489 research outputs found
Compact storage ring to search for the muon electric dipole moment
We present the concept of a compact storage ring of less than 0.5 m orbit
radius to search for the electric dipole moment of the muon () by
adapting the "frozen spin" method. At existing muon facilities a statistics
limited sensitivity of d_\mu \sim 5 \times 10^{-23} \ecm can be achieved
within one year of data taking. Reaching this precision would demonstrate the
viability of this novel technique to directly search for charged particle EDMs
and already test a number of Standard Model extensions. At a future, high-power
muon facility a statistical reach of d_\mu \sim 5 \times 10^{-25} \ecm seems
realistic with this setup.Comment: improved for submission; minor modification
Electrical Detection of Spin Accumulation at a Ferromagnet-Semiconductor Interface
We show that the accumulation of spin-polarized electrons at a forward-biased
Schottky tunnel barrier between Fe and n-GaAs can be detected electrically. The
spin accumulation leads to an additional voltage drop across the barrier that
is suppressed by a small transverse magnetic field, which depolarizes the spins
in the semiconductor. The dependence of the electrical accumulation signal on
magnetic field, bias current, and temperature is in good agreement with the
predictions of a drift-diffusion model for spin-polarized transport.Comment: Submitted to Phys. Rev. Let
Perfectly Matched Layers in a Divergence Preserving ADI Scheme for Electromagnetics
For numerical simulations of highly relativistic and transversely accelerated
charged particles including radiation fast algorithms are needed. While the
radiation in particle accelerators has wavelengths in the order of 100 um the
computational domain has dimensions roughly 5 orders of magnitude larger
resulting in very large mesh sizes. The particles are confined to a small area
of this domain only. To resolve the smallest scales close to the particles
subgrids are envisioned. For reasons of stability the alternating direction
implicit (ADI) scheme by D. N. Smithe et al. (J. Comput. Phys. 228 (2009)
pp.7289-7299) for Maxwell equations has been adopted. At the boundary of the
domain absorbing boundary conditions have to be employed to prevent reflection
of the radiation. In this paper we show how the divergence preserving ADI
scheme has to be formulated in perfectly matched layers (PML) and compare the
performance in several scenarios.Comment: 8 pages, 6 figure
Evolution of a beam dynamics model for the transport lines in a proton therapy facility
Despite the fact that the first-order beam dynamics models allow an
approximated evaluation of the beam properties, their contribution is essential
during the conceptual design of an accelerator or beamline. However, during the
commissioning some of their limitations appear in the comparison against
measurements. The extension of the linear model to higher order effects is,
therefore, demanded. In this paper, the effects of particle-matter interaction
have been included in the model of the transport lines in the proton therapy
facility at the Paul Scherrer Institut (PSI) in Switzerland. To improve the
performance of the facility, a more precise model was required and has been
developed with the multi-particle open source beam dynamics code called OPAL
(Object oriented Particle Accelerator Library). In OPAL, the Monte Carlo
simulations of Coulomb scattering and energy loss are performed seamless with
the particle tracking. Beside the linear optics, the influence of the passive
elements (e.g. degrader, collimators, scattering foils and air gaps) on the
beam emittance and energy spread can be analysed in the new model. This allows
for a significantly improved precision in the prediction of beam transmission
and beam properties. The accuracy of the OPAL model has been confirmed by
numerous measurements.Comment: 17 pages, 19 figure
A Parallel General Purpose Multi-Objective Optimization Framework, with Application to Beam Dynamics
Particle accelerators are invaluable tools for research in the basic and
applied sciences, in fields such as materials science, chemistry, the
biosciences, particle physics, nuclear physics and medicine. The design,
commissioning, and operation of accelerator facilities is a non-trivial task,
due to the large number of control parameters and the complex interplay of
several conflicting design goals. We propose to tackle this problem by means of
multi-objective optimization algorithms which also facilitate a parallel
deployment. In order to compute solutions in a meaningful time frame a fast and
scalable software framework is required. In this paper, we present the
implementation of such a general-purpose framework for simulation-based
multi-objective optimization methods that allows the automatic investigation of
optimal sets of machine parameters. The implementation is based on a
master/slave paradigm, employing several masters that govern a set of slaves
executing simulations and performing optimization tasks. Using evolutionary
algorithms as the optimizer and OPAL as the forward solver, validation
experiments and results of multi-objective optimization problems in the domain
of beam dynamics are presented. The high charge beam line at the Argonne
Wakefield Accelerator Facility was used as the beam dynamics model. The 3D beam
size, transverse momentum, and energy spread were optimized
Optical and electrical spin injection and spin transport in hybrid Fe/GaAs devices
We discuss methods for imaging the nonequilibrium spin polarization of
electrons in Fe/GaAs spin transport devices. Both optically- and
electrically-injected spin distributions are studied by scanning
magneto-optical Kerr rotation microscopy. Related methods are used to
demonstrate electrical spin detection of optically-injected spin polarized
currents. Dynamical properties of spin transport are inferred from studies
based on the Hanle effect, and the influence of strain on spin transport data
in these devices is discussed.Comment: 5 pages, 6 figs. ICPS-28 proceedings (July'06, Vienna) for J. Appl.
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