T. R. Sherwood

Antiproton Production and Collection for the CERN Antiproton Accumulator

Antiprotons are produced for the CERN Antiproton Accumulator (AA) by focusing 26 GeV/c protons onto a 3 mm diameter, 11 cm long copper wire. Negatively charged particles with momenta about 3.5 GeV/c are focused by a short focal length coaxial horn and transported to the AA by a normal quadrupole focusing channel. The yield of antiprotons was found to be considerably less than anticipated (factor about 2) and the reason is presumed to be the assumption of too large a production cross-section in the original machine design proposal. Studies involving new horn design, introduction of an axial current e 150 kA) along the target and use of lithium lenses as an alternative to the magnetic horn are under way. Some preliminary measurements involving some of these techniques have been made, both to confirm the validity of calculations and to test the feasibility of building targets and focusing systems to withstand the mechanical forces and heat load due to the proton beam and the high pulsed currents.

Beam Tests of a 2 cm Diameter Lithium Lens

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.

Conducting targets for p production of ACOL past experience and prospects

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.

Beam Optics Studies on the Antiproton Accumulator

The CERN Antiproton Accumulator (AA) was designed to accumulate 6 x 1011 antiprotons per day, using the stochastic cooling technique. Its construction was completed within two years and the first beam circulated in early July 1980. This paper describes the conceptual design of the lattice and how multipole shim corrections were applied to develop the large betatron and momentum design acceptances. We also report how a sequence of such corrections, based on optics studies with proton beams, have been applied to the point that the machine is now approaching design performance.

Injection into the New CERN Antiproton Collector Ring

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.

A Large Aperture Pulsed Septum Magnet for Antiproton Injection into the CERN AC Ring

A new collector ring (AC) is being built around the existing Antiproton Accumulator (AA) machine in order to increase the accumulation rate of antiprotons [1]. A much larger fraction of the particles produced at an improved target station will be transported to AC with a new 3.5 GeV/c beam line. This increased flux will be injected using a large aperture pulsed septum magnet capable of handling the 240 ¿.mm.mrad transverse emittances. Because the antiproton beam traverses the septum gap in air no vacuum problems arise and consequently the magnet can be of simple, glued construction. The beam requirements together with some of the unusual engineering design features of the 1.6 m long, 1 Tesla curved septum magnet are discussed.

Performance of the New CERN 50 MeV Linac

The new 50 MeV proton linac injector for the CERN accelerator complex has just commenced routine operation. In this paper the design characteristics and commissioning of the machine as well as some results of the study programmes at 750 keV and 10 MeV are briefly described, to put into perspective the present 50 MeV performance. It has already been demonstrated that the improved beam brightness and stability at 50 MeV lead to higher intensities in the subsequent accelerators and it is expected that further development of this linacs potential will be made during 1979.