9,002 research outputs found
Dust interferometers in plasmas
An interferometric imaging technique has been proposed to instantly measure
the diameter of individual spherical dust particles suspended in a gas
discharge plasma. The technique is based on the defocused image analysis of
both spherical particles and their binary agglomerates. Above a critical
diameter, the defocused images of spherical particles contain stationary
interference fringe patterns and the fringe number increases with particle
diameters. Below this critical diameter, the particle size has been measured
using the rotational interference fringe patterns which appear only on the
defocused images of binary agglomerates. In this case, a lower cut-off limit of
particle diameter has been predicted, below which no such rotational fringe
patterns are observed for the binary agglomerates. The method can be useful as
a diagnostics for complex plasma experiments on earth as well as under
microgravity condition
Direct experimental observation of binary agglomerates in complex plasmas
A defocusing imaging technique has been used as a diagnostic to identify
binary agglomerates (dimers) in complex plasmas. Quasi-two-dimensional plasma
crystal consisting of monodisperse spheres and binary agglomerates has been
created where the agglomerated particles levitate just below the spherical
particles without forming vertical pairs. Unlike spherical particles, the
defocused images of binary agglomerates show distinct, stationary/periodically
rotating interference fringe patterns. The results can be of fundamental
importance for future experiments on complex plasmas
A Method to Determine the Maximum Radius of Defocused Protons after Self-Modulation in AWAKE
The AWAKE experiment at CERN aims to drive GV/m plasma wakefields with a
self-modulated proton drive bunch, and to use them for electron acceleration.
During the self-modulation process, protons are defocused by the transverse
plasma wakefields and form a halo around the focused bunch core. The two-screen
setup integrated in AWAKE measures the transverse, time-integrated proton bunch
distribution downstream the \unit[10]{m} long plasma to detect defocused
protons. By measuring the maximum radius of the defocused protons we attempt
calculate properties of the self-modulation. In this article, we develop a
routine to identify the maximum radius of the defocused protons, based on a
standard contour method. We compare the maximum radius obtained from the
contour to the logarithmic lineouts of the image to show that the determined
radius identifies the edge of the distribution.Comment: 3 pages, 4 figures, EAAC 2017 NIMA proceeding
Indirect Self-Modulation Instability Measurement Concept for the AWAKE Proton Beam
AWAKE, the Advanced Proton-Driven Plasma Wakefield Acceleration Experiment,
is a proof-of-principle R&D experiment at CERN using a 400 GeV/c proton beam
from the CERN SPS (longitudinal beam size sigma_z = 12 cm) which will be sent
into a 10 m long plasma section with a nominal density of approx. 7x10^14
atoms/cm3 (plasma wavelength lambda_p = 1.2mm). In this paper we show that by
measuring the time integrated transverse profile of the proton bunch at two
locations downstream of the AWAKE plasma, information about the occurrence of
the self-modulation instability (SMI) can be inferred. In particular we show
that measuring defocused protons with an angle of 1 mrad corresponds to having
electric fields in the order of GV/m and fully developed self-modulation of the
proton bunch. Additionally, by measuring the defocused beam edge of the
self-modulated bunch, information about the growth rate of the instability can
be extracted. If hosing instability occurs, it could be detected by measuring a
non-uniform defocused beam shape with changing radius. Using a 1 mm thick
Chromox scintillation screen for imaging of the self-modulated proton bunch, an
edge resolution of 0.6 mm and hence a SMI saturation point resolution of 1.2 m
can be achieved.Comment: 4 pages, 4 figures, EAAC conference proceeding
- …