114 research outputs found
Power Load Characterization for Type-I ELMy H-Modes in JET
No full textELM-resolved divertor target power load studies were conducted for a wide range of discharge conditions in the JET tokamak. The magnetic configuration of these discharges was optimized for the fast divertor IR camera observing the outboard target. It is found that the ELM size estimated from the diamagnetic energy is not uniquely determining the ELM energy load at the divertor target. ELM mid-plane integral deposited power widths between 7 and 18 mm are observed, the inter-ELM widths lie in the range 2.5–6 mm. This ELM broadening is found to widen with ELM size. The temporal evolution of the ELM shape was characterized by rise and decay times. The ELM rise times are found to be in the range expected for ITER (250 µs), but the ELM decay is usually larger than assumed for the ITER design.</jats:p
Improved radiation measurements on JET - first results from an upgraded bolometer system
No full textTo improve the quality of radiation measurements, two new bolometric cameras with horizontal and vertical views of the plasma cross-section have been installed on JET. These cameras provide measurements with significantly improved spatial resolution, allowing the divertor and main chamber radiation fractions to be clearly resolved. Analysis of radiation profiles under attached and detached divertor conditions as well during the formation of an X-point MARFE (XPM) close to an ohmic density limit are presented. The radiation power fraction gamma = P-rad/P-heat increases from 0.5 to 0.8 just before XPM onset. A large fraction of this radiation is located in the divertor (p(rad)(div)/p(rad)(tot)= 0.56 at low density and about 0.67 at XPM onset). In addition, spatial distributions of radiation in recent ITER-like configuration discharges are presented. (c) 2007 Elsevier B.V. All rights reserved
Tritium retention in next step devices and the requirements for mitigation and removal techniques
No full textMechanisms underlying the retention of fuel species in tokamaks with carbon plasma-facing components are presented, together with estimates for the corresponding retention of tritium in ITER. The consequential requirement for new and improved schemes to reduce the tritium inventory is highlighted and the results of ongoing studies into a range of techniques are presented, together with estimates of the tritium removal rate in ITER in each case. Finally, an approach involving the integration of many tritium removal techniques into the ITER operational schedule is proposed as a means to extend the period of operations before major intervention is required
Massive gas injection experiments at JET - performance and characterization of the disruption mitigation valve (DMV)
No full text
Integration of a Radiative Divertor for Heat Load Control into JET Operational Scenarios
No full textConTrib: Universal and Decentralized Accounting in Shared-Resource Systems
No full textPreventing the abuse of resources is a crucial requirement in shared-resource systems. This concern can be addressed through a centralized gatekeeper, yet it enables manipulation by the gatekeeper itself. We present ConTrib, a decentralized mechanism for tracking resource usage across different shared-resource systems. In ConTrib, participants maintain a personal ledger with tamper-proof records. A record describes a resource consumption or contribution and links to other records. Fraud, maintaining multiple copies of a personal ledger, is detected by users themselves through the continuous exchange of records and by validating their consistency against known ones. We implement ConTrib and run experiments. Our evaluation with up to 1'000 instances reveals that fraud can be detected within 22 seconds and with moderate bandwidth usage. To demonstrate the applicability of our work, we deploy ConTrib in a Tor-like overlay and show how resource abuse by free-riders is effectively deterred. This longitudinal, large-scale trial has resulted in over 137 million records, created by more than 86'000 volunteers.Virtual/online event due to COVID-19Data-Intensive System
ConTrib: Maintaining fairness in decentralized big tech alternatives by accounting work
No full text“Big Tech” companies provide digital services used by billions of people. Recent developments, however, have shown that these companies often abuse their unprecedented market dominance for selfish interests. Meanwhile, decentralized applications without central authority are gaining traction. Decentralized applications critically depend on its users working together. Ensuring that users do not consume too many resources without reciprocating is a crucial requirement for the sustainability of such applications. We present ConTrib, a universal mechanism to maintain fairness in decentralized applications by accounting the work performed by peers. In ConTrib, participants maintain a personal ledger with tamper-evident records. A record describes some work performed by a peer and links to other records. Fraud in ConTrib occurs when a peer illegitimately modifies one of the records in its personal ledger. This is detected through the continuous exchange of random records between peers and by verifying the consistency of incoming records against known ones. Our simple fraud detection algorithm is highly scalable, tolerates significant packet loss, and exhibits relatively low fraud detection times. We experimentally show that fraud is detected within seconds and with low bandwidth requirements. To demonstrate the applicability of our work, we deploy ConTrib in the Tribler file-sharing application and successfully address free-riding behaviour. This two-year trial has resulted in over 160 million records, created by more than 94’000 users.Data-Intensive System
Deep Review contributions by author over time.
No full textThe total words added to the Deep Review by each author is plotted over time (final values in parentheses). These statistics were extracted from Git commit diffs of the manuscript’s Markdown source. This figure reveals the composition of written contributions to the manuscript at every point in its history. The Deep Review was initiated in August 2016, and the first complete manuscript was released as a preprint [10] in May 2017. While the article was under review, we continued to maintain the project and accepted new contributions. The preprint was updated in January 2018, and the article was accepted by the journal in March 2018 [5]. As of March 06, 2019, the Deep Review repository accumulated 755 Git commits, 317 merged pull requests, 609 issues, and 819 GitHub stars. The notebook to generate this figure can be interactively launched (https://mybinder.org/v2/gh/greenelab/meta-review/binder?filepath=analyses/deep-review-contrib/02.contrib-viz.ipynb) using Binder [11], enabling users to explore alternative visualizations or analyses of the source data.</p
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