46 research outputs found
FABRICATION OF CRYSTALS FOR CHANNELING OF PARTICLES IN ACCELERATOR
Abstract Channelling in bent crystals is technique with high potential to steer charged-particle beams for several applications in accelerators. Channeling and related techniques underwent significant progress in the last years. Distinctive features of performance increase was the availability of novel ideas other than new techniques to manufacture the crystal for channeling. We propose two methods to fabricate crystals through silicon micromachining techniques, i.e., isotropic or anisotropic silicon etchings. Characterization of the crystals accomplished for both methods to highlight that the crystals are free of lattice damage induced by the preparation. Crystals prepared by both kinds of methodologies were positively tested at the external line H8 of the SPS with 400 GeV protons for investigation on planar and axial channelings as well as on single and multiple volume reflection experiments by the H8-RD22 collaboration
Fabrication of Crystals for Channeling of Particles in Accelerators
Channelling in bent crystals is technique with high potential to steer charged-particle beams for several applications in accelerators. Channeling and related techniques underwent significant progress in the last years. Distinctive features of performance increase was the availability of novel ideas other than new techniques to manufacture the crystal for channeling. We propose two methods to fabricate crystals through silicon micromachining techniques, i.e., isotropic or anisotropic silicon etchings. Characterization of the crystals accomplished for both methods to highlight that the crystals are free of lattice damage induced by the preparation. Crystals prepared by both kinds of methodologies were positively tested at the external line H8 of the SPS with 400 GeV protons for investigation on planar and axial channelings as well as on single and multiple volume reflection experiments by the H8-RD22 collaboration
Strong reduction of the off-momentum halo in crystal assisted collimation of the SPS beam
A study of crystal assisted collimation has been continued at the CERN SPS for different energies of stored beams using 120 GeV/. c and 270 GeV/. c protons and Pb ions with 270 GeV/. c per charge. A bent silicon crystal used as a primary collimator deflected halo particles using channeling and directing them into the tungsten absorber. A strong correlation of the beam losses in the crystal and off-momentum halo intensity measured in the first high dispersion (HD) area downstream was observed. In channeling conditions, the beam loss rate induced by inelastic interactions of particles with nuclei is significantly reduced in comparison with the non-oriented crystal. A maximal reduction of beam losses in the crystal larger than 20 was observed with 270 GeV/. c protons. The off-momentum halo intensity measured in the HD area was also strongly reduced in channeling conditions. The reduction coefficient was larger than 7 for the case of Pb ions. A strong loss reduction was also detected in regions of the SPS ring far from the collimation area. It was shown by simulations that the miscut angle between the crystal surface and its crystallographic planes doubled the beam losses in the aligned crystal.peer-reviewe
Comparative results on collimation of the SPS beam of protons and Pb ions with bent crystals
New experiments on crystal assisted collimation have been carried out at the CERN SPS with stored beams of 120 GeV/. c protons and Pb ions. Bent silicon crystals of 2 mm long with about 170 μrad bend angle and a small residual torsion were used as primary collimators. In channeling conditions, the beam loss rate induced by inelastic interactions of particles with the crystal nuclei is minimal. The loss reduction was about 6 for protons and about 3 for Pb ions. Lower reduction value for Pb ions can be explained by their considerably larger ionization losses in the crystal. In one of the crystals, the measured fraction of the Pb ion beam halo deflected in channeling conditions was 74%, a value very close to that for protons. The intensity of the off-momentum halo leaking out from the collimation station was measured in the first high dispersion area downstream. The particle population in the shadow of the secondary collimator-absorber was considerably smaller in channeling conditions than for amorphous orientations of the crystal. The corresponding reduction was in the range of 2-5 for both protons and Pb ions.peer-reviewe
Observation of parametric X-rays produced by 400 GeV/c protons in bent crystals
Spectral maxima of parametric X-ray radiation (PXR) produced by 400 GeV/c protons in bent silicon crystals aligned with the beam have been observed in an experiment at the H8 external beam of the CERN SPS. The total yield of PXR photons was about 10-6 per proton. Agreement between calculations and the experimental data shows that the PXR kinematic theory is valid for bent crystals with sufficiently small curvature as used in the experiment. The intensity of PXR emitted from halo protons in a bent crystal used as a primary collimator in a circular accelerator may be considered as a possible tool to control its crystal structure, which is slowly damaged because of irradiation. The intensity distribution of PXR peaks depends on the crystal thickness intersected by the beam, which changes for different orientations of a crystal collimator. This dependence may be used to control crystal collimator alignment by analyzing PXR spectra produced by halo protons.peer-reviewe
Erratum to: "Double volume reflection of a proton beam by a sequence of two bent crystals" [Phys. Lett. B 658 (2008) 109]
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The Influence of Political Connection and Institutions to the Performance and Bank Loans of Private Listed Companies
我国有着不同于西方发达国家的制度背景和政治制度,政府对市场的管制力度较大,上市公司的高管具有一定的政治背景,其中国有企业本身大股东的政府背景性质,其政治关联很可能是与生俱来的,而民营企业政治关联的形成则具有主动性。改革开放以来,民营经济不断发展壮大,己成为我国经济增长的主要推动力量,因此,研究政治关联对民营公司的影响这一问题在中国更具有现实启发意义。 本文以民营上市公司的高级管理人员是否是前任或现任的政府官员、人大代表或政协委员来衡量公司是否具有政治关联,选取2004年—2008年中国沪深两市所有A股民营上市公司为样本,实证研究了政治关联与制度环境对民营上市公司经营绩效和银行贷款的影响。研究...Chinese current institution and political system are different from the Western developed countries. Under this system, many executives of private listed companies are relevant to politics. Therefore the study of political influence of private companies related to this issue in China is more realistic instructive. This paper focuses on whether the company has the political connection, which measu...学位:管理学硕士院系专业:管理学院财务学系_财务学学号:1762007115174
Sistema di puntamento solare
Sensore di puntamento per s istemi ad inseguimento solare
comprendente mezzi d’acquisizione dell’immagine (1), un
sensore d’ombreggiamento (2) solidale e allineato con detti
mezzi d’acquisiz ione dell’ immagine (1), un’unità di
elaborazione (11), un corpo contenitore (7) opaco alla
radiazione luminosa, che definisce il setto del sensore di
ombreggiamento (2)
SOLAR POINTING SYSTEM
A pointing sensor for solar tracking systems comprising image acquisition means ( 1 ), a shading sensor (2) integral and aligned with said image acquisition means (1), a processing unit (1 1 ) and a containing body (7) opaque to light radiation, which forms the divider of the shading sensor (2)
Sistema opto-elettronico per misure radiometriche
Uno strumento optoelettronico per effettuare misurazioni radiometriche di sorgenti luminose comprende: un sensore comprendente una matrice di pixel; un sistema ottico per formare l’immagine di una sorgente luminosa esterna sulla superficie sensibile del sensore; un filtro ottico passabanda interposto tra il sensore e la sorgente luminosa esterna per separare lo spettro della radiazione emessa dalla sorgente luminosa esterna in una prima porzione, avente larghezza di banda relativamente ristretta, che viene trasmessa verso il sensore ed una seconda porzione che non giunge al sensore; lo strumento comprende un sistema di elaborazione dati che, a partire dalla pluralità di immagini monocromatiche registrate da detto sensore, permette di calcolare la distribuzione angolare della radiazione luminosa incidente sullo strumento e l’irradianza sul piano normale alla direzione da cui proviene la radiazione luminosa