22673060
Ions for LHC: Beam Physics and Engineering Challenges
The first phase of the heavy ion physics program at the LHC aims to provide lead-lead collisions at energies of 5.5 TeV per colliding nucleon pair and ion-ion luminosity of 1027cm-2s-1. The transformation of CERN’s ion injector complex (Linac3-LEIR-PS-SPS) presents a number of beam physics and engineering challenges, which are described in this paper. In the LHC itself, there are fundamental performance limitations due to various beam loss mechanisms. To study these without risk of damage there will be an initial period of operation with a reduced number of nominal intensity bunches. While reducing the work required to commission the LHC with ions in 2008, this will still enable early physics discoveries.
121692361
First results of electron cooling experiments at LEAR
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.
121894301
Studies on ECR4 for the CERN ion program
The CERN heavy ion community, and some other high energy physics experiments, are starting to demand other ions, both heavy and light, in addition to the traditional lead ions. Studies of the behavior of the afterglow for different operation modes of the ECR4 at CERN have been continued to try to understand the differences between pulsed afterglow and continuous operation, and their effect on ion yield and beam reproducibility. The progress in adapting the source and ion beam characteristics to meet the new demands will be presented, as will new information on voltage holding problems in the extraction.
55444273
Present Performance of the CERN Proton Linac
The original 1973 design specification of the CERN 50 MeV Proton Linac was for a 150 mA beam but this intensity was rarely used. Preliminary tests for the high brightness beam required for LHC indicated that 170 mA could be produced for short pulses (30 Ps). Since then further optimisation has enabled the 170 mA to be delivered reliably, within the nominal emittances and dispersion, in long pulses (120 Ps) to the user, the PS Booster (PSB), about 80 m downstream of the linac. The improvements will be described along with the steps envisaged to attain a goal of more than 180 mA.
102555920
The LHC Lead Ion Injector Chain
119401628
The Electron Cooling Device for LEAR
The experiments1,2,3 in which low energetic protons were cooled by a “cold” electron beam have proved that this method is a very powerful technique to improve low energy beams and to increase their phase space density by several orders of magnitude in short times. The theoretical understanding of the cooling process is well advanced4,5,6. The applications of this technique, which was invented and developed in Novosibirsk, are manifold7. It seems to be clear that its main domain is the cooling of non-relativistic ions. However, also at extremely high energies, cooling of protons and antiprotons with stored electrons (cooled themselves by synchrotron radiation) can be contemplated8,9.
119432345
Electroweak symmetry breaking by extra dimensions
Electroweak symmetry breaking may be naturally induced by the observed quark and gauge fields in extra dimensions without a fundamental Higgs field. The authors show that a composite Higgs doublet can arise as a bound state of (t,b){sub L} and a linear combination of the Kaluza-Klein states of t{sub R}, due to QCD in extra dimensions. The top quark mass depends on the number of active t{sub R} Kaluza-Klein modes, and is consistent with the experimental value.
119530771
Acceleration in the linear non-scaling fixed-field alternating-gradient accelerator EMMA
In a fixed-field alternating-gradient (FFAG) accelerator, eliminating pulsed magnet operation permits rapid acceleration to synchrotron energies, but with a much higher beam-pulse repetition rate. Conceived in the 1950s, FFAGs are enjoying renewed interest, fuelled by the need to rapidly accelerate unstable muons for future high-energy physics colliders. Until now a ‘scaling’ principle has been applied to avoid beam blow-up and loss. Removing this restriction produces a new breed of FFAG, a non-scaling variant, allowing powerful advances in machine characteristics. We report on the first non-scaling FFAG, in which orbits are compacted to within 10 mm in radius over an electron momentum range of 12–18 MeV/c. In this strictly linear-gradient FFAG, unstable beam regions are crossed, but acceleration via a novel serpentine channel is so rapid that no significant beam disruption is observed. This result has significant implications for future particle accelerators, particularly muon and high-intensity proton accelerators.
126363269
Cross-section for topcolor Z-prime(t) decaying to t anti-t: Version 2.6
118703681
Top Quark and Electroweak Mass
We describe a class of models of electroweak symmetry breaking that involve strong dynamics and top quark condensation. A new scheme based upon a seesaw mechanism appears particularly promising. Various implications for the first-stage muon collider are discussed.
15093335
Topcolor assisted technicolor
A condensate, tt, arising from O(TeV) scale “topcolor”, in addition to technicolor (and ETC) may naturally explain the gauge hierarchy, the large top quark mass, and contains a rich system of testable consequences. A triplet of strongly coupled pseudo-Nambu-Goldstone bosons, “top-pions”, near the top mass scale is a generic prediction of the models. A new class of technicolor schemes and associated phenomenology is suggested in this approach.