10 research outputs found
Hot nanoindentation in inert environments
An instrument capable of performing nanoindentation at temperatures up to 500 °C in inert atmospheres, including partial vacuum and gas near atmospheric pressures, is described. Technical issues associated with the technique (such as drift and noise) and the instrument (such as tip erosion and radiative heating of the transducer) are identified and addressed. Based on these considerations, preferred operation conditions are identified for testing on various materials. As a proof-of-concept demonstration, the hardness and elastic modulus of three materials are measured: fused silica (nonoxidizing), aluminum, and copper (both oxidizing). In all cases, the properties match reasonably well with published data acquired by more conventional test methods.United States. Office of Naval Research (Contract No. N00014-08-1-0312)Massachusetts Institute of Technology. Institute for Soldier Nanotechnologie
Laser Wakefield accelerator modelling with variational neural networks
A machine learning model was created to predict the electron spectrum generated by a GeVclass laser wakefield accelerator. The model was constructed from variational convolutional neural networks which mapped the results of secondary laser and plasma diagnostics to the generated electron spectrum. An ensemble of trained networks was used to predict the electron spectrum and to provide an estimation of the uncertainty on that prediction. It is anticipated that this approach will be useful for inferring the electron spectrum prior undergoing any process which can alter or destroy the beam. In addition, the model provides insight into the scaling of electron beam properties due to stochastic fluctuations in the laser energy and plasma electron density
Recommended from our members
Traveling Arts x HCI Sketchbook: Exploring the Intersection Between Artistic Expression and Human-Computer Interaction
When thinking of arts in HCI, one might be tempted to keep one's eyes focused on prominent realms such as sketching for UX Design and design probes from participants. A closer look shows that practices go beyond this, involving a variety of arts-based expressions by researchers, the researched and third parties, e.g. graphic facilitators. Inspired by Toselli's Sketchnote Army Travelling Sketchbook, researchers and artists contributed to a 'Travelling Sketchbook for Arts in HCI', showcasing their arts-based practice in HCI. The resulting sketchbook explores the intersection between HCI and artistic expression, illuminating what it means to use art in HCI. It shows the breadth of Arts in HCI, illustrating the many fruitful possibilities for extending existing research and dissemination methods in HCI. It also calls into question current practices, which often do not recognise the significance of artist attribution, and, in turn, advocates for equal authorship between principal researchers and contributing artists
Narrow bandwidth, low-emittance positron beams from a laser-wakefield accelerator
The rapid progress that plasma wakefield accelerators are experiencing is now posing the question as to whether they could be included in the design of the next generation of high-energy electron-positron colliders. However, the typical structure of the accelerating wakefields presents challenging complications for positron acceleration. Despite seminal proof-of-principle experiments and theoretical proposals, experimental research in plasma-based acceleration of positrons is currently limited by the scarcity of positron beams suitable to seed a plasma accelerator. Here, we report on the first experimental demonstration of a laser-driven source of ultra-relativistic positrons with sufficient spectral and spatial quality to be injected in a plasma accelerator. Our results indicate, in agreement with numerical simulations, selection and transport of positron beamlets containing Ne+ ≥ 105 positrons in a 5% bandwidth around 600 MeV, with femtosecond-scale duration and micron-scale normalised emittance. Particle-in-cell simulations show that positron beams of this kind can be guided and accelerated in a laser-driven plasma accelerator, with favourable scalings to further increase overall charge and energy using PW-scale lasers. The results presented here demonstrate the possibility of performing experimental studies of positron acceleration in a laser-driven wakefield accelerator. <br/
Laser Generation of Near-GeV Low Emittance Positron Beams
We report on the first spatial and spectral characterisation of near-GeV
positron beams generated in a fully laser-driven configuration. The
energy-resolved geometric emittance, source size and spectrum were
simultaneously measured for electrons and positrons generated from a
laser-wakefield accelerated electron beam impacting on a thin high-Z converter.
More than positrons were observed within 5\% of 600 MeV, with a source
size smaller than 100 m and sub-micron geometric emittance, in agreement
with numerical modelling. We conclude that the positron emittance was dominated
by the transverse size of the primary electron beam at the converter.
Minimising the drift distance between the electron source and the converter
would allow for the generation of GeV-scale positron beams with micron-scale
source size and normalised emittance of a few microns, using a 150 TW laser
system. It is proposed that beams with these characteristics are suited for
experimental studies of positron acceleration in a plasma wakefield.Comment: 7 pages with 5 figures + supplemental materia