Optimizing direct laser-driven electron acceleration and energy gain at ELI-NP

We study and discuss electron acceleration in vacuum interacting with fundamental Gaussian pulses using specific parameters relevant for the multi-PW femtosecond lasers at ELI-NP. Taking into account the characteristic properties of both linearly and circularly polarized Gaussian beams near focus we have calculated the optimal values of beam waist leading to the most energetic electrons for given laser power. The optimal beam waist at full width at half maximum correspond to few tens of wavelengths, $\Delta w_0=\left\{13,23,41\right\}\lambda_0$, for increasing laser power $P_0 = \left\{0.1,1,10\right\}$ PW. Using these optimal values we found an average energy gain of a few MeV and highest-energy electrons of about $160$ MeV in full-pulse interactions and in the GeV range in case of half-pulse interaction.Comment: 12 pages, 10 figure

Multi-functional Diagnostic Method with Tracer-encapsulated Pellet Injection

In order to obtain a better understanding of impurity transport in magnetically confined plasmas, a Tracer-Encapsulated Soild PELlet (TESPEL) has been developed. The essential points of the TESPEL are as follows: the TESPEL has a double-layered structure, and a tracer impurity, the amount of which can be known precisely, is embedded as an inner core. This structure enables us to deposit the tracer impurity locally inside the plasma. From experiences of developing the TESPEL production technique and its injection experiments, it became clear that various plasma properties can be studied by the TESPEL injection. There are not only impurity transport in the plasma but also transport both outside and inside of the magnetic island O-point, heat transport and high-energy neutral particle flux. Therefore, the TESPEL injection has a favorable multi-functional diagnostic capability. Furthermore a Tracer-Encapsulated Cryogenic PELlet (TECPEL) has been also developed. The TECPEL has an advantage over the TESPEL in terms of no existence of carbons in the outer layer. The TECPEL injector was installed at LHD in December 2005, and the preliminary injection experiments have been carried out

Talbot phase-contrast x-ray imaging for the small joints of the hand

Efficiency as a   part of usability is a much researched topic. How we design user interfaces   though, is often a matter of convention rather than scientifically validated   patterns. There is however a reason for this; research has shown that users   form clear mental models, or expectations of how an interface should look and   work. Designing with these models in mind should therefore yield efficient   results according to some researchers. This study aimed to test the extent to   which these models affect efficiency through a quantitative quasi-experiment. The experiment   was designed to measure click cost while designing for, or contrary to, the   mental models. This was achieved by adding or subtracting the variables:   placement conventions, saliency, clutter, appearance conventions and help   text to an experimental group and a control group respectively. To ascertain   the impact of these independent variables the click cost in milliseconds has   been recorded in a web questionnaire environment, aggregated and   comparatively analyzed between the groups. The result is a clearer picture of   each variables independent effect on click costs and efficiency. The main   result show a tendency towards higher click costs for badly handled placement   conventions, saliency and appearance conventions, however the differences are   small. In the case of clutter no increase in click cost could be recoded. The   single largest increase in click cost is incurred when help texts are   omitted.Effektivitet,som en del av användbarhet, är ett väl undersökt område. Hur gränssnittutformas grundar sig oftast i allmänt accepterade normer snarare än påvetenskapliga validerade mönster. Det finns dock en anledning till detta:forskningEffektivitet,som en del av användbarhet, är ett väl undersökt område. Hur gränssnittutformas grundar sig oftast i allmänt accepterade normer snarare än påvetenskapliga validerade mönster. Det finns dock en anledning till detta:forskning visar att användare skapar mentala modeller eller förväntningar på hur ett gränssnitt bör se ut och fungera vid interaktion. Att utforma gränssnitt med dessa modeller i åtanke bör därför, enligt vissa forskare, ge effektiva resultat. Syftet med denna studie var att testa i vilken utsträckning dessa mentala modeller har en inverkan på effektiviteten i gränssnitt genom ett kvantitativt kvasiexperiment. Experimentet utformades för att mäta klickkostnaden i gränssnitt som överensstämmer med, eller strider mot, de mentala modellerna. Detta uppnåddes genom att tillföra eller ta bort variablerna: placeringspraxis, visuellt framträdande, brus, utseendepraxis och hjälptext till en testgrupp och en kontrollgrupp. För att fastställa till vilken grad dessa oberoende variabler påverkar har klickkostnaden i millisekunder uppmätts i ett webenkätsgränssnitt, aggregerats och jämförts mellan grupperna. Resultatet är en tydligare bild av varje variabels grad av påverkan på klickkostnad och effektivitet. Det huvudsakliga resultatet visar på en tendens till högre klickkostnad när placeringspraxis, visuellt framträdande och utseendepraxis frångår normerna. Differenserna är dock små. Vad gäller brus har ingen ökning i klickkostnad kunnat uppmätas. Den enskilt största ökningen i klickkostand sker när hjälptext utelämnas.

Laser driven nuclear physics at ELI–NP

Summarization: High power lasers have proven being capable to produce high energy γ-rays, charged particles and neutrons, and to induce all kinds of nuclear reactions. At ELI, the studies with high power lasers will enter for the first time into new domains of power and intensities: 10 PW and 1023 W/cm2. While the development of laser based radiation sources is the main focus at the ELI-Beamlines pillar of ELI, at ELI-NP the studies that will benefit from High Power Laser System pulses will focus on Laser Driven Nuclear Physics (this TDR, acronym LDNP, associated to the E1 experimental area), High Field Physics and QED (associated to the E6 area) and fundamental research opened by the unique combination of the two 10 PW laser pulses with a gamma beam provided by the Gamma Beam System (associated to E7 area). The scientific case of the LDNP TDR encompasses studies of laser induced nuclear reactions, aiming for a better understanding of nuclear properties, of nuclear reaction rates in laser-plasmas, as well as on the development of radiation source characterization methods based on nuclear techniques. As an example of proposed studies: the promise of achieving solid-state density bunches of (very) heavy ions accelerated to about 10 MeV/nucleon through the RPA mechanism will be exploited to produce highly astrophysical relevant neutron rich nuclei around the N~126 waiting point, using the sequential fission-fusion scheme, complementary to any other existing or planned method of producing radioactive nuclei. The studies will be implemented predominantly in the E1 area of ELI-NP. However, many of them can be, in a first stage, performed in the E5 and/or E4 areas, where higher repetition laser pulses are available, while the harsh X-ray and electromagnetic pulse (EMP) environments are less damaging compared to E1. A number of options are discussed through the document, having an important impact on the budget and needed resources. Depending on the TDR review and subsequent project decisions, they may be taken into account for space reservation, while their detailed design and implementation will be postponed. The present TDR is the result of contributions from several institutions engaged in nuclear physics and high power laser research. A significant part of the proposed equipment can be designed, and afterwards can be built, only in close collaboration with (or subcontracting to) some of these institutions. A Memorandum of Understanding (MOU) is currently under preparation with each of these key partners as well as with others that are interested to participate in the design or in the future experimental program.Παρουσιάστηκε στο: Romanian Reports in Physic