Performance of the Monitoring Light Source for the CMS Lead Tungstate Crystal Calorimeter

Light monitoring will play a crucial role in maintaining energy resolution for the CMS lead tungstate crystal calorimeter at LHC. In the last several years, a laser based monitoring light source was designed and constructed at Caltech, and was installed and commissioned at CERN. This paper presents the design of the CMS ECAL monitoring light source and its performance during beam tests. Issues related to the monitoring precision are discussed

The Stability of Underground Power Chambers in the Brittle Rock

The statistical analysis has been executed for the phenomenon of disk cores in the dam site, which has been compared with the condition of high geostresses. The mechanism to form disk cores and the stress state and energy distribution around underground power houses have been analysed with FEM. In addition, the modelling test to investigate the stability of underground house with block material is introduced. Finally some practical conclusions are proposed

Implementation of a Software Feedback Control for the CMS Monitoring Lasers

Light monitoring will play a crucial role in maintaining energy resolution for the CMS lead tungstate crystal calorimeter in situ at LHC. Since 2003, a laser based monitoring system in its final design has been installed and used in beam tests at CERN. While the stability of the laser pulse energy and FWHM width, measured in 24 hours, is at 3% level, a long term degradation and a drift of the laser pulse center timing at 2 ns/day were observed. The degradation and drift were caused by the aging of the DC Kr lamp used to pump the Nd:YLF laser, and would affect the monitoring precision. This paper presents the design and implementation of a software feedback control which stabilizes laser pulse energy, width and timing by trimming the Nd:YLF laser pumping current. For laser runs lasted for more than 650 hours a stability of pulse energy and FWHM width at 3% level and a pulse timing jitter at 2 ns have been achieved when the laser pulse center timing is used as the feedback parameter

Particle velocity profile in an inclined rotating drum

Various experimental and numerical studies have been carried out to study the velocity profiles of the particles inside horizontal rotating drums, but little emphasis has been laid on inclined rotating drums, though these drums are extensively used in granular process industries. In this study, velocity profiles of the particles in a rotating drum with 0o, 5o, 10o, and 15o inclinations have been studied by using the discrete element method. It was found that at the locations of the drum with the volumetric fill in the range of 0.2 0.8, the inclined rotating drum has a similar variation of velocity with the radial height to the horizontal rotating drum. However, the variation of the average particle velocity along the length of the drum differs for horizontal and inclined drums. Furthermore, for the inclined rotating drum, the average velocity increases with the increase in the volumetric fill

Implementation of a Software Feedback Control for the CMS Monitoring Lasers

Light monitoring will play a crucial role in maintaining the energy resolution of the CMS lead tungstate crystal electromagnetic calorimeter (ECAL) in situ at LHC. Since 2001, a laser based monitoring system has been used in the CMS ECAL beam tests at CERN. While the stability of the laser pulse energy and width, measured in 24 hours, is at a level of 3%, a long term degradation of both the laser pulse energy and the width were observed, as well as a drift of the laser pulse center timing at 2 ns/day. This degradation and drift, caused by the natural aging of the DC Kr lamp, would affect respectively the monitoring precision and the synchronization between the laser pulse and the ECAL ADC clock. This paper presents a design and implementation of a software feedback control which stabilizes the laser pulse energy, width and timing. With the software feedback implemented, a stability of the laser pulse energy and width at 3% level and a pulse timing jitter at 2 ns were observed in laser runs lasted for more than 3 months. The 0.5% energy resolution of the CMS PbWO4 crystal ECAL is maintained after applying the laser monitoring corrections in a beam irradiation test

Simulation of thermal stress and fatigue life prediction of high speed steel work roll during hot rolling considering the initial residual stress

Considerable residual stress is produced during heat treatment. Compressive residual stress at the shell is conductive to improving the thermal fatigue life of a work roll, while tensile stress in the core could cause thermal breakage. In hot rolling, thermal stress occurs under the heating-cooling cycles over the roll surface due to the contact with the hot strip and water spray cooling. The combination of thermal stress and residual stress remarkably influences the life of a work roll. In this paper, finite element method (FEM) simulation of hot rolling is performed by treating the residual stress as the initial stress. Afterwards, the effects of the initial roll temperature and cooling conditions on thermal stress considering the initial residual stress are discussed. Lastly, the thermal fatigue life of a work roll is estimated based on the strain life model. The higher initial roll temperature causes a higher temperature but a lower compressive thermal stress at the roll surface. The surface temperature and compressive stress increase significantly in the insufficient cooling conditions, as well as the center tensile stress. The calculation of the fatigue life of a work roll based on the universal slopes model according to the 10% rule and 20% rule is reasonable compared with experimental results