Pre-Excitation Studies for Rubidium-Plasma Generation

The key element in the Proton-Driven-Plasma-Wake-Field-Accelerator (AWAKE) project is the generation of highly uniform plasma from Rubidium vapor. The standard way to achieve full ionization is to use high power laser which can assure the over-barrier-ionization (OBI) along the 10 meters long active region. The Wigner-team in Budapest is investigating an alternative way of uniform plasma generation. The proposed Resonance Enhanced Multi Photon Ionization (REMPI) scheme probably can be realized by much less laser power. In the following the resonant pre-excitations of the Rb atoms are investigated, theoretically and the status report about the preparatory work on the experiment are presented.Comment: 8 pages, 6 figures, submitted to Nucl. Inst. and Meth. in Phys. Res.

Stabilization and time resolved measurement of the frequency evolution of a modulated diode laser for chirped pulse generation

We have developed experimental methods for the generation of chirped laser pulses of controlled frequency evolution in the nanosecond pulse length range for coherent atomic interaction studies. The pulses are sliced from the radiation of a cw external cavity diode laser while its drive current, and consequently its frequency, are sinusoidally modulated. By the proper choice of the modulation parameters, as well as of the timing of pulse slicing, we can produce a wide variety of frequency sweep ranges during the pulse. In order to obtain the required frequency chirp, we need to stabilize the center frequency of the modulated laser and to measure the resulting frequency evolution with appropriate temporal resolution. These tasks have been solved by creating a beat signal with a reference laser locked to an atomic transition frequency. The beat signal is then analyzed, as well as its spectral sideband peaks are fed back to the electronics of the frequency stabilization of the modulated laser. This method is simple and it has the possibility for high speed frequency sweep with narrow bandwidth that is appropriate, for example, for selective manipulation of atomic states in a magneto-optical trap

Traitement de requêtes de provenance dans des cubes RDF sous des contraintes de mémoire

International audienceThe steadily-growing popularity of semantic data on the Web and the support for aggregation queries in SPARQL 1.1 have propelled the interest in Online Analytical Processing (OLAP) and data cubes in RDF. Query processing in such settings is challenging because SPARQL OLAP queries usually contain many triple patterns with grouping and aggregation. Moreover, one important factor of query answering on Web data is its provenance, i.e., metadata about its origin. Some applications in data analytics and access control require to augment the data with provenance metadata and run queries that impose constraints on this provenance. This task is called provenance-aware query answering. In this paper, we investigate the benefit of caching some parts of an RDF cube augmented with provenance information when answering provenance-aware SPARQL queries. We propose provenance-aware caching (PAC), a caching approach based on a provenance-aware partitioning of RDF graphs, and a benefit model for RDF cubes and SPARQL queries with aggregation. Our results on real and synthetic data show that PAC outperforms significantly the LRU strategy (least recently used) and the Jena TDB native caching in terms of hit-rate and response time.La croissante popularité des données sémantiques sur le Web et la prise en charge des requêtes d'agrégation dans SPARQL 1.1 ont suscité l'intérêt pour le traitement analytique en ligne (OLAP) et les cubes de données en RDF. Le traitement des requêtes dans de tels scenarios est difficile, car les requêtes OLAP SPARQL contiennent généralement de nombreux modèles triples avec regroupement et agrégation. De plus, un facteur important de réponse à une requête sur des données Web est sa provenance, c’est-à-dire des métadonnées sur son origine. Certaines applications d’analyse de données et de contrôle d’accès nécessitent d’augmenter les données avec des métadonnées de provenance et d’exécuter des requêtes qui imposent des contraintes à cette provenance. Cette tâche est appelée réponse à une requête sensible à la provenance. Dans cet article, nous étudions les avantages de la mise en cache de certaines parties d’un cube RDF complétées par des informations de provenance lors de la réponse à des requêtes SPARQL tenant compte de la provenance. Nous proposons une mise en cache basée sur la provenance (PAC), une approche de mise en cache basée sur un partitionnement des graphes RDF tenant compte de la provenance, ainsi qu'un modèle d'avantages pour les cubes RDF et les requêtes SPARQL avec agrégation. Nos résultats sur des données réelles et synthétiques montrent que PAC dépasse de manière significative la stratégie LRU (la moins récemment utilisée) et la mise en cache native Jena TDB en termes de taux d’accès et de temps de réponse