2,739 research outputs found
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,
. 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
Heterojunction solar cell calculations
Solar cell efficiencies computed for semiconductor heterojunction cell
Auralization of Air Vehicle Noise for Community Noise Assessment
This paper serves as an introduction to air vehicle noise auralization and documents the current state-of-the-art. Auralization of flyover noise considers the source, path, and receiver as part of a time marching simulation. Two approaches are offered; a time domain approach performs synthesis followed by propagation, while a frequency domain approach performs propagation followed by synthesis. Source noise description methods are offered for isolated and installed propulsion system and airframe noise sources for a wide range of air vehicles. Methods for synthesis of broadband, discrete tones, steady and unsteady periodic, and a periodic sources are presented, and propagation methods and receiver considerations are discussed. Auralizations applied to vehicles ranging from large transport aircraft to small unmanned aerial systems demonstrate current capabilities
Crunch-in regime - Non-linearly driven hollow-channel plasma
Plasma wakefields driven inside a hollow-channel plasma are significantly different from those driven in a homogeneous plasma. This work investigates the scaling laws of the accelerating and focusing fields in the "crunch-in" regime. This regime is excited due to the collapse of the electron-rings from the channel walls onto the propagation axis of the energy-source, in its wake. This regime is thus the non-linearly driven hollow channel, since the electron-ring displacement is of the order of the channel radius. We present the properties of the coherent structures in the "crunch-in" regime where the channel radius is matched to the beam properties such that channel-edge to on-axis collapse time has a direct correspondence to the energy source intensity. We also investigate the physical mechanisms that underlie the "crunch-in" wakefields by tuning the channel radius. Using a theoretical framework and results from PIC simulations the possible applications of the "crunch-in" regime for acceleration of positron beams with collider-scale parameters is presented
Security Issues Threats in IoT Infrastructure
IoT (Internet of Things) expands the future Internet, and has drawn much attention. As more and more gadgets (i.e. Things) connected to the Internet, the huge amount of data exchanged has reached an unprecedented level.IoT today has a wide scope and researches say that IoT will definitely be a huge reason in the change of human lifestyle. But irrespective of the scope of IoT, we cannot be sure enough to implement it due to the security concerns. There is a genuine need to secure IoT, which has therefore resulted in a need to comprehensively understand the threats and attacks on IoT infrastructure. This paper discusses about the flaws in the security structure of IoT, it is a study about the various layers of IoT and how differentattacks are possible in those layers
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 (). 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- 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
The Coldest Place in the Universe: Probing the Ultra-Cold Outflow and Dusty Disk in the Boomerang Nebula
Our Cycle 0 ALMA observations confirmed that the Boomerang Nebula is the
coldest known object in the Universe, with a massive high-speed outflow that
has cooled significantly below the cosmic background temperature. Our new CO
1-0 data reveal heretofore unseen distant regions of this ultra-cold outflow,
out to AU. We find that in the ultra-cold outflow, the
mass-loss rate (dM/dt) increases with radius, similar to its expansion velocity
() - taking , we find . The mass in
the ultra-cold outflow is Msun, and the Boomerang's main-sequence
progenitor mass is Msun. Our high angular resolution (0".3) CO
J=3-2 map shows the inner bipolar nebula's precise, highly-collimated shape,
and a dense central waist of size (FWHM) 1740 AU AU. The
molecular gas and the dust as seen in scattered light via optical HST imaging
show a detailed correspondence. The waist shows a compact core in thermal dust
emission at 0.87-3.3 mm, which harbors Msun~of very large
(mm-to-cm sized), cold ( K) grains. The central waist
(assuming its outer regions to be expanding) and fast bipolar outflow have
expansion ages of yr and yr: the "jet-lag" (i.e.,
torus age minus the fast-outflow age) in the Boomerang supports models in which
the primary star interacts directly with a binary companion. We argue that this
interaction resulted in a common-envelope configuration while the Boomerang's
primary was an RGB or early-AGB star, with the companion finally merging into
the primary's core, and ejecting the primary's envelope that now forms the
ultra-cold outflow.Comment: accepted ApJ, 12 Apr, 201
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