Search

Very intense neutrino beams and large neutrino detectors will be needed to enable the discovery of CP violation in the leptonic sector. The European Spallation Source (ESS), currently under construction in Lund, Sweden, is a research center that will provide, by 2023, the world's most powerful neutron source. The average power will be 5 MW. Pulsing this linac at higher frequency, at the same instantaneous power, will make it possible to raise the average beam power to 10 MW to produce, in parallel with the spallation neutron production, a high performance neutrino Super Beam of about 0.4 GeV mean neutrino energy. The ESS neutrino Super Beam, ESSnuSB, operated with a 2.0 GeV linac proton beam, together with a large underground Water Cherenkov detector located at 540 km from Lund, close to the second oscillation maximum, will make it possible to discover leptonic CP violation at 5 sigma significance level in 56 percent (65 percent for an upgrade to 2.5 GeV beam energy) of the leptonic Dirac CP-violating phase range after 10 years of data taking. The paper gives an overview of the proposed facility and presents the outstanding physics reach possible for CP violation with ESSnuSB., This article is withdrawn several and should not exist at all

The field strength and homogeneity of all the LHC superconducting magnets were measured as a part of the production control and qualification process that has taken place during the past four years. In addition to field measurements at room temperature performed on the integral of the production, a significant part of the magnets has been subjected to extensive magnetic measurements at cold. The measurements at cryogenic temperatures, generally performed up to excitation currents of 12 kA corresponding to the ultimate LHC energy of 7.6 TeV, were mainly based on static and dynamic field integral and harmonic measurements. This allowed us to study in detail the DC effects from persistent current magnetization and long-term decay during constant current excitation. These effects are all expected to be of relevance for the field setting and error compensation in the LHC. This paper reports the main results obtained during these tests executed at operating conditions. The integrated field quality is discussed in terms of distribution (average and spread) of the field strength and low-order harmonics as obtained for all the main ring magnet families (dipoles, main and matching quadrupoles). The dependence of field quality on coil geometry, magnet and cable manufacturer is analyzed. A projection of the field quality expected for the critical components in the machine is presented., peer-reviewed

In August 2006, about 95 % of the production of the 1232 LHC superconducting dipole cold masses, whose coils are wound with Cu/Nb-Ti cables, is completed. One of the 3 manufacturers, having produced one third of the required magnets, completed its production in the end of 2005. The acceptance of the magnets takes place after the 1.9 K performance tests and has been issued for more then 1000 magnets so far. More then half of the dipole magnets are already installed in the tunnel. The paper reviews the main features of the dipoles, the most important steps of the manufacturing and the most critical operations. The quality control and the critical nonconformities that have led, for instance, to a swift campaign of investigations and repairs of few subcomponents (diode assembly, cold bore tube to welding flare fillet weld) are discussed. The status of the production and the performance of the tested dipoles will be presented. Finally the expected schedule for the completion of the production will be shown.

We report in this article on two issues of precision accelerator physics, performed at the LEP collider, that challenged international collaborations. The first result is an increase of the polarisation degree from an almost vanishing natural level to 50%, opening the way to energy calibration by resonant depolarisation. The second result is a systematic and precise determination of the collider centre-of-mass energy correcting for subtle effects such as the azimuthal variation of the beam energy, the magnets temperature, the effects of parasitic earth currents and terrestrial tides. It resulted in an extremely accurate test of the Standard Model and set significant constraints on the top quark and Higgs masses. To cite this article: J.-P. Koutchouk, M. Placidi, C. R. Physique 3 (2002) 1121–1130.

Very intense neutrino beams and large neutrino detectors will be needed in order to enable the discovery of CP violation in the leptonic sector. We propose to use the proton linac of the European Spallation Source currently under construction in Lund, Sweden to deliver, in parallel with the spallation neutron production, a very intense, cost effective and high performance neutrino beam. The baseline program for the European Spallation Source linac is that it will be fully operational at 5 MW average power by 2022, producing 2 GeV 2.86 ms long proton pulses at a rate of 14 Hz. Our proposal is to upgrade the linac to 10 MW average power and 28 Hz, producing 14 pulses/s for neutron production and 14 pulses/s for neutrino production. Furthermore, because of the high current required in the pulsed neutrino horn, the length of the pulses used for neutrino production needs to be compressed to a few $\mu$s with the aid of an accumulator ring. A long baseline experiment using this Super Beam and a megaton underground Water Cherenkov detector located in existing mines 300-600 km from Lund will make it possible to discover leptonic CP violation at 5 $\sigma$ significance level in up to 50% of the leptonic Dirac CP-violating phase range. This experiment could also determine the neutrino mass hierarchy at a significance level of more than 3 $\sigma$ if this issue will not already have been settled by other experiments by then. The mass hierarchy performance could be increased by combining the neutrino beam results with those obtained from atmospheric neutrinos detected by the same large volume detector. This detector will also be used to measure the proton lifetime, detect cosmological neutrinos and neutrinos from supernova explosions. Results on the sensitivity to leptonic CP violation and the neutrino mass hierarchy are presented. Very intense neutrino beams and large neutrino detectors will be needed in order to enable the discovery of CP violation in the leptonic sector. We propose to use the proton linac of the European Spallation Source currently under construction in Lund, Sweden, to deliver, in parallel with the spallation neutron production, a very intense, cost effective and high performance neutrino beam. The baseline program for the European Spallation Source linac is that it will be fully operational at 5 MW average power by 2022, producing 2 GeV 2.86 ms long proton pulses at a rate of 14 Hz. Our proposal is to upgrade the linac to 10 MW average power and 28 Hz, producing 14 pulses/s for neutron production and 14 pulses/s for neutrino production. Furthermore, because of the high current required in the pulsed neutrino horn, the length of the pulses used for neutrino production needs to be compressed to a few μs with the aid of an accumulator ring. A long baseline experiment using this Super Beam and a megaton underground Water Cherenkov detector located in existing mines 300–600 km from Lund will make it possible to discover leptonic CP violation at 5 σ significance level in up to 50% of the leptonic Dirac CP-violating phase range. This experiment could also determine the neutrino mass hierarchy at a significance level of more than 3 σ if this issue will not already have been settled by other experiments by then. The mass hierarchy performance could be increased by combining the neutrino beam results with those obtained from atmospheric neutrinos detected by the same large volume detector. This detector will also be used to measure the proton lifetime, detect cosmological neutrinos and neutrinos from supernova explosions. Results on the sensitivity to leptonic CP violation and the neutrino mass hierarchy are presented. Very intense neutrino beams and large neutrino detectors will be needed in order to enable the discovery of CP violation in the leptonic sector. We propose to use the proton linac of the European Spallation Source currently under construction in Lund, Sweden to deliver, in parallel with the spallation neutron production, a very intense, cost effective and high performance neutrino beam. The baseline program for the European Spallation Source linac is that it will be fully operational at 5 MW average power by 2022, producing 2 GeV 2.86 ms long proton pulses at a rate of 14 Hz. Our proposal is to upgrade the linac to 10 MW average power and 28 Hz, producing 14 pulses/s for neutron production and 14 pulses/s for neutrino production. Furthermore, because of the high current required in the pulsed neutrino horn, the length of the pulses used for neutrino production needs to be compressed to a few $\mu$s with the aid of an accumulator ring. A long baseline experiment using this Super Beam and a megaton underground Water Cherenkov detector located in existing mines 300-600 km from Lund will make it possible to discover leptonic CP violation at 5 $\sigma$ significance level in up to 50% of the leptonic Dirac CP-violating phase range. This experiment could also determine the neutrino mass hierarchy at a significance level of more than 3 $\sigma$ if this issue will not already have been settled by other experiments by then. The mass hierarchy performance could be increased by combining the neutrino beam results with those obtained from atmospheric neutrinos detected by the same large volume detector. This detector will also be used to measure the proton lifetime, detect cosmological neutrinos and neutrinos from supernova explosions. Results on the sensitivity to leptonic CP violation and the neutrino mass hierarchy are presented.

To improve the measurements of the Z boson mass and resonance width, the 1993 Large Electron Positron Collider (LEP) run was devoted to a three point beam energy scan, with one point close to the peak of the Z resonance and two points roughly 880 MeV below and above the peak. Operational energy calibration by resonant depolarization was successfully commissioned for all three beam energies. 24 energy calibrations were performed at the end of physics fills. The accuracy of each calibration is better than 1 MeV. About one third of the total integrated luminosity was recorded in calibrated fills below and above the resonance and a regular tracking of the beam energies throughout the scan was possible. The evolution of the beam energies in the course of the year showed a large variation of up to 20 MeV. Results from the energy calibrations will be presented and possible explanations for the changes of the beam energy during the year will be described.

A possible scenario for the luminosity upgrade of the Large Hadron Collider is based on large aperture quadrupoles to lower ${\ensuremath{\beta}}^{*}$ in the interaction regions. Here we analyze the measurements relative to the field quality of the RHIC and LHC superconducting quadrupoles to find out the dependence of field errors on the size of the magnet aperture. Data are interpreted in the framework of a Monte Carlo analysis giving the reproducibility in the coil positioning reached in each production. We show that this precision is likely to be independent of the magnet aperture. Using this result, we can carry out an estimate of the impact of the field quality on the beam dynamics for the collision optics.

A significant reduction of beta* requires a new beam crossing scheme to overcome the consequence of the luminosity loss factor. We define in this paper the parameters of a possible solution taking advantage of an early separation scheme optionally supplemented by a weak crab crossing. Large aperture (150 mm) Nb3Sn triplet quadrupoles are chosen for their compactness, temperature margin and ability to relax the collimator gap and impedance. This concept offers high performance for a moderate increase of complexity. An open issue is the possibility of integrating dipoles inside the detectors.

Space-charge effects have been identified as the most serious intensity limitation in the CERN PS and PS Booster, on the way towards ultimate LHC performance and beyond. We here explore the application of several previously proposed space-charge compensation methods to the two LHC pre-injector rings, and the challenges which need to be overcome. The methods considered include the reduction of tune shift and resonance strengths via octupoles, pole-face windings, electron lenses, or neutralisation.

Random components of field harmonics in superconducting quadrupoles are usually estimated by computing the effect of a random positioning of the coil blocks with an r.m.s. of 0.05 mm. Here, we review the experience acquired in the construction of 7 superconducting quadrupoles in the RHIC and in the LHC projects to estimate the reproducibility in the coil positioning. Post-processed data show that the reproducibility is around 0.020 mm r.m.s., and independent of the aperture. Using this result, we work out a scaling law for the random components as a function of the magnet aperture. As an application, we analyse the impact on geometrical aberrations of the expected field errors in presence of large beta functions in the triplet.

Experimental results on the observation of transverse polarization in LEP at 46.5 GeV/beam are presented and discussed. The level of transverse polarization was determined by monitoring the mean shift of the vertical distributions of the backscattered photons under helicity reversal of the circularly polarized laser light. Plans for polarization studies and absolute LEP energy calibration are also presented. >

Radiative spin polarization has been studied in the Large Electron-Positron Collider (LEP) at CERN for beam energies from 40 GeV to 100 GeV. The data cover a unique range of spin dynamics, not previously accessible with other storage rings. After optimization of machine parameters and the successful application of new Harmonic Spin Matching techniques, a transverse beam polarization of 57% was obtained at 44.7 GeV. At 60.6 GeV the maximum level reached 8%. The observed energy dependence of radiative spin polarization at LEP is in excellent agreement with the theoretically expected behavior. The LEP data provide the first experimental confirmation for a theory of depolarization at very high energies, first developed in the 1970s by Derbenev and Kontratenko. The results will help to guide the design of any future high energy electron-positron storage ring requiring polarized beams.

Tune, chromaticity and orbit of the LHC beams have to be precisely controlled by synchronising the magnetic field of quadrupole, sextupole and corrector magnets. This is a challenging task for an accelerator using superconducting magnets, whose field and field errors will have large dynamic effects. The accelerator physics requirements are tight due to the limited dynamic aperture and the large energy stored in the beams. The power converters need to be programmed in order to generate the magnetic functions with defined tolerances. During the injection process and the energy ramp the magnetic performance cannot be predicted with sufficient accuracy, and therefore real-time feedback systems based on magnetic measurements and beam observations are proposed. Beam measurements are used to determine a correction factor for some of the power converters. From magnetic measurements the excitation of small magnets to compensate the sextupolar (b/sub 3/) and decapolar (b/sub 5/) field components in the dipole magnets will be derived. To meet these requirements a deterministic control system is envisaged.

The lattice of the CERN Large Hadron Collider is designed with 23 regular cells per are, each containing 6 tightly packed 14.2 m long dipoles. This allows to reach 7 TeV per beam with a dipole field of 8.4 Tesla. There are four experimental insertions, two of which are devoted to high luminosity experiments with /spl plusmn/23 m of free space for the detector. The other two experimental insertions are combined with injection. The value of /spl beta/* at the interaction points is tunable from 6 m at injection to 0.5 m in collision. The energy deposition in the inner triplets is carefully reduced to sustain the nominal luminosity of 10/sup 34/ cm/sup -2/ s/sup -1/. Two insertions are devoted to collect the halo particles with large emittance and momentum spread surrounding the beam core: escaping rates of the protons are estimated to be less than 4/spl middot/10/sup 6/ sec/sup -1/ m/sup -1/. Finally, one insertion is used to extract the particles in the vertical direction with a minimized deflecting strength.

A transverse beam polarization of around 10% reproducibly observed in LEP in 1991. Resonant spin depolarization was performed at four occasions, from September 16 to November 11, providing measurements of the beam energy with a precision of ± 1.5 × 10−5. Several cross-checks were performed to ascertain that the observed resonance corresponds to the fundamental spin precession frequency. The variability of the results, ± 6 × 10−5, is consistent with the expected stability and reproducibility of the machine.

The performance of LEP (Large Electron Positron colliding beam accelerator) has been steadily improving: 750000 Z/sup 0/ were produced in 1990. Many of the design parameters have been reached separately, showing that the machine behaves basically as expected. In fact, some design parameters have been exceeded ( beta *, emittance ratio) and a significant level of polarization was obtained. An improvement by a factor of up to four in integrated luminosity is still to be expected by overcoming the identifiable limitations: strong synchrobetatron resonances and blow-up of the beam due to the beam-beam effect. Solutions to these problems have been devised and will be tested in a machine study program. The long-term LEP experimental program has been defined by the physics community: a pretzel scheme will be installed to increase the luminosity. It will be followed by the LEP 200 program to increase the energy up to and beyond the W pair threshold. >

A significant asymmetry of the Compton back-scattered photons was observed when illuminating the LEP beam with circularly polarized laser shots. The corresponding polarization level is estimated to be about 9%. The asymmetry could be modified by exciting a spin resonance. This experiment was made at dedicated energy and machine optics. The consistency of the measurement with the prediction of the polarization is satisfactory.

As part of the study of the LEP electron-positron storage ring, the influence of technological trends on control system design is being assessed. These include availability of cheap processing power and data storage at all levels, wide-band communication by optical fibres, new modular interfacing systems and software concepts. It is suggested that the LEP control system will be based on two principles : - location of real-time and signal-processing functions within the controlled equipment. Micro-processors will deal with sequencing, monitoring, program generation and the equipment will have to be designed appropriately from the outset to achieve the potential cost savings and improved flexibility. The equipment will be connected by serial lines to a global communications system, structured hierarchically, and performing no significant processing outside the system control computers. Control actions will be caused by messages rather than loading of individual words into registers. The paper describes how the above principles could be applied to LEP and mentions some of the practical difficulties.

Due to the recent improvements in phase displacement acceleration, operating techniques and beam diagnostics, considerable progress has been achieved in operating the ISR at the maximum energy of 31.4 GeV (this centre of mass energy corresponds to a 2 TeV fixed target machine). High intensity stacks are stored at 26.6 GeV before acceleration by phase displacement to 31.4 GeV. At this energy up to 34 Amps are obtained with corresponding initial luminosities of 2.1031cm-2s-1 per intersection and 4.3 1031cm-2s-1 in a low-s intersection. Due to the long beam lifetime, physics data taking may be performed over periods of 60 hours. The principle of phase displacement and the associated beam phenomena are discussed together with the control of the magnetic machine and the mutual interaction of the two beams. The operational technique is described and it is shown that the present day performance of the ISR at 31.4 GeV is comparable to the previous performance (1977) at 26.6 GeV. Consequently, in 1978 about 90% of the time requested for physics data collection was at 31.4 GeV.

In a plane electron ring like LEP, the depolarization arises from the parasitic horizontal magnetic fields due to misalignments and field imperfections. We show in this paper that their statistical properties are an important factor that must be taken into account in the computation of the asymptotic polarization level. It is found indeed that random magnetic defects only drive a subset of spin resonances, grouped around ‘‘systematic’’ integer resonances. After closed orbit correction, the horizontal spurious fields, including orbit correctors, are highly correlated; they then drive all spin resonances. For LEP, the polarization level before a specific polarization optimization is divided by two when taking into account a proper orbit spectrum. A hint is given for a simple improvement of existing polarization programs to better simulate a corrected closed orbit.

Previously stabilization of large beams against the transverse resistive wall instability was achieved in the ISR by active damping and by imposing a constant chromaticity over the energy aperture. The introduction of the beam transfer function set-up has opened up the possibility of measuring the actual beam stability diagram. Based upon it, the stability margin is estimated. The influence of the complex wall impedance and of the betatron distribution is compensated by modulation of the chromaticity. A 55 A stack has been accumulated under such conditions.