R. Steerenberg

MULTITURN EXTRACTION BASED ON TRAPPING IN STABLE ISLANDS

Recently a novel approach to perform multi-turn extraction was proposed based on beam splitting in the transverse phase space by means of trapping inside stable islands. During the year 2002, preliminary measurements at the CERN Proton Synchrotron with a low-intensity, singlebunch, proton beam, confirmed the possibility of generating various beamlets starting from a single Gaussian beam. The experimental campaign continued also during the year 2003 to assess a number of key issues, such as the feasibility of trapping with high-intensity beam and capture efficiency. The experimental results are presented and discussed in detail in this paper.

Adiabatic beam trapping in stable islands of transverse phase space: measurement results at CERN Proton Synchrotron

Recently a novel approach to the problem of multi-turn extraction was proposed. It consists of splitting the beam by adiabatic capture inside stable islands created in the transverse phase space by sextupoles and octupoles. Numerical simulations indicate that such a technique should be feasible and potentially superior to the method presently used at the CERN Proton Synchrotron. During 2002, intense efforts were devoted to the experimental verification of this newly proposed extraction mode. Finally, beam capture into the islands was observed. In this paper, the extraction principle is briefly reviewed and the experimental results are presented and discussed in detail.

Recent Intensity Increase in the CERN Accelerator Chain

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.

Measurements of transverse space-charge effects in the CERN Proton Synchrotron

Several beam dynamics codes are used in the design of the next generation of high beam power accelerators. They are all capable of simulating the full six-dimensional motion through a machine lattice in the presence of strong space-charge effect and beam-to-wall interaction. A key issue is the validation of these codes. This is usually accomplished by comparing simulation results against available theories, and more importantly, against experimental observations. To this aim, a number of well-defined test cases, obtained by accurate measurements made in existing machines, are of high interest. This paper reports and discusses precise measurements of transverse emittance blow-up due to space-charge induced crossing of the integer or half-integer stop band.

Fifty years of the CERN Proton Synchrotron : Volume 2

This report sums up in two volumes the first 50 years of operation of the CERN Proton Synchrotron. After an introduction on the genesis of the machine, and a description of its magnet and powering systems, the first volume focuses on some of the many innovations in accelerator physics and instrumentation that it has pioneered, such as transition crossing, RF gymnastics, extractions, phase space tomography, or transverse emittance measurement by wire scanners. The second volume describes the other machines in the PS complex: the proton linear accelerators, the PS Booster, the LEP pre-injector, the heavy-ion linac and accumulator, and the antiproton rings.

Space-Charge Experiments at the CERN Proton Synchrotron

Benchmarking of the simulation codes used for the design of the next generation of high beam power accelerators is of paramount importance due to the very demanding requirements on the level of beam losses. This is usually accomplished by comparing simulation results against available theories, and more importantly, against experimental observations. To this aim, a number of well‐defined test cases, obtained by accurate measurements made in existing machines, are of great interest. Such measurements have been made in the CERN Proton Synchrotron to probe three space‐charge effects: (i) transverse emittance blow‐up due to space‐charge induced crossing of the integer or half‐integer stop‐band, (ii) space‐charge and octupole driven resonance trapping, and (iii) intensity‐dependent emittance transfer between the two transverse planes. The last mechanism is discussed in detail in this paper and compared to simulation predictions.

Optics studies for the CERN Proton Synchrotron: linear and nonlinear modeling using beam based measurements

The CERN Proton Synchrotron machine is built using combined function magnets. The control of the linear tune as well as the chromaticity in both planes is achieved by means of special coils added to the main magnets, namely two pole-face-windings and one figure-of-eight loop. As a result, the overall magnetic field configuration is rather complex not to mention the saturation effects induced at top-energy. For these reasons a linear model of the PS main magnet does not provide sufficient precision to model particle dynamics. On the other hand, a sophisticated optical model is the key element for the foreseen intensity upgrade and, in particular, for the novel extraction mode based on adiabatic capture of beam particles inside stable islands in transverse phase space. A solution was found by performing accurate measurement of the nonlinear tune as a function of both amplitude and momentum offset so to extract both linear and nonlinear properties of the lattice. In this paper the measurement results are presented and the derived optical model is discussed in detail.

Can the proton injectors meet the HL-LHC requirements after LS2?

The LIU project has as mandate the upgrade of the LHC injector chain to match the requirements of HLLHC. The present planning assumes that the upgrade work will be completed in LS2, for commissioning in the following operational year. The known limitations in the different injectors are described, together with the various upgrades planned to improve the performance. The expected performance reach after the upgrade with 25 and 50 ns beams is examined. The project planning is discussed in view of the present LS1 and LS2 planning. The main unresolved questions and associated decision points are presented, and the key issues to be addressed by the end of 2012 are detailed in the context of the machine development programs and hardware construction activities. HL-LHC REQUIREMENTS AFTER LS2 The stated performance objective of HL-LHC is to accumulate 3000 fb of integrated p-p luminosity at 14 TeV centre of mass collision energy [1]. In order to achieve this, an annual figure of 250-300 fb has been posited, requiring instantaneous luminosity capability of around 7–8×10 cms, levelling to 5×10 cms and high machine efficiency [2]. The present paper covers the first of these challenging requirements: how to deliver the beam from the injector complex for these luminosities almost an order of magnitude above LHC design. The HL-LHC project has previously outlined possible parameter sets for 25 and 50 ns spacing which give the required luminosity, summarised in Tab. 1, adapted from [2]. Strictly speaking the HL-LHC needs the specified beams from the SPS after LS3, when the major work for the HL-LHC project is planned. The LIU work will take place largely in LS2, so that the period LS2 to LS3 will be an important one in terms of achieving the maximum performance from the injector chain. The figures quoted are for beams at the start of the collision process at 7 TeV – any beam loss or emittance dilution after extraction from the SPS is not included. The assumptions on the beam loss and emittance dilution for all machines are given in Tab. 2, where it can be seen that the total assumed beamloss -ΔI/I0 is 27%, and the emittance growth Δε/ε0 is 33%, corresponding to a brightness which is reduced to 55% of the original value. Table 1: Parameters and requirements from HL-LHC Parameter Nom. HL 25 ns HL 50 ns N [e11 p+] 1.15 2.0 3.3

The CERN PS multi-turn extraction based on beam splittting in stable islands of transverse phase space

The PS Multi-Turn Extraction Study Group M. J. Barnes*, O. E. Berrig, A. Beuret, J. Borburgh, P. Bourquin, R. Brown, J.-P. Burnet, F. Caspers, J.-M. Cravero, T. Dobers, T. Fowler, S. Gilardoni, M. Giovannozzi (Study Group Leader), M. Hourican, W. Kalbreier, T. Kroyer, F. di Maio, M. Martini, V. Mertens, E. Métral, K.-D. Metzmacher, C. Rossi, J.-P. Royer, L. Sermeus, R. Steerenberg, G. Villiger, T. Zickler

High‐Density and High‐Intensity Beams at the CERN PS

The production of high‐density and high‐intensity beams has been a constant activity at the CERN Proton Synchrotron (PS) since many years. This paper is a status report of the present situation, including also a discussion of ongoing studies and future activities.