the existing AAC Hall are given.

In view of a possible future programme of physics with low-energy antiprotons, a simplified scheme for the provision of antiprotons at 100 MeV/c has been studied. It uses the present target area and the modified Antiproton Collector (AC) in its present location. In this report the modifications and the operation are discussed.

The Antiproton Generation and Storage Facility (AGSF) creates copious quantities of antiprotons, for bottling and transportation to remote cancer therapy centers. The first step in the generation and storage process is to accelerate an intense proton beam down the Main Linac for injection into the Main Ring, which is a Rapid Cycling Synchrotron that accelerates the protons to high energy. The beam is then extracted from the ring into a transfer line and into a Proton Target. Immediately downstream of the target is an Antiproton Collector that captures some of the antiprotons and focuses them into a beam that is transported sequentially into two antiproton rings. The Precooler ring rapidly manipulates antiproton bunches from short and broad (in momentum) to long and thin. It then performs some preliminary beam cooling, in the fraction of a second before the next proton bunch is extracted from the Main Ring. Pre-cooled antiprotons are passed on to the Accumulator ring before the next antiprotons arrive from the target. The Accumulator ring cools the antiprotons, compressing them into a dense state that is convenient for mass storage over many hours. Occasionally the Accumulator ring decelerates a large number of antiprotons, injecting them into a Decelerationmore » Linac that passes them into a waiting Penning trap.« less

Stochastic cooling, which played such an important role in the last decade of accelerator development, was first tested with very modest equipment, namely a standard wide-band pick-up and RF amplifiers having a bandwidth of the order of a hundred MHz [I][2] Since these early days, the natural evolution of stochastic cooling was to use larger and larger bandwidths providing faster and faster cooling rates. Nowadays RF power amplifiers used in the cooling systems of antiproton collector and accumulator rings work in the range of a few GHz, thanks to the progress of RF technology during the last decade. The technology of pick-ups and kickers evolved similarly towards broader-band devices (slot-type pick-ups [3] , Cerenkov pick-ups [4j" or planar slot-line type [5]) having a high sensitivity (multiple arrays, movable cryogenic pick-ups[6]).

CERN has built a new experimental facility, called the Antiproton Decelerator (AD), by transforming two existing machines: the "Antiproton Collector" (AC) and the "Antiproton Accumulator" (AA). To achieve adequate beam performance once the antiproton beam is decelerated to its final value of 0.1 GeV/c, it was necessary to lower the average pressure by nearly two orders of magnitude. For this purpose, a large number of additional pumps were installed and a very careful preparation was applied to a variety of special machine equipment which, in its original construction, was not designed for ultra-high vacuum operation. An important improvement in the outgassing rates was achieved through an extended, mild bake-out of tanks and vacuum vessels containing large amounts of ferrite material and multi-layer thermal insulation. This paper describes the necessary modifications of the vacuum system and in more detail the various steps taken to obtain the required pressure in the low 10/sup -10/ mbar range. It will also report on the unexpected difficulties which were encountered by re-using vacuum components that were not initially designed for bake-out.

Computations with magnetohydrodynamic z-pinch models have been compared with experimental results obtained from a CERN plasma lens prototype designed for antiproton focusing in the antiproton collector ACOL. The focusing azimuthal magnetic field is generated by a z-pinch discharge. Typical pinch parameters are microsecond pinch times, pinch radii of 20 mm, a 250-mm-long plasma channel, and a maximum current of 300 kA. A model whose analysis includes the motion of shockwaves has been improved by taking into account energy losses due to dissociation and ionization of neutrals and by introducing a variable ionization degree. Parameters extrapolated for a final plasma lens scaling that should fulfil the ACOL requirements, e.g. magnetic field strength of about 4 T and pinch duration of at least 0.5 mu s, are represented in the model. >

The developmental work on plasma lens prototypes for antiproton collection is summarized. The antiproton yield with a plasma lens is estimated. Results of the latest z-pinch model describing the plasma dynamics in such a lens are presented. The scaling of the final plasma lens parameters is based on both model and measurement. Destruction rates of insulator tube and electrodes have been measured. A final set of parameters is proposed. Scaling from the experimental and numerical results shows that for the final Antiproton Collector plasma lens a new pulse generator is required, featuring a cycle time of more than 30 mu s (twice that of the present test generator) and a stored pulse energy of more than 25 kJ at 10-13-kV charging voltage. >

Heavy beam loading is encountered in the main RF system of the CERN Proton Synchrotron (PS). This consists of 11 ferrite loaded cavities, each one capable of developing 20 kVp between 2.6 and 10 MHz. Harmonic 20 is normally used for acceleration, and feedforward compensation has been used in the past to suppress beam loading instabilities. This technique could not satisfy the stringent requirements of the antiproton production beam for the Antiproton Collector. RF feedback around the final amplifier and the cavity has been implemented. All power amplifiers have been rebuilt, adding amplification stages and auxiliary equipment, but keeping the same high-power tetrode to drive the cavity (RS 1084 with 80-kW plate dissipation). The installation was completed in February 1988, and many different types of beams have been successfully handled since, including a record intensity of 2.34 e13 protons per pulse. >

Since the end of 1990, CERN has been operating an irradiation facility behind the antiproton production target. The target is hit by 26 GeV protons from the PS (proton synchrotron); the antiprotons are collected by the ACOL machine (antiproton collector) The strong emission of secondary high-energy particles allows the irradiation of small items, in an environment typical of the particle accelerators and of future multi-TeV detectors. On-line measurements can be carried out during the irradiation. Dosimetry, as well as neutron-flux measurements by activation detectors, were carried out. The irradiation facility, as well as the dosimetric methods, are described and the results are given. >

The deceleration of the beam down to 0.1 GeV/c in the ring previously used as Antiproton Collector (AC) at 3.5 GeV/c, requires a number of modifications to the lattice. The insertion of the electron cooling, needed to cool the antiproton beam at low energy, implies the re-arrange-ment of quadrupoles. The optical functions then need to be readjusted in order to keep the large acceptance and to cope with the electron and stochastic cooling environ-ment. Calculations of the linear optics and of the accep-tance are reported. Tests of beam deceleration in the AC show the need for closed-orbit correction at low momentum in addition to the static correction by the movement of the quadrupoles available in the present configuration. The deceleration tests will be discussed and a correction system, which includes trim supplies on the main bending magnets, will be described.

The Antiproton Decelerator (AD) is a simplified source of antiprotons which provides low energy antiprotons for experiments, replacing four machines: AC (Antiproton Collector), AA (Antiproton Accumulator); PS and LEAR (Low Energy Antiproton Ring), shutdown in 1996. The former AC was modified to include deceleration and electron cooling. The AD started operation in July 2000 and has since delivered cooled beam at 100 MeV/c (kinetic energy of 5.3 MeV) to 3 experiments (ASACUSA, ATHENA and ATRAP) for 1500 h. The flux (up to 2.5 /spl times/ 10 pbar /s delivered in short pulses of 330 ns every 110 s) and the quality of the ejected beam are not far from the design specifications. A linear RF quadrupole decelerator (RFQD) was commissioned in November 2000 to post-decelerate the beam for ASACUSA from 5.3 MeV to about 15 keV. Problems encountered in converting the fixed energy AC into a decelerating machine will be outlined, and the present status of the AD, including the performance of the cooling systems and the special diagnostics to cope with beams of less than 10/sup 7/ pbars, will be reviewed. Possible future developments will be sketched.

The former Antiproton Collector (AC) at CERN has been transformed into an Antiproton Decelerator (AD) to supply high quality antiproton beams with a momentum of 100 MeV/c (kinetic energy of 5.3 MeV). As in AC, antiprotons are injected at 3.57 GeV/c and cooled by stochastic cooling system. To facilitate the deceleration and to prepare a small emittance beam for the experiments, stochastic cooling at 2 GeV/c and electron cooling at 300 MeV/c and 100 MeV/c has been incorporated. The required optics modifications are described and the results of machine commissioning are discussed.

The Antiproton Decelerator (AD) is a simplified scheme for the provision of antiprotons at 100 MeV/c based on fast extraction. It uses the existing antiproton production target area and the modified Antiproton Collector Ring in their current locations. The machine modifications necessary to deliver batches of 1 × 10 7 antiproton/mn at 100 MeV/c are well under way. Commissioning with test-protons is foreseen to start this September (1998), running-in with antiprotons is planned to start after the shut down (December 1998-April 1999) in Spring 1999. First physics runs are planned for late Summer/Autumn 1999. The status of the machine is described.

Low energy antiprotons are available for physics experiments at CERN since the 1980s and have been used by a large variety of experiments. The Low Energy Antiproton Ring LEAR has been constructed as a complementary use of antiprotons available at that time for high energy physics and delivered beam to experiments mainly using slow extraction. After completion of LEAR exploitation, the Antiproton Decelerator (AD) was constructed (adaptation of the existing Antiproton Collector, AC) to allow for a simpler low energy antiproton scheme (only one accelerator operated with Antiprotons) with fast extraction well suited for trap experiments. The Extra Low ENergy Antiproton ring ELENA is a small synchrotron presently constructed to further decelerate antiprotons from the AD in a controlled manner, and to reduce emittances with the help of an electron cooler to improve the capture efficiencies of existing experiments and allow for additional ones.

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.

Thanks to external funding, antimater research at CERN will continue. CERN's antiproton complex, which in the fall of 1995 was the first to produce antihydrogen, was closed at the end of last year to free up money for the Large Hadron Collider. Now, however, one part of this complex, the antiproton collector, is to be upgraded and rechristened the “antiproton decelerator,” scheduled to begin operating in early 1999.

A new antihydrogen facility will be created in Europe by transforming an existing machine at CERN, the European laboratory for particle physics. CERN had shut down antihydrogen research at the end of last year for financial reasons. But now money from Japan means the lab can now afford to convert its antiproton collector into an antiproton decelerator (AD). Experiments will start in spring 1999.

As part of the upgrading of the CERN Antiproton Collector source facility, the target station and injection line are being rebuilt. The beam transport magnets immediately downstream of the target are expected to receive a lifetime radiation dose in the range 10/sup 8/ to 10/sup 9/ Gy. A description is given of these magnets, two quadrupoles and two dipoles which are made entirely of inorganic materials. They are to be powered by existing pulse power supplies which have 25-kJ capacitor banks operating at 4 kV. In the quadrupole magnets, each pole has eight turns insulated by air and supported by ceramic pieces. The peak current is 4 kA. For the dipole magnets, it was decided to use a single turn carrying a peak current of 70 kA together with a 18:1 turns-ratio matching transformer. The coil insulation is a combination of air and pieces made from a hydrated calcium aluminate cement. >

The design and construction of the CERN antiproton collider's special injection region are summarized. Among 56 quadrupoles, 16 are displaced to participate in the bending field made up of 24 dipoles. Some magnets for antiproton injection and extraction are used also as ring-lattice magnets to store the beam. A shield has been added around the vacuum chamber to minimize the effect of magnetic flux when the injected beam crosses a dipole core. One ring quadrupole with combined functions has a large aperture with a strong field at the edges and acts simultaneously on the injected and circulating beam. Another quadrupole, with combined functions, was designed with two semi-quadrupoles. One belongs to the injection lattice and another to the ring lattice where the circulating and ejected beams pass through it. >

As part of the CERN Antiproton Collector project, strong lenses are required to focus a 26-GeV proton beam onto the antiproton production target as well as to collect the liberated antiprotons. Gradients of 1500 T/m are expected, making possible a very short and compact lens and thus avoiding excessive absorption of beam particles by the lens material. The problems caused by the skin effect are overcome by subdivision of the lens into three mutually insulated concentric tubes connected in series through electron-beam-welded return tubes. Characteristics of this lens such as the distribution of the penetrating current, and the resulting field distributions, as well as the ohmic temperatures and the magnetic and thermal stresses computed are described. The design of the lens and the present state of this development are discussed. >

The Antiproton Collector (ACOL) project at CERN calls for a production target providing at least twice as many antiprotons into a given acceptance as the present passive target. The pulsed target under study must be able to withstand large current pulses of a hundred kiloamperes or more for 10 to 20 μs whilst at the same time it is hit by the proton beam of up to 2 - 1013 ppp. Because of the very high radioactivity of the target region this new device should show a sufficient reliability before it is put into operation. Previous experimental work with an active target, both in the laboratory and in the AA proton beam line, has shown that such a target gives a measured gain of 50% in the p production yield, although the problem of making an assembly to withstand many weeks of pulsing has not been solved. A comparison of the main features of the four tests made in the AA is given. The mechanical and thermal behavior of a conducting metallic, solid or liquid target is studied, with particular emphasis on the shock wave, the thermal expansion and the magnetic unstable pinch effects, by means of computer calculations. A preliminary design of a metal conducting target is reported.

Maxwell's equations with appropriate boundary conditions are solved for a pulsed cylindrical conductor. The results are applied to the lithium lens used as an antiproton collector for the Fermilab p?p collider. The magnetic field is expressed as a function of radial distance and time. The time corresponding to maximum linearity is calculated. A method for measuring the current density at the surface is discussed and the Joule heat produced per pulse is calculated.

The aim of this paper is to present the results, of 3-D calculations, on the interferences between a dipole and a quadrupole magnet in the CERN Antiproton Collector lattice.

Following the pioneering work on lithium lenses at INP, Novosibirsk, a 2 cm diameter lens was designed and built at Fermilab as an antiproton collector for the antiproton source of the Tevatron I project. A lens of this type was tested at the CERN Antiproton Accumulator (AA) as an antiproton collector and then as a prefocusing element before the AA pulsed current target. In the latter case the purpose was to increase the proton beam convergence at the target to compensate the defocusing effect on the proton beam of the current in the target. As an antiproton collector the lithium lens performed as predicted increasing the antiproton yield into the AA by 40%. In the prefocusing configuration beam convergence and spot size on the target were considerably improved over the standard arrangement using a pulsed quadrupole triplet and the lens has survived 1.4 M pulses of current from 290 to 350 kA in a 26 GeV/c beam of up to 1.4 × 1013 protons.

must provide phase-space matching between the source and the AC, as well as having a region of momentum dispersion. It must also satisfy the constraints imposed by the apertures of the bending and quadrupole magnets which are to a large extent determined by the costs involved and the very limited distance available between the antiproton source and the ring. The design of the components for this line is also dei;endent on the necessity to provide remote-handling capability, particularly for those elements nearest the source. The detailed design 1s not yet completed. &adlation from the AA Hall The antiproton production target is an intense source of radiation. The shieldinq for the source is determined by the need to keep the radiation dose at the CERN site boundaries within the accepted nurms. This radiation will come mostly from neutrons qenerated by plans entering the AA hall and interacting in the machine components and shield that will surround the two rlnqs.

Because of their high centre-of-mass energies, the proton-antiproton colliders at CERN and FNAL offer very large cross-sections for producing pairs of charm and bottom particles. At the CERN \( p\bar p \) Collider (\( \sqrt s \ \) = 630 GeV) the predicted cross-sections1 are σ(\( b\bar b \)) ≈ 100 µb and σ(\( b\bar b \)) ≈10 µb. The integrated luminosity delivered to UA1 is ~ 1 pb−1, so ~ 108 \( c\bar c \) and ~ 107 \( b\bar b \) pairs must have already been produced. The Antiproton Collector (ACOL) ring at CERN will increase the luminosity of the CERN Collider by about a factor of 20.

For efficient antiproton production, a maximum number of protons must be concentrated within one quarter of the CERN Proton Synchrotron (PS) ring before sending the beam to the production target. With the Antiproton Collector (AC) added to the Antiproton Accumulator (AA), the bunch length has to be shorter (by about 20 ns) than before to allow bunch rotation in the AC. While a more ambitious scheme providing such a beam is being implemented, a funneling method, in which beams of two rings of the four-ring Proton Synchrotron Booster (PSB) are recombined in pairs by an RF dipole that permits longitudinal interleaving of successive bunches, has been in operation since the start-up of the AC. Preliminary experiments had shown that the PS space-charge limit had to be overcome in order to make the scheme feasible. After raising the PSB output energy from 815 MeV to 1 GeV, beams of >10/sup 13/ protons compressed into one quarter of the PS ring were achieved. Related to this development, a record proton beam for fixed-target physics was accelerated in the Super Proton Synchrotron, while beam losses in the Proton Synchrotron Booster-Proton Synchrotron Ring (PSB-PS) line were reduced. >

The second course of the International School on Physics with Low Energy Antiprotons was held in Erice, Sicily at the Ettore Majorana Centre for Scientific Culture, from May 20 to May 31, 1987. The School is dedicated to physics accessible to experiments using low energy antiprotons, especially in view of operation of the LEAR facility at CERN with the upgraded antiproton source AAC (Antiproton Accumulator AA and Antiproton Collector ACOL). The first course in 1986 covered topics related to fundamental symmetries. This book contains the proceedings of the second course which focused on spectroscopy of light and heavy quarks. These proceedings contain both the tutorial lectures and contri butions presented by participants during the School. The papers are organized in four sections: The first section includes theoretical reviews. Section II contains experimental reviews and covers the results in meson spectroscopy from DM2, MARK III, GAMS and n-WA76. Section III presents the new meson spectroscopy experiments in pre paration at CERN and Fermilab: Crystal Barrel, OBELIX, Jetset and E760. Section IV is dedicated to LEAR and to future facilities where meson spectroscopy would be a principal component of the physics programme. We should like to thank Dr. Alberto Gabriele and the staff of the Ettore Majorana Centre who provided for a smooth running of the School and a very pleasant stay. We are particularly grateful to Mrs. Anne Marie Bugge for her crucial help during the preparation and running of the School and for the editing of these Proceedings."

Maxwell's equations with appropriate boundary conditions are solved for a pulsed cylindrical conductor. The results are applied to the lithium lens used as an antiproton collector for the Fermilab pp collider. The magnetic field is expressed as a function of radial distance and time. The time corresponding to maximum linearity is calculated. A method for measuring the current density at the surface is discussed and the Joule heat produced per pulse is calculated.

Stochastic cooling, a technique of prime importance for obtaining antiproton beams usable at high-energy colliders, requires wide-band and low-noise signal acquisition and processing. For this purpose, the CERN Antiproton Collector (ACOL), presently under construction, is equipped with six beam pick-up stations operating at cryogenic temperatures. Each station consists of a high-vacuum vessel housing two mobile arrays of pick-up electrodes, cooled to about 100 K by radiation to a surrounding thermal shield, and two preamplifiers kept below 20 K. Refrigeration is provided by a pair of two-stage Gifford-McMahon helium cryogenerators, thermally linked to the preamplifiers and to the thermal shield. The cryogenerators also cool activated charcoal cryopanels, in order to maintain a residual pressure in the vessel below 10−8 mbar. The choice of such cryogenic options is dictated by performance (steady-state and cool-down), simplicity of operation and maintenance, and high reliability.

During the first five years of operation of the Antiproton Accumulator (AA), a whole set of limiting phenomena induced by the residual neutralization by ions was observed and identified: charged dust particles causing beam blow-up, dipolar and quadrupolar coherent instabilities, and excitation of high-order, nonlinear resonances. During construction of the Antiproton Collector (ACOL), the AA was upgraded to cope with the higher antiproton flux. New clearing electrodes were added together with individual computer control of applied clearing voltage and acquisition and recording of clearing currents. A general description of the new AA ion clearing system is given together with a first account of the clearing current's behavior. The new, computer-controlled clearing system based on specially designed electrometers capable of measuring each individual clearing current in the pA range is being commissioned. >

Nonlinear fields are so important in modern accelerators or storage rings that they have to be included in the basic lattice design for both chromaticity correction and aperture determination. The power of prediction of a nonlinear theory is not yet firm enough and numerical simulations are necessary. These lectures deal with the principles of particle tracking, the equations of the betatron motion and the envelope distortions and tune shifts induced by multipole fields. The theory is applied to the correction of beam envelope distortions produced by chromaticity sextupoles in a large acceptance machine, the Antiproton Collector.

The upgrade of the CERN antiproton source, meant to gain an order of magnitude in antiproton flux, required the construction of an additional ring to complement the existing antiproton accumulator (AA) and an entire rebuild of the target zone. The AA also needed major modifications to handle the increased flux and perform purely as an accumulator, preceded by collection in the collector ring (AC). The upgrade, known as the ACOL (antiproton collector) project, was approved under strict time and budgetary constraints and the existing AA control system, based on the Proton Synchrotron (PS) Divisional norms of CAMAC and Norsk-Data computers, had to be extended in the light of this. The limited (9 months) installation period for the whole upgrade meant that substantial preparatory and planning activities had to be carried out during the normal running of the AA. Advantage was taken of the upgrade to improve and consolidate the AA. Some aspects of the control system related to this upgrade are discussed together with the integration of new applications and instrumentation. The overall machine installation and running-in was carried out within the defined milestones and the project has now achieved the physics design goals.

The author presents an overview of the end-1988 performance and limitations of the whole CERN hadron collider complex since the ACOL (Antiproton Collector) upgrade was begun. The post-ACOL design goals for the collider are a peak luminosity of 4*10/sup 30/ cm/sup -2/ s/sup -1/ along with a luminosity lifetime appreciable greater than 10 h. In order to achieved this the antiproton production rate must approach 6*10/sup 10/ p/hr with an accumulated peak beam of 1*10/sup 12/ circulating antiprotons. During 1988, the collider got to within two thirds of its full promise. Some of the problems preventing the attainment of the design goals are described along with the prescribed solutions for 1989. >

A number of results, obtained in the UA1 experiment before the upgrade of the proton-antiproton collider at CERN, are discussed. In most cases they are the final statements that can be made from the data, based on integrated luminosities of ~ 130 nb-1 at √s = 546 GeV recorded in 1983 and ~ 570 nb-1 at √s = 630 GeV in 1984 and 1985. Where appropriate, an indication of the improvement in precision to be expected with ACOL, the new antiproton collector, is given.

The new antiproton collector machine (ACOL)[1] presently under development at CERN, requires the highest possible proton intensity (more than 1013 protons per pulse) in one quarter of the PS circumference, and a guaranteed bunching factor, for its p production beam: possibly less than 25ns bunches, 105 ns apart. The present 26 GeV longitudinal merging technique [2], cannot meet these specifications, so that new quasi-adiabatic processes had to be imagined [3]. First, before transition energy, a "bunch pair merging" operation reduces from 10 to 5 the number of bunches, with a moderate blow-up, by slowly bunching the beam on half the initial harmonic number. Then, on the high energy flat top, the length of circumference occupied by the bunches is halved, by a technique tentatively named "bunch batch compression". This is basically a slow increase of the RF harmonic number seen by the beam, implemented by operating part of the existing cavities stepwise at increasing harmonic numbers (10, 12, 14, 16, 18 and finally 20). Computer outputs are presented, together with machine experiment results.

A simplified scheme for the provision of antiprotons at 100 MeV/c in fast extraction is described. The scheme uses the existing p production target area and the modified Antiproton Collector Ring in their current location. Some modifications necessary to deliver batches of 1 × 10 7 antiprotons every minute at 100 MeV/c are described, details of the machine layout and the experimental area in the existing AAC Hall are given.