A Compact Source of Positron Beams with Small Thermal Emittance

We investigate electrostatic traps as a novel source of positron beams for accelerator physics applications. Penning-Malmberg (PM) traps are commonly employed in low-energy antimatter experiments. Positrons contained in the trap are cooled to room temperature or below. We calculate the thermal emittance of the positrons in the trap and show that it is comparable to or better than the performance of state-of-the-art photocathode guns. We propose a compact positron source comprised of a PM trap, electrostatic compressor, and rf accelerator that can be built and operated at a fraction of the cost and size of traditional target-based positron sources, albeit at a reduced repetition rate. We model the acceleration of a positron bunch up to an energy of 17.6 MeV with a final thermal emittance of 0.60 $\mu$m-rad and bunch length of 190 $\mu$m. This system may be useful for acceleration physics studies, such as investigations of flat-beam sources for linear colliders and positron plasma wakefield acceleration

External Electron Injection for the AWAKE Experiment

We summarize and explain the realization of witness particle injection into wakefields for the AWAKE experiment. In AWAKE, the plasma wakefields are driven by a self-modulating relativistic proton bunch. To demonstrate that these wakefields can accelerate charged particles, we inject a \unit[10-20]{MeV} electron bunch produced by a photo-injector. We summarize the experimental challenges of this injection process and present our plans for the near future.Comment: 4 pages, 3 figure

Energy recovery in filament-regime plasma wakefield acceleration of positron beams

Plasma wakefield acceleration using an electron filament offers stable, high-gradient, high-quality acceleration of positron beams analogous to the acceleration of electrons in the blowout regime. However, low energy-transfer efficiency is currently a limiting factor for future collider applications. We explore the addition of a secondary electron bunch in the electron filament plasma wakefield acceleration scheme to recover additional energy from the wake. Particle-in-cell simulations using HiPACE++ are used to demonstrate various energy recovery schemes. In addition to confirming the energy efficiency gains with a recovery electron beam, we also develop energy recovery schemes in the context of future plasma colliders

Yeast and macroinvertebrate communities associated with leaf litter decomposition in a second order stream

The composition of yeast and macroinvertebrate communities was studied on black alder, blue gum eucalyptus and English oak leaves decaying in a stream during a six‐month period. ANOVA analysis showed significantly different values (p < 0.0001) of yeast and macroinvertebrate densities among the three leaf litters. Some yeast species such as Cryptococcus albidus (Saito), C. laurentii (Kufferath), Rhodothorula glutinis (Fresenius), R. colostri (Castelli), and Debaryomyces hansenii (Lodder and Kreger‐van Rij) were present in all litter types. Other yeasts were restricted to a specific type of litter. Macroinvertebrates were dominated by collectors‐gatherers on oak and eucalyptus leaves. Shredders reached highest densities in alder leaves

Predicting the Trajectory of a Relativistic Electron Beam for External Injection in Plasma Wakefields

We use beam position measurements over the first part of the AWAKE electron beamline, together with beamline modeling, to deduce the beam average momentum and to predict the beam position in the second part of the beamline. Results show that using only the first five beam position monitors leads to much larger differences between predicted and measured positions at the last two monitors than when using the first eight beam position monitors. These last two positions can in principle be used with ballistic calculations to predict the parameters of closest approach of the electron bunch with the proton beam. In external injection experiments of the electron bunch into plasma wakefields driven by the proton bunch, only the first five beam position monitors measurements remain un-affected by the presence of the much higher charge proton bunch. Results with eight beam position monitors show the prediction method works in principle to determine electron and proton beams closest approach within the wakefields width ($<$1\,mm), corresponding to injection of electrons into the wakefields. Using five beam position monitors is not sufficient.Comment: seven pages, five figures, submitted for EAAC 2019 Proceeding

Temporal Evolution of the Light Emitted by a Thin, Laser-ionized Plasma Source

We present an experimental and simulation-based investigation of the temporal evolution of light emission from a thin, laser-ionized Helium plasma source. We demonstrate an analytic model to calculate the approximate scaling of the time-integrated, on-axis light emission with the initial plasma density and temperature, supported by the experiment, which enhances the understanding of plasma light measurement for plasma wakefield accelerator (PWFA) plasma sources. Our model simulates the plasma density and temperature using a split-step Fourier code and a particle-in-cell (PIC) code. A fluid simulation is then used to model the plasma and neutral density, and the electron temperature as a function of time and position. We then show the numerical results of the space-and-time-resolved light emission and that collisional excitation is the dominant source of light emission. We validate our model by measuring the light emitted by a laser-ionized plasma using a novel statistical method capable of resolving the nanosecond-scale temporal dynamics of the plasma light using a cost-effective camera with microsecond-scale timing jitter. This method is ideal for deployment in the high radiation environment of a particle accelerator that precludes the use of expensive nanosecond-gated cameras. Our results show that our models can effectively simulate the dynamics of a thin, laser-ionized plasma source and this work is useful to understand the plasma light measurement, which plays an important role in the PWFA.Comment: 12 pages, 11 figure

Synthesis, characterization, and reactivity of a uranium(VI) carbene imido oxo complex

We report the uranium(VI) carbene imido oxo complex [U(BIPMTMS)(NMes)(O)(DMAP)2] (5, BIPMTMS=C(PPh2NSiMe3)2; Mes=2,4,6-Me3C6H2; DMAP=4-(dimethylamino)pyridine) which exhibits the unprecedented arrangement of three formal multiply bonded ligands to one metal center where the coordinated heteroatoms derive from different element groups. This complex was prepared by incorporation of carbene, imido, and then oxo groups at the uranium center by salt elimination, protonolysis, and two-electron oxidation, respectively. The oxo and imido groups adopt axial positions in a T-shaped motif with respect to the carbene, which is consistent with an inverse trans-influence. Complex 5 reacts with tert-butylisocyanate at the imido rather than carbene group to afford the uranyl(VI) carbene complex [U(BIPMTMS)(O)2(DMAP)2] (6)

Demonstration of a positron beam-driven hollow channel plasma wakefield accelerator

International audiencePlasma wakefield accelerators have been used to accelerate electron and positron particle beams with gradients that are orders of magnitude larger than those achieved in conventional accelerators. In addition to being accelerated by the plasma wakefield, the beam particles also experience strong transverse forces that may disrupt the beam quality. Hollow plasma channels have been proposed as a technique for generating accelerating fields without transverse forces. Here we demonstrate a method for creating an extended hollow plasma channel and measure the wakefields created by an ultrarelativistic positron beam as it propagates through the channel. The plasma channel is created by directing a high-intensity laser pulse with a spatially modulated profile into lithium vapour, which results in an annular region of ionization. A peak decelerating field of 230 MeV/m is inferred from changes in the beam energy spectrum, in good agreement with theory and particle-in-cell simulations