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

Generation of ultrarelativistic monoenergetic electron bunches via a synergistic interaction of longitudinal electric and magnetic fields of a twisted laser

We use 3D simulations to demonstrate that high-quality ultrarelativistic electron bunches can be generated on reflection of a twisted laser beam off a plasma mirror. The unique topology of the beam with a twist index | l | = 1 creates an accelerating structure dominated by longitudinal laser electric and magnetic fields in the near-axis region. We show that the magnetic field is essential for creating a train of dense monoenergetic bunches. For a 6.8 PW laser, the energy reaches 1.6 GeV with a spread of 5.5%. The bunch duration is 320 as, its charge is 60 pC, and density is ∼ 10 27     m − 3 . The results are confirmed by an analytical model for the electron energy gain. These results enable development of novel laser-driven accelerators at multi-PW laser facilities

Direct Laser-Driven Electron Acceleration and Energy Gain in Helical Beams

A detailed study of direct laser-driven electron acceleration in paraxial Laguerre–Gaussian modes corresponding to helical beams LG 0 m with azimuthal modes m = 1,2,3,4,5 is presented. Due to the difference between the ponderomotive force of the fundamental Gaussian beam LG 00 and helical beams LG 0 m , we found that the optimal beam waist leading to the most energetic electrons at full width at half maximum is more than twice smaller for the latter and corresponds to a few wavelengths Δ w 0 = 6,11,19 λ 0 for laser powers of P 0 = 0.1 , 1,10  PW. We also found that, for azimuthal modes m ≥ 3 , the optimal waist should be smaller than Δ w 0 &lt; 19 λ 0 . Using these optimal values, we have observed that the average kinetic energy gain of electrons is about an order of magnitude larger in helical beams compared to the fundamental Gaussian beam. This average energy gain increases with the azimuthal index m leading to collimated electrons of a few 100 MeV energy in the direction of the laser propagation.</jats:p

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.