529 research outputs found
Beam Dynamics in High Intensity Cyclotrons Including Neighboring Bunch Effects: Model, Implementation and Application
Space charge effects, being one of the most significant collective effects,
play an important role in high intensity cyclotrons. However, for cyclotrons
with small turn separation, other existing effects are of equal importance.
Interactions of radially neighboring bunches are also present, but their
combined effects has not yet been investigated in any great detail. In this
paper, a new particle in cell based self-consistent numerical simulation model
is presented for the first time. The model covers neighboring bunch effects and
is implemented in the three-dimensional object-oriented parallel code
OPAL-cycl, a flavor of the OPAL framework. We discuss this model together with
its implementation and validation. Simulation results are presented from the
PSI 590 MeV Ring Cyclotron in the context of the ongoing high intensity upgrade
program, which aims to provide a beam power of 1.8 MW (CW) at the target
destination
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
Towards Quantitative Simulations of High Power Proton Cyclotrons
PSI operates a cyclotron based high intensity proton accelerator routinely at
an average beam power of 1.3MW. With this power the facility is at the
worldwide forefront of high intensity proton accelerators. The beam current is
practically limited by losses at extraction and the resulting activation of
accelerator components. Further intensity upgrades and new projects aiming at
an even higher average beam power, are only possible if the relative losses can
be lowered in proportion, thus keeping absolute losses at a constant level.
Maintaining beam losses at levels allowing hands-on maintenance is a primary
challenge in any high power proton machine design and operation. In
consequence, predicting beam halo at these levels is a great challenge and will
be addressed in this paper. High power hadron driver have being used in many
disciplines of science and, a growing interest in the cyclotron technology for
high power hadron drivers are being observed very recently. This report will
briefly introduce OPAL, a tool for precise beam dynamics simulations including
3D space charge. One of OPAL's flavors (OPAL-cycl) is dedicated to high power
cyclotron modeling and is explained in greater detail. We then explain how to
obtain initial conditions for our PSI Ring cyclotron which still delivers the
world record in beam power of 1.3 MW continuous wave (cw). Several crucial
steps are explained necessary to be able to predict tails at the level of
3\sigma ... 4\sigma in the PSI Ring cyclotron. We compare our results at the
extraction with measurements, obtained with a 1.18 MW cw production beam. Based
on measurement data, we develop a simple linear model to predict beam sizes of
the extracted beam as a function of intensities and confirm the model with
simulations.Comment: Corrections and new figur
Options for the second Bunch Compressor Chicane of the CLIC Main Beam Line
For the second bunch compressor chicane at CLIC a maximum emittance growth of only 5% in the horizontal plane is allowed. The emittance growth is the conse- quence of incoherent and coherent synchrotron radiation emitted by the electrons along the chicane. Both effects are reviewed and various chicanes are compared in computer simulations. A chicane layout is found which preserves the emittance well within the specifications
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
Cyclotrons as Drivers for Precision Neutrino Measurements
As we enter the age of precision measurement in neutrino physics, improved
flux sources are required. These must have a well-defined flavor content with
energies in ranges where backgrounds are low and cross section knowledge is
high. Very few sources of neutrinos can meet these requirements. However,
pion/muon and isotope decay-at-rest sources qualify. The ideal drivers for
decay-at-rest sources are cyclotron accelerators, which are compact and
relatively inexpensive. This paper describes a scheme to produce decay-at-rest
sources driven by such cyclotrons, developed within the DAEdALUS program.
Examples of the value of the high precision beams for pursuing Beyond Standard
Model interactions are reviewed. New results on a combined DAEdALUS--Hyper-K
search for CP-violation that achieve errors on the mixing matrix parameter of 4
degrees to 12 degrees are presented.Comment: This paper was invited by the journal Advances in High Energy Physics
for their upcoming special issue on "Neutrino Masses and Oscillations," which
will be published on the 100th anniversary of Pontecorvo's birt
Strong spin relaxation length dependence on electric field gradients
We discuss the influence of electrical effects on spin transport, and in
particular the propagation and relaxation of spin polarized electrons in the
presence of inhomogeneous electric fields. We show that the spin relaxation
length strongly depends on electric field gradients, and that significant
suppression of electron spin polarization can occur as a result thereof. A
discussion in terms of a drift-diffusion picture, and self-consistent numerical
calculations based on a Boltzmann-Poisson approach shows that the spin
relaxation length in fact can be of the order of the charge screening length.Comment: 4 pages, 3 figures, to be presented at PASPSI
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