9,593 research outputs found
Hamilton--Jacobi theory for continuation of magnetic field across a toroidal surface supporting a plasma pressure discontinuity
The vanishing of the divergence of the total stress tensor (magnetic plus
kinetic) in a neighborhood of an equilibrium plasma containing a toroidal
surface of discontinuity gives boundary and jump conditions that strongly
constrain allowable continuations of the magnetic field across the surface. The
boundary conditions allow the magnetic fields on either side of the
discontinuity surface to be described by surface magnetic potentials, reducing
the continuation problem to that of solving a Hamilton--Jacobi equation. The
characteristics of this equation obey Hamiltonian equations of motion, and a
necessary condition for the existence of a continued field across a general
toroidal surface is that there exist invariant tori in the phase space of this
Hamiltonian system. It is argued from the Birkhoff theorem that existence of
such an invariant torus is also, in general, sufficient for continuation to be
possible. An important corollary is that the rotational transform of the
continued field on a surface of discontinuity must, generically, be irrational.Comment: Prepared for submission to Phys. Letts.
Performance studies of scintillating ceramic samples exposed to ionizing radiation
Scintillating ceramics are a promising, new development for various
applications in science and industry. Their application in calorimetry for
particle physics experiments is expected to involve an exposure to high levels
of ionizing radiation. In this paper, changes in performance have been measured
for scintillating ceramic samples of different composition after exposure to
penetrating ionizing radiation up to a dose of 38 kGy.Comment: 6 pages, 8 figures, to be published in the 2012 IEEE Nuclear Science
Symposium Conference Recor
Crystals for high-energy calorimetry in extreme environments
Crystals are used as a homogeneous calorimetric medium in many high-energy
physics experiments. For some experiments, performance has to be ensured in
very difficult operating conditions, like a high radiation environment, very
large particle fluxes, high collision rates, placing constraints on response
and readout time. An overview is presented of recent achievements in the field,
with particular attention given to the performance of Lead Tungstate (PWO)
crystals exposed to high particle fluxes.Comment: To be published in Proc. of the Meeting of the Division of Particles
and Fields of the American Physical Society, DPF2004 (Riverside, USA, August
26th to 31st, 2004
A visualization of the damage in Lead Tungstate calorimeter crystals after exposure to high-energy hadrons
The anticipated performance of calorimeter crystals in the environment
expected after the planned High-Luminosity upgrade of the Large Hadron Collider
(HL-LHC) at CERN has to be well understood, before informed decisions can be
made on the need for detector upgrades. Throughout the years of running at the
HL-LHC, the detectors will be exposed to considerable fluences of fast hadrons,
that have been shown to cause cumulative transparency losses in Lead Tungstate
scintillating crystals. In this study, we present direct evidence of the main
underlying damage mechanism. Results are shown from a test that yields a direct
insight into the nature of the hadron-specific damage in Lead Tungstate
calorimeter crystals exposed to 24 GeV/c protons.Comment: 8 pages, 6 figure
Model Data Fusion: developing Bayesian inversion to constrain equilibrium and mode structure
Recently, a new probabilistic "data fusion" framework based on Bayesian
principles has been developed on JET and W7-AS. The Bayesian analysis framework
folds in uncertainties and inter-dependencies in the diagnostic data and signal
forward-models, together with prior knowledge of the state of the plasma, to
yield predictions of internal magnetic structure. A feature of the framework,
known as MINERVA (J. Svensson, A. Werner, Plasma Physics and Controlled Fusion
50, 085022, 2008), is the inference of magnetic flux surfaces without the use
of a force balance model. We discuss results from a new project to develop
Bayesian inversion tools that aim to (1) distinguish between competing
equilibrium theories, which capture different physics, using the MAST spherical
tokamak; and (2) test the predictions of MHD theory, particularly mode
structure, using the H-1 Heliac.Comment: submitted to Journal of Plasma Fusion Research 10/11/200
Cosmogenic rare gases and 10-Be in a cross section of Knyahinya
The concentrations of cosmogenic nuclides were studied as a function of shielding on samples from a cross section of the 293 kg main fragment of the L5 chondrite Knyahinya. The stone broke into two nearly symmetrical parts upon its fall in 1866. The planar cross section has diameters between 40 and 55 cm. He, Ne, and Ar were measured on about 20 samples by mass spectrometry and the 10-Be activities on aliquots of 10 selected samples were determined by AMS. The 10-Be data are presented and the abundances of spallogenic nuclides are compared with the model calculations reported by Reedy for spherical L chondrites. The 10-Be production rates in Knyahinya are shown versus the shielding parameter 22-Ne/21-Ne
Proof-of-principle of a new geometry for sampling calorimetry using inorganic scintillator plates
A novel geometry for a sampling calorimeter employing inorganic scintillators
as an active medium is presented. To overcome the mechanical challenges of
construction, an innovative light collection geometry has been pioneered, that
minimises the complexity of construction. First test results are presented,
demonstrating a successful signal extraction. The geometry consists of a
sampling calorimeter with passive absorber layers interleaved with layers of an
active medium made of inorganic scintillating crystals. Wavelength-shifting
(WLS) fibres run along the four long, chamfered edges of the stack,
transporting the light to photodetectors at the rear. To maximise the amount of
scintillation light reaching the WLS fibres, the scintillator chamfers are
depolished. It is shown herein that this concept is working for cerium fluoride
(CeF) as a scintillator. Coupled to it, several different types of
materials have been tested as WLS medium. In particular, materials that might
be sufficiently resistant to the High-Luminosity Large Hadron Collider
radiation environment, such as cerium-doped Lutetium-Yttrium Orthosilicate
(LYSO) and cerium-doped quartz, are compared to conventional plastic WLS
fibres. Finally, an outlook is presented on the possible optimisation of the
different components, and the construction and commissioning of a full
calorimeter cell prototype is presented.Comment: Submitted to Proceedings CALOR 2014, the 16th International
Conference on Calorimetry in High-Energy Physics, Giessen (Germany) 6 - 11
April 2014. To be published in Journal of Physics: Conference Series (10
pages, 15 figures
The super-LHC
We review here the prospects of a long-term upgrade programme for the Large
Hadron Collider (LHC), CERN laboratory's new proton-proton collider. The
super-LHC, which is currently under evaluation and design, is expected to
deliver of the order of ten times the statistics of the LHC. In addition to a
non-technical summary of the principal physics arguments for the upgrade, I
present a pedagogical introduction to the technological challenges on the
accelerator and experimental fronts, and a review of the current status of the
planning.Comment: To appear in Contemporary Physic
Proposal for SPS beam time for the baby MIND and TASD neutrino detector prototypes
The design, construction and testing of neutrino detector prototypes at CERN
are ongoing activities. This document reports on the design of solid state baby
MIND and TASD detector prototypes and outlines requirements for a test beam at
CERN to test these, tentatively planned on the H8 beamline in the North Area,
which is equipped with a large aperture magnet. The current proposal is
submitted to be considered in light of the recently approved projects related
to neutrino activities with the SPS in the North Area in the medium term
2015-2020
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