D. Manglunki

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).

Measurements of H− intra-beam stripping cross section by observing a stored beam in lear

Abstract The cross section for H − “intra-beam stripping”: H − + H − → H − + H 0 + e − was measured by analysing the decay of a stored H − beam. Results ( σ max = 3.6 × 10 −15 cm 2 ± 30%) agree with recently published classical trajectory Monte Carlo calculations but suggest a smaller cross section than obtained from earlier theoretical models. This sets more favourable conditions for the storage of H − beams than previously assumed.

Operational Beams for the LHC

The variety of beams, needed to set-up in the injectors as requested in the LHC, are reviewed, in terms of priority but also performance expectations and reach during 2015. This includes the single bunch beams for machine commissioning and measurements (probe, Indiv) but also the standard physics beams with 50 ns and 25 ns bunch spacing and their high brightness variants using the Bunch Compression Merging and Splitting (BCMS) scheme. The required parameters and target performance of special beams like the doublet for electron cloud enhancement and the more exotic 8b

Measurement and optimisation of the PS-SPS transfer line optics

\oplus

Production of MeV antiprotons

4e beam, compatible with some post-scrubbing scenarios are also described. The progress and plans for the LHC ion production beams during 2014-2015 are detailed. Highlights on the current progress of the setting up of the various beams are finally presented with special emphasis on potential performance issues across the proton and ion injector chain.

Heavy Ions in 2011 and beyond

The beam optics of the PS-SPS transfer line at CERN has been studied and optimised for a variety of beams. Betatron and dispersion matching has been performed for the fixed-target proton and ion beams, as well as for the future LHC proton beam. The techniques applied to the measurement of the optical parameters in the transfer line are discussed and experimental results are presented.

First Results of Electron Cooling Experiments at LEAR

In view of a future antihydrogen programme at CERN, the options for producing MeV antiprotons are revisited. The current limitations, operational performances and foreseen improvements are detailed. An alternative scheme using a dedicated machine for production and deceleration is also discussed.

Plans for ions in the injector complex

The LHCs first heavy ion run set and tested the operational pattern for 2011 and later years: a rapid commissioning strategy intended to ensure delivery of integrated luminosity despite the risks associated with the short time-frame. It also gave us hard data to test our understanding of the beam physics that will limit performance. The 2010 experience is fed into the commissioning plan, parameter choices and projected performance for 2011. The prospects for future stages of the LHC ion program, Pb-Pb collisions at higher energy and luminosity, hybrid collisions and other species, depend critically on the scheduling of certain hardware upgrades.

Acceleration of lead ions in the CERN PS Booster and the CERN PS

The first results are presented of electron cooling experiments in the Low-Energy Antiproton Ring (LEAR) at CERN, performed with a proton beam of about 50 and 21 MeV. The number of stored protons ranged from 107 to 3 × 109. Cooling times of the order 1 s and proton drag rates of up to 0.7 MeV/s were obtained. The capture of cooling electrons by protons producing hydrogen atoms was used to derive an effective electron temperature (0.25 eV). From the angular profile of the neutral hydrogen beam an upper limit of 3π mm.mrad could be deduced for the horizontal equilibrium proton-beam emittance. The lowest equilibrium momentum spread was 2 × 105 (FWHM), as derived from the analysis of the longitudinal Schottky signal. This Schottky signal exhibited an unusual behaviour with beam intensity and under certain conditions showed a doublepeak structure which was associated with collective beam noise. For very cold beams transverse instabilities were observed, which resulted in a rapid spill-off of protons and a stabilization at lower intensities. The threshold of these instabilities was raised by heating the proton or the electron beam. The cooling of a bunched proton beam was investigated. The reduction of the proton momentum spread led to bunch lengths of about 2 m, containing 3 × 108 protons.

A carbon jet beam profile monitor for LEAR

The heavy ion beams required during the HL-LHC era will imply significant modifications to the existing injector chain. We review the various options, highlighting the importance of an early definition of the future needs and keeping in mind the compatibility with the rest of the future CERN physics programme. DESIGN & CURRENT PERFORMANCE In the LHC design report [1], a peak luminosity of 10 27 cm -2 s -1 was predicted for collisions at 7 ZTeV (p = 2.76 TeV/c/u) in the nominal scheme, with 592 bunches per ring, and a spacing of 100ns. Those bunches were produced by splitting the LEIR bunches in two in the PS, on an intermediate flat top. In order to combat expected IBS and space charge effects on the 40-second long SPS injection flat-bottom, complicated RF gymnastics involved further splitting the bunches into bunchlets prior to PS extraction, and recombining them in the SPS just before acceleration, using a 100 MHz RF system to be re-installed (Fig. 1). To compensate for a somewhat lower current at the output of Linac3, and to meet the high expectations which followed the 2010 run with the “early” beam [2], a different scheme than the “nominal” one was implemented. Inaptly named “intermediate”, this new scheme skipped the splitting process in the PS machine, replacing it by a rebucketing from h = 12 to h = 24 (Fig. 2). This yields denser bunches, at the expense of a smaller number of bunches, and a larger bunch spacing – 200 ns instead of 100 ns [3]. The experience with the Pb beam in 2010 had already demonstrated that the IBS and space charge issues on a 40 second long SPS front porch, although quite harmful, were less severe than anticipated, even for denser bunches than originally designed, and did not impose the implementation of the bunchlet scheme. Another feature of the “intermediate” scheme was a 200 ns batch spacing, made possible by the short SPS kicker rise time at the low magnetic rigidity of the Pb ion beam at injection (equivalent to 17 GeV/c protons). Eventually the intermediate beam allowed to reach a peak luminosity of 5×10 26 cm -2 s -1 at 3.5 ZTeV/c per beam (p = 1.38 TeV/c/u). Scaled to the nominal momentum of 7 ZTeV/c per beam where the β and physical transverse emittances are halved, this corresponds to twice the design goal [4]. Table 1 compares the performance expected with the “nominal beam”, and the one achieved in 2011 with the “intermediate beam”. Figure 1: Nominal scheme, as planned in the LHC Design Report. Figure 2: Intermediate scheme, as achieved during the 2011 run. Table 1: Design and achieved performance.