This paper describes the acceleration tests performed at the Catania LNS Laboratory on a 3 GHz linac module of the side coupled type, which boosts the proton energy of a beam extracted from a ...cyclotron from 62 to 72 MeV. The output proton energy was measured with two devices: a NaI(Tl) crystal and a bending magnet. The experimental spectra are in good agreement with the calculated ones. From their shape it is obtained that (18A-3.0)% of the transmitted protons fall in a A-2 MeV interval centered around 72 MeV. This result is in good agreement with the 20% value derived from the simulation of the acceleration process. The measured energy of the accelerated protons was used to check that the shunt impedance of the structure is equal to the computed one within 3%. This was the first time that a 3 GHz structure has been used to accelerate protons, and the results of the tests have demonstrated that a high frequency linac can be used as a cyclotron booster.
LIBO is a proton accelerator that operates at
3
GHz
, the same frequency as the one adopted in the about 7500 electron linacs used for radiotherapy all over the world. Such a high frequency was ...chosen to obtain a large gradient (on average more than
10
MV/m
), and thus a short linac (about
15
m
) to boost the energy of the protons, extracted at about
60
MeV
from a cyclotron, up to the
200
MeV
needed for the treatment of deep-seated tumours.
This paper describes the design study of the full
3
GHz
Side Coupled Linac (modular structure, nine modules) and the construction and tests of the LIBO prototype (first module), which was built to accelerate protons from 62 to
74
MeV
with an RF peak power of
4.4
MW
. The items discussed are the beam dynamics parameters of the module (longitudinal and transverse acceptances), the constructional elements and procedures, the accuracies of the various mechanical elements, the cooling system, the RF tuning, the RF measurement and the RF power tests. These tests showed that, after a short conditioning time, the gradient in each of the four tanks of the module could reach
28.5
MV/m
, much larger than the nominal project value
(15.8
MV/m)
. The last section of the paper describes the successful acceleration tests performed at the Laboratori Nazionali del Sud of INFN in Catania with a solid-state
3
GHz
modulator lent by IBA.
The electrical insulation of the Large Hadron Collider (LHC) cables constitutes a thermal barrier between the conductor and the superfluid helium bath. This can prevent removal of the heat dissipated ...in the cable by the current rise in the dipoles or by the beam losses. The main experimental results, obtained with stacks of insulated conductors representing a piece of the actual coil, are given. The mock-ups vary only by the material composition and the structure of the electrical insulation. Analysis of the temperature distribution measured in the conductors as a function of the dissipated heat power makes it possible to determine the dominant heat transfer mode in each type of tested insulation and to classify these according to their permeability to superfluid helium. Thermal numerical modelling of the experimental mock-ups clarifies the heat transfer path in the complex structure of the insulation and enables calculating values of the thermal quantities characteristic of each insulation. The results of these studies have led to the choice of the cable insulation of the LHC magnets.
The electrical insulation system comprising composites and organic films for the prototype superconducting dipole magnets for the Large Hadron Collider currently under construction at CERN is ...presented. The electrical and mechanical aspects of the different components are described and some choices and options are discussed. The mechanical and electrical stresses on the insulation during the production process, storage at room temperature and at operational temperature (below 2
K) and when powered are important due to the dimensions of the cable and due to the forces on the cable and on the coil.
This paper describes the acceleration tests performed at the Catania LNS Laboratory on a 3GHz linac module of the side coupled type, which boosts the proton energy of a beam extracted from a ...cyclotron from 62 to 72MeV. The output proton energy was measured with two devices: a NaI(Tl) crystal and a bending magnet. The experimental spectra are in good agreement with the calculated ones. From their shape it is obtained that (18±3.0)% of the transmitted protons fall in a ±2MeV interval centered around 72MeV. This result is in good agreement with the 20% value derived from the simulation of the acceleration process. The measured energy of the accelerated protons was used to check that the shunt impedance of the structure is equal to the computed one within 3%. This was the first time that a 3GHz structure has been used to accelerate protons, and the results of the tests have demonstrated that a high frequency linac can be used as a cyclotron booster.
The Large Hadron Collider's superconducting magnets are cooled by superfluid helium at 1.8
K and housed in cryostats that minimise the heat inleak to this temperature level by extracting heat at 70
K ...and 5
K. In the first generation of prototype cryostats, the radiative heat to the 1.8
K temperature level accounted for 70% of the total heat inleak. An alternative to enhance the cryostat thermal performance incorporates a thermalised radiation screen at 5
K. In order to avoid contact between the 5
K radiation screen and the cold mass, insulators are placed between both surfaces. Sets of commercial fibre glass nets (spacers) are insulator candidates to minimise the heat inleak caused by any accidental contact between the two temperature levels. A model to estimate their performance is presented. A set-up to thermally characterise them has been designed and is also described in the paper. Finally, results as a function of the number of nets forming the spacer, the boundary temperatures and the compressive force in the spacer are presented.
The results of a search for pair production of the scalar partners of bottom quarks in 2.05 fb(-1) of pp collisions at sqrts=7 TeV using the ATLAS experiment are reported. Scalar bottom quarks are ...searched for in events with large missing transverse momentum and two jets in the final state, where both jets are identified as originating from a bottom quark. In an R-parity conserving minimal supersymmetric scenario, assuming that the scalar bottom quark decays exclusively into a bottom quark and a neutralino, 95% confidence-level upper limits are obtained in the b(1) - χ(1)(0) mass plane such that for neutralino masses below 60 GeV scalar bottom masses up to 390 GeV are excluded.
Using the ATLAS detector, a centrality-dependent suppression has been observed in the yield of J/psi mesons produced in the collisions of lead ions at the Large Hadron Collider. In a sample of ...minimum-bias lead-lead collisions at a nucleon-nucleon centre of mass energy inline image, corresponding to an integrated luminosity of about 6.7 microbsuper-1, J/psi mesons are reconstructed via their decays to microsuper+microsuper- pairs. The measured J/psi yield, normalized to the number of binary nucleon-nucleon collisions, is found to significantly decrease from peripheral to central collisions. The centrality dependence is found to be qualitatively similar to the trends observed at previous, lower energy experiments. The same sample is used to reconstruct Z bosons in the microsuper+microsuper- final state, and a total of 38 candidates are selected in the mass window of 66 to 116 GeV. The relative Z yields as a function of centrality are also presented, although no conclusion can be inferred about their scaling with the number of binary collisions, because of limited statistics. This analysis provides the first results on J/psi and Z production in lead-lead collisions at the LHC.
Dijet angular distributions from the first LHC pp collisions at center-of-mass energy sqrt(s) = 7 TeV have been measured with the ATLAS detector. The dataset used for this analysis represents an ...integrated luminosity of 3.1 pb-1. Dijet $\chi$ distributions and centrality ratios have been measured up to dijet masses of 2.8 TeV, and found to be in good agreement with Standard Model predictions. Analysis of the $\chi$ distributions excludes quark contact interactions with a compositeness scale $\Lambda$ below 3.4 TeV, at 95% confidence level, significantly exceeding previous limits.
Fabrication and test of a LHC NbTi dipole model magnet with a split collar system Zerobin, F.; Leroy, D.; Szeless, B.
IEEE Transactions on Magnetics (Institute of Electrical and Electronics Engineers); (United States),
1992-Jan., 1992-01-00, 19920101, 1992-01-01, Letnik:
28, Številka:
1
Journal Article, Conference Proceeding
A model magnet having the full cross section of the twin-aperture dipole studied for the LHC (Large Hadron Collider) has been fabricated. To investigate various techniques, some special features have ...been developed for the magnet. The design details are discussed as well as the manufacturing and test of the magnet. The fabrication methods have shown to be feasible in an industrial manner. The highly compacted twin-aperture dipole reached 9.05 T at 2 K. This value corresponds to 92% of the short sample limit. At 4.2 K, the short sample limit of 9.7 T was obtained.< >
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