F. Caspers

Stochastic cooling at the ESR

Stochastic precooling at the ESR storage ring of GSI will be used mainly for experiments with stored radioactive fragment beams. They arrive from the fragment separator with momentum spreads and emittances for which electron cooling is too slow. The installation of components at the ESR is now complete and rst commissioning experiments have been performed. Both longitudinal and transverse stochastic cooling have been demonstrated. The paper gives a short account of the system architecture, and of the response of quarter-wave plates and superelectrodes at intermediate energies. The preparation of fragment beams suitable for subsequent electron cooling is discussed for the case that a mixture of di!erent ion species is present in the cooler ring. Results of commissioning and future prospects are presented. ( 2000 Elsevier Science B.V. All rights reserved.

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.

Transverse impendance of LHC collimators

The transverse impedance in the LHC is expected to be dominated by the numerous collimators, most of which are made of Fibre-Reinforced-Carbon to withstand the impacts of high intensity proton beams in case of failures, and which will be moved very close to the beam, with full gaps of few millimetres, in order to protect surrounding super-conducting equipments. We present an estimate of the transverse resistive-wall impedance of the LHC collimators, the total impedance in the LHC at injection and top energy, the induced coupled-bunch growth rates and tune shifts, and finally the result of the comparison of the theoretical predictions with measurements performed in 2004 and 2006 on a prototype collimator installed in the SPS.

An improved beam screen for the lhc injection kickers

The two LHC injection kicker magnet systems must produce a kick of 1.3 T.m with a flattop duration variable up to 7860 ns, and rise and fall times of less than 900 ns and 3000 ns, respectively. Each system is composed of two resonant charging power supplies (RCPSs) and four 5 Omega transmission line kicker magnets with matched terminating resistors and pulse forming networks (PFNs). A beam screen is placed in the aperture of the magnets: the screen consists of a ceramic tube with conductors on the inner wall. The conductors provide a path for the image current of the, high intensity,LHC beam and screen the ferrite against Wake fields. The conductors initially used gave adequately low beam coupling impedance however inter-conductor discharges occurred during pulsing of the magnet: an alternative design was discharge free at the nominal operating voltage but the impedance was too high for the ultimate LHC beam. This paper presents the results of a new development undertaken to meet the often conflicting requirements for low beam coupling impedance, fast magnetic field rise- time and good high voltage behaviour. High voltage test results and thermal measurements are also presented.

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.

Design aspects of the RF contacts for the LHC beam vacuum interconnects

The LHC requires a very low longitudinal and transverse beam coupling impedance, in particular at low frequencies. This implies an admissible DC contact resistance of less than 0.1 m/spl Omega/ for the RIF contacts inside the vacuum bellows which must carry the image current (up to 50 A peak) of the beam at each vacuum chamber interconnect. Technological aspects, measurement methods and test results are presented for the contacts which will be used in the LHC. The modified mechanical design and the justifications for specific choices will be discussed.

Status of the antiproton decelerator: AD

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.

First observation of two hyperfine transitions in antiprotonic 3He

We report on the first experimental results for microwave spectroscopy of the hyperfine structure of p¯3He+. Due to the helium nuclear spin, p¯3He+ has a more complex hyperfine structure than p¯4He+, which has already been studied before. Thus a comparison between theoretical calculations and the experimental results will provide a more stringent test of the three-body quantum electrodynamics (QED) theory. Two out of four super-super-hyperfine (SSHF) transition lines of the (n,L)=(36,34) state were observed. The measured frequencies of the individual transitions are 11.12559(14) GHz and 11.15839(18) GHz, less than 1 MHz higher than the current theoretical values, but still within their estimated errors. Although the experimental uncertainty for the difference of these frequencies is still very large as compared to that of theory, its measured value agrees with theoretical calculations. This difference is crucial to be determined because it is proportional to the magnetic moment of the antiproton.

Ultrasound diagnostics of the superconducting cable connections between the main ring magnets of LHC

As part of the LHC assembly program, the superconducting magnets are interconnected after installation. Electrical continuity between the magnets is ensured via a specifically designed cable junction box which allows the cables to be electrically joined by an automated low temperature soldering technique. The electrical resistance and mechanical strength of the cable junctions depend on the quality of the soldered joint. An ultrasound diagnostic of the soldered junction has been developed to accompany the visual inspection and reinforce the quality control process. Non-standard ultrasound diagnostic techniques, without using matching liquids or gel in the harsh and congested working environment, applied to the sandwich structure of the cable junction box, which presents high ultra-sonic losses due to multiple scattering, have been developed. The equipment and methods implemented are described in detail, together with results of quality control tests made in the production environment.

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.