Establishing Applicability of SSDs to LHC Tier-2 Hardware Configuration

Solid State Disk technologies are increasingly replacing high-speed hard disks as the storage technology in high-random-I/O environments. There are several potentially I/O bound services within the typical LHC Tier-2 - in the back-end, with the trend towards many-core architectures continuing, worker nodes running many single-threaded jobs and storage nodes delivering many simultaneous files can both exhibit I/O limited efficiency. We estimate the effectiveness of affordable SSDs in the context of worker nodes, on a large Tier-2 production setup using both low level tools and real LHC I/O intensive data analysis jobs comparing and contrasting with high performance spinning disk based solutions. We consider the applicability of each solution in the context of its price/performance metrics, with an eye on the pragmatic issues facing Tier-2 provision and upgradesComment: 6 pages, 1 figure, 4 tables. Conference proceedings for CHEP201

Room temperature and cryogenic Yb:YAG thin disk laser : single crystal and ceramic

The focus of this dissertation is to design, optimize and build an efficient high power multi kilowatt thin-disk laser system. We improve the thin-disk beam quality by eliminating thermally induced lensing and disk bowing. The characteristics and performance of a ceramic and single crystal Yb:YAG thin disk (TD) lasers are analyzed both experimentally and theoretically. We perform these experiments at room and at cryogenic temperatures. Novel composite substrate materials are explored for thermal management. Thermal and stress computations are modeled in detail using the finite element analysis COMSOL software. Geometrical and physical optics models, employing ZEMAX and other numerical techniques, are used to evaluate beam quality. Theoretical modeling results are combined to further explain physical mechanisms that influence a high power output laser beam. An analytical amplified spontaneous emission (ASE) model in thin-disk laser is developed. Experimental data includes: thermal measurements of thin-disk and output couplers; small signal gain; wavefront; spectrum; lifetime and fluorescence measurements. Most importantly, for the first time, thin-disk laser performance at room and cryogenic temperatures using a novel two phase boiling cooling system is investigated. Our unique setup allows us to directly compare the same material performance at these two temperatures. Our cryogenic results show that operating the laser as a four level system could be the key in achieving very high output power with less complicated system since there is a higher cross-section, and a fewer number of pump bounces is required. Thin-disks for cryogenic operation do not have to be as thin, which also makes it easier to manufacture them. Techniques developed in these experiments are of fundamental importance in future work related to high power solid state lasers; material science, particularly ceramic lasers, and composite materials manufacturing; and cryogenic operation lasers. A thorough and detailed design of a high power thin-disk laser supported by experimental data is presented

Humidity-Induced Degradation of Lithium-Stabilized Sodium-Beta Alumina Solid Electrolytes

Sodium-beta alumina is a solid-state electrolyte with outstanding chemical, electrochemical, and mechanical properties. Sodium polyaluminate is successfully employed in established Na–S and Na–NiCl 2 cell systems. It is a promising candidate for all-solid-state sodium batteries. However, humidity affects the performance of this solid electrolyte. In this work, the effect of humidity on disk-shaped samples of Li-stabilized sodium-beta alumina stored in three different environments is quantified. We used impedance analysis and additional characterizations to investigate the consequences of the occurring degradation, namely ion exchange and subsequent buildup of surface layers. Sodium-beta alumina’s ionic conductivity gradually deteriorates up to two orders of magnitude. This is due to layers developed superficially during storage, while its fracture strength of 240 MPa remains unaffected. Changes in microstructure, composition, and cycle life of Na|BASE|Na cells highlight the importance of proper storage conditions: In just one week of improper storage, the critical current density collapsed from the maximum of 9.1 mA cm −2 , one of the highest values reported for sodium-beta alumina, to 1.7 mA cm −2 at 25 °C. The results validate former observations regarding sodium-beta alumina’s moisture sensitivity and suggest how to handle sodium-beta alumina used in electrochemical cell systems

Improving I/O performance through an in-kernel disk simulator

This paper presents two mechanisms that can significantly improve the I/O performance of both hard and solid-state drives for read operations: KDSim and REDCAP. KDSim is an in-kernel disk simulator that provides a framework for simultaneously simulating the performance obtained by different I/O system mechanisms and algorithms, and for dynamically turning them on and off, or selecting between different options or policies, to improve the overall system performance. REDCAP is a RAM-based disk cache that effectively enlarges the built-in cache present in disk drives. By using KDSim, this cache is dynamically activated/deactivated according to the throughput achieved. Results show that, by using KDSim and REDCAP together, a system can improve its I/O performance up to 88% for workloads with some spatial locality on both hard and solid-state drives, while it achieves the same performance as a ‘regular system’ for workloads with random or sequential access patterns.Peer ReviewedPostprint (author's final draft