E. Chiaveri

THE STUDY OF A EUROPEAN NEUTRINO FACTORY COMPLEX

The Neutrino Factory is a new concept for an accelerator that produces a high-intensity, high-energy beam of electron and muon neutrinos – the ultimate tool for neutrino oscillation studies and the only machine conceived up today that could help detect CP violation of leptons. The basic concept of the Neutrino Factory is the production of neutrinos from the decay of high-energy muons. Due to their short lifetime, these muons have to be accelerated very fast. Several new accelerator techniques, like a high-intenstiy proton linac, high-power targets, ionization cooling or recirculating muon linacs are required. This paper presents a snapshot of the accelerator design at CERN. Although some aspects of this European Neutrino Factory Scheme have been optimised for the CERN site, the basic principle is siteindependent.

Improved surface treatment of the superconducting TESLA cavities

Abstract The proposed linear electron–positron collider TESLA is based on 1.3 GHz superconducting niobium cavities for particle acceleration. For a centre-of-mass energy of 500 GeV , an accelerating field of 23.4 MV/m is required which is reliably achieved with a niobium surface preparation by chemical etching. An upgrade of the collider to 800 GeV requires an improved cavity preparation technique. In this paper, results are presented on single-cell cavities which demonstrate that fields of up to 40 MV/m are accessible by electrolytic polishing of the inner surface of the cavity.

Superconducting niobium sputter-coated copper cavity modules for the LEP energy upgrade

Experience from the construction, assembly, and tests of two superconducting cavity modules for the Large Electron Positron colliding beam accelerator (LEP) are given. Each module consists of four individual four-cell 352 MHz Nb sputter-coated Cu cavities equipped with an RF power coupler, higher-order-mode (HOM,) dampers, and a frequency tuner, all housed in a single cryostat. The demountable HOM dampers of a new type designed for sputter-coated cavities allow Q/sub ext/ of 9000 for the HOMs with the largest (R/Q). Q values are higher (4.5 to 11*10/sup 9/) than those for similar Nb sheet cavities up to the maximum accelerating fields obtained (6 to 9.5 MV/m). The field limitation is electron loading and never thermal breakdown. Results on vertical tests of individual cavities are reported (Q value, maximum accelerating fields, residual resistance). They are complemented by results on horizontal tests of individual cavities, and on the fully equipped klystron-driven four-cavity module.<<ETX>>

GEANT4 simulation of the neutron background of the C6D6 set-up for capture studies at n_TOF

The neutron sensitivity of the C6D6 detector setup used at n TOF for capture measurements has been studied by means of detailed GEANT4 simulations. A realistic software replica of the entire n TOF experimental hall, including the neutron beam line, sample, detector supports and the walls of the experimental area has been implemented in the simulations. The simulations have been analyzed in the same manner as experimental data, in particular by applying the Pulse Height Weighting Technique. The simulations have been validated against a measurement of the neutron background performed with a nat C sample, showing an excellent agreement above 1 keV. At lower energies, an additional component in the measured nat C yield has been discovered, which prevents the use of nat C data for neutron background estimates at neutron energies below a few hundred eV. The origin and time structure of the neutron background have been derived from the simulations. Examples of the neutron background for two di erent samples are demonstrating the important role of accurate simulations of the neutron background in capture cross section measurements.

Designing and building a collimation system for the high-intensity LHC beam

The Large Hadron Collider (LHC) will collide proton beams at 14 TeV c.m. with unprecedented stored intensities. The transverse energy density in the beam will be about three orders of magnitude larger than previously handled in the Tevatron or in HERA, if compared at the locations of the betatron collimators. In particular, the population in the beam halo is much above the quench level of the superconducting magnets. Two LHC insertions are dedicated to collimation with the design goals of preventing magnet quenches in regular operation and preventing damage to accelerator components in case of irregular beam loss. We discuss the challenges for designing and building a collimation system that withstands the high power LHC beam and provides the required high cleaning efficiency. Plans for future work are outlined.

A detector of high frequency gravitational waves based on coupled microwave cavities

Superconducting microwave cavities have been proposed for the detection of gravitational waves in the high frequency range of the spectrum. The interaction of the gravitational wave with the cavity walls, and the resulting motion, induces the transition of some electromagnetic energy from an initially excited cavity mode to an empty one. The energy transfer is maximum when the frequency of the wave is equal to the frequency difference of the two cavity modes. In this paper, some ideas for the development of a tunable detector of gravitational waves around 10 kHz are discussed; the outline of a possible detector design and its expected sensitivity are also shown.

A new instrument to measure the surface resistance of superconducting samples at 400 MHz

A 400-MHz niobium quadrupole resonator has been manufactured to study the rf properties of superconducting bulk and thin film samples at low temperatures. We describe the apparatus, i.e., the construction of the resonator, field calculations with MAFIA, and the experimental procedure. In first validation tests the surface resistance Rs of a reactor-grade bulk niobium sample as a function of temperature and applied rf field has been investigated by using a calorimetric “rf-dc-compensation” method. A critical temperature Tc=9.15±0.02 K, a thermal conductivity λ(4.2 K)=6.9±0.7 W/mK, a residual resistance Rres=19.0±0.3 nΩ, and a superconducting energy gap of Δ/kBTc=1.82±0.01 have been measured. At 4.2 K we achieved a calorimetric detection limit for Rs of 0.16 nΩ at a peak field of 25 mT.

First Results on a Superconducting RF-Test Cavity for LEP

In 1979 a feasibility study for the application of superconducting accelerator cavities to LEP was started at CERN. In a first series of measurements using a single cell test cavity (f= 500 MHz) quality factors of 2.1 × 109 and maximum acceleration fields of 4.6 MV/m were reached at 4.2 K. A short survey of the experimental layout and the results are given. For the measurements a chain of carbon resistors and solid state X-ray detectors was used for temperature and X-ray mapping of the cavity surface. Together with a visual inspection of the cavity interior during operation a better insight in field breakdowns mechanism and electron loading could be obtained.

Superconducting cavities for particle accelerators: achievements and problems

Abstract Superconducting RF accelerating cavities of different frequencies are presently operating on various accelerators world wide. The large majority of these cavities are made of niobium sheet, by lathe spinning and welding. In one case only, i.e. LEP2 at CERN, the majority of cavities is made of copper, internally coated with a thin layer of sputtered niobium. The main motivation for developing Nb-coated copper cavities mustbe found in the higher stability against quenching, consequent to the higher thermal conductivity of copper at liquid helium temperatures. Additional advantages are higher Q 0 values at low fields, insensitivity to trapped earth magnetic field and lower cost. Beside these advantages, the Nb-coated cavities unfortunately suffer from a faster Q 0 degradation with increasing the accelerating field. The performances of Nb-sheet and Nb-coated cavities are critically compared on the grounds of the large industrial production required by the LEP2 project.

The Second Beam-Line and Experimental Area at n_TOF: A New Opportunity for Challenging Neutron Measurements at CERN

Since 2001, a wealth of neutron capture and neutron-induced fission reactions has been measured at n_TOF, providing an important contribution to a wide variety of research fields. The experimental activity is driven mostly by two motivations: on the one hand, capture reactions are studied with the aim of improving current models of stellar nucleosynthesis of heavy elements. A review of the needs related to nuclear astrophysics and the contribution of the n_TOF program can be found in [1, 2].