New results on ATLAS RPC's aging at CERN's GIF

In order to ensure that the resistive plate chambers used in the ATLAS experiment will not show, during their operation, any abnormal aging effect which could degrade their performances, an aging test is being performed at X5-GIF, CERN's gamma irradiation facility. In this paper, the latest results are presented, together with an example of successful damage recovery technique.     

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.     

在加速器质谱仪上测量 14C的虚拟双参数多道分析器系统设计

介绍了基于LabVIEW平台与多功能数据采集卡设计的虚拟双参数多道分析器系统 ,及其在加速器质谱仪上测量14 C双参数谱的应用     

Development of Conventional Quadrupole Mass Analyzer for RI Target Analysis and Its Performance

A Knudsen-cell-based quadrupole mass analyzer has been developed for the analysis of a small amount of RI sample. To achieve a high signal/noise ratio, a continuous dynode electron multiplier was installed at the end of the mass filter and was operated in a pulse counting mode. Furthermore, the cylindrical shape molecular trap was set around the mass analyzer to reach high degree of vacuum and to reduce the RI contamination area in the apparatus.

The isotope ratio of ¹³⁵Cs/¹³⁷Cs samples has been measured to demonstrate the performance of the mass analyzer. Taking the advantage of the Knudsen-cell's precise controllability over temperature, the contribution of the isobar ¹³⁷Ba was successfully removed in the mass spectrum of cesium. With samples containing about 0.3μg ¹³⁷Cs and almost the same amount of ¹³⁵Cs, the isotope ratio measurement with the total error of 3% has been achieved. The molecular trap was also shown to be effective to reduce the contamination area in the apparatus.     

Operation of the ATLAS muon drift-tube chambers at high background rates and in magnetic fields

In the ATLAS muon spectrometer, large drift-tube chambers are used for precision tracking. The chambers will be operated at a high neutron and /spl gamma/ background resulting in count rates of up to 500 Hz cm/sup -2/ corresponding to 300 kHz per tube. The spatial resolution of the drift tubes is degraded from 82 /spl mu/m without background to 108 /spl mu/m at 500 Hz cm/sup -2/ background count rate. Due to afterpulsing in the Ar/CO/sub 2/ gas mixture used in the drift tubes, ionizing radiation causes more than one hit in a tube within the maximum drift time of about 800 ns which is expected for magnetic field strengths around 1.2 T. In order to limit the count rate, the drift tubes are read out with an artificial dead time of 790 ns which causes an efficiency loss of 23% at a rate of 300 kHz per tube. The space-to-drift-time relationship of the tubes varies with background rate, temperature, and magnetic field strength. The mean magnetic field strength in a muon chamber is 0.4 T on the average, but may vary by up to 0.4 T within a chamber. The space-to-drift-time relationship must therefore be determined in short time intervals with an accuracy better than 20 /spl mu/m using muon tracks and applying corrections for measured magnetic field variations.     

Operational Model of the ATLAS TDAQ Network

The ATLAS TDAQ network consists of four separate Ethernet based networks which together total over 4000 ports with 200 edge switches and 6 multi-blade chassis switches at the core. System checks are invoked at every level of the installation. The full installation is described in different static databases. Tools are provided to automatically cross-check these for consistency. The configuration management is centralized: configuration files stored in a database are distributed to all devices and the actual settings are periodically verified. Monitoring systems are deployed to validate the connectivity, identify malfunctions and confirm the resources availability upon request from TDAQ control. Relevant operational statistics (e.g., port status and throughput) are continuously logged and made available to TDAQ control. Watches and alarms are set for dynamic threshold violations and the complete instantaneous status can be viewed at different levels of abstraction in a 3D fly-through. A tool-set has been developed to demonstrate aggregate achievable cross-sectional bandwidth for TDAQ-specific traffic profiles, as well as to analyze traffic flows and hot spot behaviour.     

Physical Startup of the LEPTA Accumulator

The LEPTA setup (Low Energy Particle Torroidal Accumulator) is being constructed at the Joint Institute of Nuclear Research. The main purpose of this setup is to generate intense fluxes of positronium ions and perform experiments in positronium physics. The main component of the setup is the low-energy positron accumulator with a electronic cooling system. A special feature of the accumulator is that it uses a longitudinal magnetic field to focus a circulating beam. The physical startup of the accumulator was performed in September 2004. The results of the adjustment of the main components of the accumulator, the method for obtaining a circulating beam, and the first results of measurements of its parameters are presented.__________Translated from Atomnaya Energiya, Vol. 98, No. 3, pp. 225–233, March, 2005.     

Study of Fission Fragment Mass Distribution in ~(28)Si+~(174)Yb at Energy near Coulomb Barrier

正The study of heavy-ion fusion-fission reaction at near-barrier energy region is critical for us to understand the evolution process of the heavyion nuclear reaction and also provides a vital theoretical support for the synthesis of super-heavy nuclei.For the reaction systems with more quasifission,the width of the fission fragment mass     

数字化物理启动系统在HTR-10物理启动试验中的应用

10MW高温气冷堆在国内首次应用数字化物理启动系统实现了临界。本文着重介绍了数字化物理启动系统的硬件组成和人机操作界面功能,并结合10MW高温堆介绍了系统的应用特点,以及利用本系统完成的各项试验。     

Mass measurements of exotic nuclei at the ESR

We plan to measure masses of exotic nuclei far from the valley of β-stability using the Experimental Storage Ring (ESR) at GSI, Darmstadt, as a time-of-flight (TOF), multi-turn mass spectrometer. For this purpose the ring must be tuned to an isochronous mode, so that the flight time per turn of an ion depends only on its mass-to-charge ratio and not on its velocity spread. For these measurements the timing detector is planned to be placed directly in the ESR to record each circulating ion.     

Physical Startup of the TWAC Storage Ring

C⁶⁺ ions with energy 200 MeV/nucleon have been accumulated in the chamber of the ring magnet of the U-10 proton synchrotron used as a storage ring in the TWAC setup. A C⁴⁺ ion beam from the laser source was first accelerated in the I-3 injector up to 1.3 MeV/nucleon and in the UK booster synchrotron up to final energy with periodicity 3.5 sec. Ions have been accumulated in U-10 using the multiple charge-exchange injection scheme C⁴⁺ C⁶⁺. An increase in the ion intensity in the accumulator has been observed during several injection cycles. Experimental data on the attained parameters of the accumulated beam are presented, and the status of the optimization of the accumulation regime is discussed.     

Commissioning of the ATLAS thermal-hydraulic integral test facility

KAERI recently constructed a new thermal-hydraulic integral test facility for advanced pressurized water reactors (PWRs) – ATLAS. The ATLAS facility has the following characteristics: (a) 1/2-height&length, 1/288-volume, and full pressure simulation of APR1400, (b) maintaining a geometrical similarity with APR1400 including 2(hot legs) × 4(cold legs) reactor coolant loops, direct vessel injection (DVI) of emergency core cooling water, integrated annular downcomer, etc., (c) incorporation of specific design characteristics of OPR1000 such as cold leg injection and low-pressure safety injection pumps, (d) maximum 10% of the scaled nominal core power. The ATLAS will mainly be used to simulate various accident and transient scenarios for evolutionary PWRs, OPR1000 and APR1400: the simulation capability of broad scenarios including the reflood phase of a large-break loss-of-coolant accident (LOCA), small-break LOCA scenarios including DVI line breaks, a steam generator tube rupture, a main steam line break, a feed line break, a mid-loop operation, etc. The ATLAS is now in operation after an extensive series of commissioning tests in 2006.     

Sub Farm Interface of the ATLAS Dataflow System

Sub Farm Interface is the event builder of the ATLAS（A Toroidal LHC ApparatuS） Dataflow System. It receives event fragments from the Read Out System, builds full events and sends complete events to the Event Filter for high level event selection. This paper describes the implementation of the Sub Farm Interface. Furthermore, this paper introduces some issues on SFI（Sub Farm Interface） optimization and the monitoring service inside SFI.     

基于傅里叶级数展开的裂变位能曲面与碎片质量分布计算

裂变位能曲面是裂变核结构性质和裂变动力学研究的基础。本文使用傅里叶级数展开方法描述裂变过程中原子核的形状,采用基于Lublin Strasbourg Drop(LSD)宏观模型和Yukawa Folded微观模型计算了236U多维裂变位能曲面,研究了位能曲面随不同集体自由度(原子核拉长形变、左右碎片质量不对称度以及颈部宽度)的变化情况以及温度对位能曲面的影响。在位能曲面基础上采用基于Born Oppenheimer近似的三维集体模型描述原子核裂变过程,计算了236U裂变碎片质量分布,计算结果与实验数据符合较好,特别是质量分布的峰位,同时分析了核温度、零点能和颈部断裂概率半宽度对裂变碎片质量分布计算结果的影响。     

A MCM-D-type module for the ATLAS pixel detector

For the ATLAS experiment at the planned Large Hadron Collider (LHC) at CERN hybrid pixel detectors are being built as innermost layers of the inner tracking detector system. Modules are the basic building blocks of the ATLAS pixel detector. A module consists of a sensor tile with an active area of 16.4 mm×60.4 mm, 16 read out ICs, each serving 24×160 pixel unit cells, a module controller chip, an optical transceiver and the local signal interconnection and power distribution busses. The dies are attached by flip-chip assembly to the sensor diodes and the local busses. In the following a module based on MCM-D technology will be discussed and prototype results will be presented     

多道分析器数据的远程实时压缩传送

对多道数据的特性和压缩传送问题进行了详细研究,提出了用动态比压缩方法和等计数压缩方法完成多道数据的远程实时无损压缩传送,给出了方法原理和实验结果。     

医院中子照射器物理启动

医院中子照射器是专门用于硼中子俘获治疗的核装置。在堆芯相对两侧,设有热中子束流和超热中子束流用于治疗,另外,在热中子束流内引出1条热中子束流用于病人血硼浓度测量。本文介绍其物理启动的6个实验,实验结果表明：满功率最大运行时间为12 h,最终后备反应性为4.2 mk,满功率运行时各工艺房间辐射水平满足设计辐射分区要求,4.2 mk反应性释放实验证明医院中子照射器具有固有安全特性。