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.
115300845
Status and first beam measurements on the CERN RFQ
102555920
The LHC Lead Ion Injector Chain
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.
137745598
Concept for a lead-ion accelerating facility at CERN
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.
14139978
THE DIFFRACTIVE QUANTUM LIMITS OF PARTICLE COLLIDERS
Quantum Mechanics places limits on achievable transverse beam spot sizes of particle accelerators. We estimate this limit for a linear collider to be \Delta x > \hbar c f/E\delta_0 where f is the final focal length, E the beam energy, and \delta_0 the intrinsic transverse Gaussian width of the electron wave-function. \delta_0 is determined in the phase space damping rings, and we find \delta_0 \approx \sqrt{\hbar c /eB} where B is the typical wiggler magnetic field strength in this system. For the NLC \delta_0 = 25 nm, and \Delta x = 0.06 nm, about two orders of magnitude smaller than the design goal. We can recover a crude estimate of the classical result when we include radiative relaxation effects. We also consider a synchrotron and obtain \Delta x > \sqrt{\hbar c f/E} = O(1.0) nm. We discuss formulation of quantum beam optics relevant to these issues.
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.
119473346
Renormalization group fixed points and the Higgs boson spectrum
Abstract We study numerically the renormalization group equations for the Higgs potential of the two-doublet model assuming perturbative unification and sufficiently large initial quartic and Higgs-Yukawa couplings such that the full nonlinearities interplay. We obtain predictions for the physical Higgs boson spectrum in the two-doublet model up to systematic differences in fermion coupling schemes. Unambiguous predictions emerge only when there exists a heavy generation in which quarks couple to both doublets. In other cases we find that the potential can become quartically unstable at low energies for arbitrary initial stable values of the coupling constants.
15028896
Fractal theory space: Space-time of noninteger dimensionality
We construct matter field theories in ``theory space'' that are fractal, and invariant under geometrical renormalization group (RG) transformations. We treat in detail complex scalars, and discuss issues related to fermions, chirality, and Yang-Mills gauge fields. In the continuum limit these models describe physics in a noninteger spatial dimension which appears above a RG invariant ``compactification scale,'' M. The energy distribution of KK modes above M is controlled by an exponent in a scaling relation of the vacuum energy (Coleman-Weinberg potential), and corresponds to the dimensionality. For truncated-s-simplex lattices with coordination number s the spacetime dimensionality is 1+(3+2ln(s)/ln(s+2)). The computations in theory space involve subtleties, owing to the 1+3 kinetic terms, yet the resulting dimensionalites are equivalent to thermal spin systems. Physical implications are discussed.
119634910
Energy-density fluctuations in de Sitter space
Abstract Quantum fluctuations in de Sitter space or in the de Sitter phase of an inflationary universe give rise to a spectrum of classical energy-density perturbations which is scale invariant. The analysis presented in this letter is based on a consistent expansion in powers of ħ, and on the functional Schrodinger approach to quantum field theory in de Sitter space. The result holds for a large class of initial states of the quantum field, including the Bunch-Davies vacuum.