Implementation and performance of the third level muon trigger of the ATLAS experiment at LHC

The trigger system of the ATLAS experiment at the LHC aims at a high selectivity in order to keep the full physics potential while reducing the 40 MHz initial event rate imposed by the LHC bunch crossing down to /spl sim/100 Hz, as required by the data acquisition system. Algorithms working in the final stage of the trigger environment (Event Filter) are implemented to run both in a "wrapped" mode (reconstructing tracks in the entire Muon Spectrometer) and in a "seeded" mode (according to a dedicated strategy that performs pattern recognition only in regions of the detector where trigger hypotheses have been produced at earlier stages). The working principles of the offline muon reconstruction and identification algorithms (MOORE and MuId) implemented and used in the framework of the Event Filter are discussed in this paper. The reconstruction performance of these algorithms is presented for both modes in terms of efficiency, momentum resolution, rejection power and execution times on several samples of simulated single muon events, also taking into account the high background environment expected for ATLAS.     

Chiral phase transition of quark matter in the background of parallel electric and magnetic fields

We report on our results about spontaneous chiral symmetry breaking for quark matter in the background of static and homogeneous parallel electric field,E,and magnetic field,B.A Nambu–Jona–Lasinio model is used to compute the dependence of the chiral condensate at finite temperature,E and B.We study the effect of this background on inverse catalysis of chiral symmetry breaking for E and B of the same order of magnitude.We also consider the effect of equilibration of chiral density,n_5,produced by axial anomaly on the critical temperature.The equilibration of n_5 allows for the introduction of the chiral chemical potential,u_5,which is computed selfconsistently as a function of temperature and field strength.We find that even if the chiral medium is produced by the fields the thermodynamics,with particular reference to the inverse catalysis induced by the external fields,it is not very affected by n_5 at least if the average u_5,at equilibrium is not too large.     

Test of piezo-ceramic motor technology in ITER relevant high magnetic fields

In the framework of a Fusion for Energy (F4E) grant, a test campaign started in 2012 in order to assess the performance of the in-vessel viewing system (IVVS) probe concept and to verify its compatibility when exposed to ITER typical working conditions. ENEA laboratories went through with several tests simulating high magnetic fields, high temperature, high vacuum, gamma radiation and neutron radiation.A customized motor has been adopted to study the performances of ultrasonic piezo motors technology in high magnetic field conditions. This paper reports on the testing activity performed on the motor in a multi Tesla magnetic field. The job was carried out in a test facility of ENEA laboratories able to achieve 14 T. A maximum field of 10 T, fully compliant with ITER requirements (8 T), was applied. A specific mechanical assembly has been designed and manufactured to hold the motor in the region with high homogeneity of the field. Results obtained so far indicate that the motor is compatible with high magnetic fields, and are presented in the paper.     

Magnetoelastic bending and snapping of ferromagnetic plates in oblique magnetic fields

Ferritic stainless steel has been considered for structural components such as first walls and blankets of fusion power reactors because the material shows low rates of irradiation swelling. Since it is magnetizable, the magnetoelastic interaction between magnetic field and deformation of the structures in a fusion reactor is so strong that their safety is of concern due to the magnetoelastic bending, buckling and magnetic damping, etc. Basic research of the magnetoelastic characteristics of ferromagnetic plate has been paid special attention by researchers. In this paper, the magnetoelastic bending and snapping are studied for a ferromagnetic plate in an oblique magnetic field. The theoretical model is based on the variational principle where the functional is employed as real total energy in the system including external work. The obtained expression of magnetic force on the plate is the same as that derived from the dipole model when the total magnetic field in the ferromagnetic medium is considered. In order to effectively solve the nonlinearly coupled interaction problem between magnetic field and mechanical deformation, a numerical program combining the finite element method for analyzing the magnetic field with the finite difference technique for finding out the bending deformation of the plate is employed to obtain the solution of magnetoelastic bending of a soft ferromagnetic plate. The numerical calculations are carried out for the typical example of a ferromagnetic cantilevered beam-plate in an oblique magnetic field. From the bending curves, that is the tip deflection versus applied magnetic fields, the critical magnetic field for the magnetoelastic snapping is predicted by the Southwell plot. The theoretical predictions show that the critical magnetic field decreases with the increase in incident angle of the oblique magnetic field. By the effect of incident angle on the magnetic buckling, the discrepancy between theoretical and experimental data can be explained well.     

Experimental validation of material discrimination ability of muon scattering tomography at the TUMUTY facility

Muon scattering tomography is believed to be a promising technique for cargo container inspection, owing to the ability of natural muons to penetrate into dense materials and the absence of artificial radiation. In this work, the material discrimination ability of muon scattering tomography is evaluated based on experiments at the Tsinghua University cosmic ray muon tomography facility,with four materials: flour(as drugs substitute), aluminum,steel, and lead. The features of the different materials could be discriminated with cluster analysis and classifiers based on support vector machine. The overall discrimination precisions for these four materials could reach 70, 95, and 99% with 1-, 5-, and 10-min-long measurement,respectively.     

The neutron background at the surface of the earth

Conclusions The calculations that were made have shown that the production of neutrons by cosmic rays in the upper layers of the earth's crust can exert a strong influence on the slow neutron flux at sea level.In order for us to compare calculation with experiment, it would have been necessary to compute the slow neutron flux at surface of the ground which arises from neutrons produced in the atmosphere. For such an estimate, it is necessary to know the intensity and spectrum of atmospheric neutrons and the possible distortions of them at the surface of the earth. We did not have such data available, and therefore such an estimate was not made in this paper.However, it is clear that the contribution of the neutrons which are produced in granite by cosmic rays to the total neutron flux above its surface is considerably greater than in the case of water. Therefore, one can suppose that the difference in slow neutron fluxes above water and soil surfaces are caused to a considerable degree by the cosmic ray production of neutrons in the upper layers of the earth's crust.Translated from Atomnaya Énergiya, Vol. 17, No. 6, pp. 492–496, December, 1964     

Geometrical aspects of cylindric magnetic shields in strong static fields

Motivated by rrER (the International Thermonuclear Experimental Reactor),research on a magnetic shield against a strong field has been carried out.In this paper,a cylindric magnetic shield is studied by using the finite element method with a nonlinear magnetization curve.The geometrical aspects of shielding performance are identified and corresponding suggestions for application are provided.Among them,the effects of the edge and cover thickness have not been mentioned elsewhere to our knowledge.     

PIN半导体剂量率探测器的研究

利用大面积PIN硅光电二极管作为探测器,对北京正负电子对撞机BEPCI在同步辐射运行、束流注入、束流切断等情况下对撞区的辐射水平进行测量,并分析辐射本底的强度、来源及特点;研究PIN半导体探测器在BEPCI对撞区的工作状况,为第三代北京谱仪BESⅢ的剂量率在线检测奠定基础。