Optimal positron-beam excited plasma wakefields in Hollow and Ion-Wake channels

A positron-beam interacting with the plasma electrons drives radial suck-in, in contrast to an electron-beam driven blow-out in the over-dense regime, $n_b>n_0$. In a homogeneous plasma, the electrons are radially sucked-in from all the different radii. The electrons collapsing from different radii do not simultaneously compress on-axis driving weak fields. A hollow-channel allows electrons from its channel-radius to collapse simultaneously exciting coherent fields. We analyze the optimal channel radius. Additionally, the low ion density in the hollow allows a larger region with focusing phase which we show is linearly focusing. We have shown the formation of an ion-wake channel behind a blow-out electron bubble-wake. Here we explore positron acceleration in the over-dense regime comparing an optimal hollow-plasma channel to the ion-wake channel. The condition for optimal hollow-channel radius is also compared. We also address the effects of a non-ideal ion-wake channel on positron-beam excited fields.Comment: Proceedings of IPAC2015, Richmond, VA, USA 3: Alternative Particle Sources and Acceleration Techniques A22 - Plasma Wake eld Acceleration http://accelconf.web.cern.ch/AccelConf/IPAC2015/papers/wepje001.pdf, 2015 (ISBN 978-3-95450-168-7) pp 2674-267

Extreme plasmons

Nanosciences largely rely on plasmons which are quasiparticles constituted by collective oscillations of quantum electron gas composed of conduction band electrons that occupy discrete quantum states. Our work has introduced non-perturbative plasmons with oscillation amplitudes that approach the extreme limit set by breakdown in characteristic coherence. In contrast, conventional plasmons are small-amplitude oscillations. Controlled excitation of extreme plasmons modeled in our work unleashes unprecedented Petavolts per meter fields. In this work, an analytical model of this new class of plasmons is developed based on quantum kinetic framework. A controllable extreme plasmon, the surface "crunch-in" plasmon, is modeled here using a modified independent electron approximation which takes into account the quantum oscillation frequency. Key characteristics of such realizable extreme plasmons that unlock unparalleled possibilities, are obtained

Quasi-monoenergetic Laser-Plasma Positron Accelerator using Particle-Shower Plasma-Wave interactions

An all-optical centimeter-scale laser-plasma positron accelerator is modeled to produce quasi-monoenergetic beams with tunable ultra-relativistic energies. A new principle elucidated here describes the trapping of divergent positrons that are part of a laser-driven electromagnetic shower with a large energy spread and their acceleration into a quasi-monoenergetic positron beam in a laser-driven plasma wave. Proof of this principle using analysis and Particle-In-Cell simulations demonstrates that, under limits defined here, existing lasers can accelerate hundreds of MeV pC quasi-monoenergetic positron bunches. By providing an affordable alternative to kilometer-scale radio-frequency accelerators, this compact positron accelerator opens up new avenues of research.Comment: submitted to Physical Review Letters, January 201

Motion of the Plasma Critical Layer During Relativistic-electron Laser Interaction with Immobile and Comoving Ion Plasma for Ion Acceleration

We analyze the motion of the plasma critical layer by two different processes in the relativistic-electron laser-plasma interaction regime ($a_0>1$). The differences are highlighted when the critical layer ions are stationary in contrast to when they move with it. Controlling the speed of the plasma critical layer in this regime is essential for creating low-$\beta$ traveling acceleration structures of sufficient laser-excited potential for laser ion accelerators (LIA). In Relativistically Induced Transparency Acceleration (RITA) scheme the heavy plasma-ions are fixed and only trace-density light-ions are accelerated. The relativistic critical layer and the acceleration structure move longitudinally forward by laser inducing transparency through apparent relativistic increase in electron mass. In the Radiation Pressure Acceleration (RPA) scheme the whole plasma is longitudinally pushed forward under the action of the laser radiation pressure, possible only when plasma ions co-propagate with the laser front. In RPA the acceleration structure velocity critically depends upon plasma-ion mass in addition to the laser intensity and plasma density. In RITA, mass of the heavy immobile plasma-ions does not affect the speed of the critical layer. Inertia of the bared immobile ions in RITA excites the charge separation potential whereas RPA is not possible when ions are stationary.Comment: Invited paper (submitted), Division of Plasma Physics, American Physical Society, Nov 2013, Denver, C

Flow cross-overs under surface fluctuations in cylindrical nano-channel

We analyse surface-fluctuations-driven fluid flow through nano-channels to investigate the interplay between boundary layer flow structures and the bulk flow of fluid under a pressure-head. Surface fluctuations of a wide range of frequencies (up to several thousands of Hertz) in a nano-channel keep the flow in the low Reynolds number regime. Using this advantage of low Reynolds number flow, we develop a perturbation analysis of the fluid flow that clearly distinguishes the bulk flow under a pressure head around the axis of a nano-tube from its surface flow structure induced by fluctuations. In terms of particle transport under such flow conditions, there exists the opportunity to drag particles near the periphery of the nano-tube in a direction opposite to the bulk flow near the axis. This can potentially find applications in the separation, trapping, and filtration of particles under surface-driven flow through nano-tubes under widely varying conditions.Comment: 8 pages, 2 figur