56569647
EXPERIMENTAL INVESTIGATION OF ELECTRON COOLING AND STACKING OF LEAD IONS IN A LOW ENERGY ACCUMULATION RING
This report gives the results of a programme of experimental investigations, which were carried out to test stacking of lead ions in a storage ring (the former Low Energy Anti­ proton Ring, LEAR) at 4.2 MeV per nucleon. The motivation was to demonstrate the feasibility of gaining the large factor in the phase-space density required for injection into the Large Hadron Collider (LHC). In the first part of the report, the layout of the experiments is described, the choice of the parameters of the electron cooling system used for stacking is reported and the multiturn injection using horizontal- and longitudinal­ (and in the final project also vertical-) phase space is discussed. In the second part the experimental results are presented. Factors ofvital importance are the stacking efficiency, the beam life-time and the cooling time of the ions. The beam decay owing to charge exchange with the residual gas and to recombination by the capture of cooling electrons was intensively studied. Beam instabilities and space-charge effects in the ion beamturned out to be additional, although less serious, limitations of the accumulation rate. The cooling speed as a function of cooler and storage-ring properties was investigated over a wide range of parameters. Among the 'surprises' encountered are an anomalously fast recombination rate for certain ion charge states (Pb 53 +), a strong dependence of the cooling time on the dispersion function of the storage ring, and an intensity-dependent outgassing ofequipment in the vacuum chamber. After a careful choice ofparameters and antidotes, an overall factor of 120 in intensity could be gained, by multi-turn injection and stacking for 4 s. The intensity obtained (6 x 10 8 ions with a length corresponding to four LHC bunches) is only a factor oftwo short of the LHC requirement, and the stacking time (4 s instead of 2 s foreseen for filling each LHC ring in 8 min) is another factor of 2 off.
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.
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.
55729922
Experiments on a 14.5 GHz ECR Source
A device for measuring the speed of the wind at medium altitude by the Doppler effect within the visible frequency range comprises a laser which emits pulses of light, a telescope which receives a scattered light and an interferometer used to measure the spectral shift of the scattered light in relation to the emitted pulse of light. The interferometer is a Fabry-Perot interferometer in which a part of one of the two mirrors of the interferometer is covered with an excess thickness of silica to form two separate filters. The spacing of the two mirrors and the excess thickness of silica are determined in such a manner that the pass bands of each one of the two filters thus constructed are centered on the flanks of the spectral distribution of the backscattered light.
102555920
The LHC Lead Ion Injector Chain
115300845
Status and first beam measurements on the CERN RFQ
16412795
Deconstructing 5D QED
We discuss periodic compactification and latticization of a 5D $U(1)$ theory with a Dirac fermion, yielding a $1+3$ effective theory. We address subtleties in the lattice fermionic action, such as fermion doubling and the Wilson term. We compute the Coleman-Weinberg potential for the Wilson line which is finite for N-branes $g~3,$ due to the ${Z}_{N}$ symmetry, which replaces translations in the $5\mathrm{th}$ dimension. This mode becomes a PNGB in the low energy $1+3$ theory. We derive its anomalous coupling to the ``photon'' and its KK modes.
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.
32908492
Topological Physics of Little Higgs Bosons
Topological interactions will generally occur in composite Higgs or Little Higgs theories, extra-dimensional gauge theories in which A5 plays the role of a Higgs boson, and among the pNGB's of technicolor. This phenomena arises from the chiral and anomaly structure of the underlying UV completion theory, and/or through chiral delocalization in higher dimensions. These effects are described by a full Wess-Zumino-Witten term involving gauge fields and pNGB's. We give a general discussion of these interactions, some of which may have novel signatures at future colliders, such as the LHC and ILC.
53579013
Observability of Higgs produced with top quarks and decaying to bottom quarks
The decay, H → bb, is dominant for a Standard Model Higgs boson in the mass range just above the exclusion limit of 114.4 GeV/c 2 reported by the LEP experiments. Unfortunately, an overwhelming abundance of b¯ b events arising from more mundane sources, together with the lack of precision inherent in the reconstruction of the Higgs mass, renders this decay modeaprioriundetectable in the case of direct Higgs production at the LHC. It is therefore of no small interest to investigate whether H → bb can be observed in those cases where the Higgs is produced in association with other massive particles. In this note, the results of a study of Higgs bosons produced in association with top quarks and decaying via H → bb are presented. The study was performed as realistically as possible by employing a full and detailed Monte Carlo simulation of the CMS detector followed by the application of trigger and reconstruction algorithms that were developed for use with real data. Important systematic effects resulting from such sources as the uncertainties in the jet energy scale and the estimated rates for correctly tagging b jets or mistagging non-b jets have been taken into account. The impact of large theoretical uncertainties in the cross sections for t tp lusN jets processes due to an absence of next-to-leading order calculations is also considered.
54867630
Superconducting cosmic strings with massive fermions
Abstract Fermions which couple to the fields comprising a Nielsen-Olesen vortex (cosmic string) can generally exist as massive bound modes on the string. If these fermions carry electromagnetic charge then the string will interact with external electromagnetic fields in a manner significantly altered from the superconducting string scenario of Witten. The current in the string oscillates at a characteristic resonant frequency, ∼ ω , and therefore produces a signature of narrow band radiation. We also give an accounting of the relevant anomalies responsible for fermionic superconducting strings.