229 research outputs found
Beam-induced backgrounds in the CLIC 3 TeV CM energy interaction region
Luminosity spectrum and accelerator background levels strongly influence the
experimental conditions and have an important impact on detector design. The
expected rates of the main beam-beam products at CLIC 3 TeV CM energy, taking
into account for machine imperfections, are computed. Among the other
machine-induced background the photon fans from the Incoherent Synchrotron
Radiation (ISR) photons emitted in the final doublet are evaluated.Comment: Proceedings of LCWS1
First Evaluation of Dynamic Aperture at Injection for FCC-hh
In the Hadron machine option, proposed in the context of the Future Circular
Colliders (FCC) study, the dipole field quality is expected to play an
important role, as in the LHC. A preliminary evaluation of the field quality of
dipoles, based on the NbSn technology, has been provided by the magnet
group. The effect of these field imperfections on the dynamic aperture, using
the present lattice design, is presented and first tolerances on the b and
b multipole components are evaluated
Status report of the baseline collimation system of CLIC. Part II
Important efforts have recently been dedicated to the characterisation and
improvement of the design of the post-linac collimation system of the Compact
Linear Collider (CLIC). This system consists of two sections: one dedicated to
the collimation of off-energy particles and another one for betatron
collimation. The energy collimation system is further conceived as protection
system against damage by errant beams. In this respect, special attention is
paid to the optimisation of the energy collimator design. The material and the
physical parameters of the energy collimators are selected to withstand the
impact of an entire bunch train. Concerning the betatron collimation section,
different aspects of the design have been optimised: the transverse collimation
depths have been recalculated in order to reduce the collimator wakefield
effects while maintaining a good efficiency in cleaning the undesired beam
halo; the geometric design of the spoilers has been reviewed to minimise
wakefields; in addition, the optics design has been optimised to improve the
collimation efficiency. This report presents the current status of the the
post-linac collimation system of CLIC. Part II is mainly dedicated to the study
of the betatron collimation system and collimator wakefield effects.Comment: 25 pages, 13 figure
Observation of mesoscopic conductance fluctuations in YBaCuO grain boundary Josephson Junctions
Magneto-fluctuations of the normal resistance R_N have been reproducibly
observed in high critical temp erature superconductor (HTS) grain boundary
junctions, at low temperatures. We attribute them to mesoscopic transport in
narrow channels across the grain boundary line. The Thouless energy appears to
be the relevant energy scale. Our findings have significant implications on
quasiparticle relaxation and coherent transport in HTS grain boundaries.Comment: Revised version, minor changes. 4 pages, 4 figure
Magnetic moment non-conservation in magnetohydrodynamic turbulence models
The fundamental assumptions of the adiabatic theory do not apply in presence
of sharp field gradients as well as in presence of well developed
magnetohydrodynamic turbulence. For this reason in such conditions the magnetic
moment is no longer expected to be constant. This can influence particle
acceleration and have considerable implications in many astrophysical problems.
Starting with the resonant interaction between ions and a single parallel
propagating electromagnetic wave, we derive expressions for the magnetic moment
trapping width (defined as the half peak-to-peak difference in the
particle magnetic moment) and the bounce frequency . We perform
test-particle simulations to investigate magnetic moment behavior when
resonances overlapping occurs and during the interaction of a ring-beam
particle distribution with a broad-band slab spectrum.
We find that magnetic moment dynamics is strictly related to pitch angle
for a low level of magnetic fluctuation, , where is the constant and uniform background magnetic field.
Stochasticity arises for intermediate fluctuation values and its effect on
pitch angle is the isotropization of the distribution function .
This is a transient regime during which magnetic moment distribution
exhibits a characteristic one-sided long tail and starts to be influenced by
the onset of spatial parallel diffusion, i.e., the variance
grows linearly in time as in normal diffusion. With strong fluctuations
isotropizes completely, spatial diffusion sets in and
behavior is closely related to the sampling of the varying magnetic field
associated with that spatial diffusion.Comment: 13 pages, 10 figures, submitted to PR
BDS tuning and Luminosity Monitoring in CLIC
The emittance preservation in the Beam Delivery System (BDS) is one of the
major challenges in CLIC. The fast detuning of the final focus optics requires
an on-line tuning procedure in order to keep luminosity close to the maximum.
Different tuning techniques have been applied to the CLIC BDS and in particular
to the Final Focus System (FFS) in order to mitigate static and dynamic
imperfections. Some of them require a fast luminosity measurement. Here we
study the possibility to use beam-beam backgrounds processes at CLIC 3 TeV CM
energy as fast luminosity signal. In particular the hadrons multiplicity in the
detector region is investigated.Comment: Proceedings of LCWS1
Halo and tail simulations with applications to the CLIC drive beam
We report about generic halo and tail simulations and estimates. Previous studies weremainly focused on very high energies as relevant for the beam delivery systems of linear colliders. We have now studied, applied and extended these simulations to lower energies as relevant for the CLIC drive beam
Coherent quasiparticle transport in grain boundary junctions employing high-Tc superconductors
Magneto-fluctuations of the normal resistance RN have been reproducibly
observed in YBa2Cu3O7-d biepitaxial grain boundary junctions at low
temperatures. We attribute them to mesoscopic transport in narrow channels
across the grain boundary line, occurring in an unusual energy regime. The
Thouless energy appears to be the relevant energy scale. Possible implications
on the understanding of coherent transport of quasiparticles in HTS and of the
dissipation mechanisms are discussed.Comment: Submitted on behalf of TIMA Editions
(http://irevues.inist.fr/tima-editions
First determination of the one-proton induced Non-Mesonic Weak Decay width of p-shell {\Lambda}-Hypernuclei
Previous studies of proton and neutron spectra from Non-Mesonic Weak Decay of
eight Lambda-Hypernuclei (A = 5-16) have been revisited. New values of the
ratio of the two-nucleon and the one-proton induced decay widths,
Gamma_2N/Gamma_p, are obtained from single proton spectra, Gamma_2N/Gamma_p =
0.50 +/- 0.24, and from neutron and proton coincidence spectra,
Gamma_2N/Gamma_p = 0.36 +/- 0.14stat +0.05sys -0.04sys , in full agreement with
previously published ones. With these values, a method is developed to extract
the one-proton induced decay width in units of the free Lambda decay width,
Gamma_p/Gamma_Lambda, without resorting to Intra Nuclear Cascade models but by
exploiting only experimental data, under the assumption of a linear dependence
on A of the Final State Interaction contribution. This is the first systematic
determination ever done and it agrees within the errors with recent theoretical
calculations.Comment: 16 pages, 3 figures, 2 table
STUDY OF FRINGE FIELDS EFFECTS FROM FINAL FOCUS QUADRUPOLES ON BEAM BASED MEASURED QUANTITIES
Accelerator physics needs advanced modeling and simulation
techniques, in particular for beam stability studies.
A deeper understanding of the effects of magnetic fields
non-linearities will greatly help in the improvement of future
colliders design and performance. In previous papers, a
new tracking method was proposed to study the effect of
the longitudinal dependency of the harmonics on the beam
dynamics. In this paper, the study will focus on the effects
on observable quantities in beam based measurements, for
the case of HL-LHC Inner Triplet and with possible tests in
LHC
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