D. Möhl

Physics and technique of stochastic cooling

Abstract A survey of the theory of stochastic cooling is presented followed by a report on experiments in this field. It is shown that the results of these experiments agree with the theoretical predictions.

Measurement of the lifetime of Pb52+, Pb53+ and Pb54+ beams at 4.2 MeV per nucleon subject to electron cooling

Abstract 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 antiproton decelerator: AD

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.

Measurement of antiproton lifetime using the ice storage ring

Antiprotons have been stored in the ICE Storage Ring and held for 85h with the help of stochastic cooling. We set a limit of at least 32 h for the antiproton lifetime (in its rest frame).

On the theory of coherent instabilities due to coupling between a dense cooled beam and charged particles from the residual gas

The authors discuss intensity limitations due to ions trapped in the p-beam and assess antidotes which have recently been applied in the Antiproton Accumulator (AA) at CERN. They reexamine the theory and analyze Landau damping of dipole and quadrupole modes, stabilization by the appropriate choice of the working point, and ion clearing by shaking of the p-beam.<<ETX>>

Further results and evaluation of electron cooling experiments at LEAR

Abstract 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).

The Antiproton Decelerator: AD

Abstract 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.

Production of low-energy antiprotons

The production, collection and deceleration of antiprotons is reviewed with the aim of establishing guidelines for the design of a simple yet efficient source of stopped antiprotons. A high-energy (20–100 GeV) high-intensity (∼1013 protons/pulse) proton accelerator is needed to produce antiprotons in copious numbers. A “passive” conversion-target consisting of a thin iridium rod embedded in graphite, and a magnetic-horn type lens to collect the antiproton flux from the target represent a good compromise between yield and reliability. To transport the flux to low energy a large-acceptance cooling and deceleration ring working up to an energy equal to one-eighth to one-tenth of the primary proton energy is required. Stochastic cooling (at high energy) and electron cooling (at lower energy) are indispensable for providing low-energy beams of useful density.

Commissioning and first operation of the Antiproton Decelerator (AD)

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 STATUS OF STOCHASTIC COOLING

Abstract Presented at a symposium to celebrate the 30th anniversary of electron cooling, this report is intended to give the status of the companion technique, stochastic cooling, some 28 years after its invention. An overview of past developments reveals the close relationship between the two cooling ideas. Then the report concentrates on the principal ingredients of stochastic cooling in order to discuss the limits encountered and some recent ideas for pushing back these limits.