799 research outputs found
Localization of Electrical Insulation Failures in Superconducting Collared Coils by Analysis of the Distortion of a Pulsed Magnetic Field
The localization of possible electrical faults in superconducting accelerator magnets may, in most cases, be a complex, expensive and time-consuming process. In particular, inter-turn short circuits and failures of the ground insulation are well detectable when the magnet is collared, but often disappear after disassembly for repair due to the release of the pre-stress in the coils. The fault localization method presented in this paper is based on the measurement and analysis of the magnetic field generated inside the magnet aperture by a high voltage pulse. The presence of the fault modifies the distribution of the current in the coils and produces a distortion of the magnetic field. The described method aims at locating both the longitudinal and azimuthal position of the fault-affected area. The test method, the transient case FEM models and the implemented experimental set-up are presented and discussed for the LHC dipole models
Asymptotics of the solutions of the stochastic lattice wave equation
We consider the long time limit theorems for the solutions of a discrete wave
equation with a weak stochastic forcing. The multiplicative noise conserves the
energy and the momentum. We obtain a time-inhomogeneous Ornstein-Uhlenbeck
equation for the limit wave function that holds both for square integrable and
statistically homogeneous initial data. The limit is understood in the
point-wise sense in the former case, and in the weak sense in the latter. On
the other hand, the weak limit for square integrable initial data is
deterministic
Long time, large scale limit of the Wigner transform for a system of linear oscillators in one dimension
We consider the long time, large scale behavior of the Wigner transform
W_\eps(t,x,k) of the wave function corresponding to a discrete wave equation
on a 1-d integer lattice, with a weak multiplicative noise. This model has been
introduced in Basile, Bernardin, and Olla to describe a system of interacting
linear oscillators with a weak noise that conserves locally the kinetic energy
and the momentum. The kinetic limit for the Wigner transform has been shown in
Basile, Olla, and Spohn. In the present paper we prove that in the unpinned
case there exists such that for any the
weak limit of W_\eps(t/\eps^{3/2\gamma},x/\eps^{\gamma},k), as \eps\ll1,
satisfies a one dimensional fractional heat equation with . In the pinned case an analogous
result can be claimed for W_\eps(t/\eps^{2\gamma},x/\eps^{\gamma},k) but the
limit satisfies then the usual heat equation
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