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Scientific Report 2007-2009 Laboratories and Facilities of the Department of Physics F3. The Tier–2 Computing Centre for LHC The Tier–2 Computing Centre for LHC is a joint INFN–University effort, as most of the research activities in high energy physics in Italy. As a result most of the resources come from INFN–Sez. di Roma, while manpower is both from INFN and from University. LHC experiments at CERN need large computing resources as well huge storage. In fact, each general purpose LHC experiment, such as ATLAS and CMS, is going to collect as much as 2–4 billions of events per year. Event size is of the order of 1 MB, resulting in a total of 2–4 PB of data to be stored. Data processing, moreover, is a CPU time–consuming activity for which the only solution is to parallelize jobs on many CPU cores. Taking into account that data analysis requires the comparison with simulated Monte Carlo events, and that the number of these events must be of the same order of magnitude of real data and is extremely costly in terms of CPU time, the figures given above almost double. Another factor 2–4 is required in order to guarantee some redundancy. Moreover, the experiments are expected to run for 10–15 years and data must be available for analysis for at least 20 years. No single laboratory is able to concentrate enough computing power and enough storage in a single place, so that computing for LHC experiments is a distributed activity. We benefit from the existing GRID services, partly developed in Italy, to distribute both data and CPU load over several centres around the world, in a transparent way for the users. Resources are arranged hierarchically to make the system scalable. Data collected close to experiments are stored in the so–called Tier–0 at CERN, where they are initially processed as fast as possible. Once physics data have been reconstructed, events are distributed to few Tier–1 centres around the world, one of which is located in Bologna. Tier–1 centres have custodial responsibility of data and are in charge for data reprocessing, when needed. From Tier–1’s, data are distributed to Tier–2’s that usually host a fraction of 20 % of data collected in a Tier–1. Tier–2’s also provide computing power both for physicists’ data analysis and for Monte Carlo production teams. Users submit their jobs to a Resource Broker on the GRID which knows the location of data as well as the availability of computing power in each centre. It then distributes the jobs to many Tier–2’s, close to target data, collects and merge all the results and returns them back to the user. Users, then, do not need to know about the exact location of data, nor those of computer centre. They do not need to know specific data file names, either. They just provide the dataset name, i.e. a conventional, human readable identifier of a large data sample: the system associates it to a set of files that can be distributed and/or replicated to few centres. Databases are used to keep track of data and their location. One of the LHC Tier–2’s is located in Roma, in the basement of the Department of Physics, serving both the ATLAS and CMS experiments. It hosts, in a dedicated room, seven innovative water cooled racks, each 42U high. All the racks are currently almost filled with rack CPU servers and storage units. The centre has been designed to host up to 14 racks. Three tons of water are kept in a reservoir at 12 ◦ C by a redundant system of two chillers. A set of three computer controlled pumps makes the water flushing into a large pipe to which racks are attached in parallel. The racks, closed on all sides, contain a heat exchanger and three fans that produce a depression such that cool air from the bottom goes to the top of the rack creating a cool layer in front of the rack. Fresh air passes then through CPU’s thanks to the fans contained in each server and goes to the back of the rack, where it is pushed to the bottom to be cooled down again. The usage of water instead of air to keep the units at the right temperature has many advantages: it consistently reduces power consumption, it makes the temperature much more stable (the temperature is stable around (18 ± 0.1) ◦ C), it keeps the temperature of the environment comfortable and allows for some inertia in case of damages (the water stored in the reservoir is enough to keep the whole centre at a reasonable temperature for about 20 minutes, allowing for interventions). All the racks are connected to a UPS protected power line up to 120 kVA that is able to maintain the system running for about 30 minutes in case of troubles on the electrical line. Moreover the centre is provided with sensors for floods and smoke detectors, as well as with an automatic fire extinguishing system, connected to sound and visual alarms. Servers are internally connected by a 1 Gb LAN (to be upgraded to 10 Gb). The connection with the WAN is assured by two redundant connections to two different Garr POP’s, via as many 10 Gb fibers. A lot of effort has been spent to have the centre under full control. In particular we developed many monitoring tools that measure several quantities and report any anomaly to a centralized system from which we can check the current status and the history up to one year before of any monitored quantity. Every information is accessible via web even remotely and some intelligent agent has been deployed to automatically recover known problems. Moreover, the centre is equipped with a GSM interface that can be used either to send alarms to cell phones via SMS, or to receive commands from them in the form of an SMS. With this system we can remotely interrogate the databases as well as change some predefined configuration, even in the absence of any Internet access. The centre runs almost smoothly since two years 7/24. Related research activities: P1, P2, P3, P4, P5, P6. Sapienza Università di Roma 199 Dipartimento di Fisica
Scientific Report 2007-2009 Laboratories and Facilities of the Department of Physics F4. The Electronics Lab LABE The LABE Laboratory is operated by the INFN unit in our Department. In the recent years it has been mainly engaged in building big electronics components for the LHC. In particular in the last decade was committed to design and assemble the Level 1 ATLAS muon trigger and to design and build the control Electronics of the LHCb experiment Muon Chambers. Moreover different experiments and projects like KLOE, Cuore, Opera and the student’s laboratory received a useful support from LABE laboratory. The Structure of LABE is mainly divided in three environments: the conceptual design of the architecture of the systems, the design and the project of sub-systems, the construction of electronic modules, and the test and debugs features of single modules. The Laboratory is equipped with the state of the art of Electronic Design Automation (EDA) tools, a category of software tools dedicated to the design of electronic systems, such as printed circuit boards and integrated circuits. Using this facility we build inside the LABE different electronics modules with VLSI circuits: custom designed FPGA (Field Programmable Gate Array) and ASIC (Application specific Integrated Circuit) have been designed inside LABE. During the LHC design period we acquired competences to design Electronics for radiation environments, like space and high luminosity accelerators, an investigation that involves specific and different design techniques and technologies, like antifuse and Flash based FPGA. We also acquire abilities to test and to certificate electronics components Figure 1: Reworking system for High densiy electronics packages. using high intensity radiation sources and accelerator beams. In the context of the Cuore experiment, we have acquired competence in the modern battery powered detectors, based on Zigbee IEEE 802.15.4 wireless personal area networks, designing and realizing a network wireless pressure detectors. Moreover the laboratory mantains some equipment for small productions of electronics prototype and for repairing, debugging and reworking modern electronics. A microscope,a Ball Grid Array reworking machine and two Surface Mounting reworking station are used to manage the modern electronics technology with High density pin out and a Printed Circuit Board (PCB) prototyping machine for fast prototyping of simple PCB. LABE is equipped with a small Mechanics workshop with a milling machine, drill press and a bending machine to provide the simple mechanics to support electronics. The LABE electronics instrumentations is equipped with the most advanced digital scopes, function generators, computers with VME, CANbus, I2c, SPI, and GPIB interfaces. An open space inside the LABE is provided to test instrumentation, measure and debug electronics. This space is now equipped with the system test for the LHCb muon chamber electronics, the system test for the Atlas Level 1 Muon electronics and test-bench for the SuperB Electromagnetic Calorimeter front-end Electronics. Figure 2: BGA(Ball Grid Array) packaging is commonly used to realize the huge number of connections between VLSI and multilayer PCB http://maclabe.roma1.infn.it/ Related research activities: P3,P19,P20,P21,P25,P26. Sapienza Università di Roma 200 Dipartimento di Fisica
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