Abstract
Electron beam polarization in the bubble regime of the interaction between a high-intensity laser and a longitudinally pre-polarized plasma is investigated by means of the ...Thomas–Bargmann–Michel–Telegdi equation. Using a test-particle model, the dependence of the accelerated electron polarization on the bubble geometry is analysed in detail. Tracking the polarization dynamics of individual electrons reveals that although the spin direction changes during both the self-injection process and acceleration phase, the former has the biggest impact. For nearly spherical bubbles, the polarization of electron beam persists after capture and acceleration in the bubble. By contrast, for aspherical bubble shapes, the electron beam becomes rapidly depolarized, and the net polarization direction can even reverse in the case of a oblate spheroidal bubble. These findings are confirmed via particle-in-cell simulations.
Abstract
Current laser-plasma based accelerators are promising options with respect to the acceleration of spin-polarized particle beams. We give an overview over the effects relevant during the ...acceleration process and more specifically discuss the acceleration of protons via Magnetic Vortex Acceleration (MVA). With the aid of particle-in-cell simulations we show that the length of the density down-ramp at the end of the plasma target affects the final beam quality regarding its collimation. The average spin-polarization of the obtained bunch remains largely robust at about 80% and only decreases for significantly longer ramps.
Circularly polarized (CP) extreme ultraviolet- and x-ray radiation is an essential tool for analyzing the magnetic properties of materials. Elliptically polarized high harmonic generation (HHG) has ...been demonstrated by focusing bi-chromatic (800 + 400 nm wavelengths), counter-rotating CP laser pulses into gas targets (Fleischer et al 2014 Nat. Photonics 8 543). More recent theoretical studies indicate that a bi-circular laser driver can also work in both under- and overdense plasmas with analogous selection rules to those in gases: for example, every third harmonic is suppressed and adjacent harmonics have opposite helicity for counter-polarized CP ω0 and 2ω0 pumps. In this work, an analytical theory of bi-circular HHG from underdense plasmas is formulated which provides quantitative predictions of harmonic efficiency scaling, selectivity and helicity for both co- and counter-polarized drivers of arbitrary frequency ratio. This is compared to a fully non-linear, one-dimensional fluid model and particle-in-cell simulations, showing good agreement with both.
A number of laser facilities coming online all over the world promise the capability of high-power laser experiments with shot repetition rates between 1 and 10 Hz. Target availability and technical ...issues related to the interaction environment could become a bottleneck for the exploitation of such facilities. In this paper, we report on target needs for three different classes of experiments: dynamic compression physics, electron transport and isochoric heating, and laser-driven particle and radiation sources. We also review some of the most challenging issues in target fabrication and high repetition rate operation. Finally, we discuss current target supply strategies and future perspectives to establish a sustainable target provision infrastructure for advanced laser facilities.
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With the construction of the European Spallation Source ESS, the European neutron user community is looking forward to the brightest source worldwide. At the same time there is an ongoing ...concentration of research with neutrons to only a few but very powerful neutron facilities. Responding to this situation the Jülich Centre for Neutron Science has initiated a project for a compact accelerator driven high-brilliance neutron source, optimized for neutron scattering on small samples and to be realized at reasonable costs. The project deals with the optimization of potential projectiles, target and moderator concepts, versatile accelerator systems, cold sources, beam extraction systems and optimized instrumentation. A brief outline of the project, the achievements already reached, will be presented, as well as a vision for the future neutron landscape in Europe.
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