96,665 research outputs found
Emittance increase caused by core depletion in collisions
A new effect is presented, which changes the emittance during colliding-beam
operation in circular colliders. If the initial transverse distribution is
Gaussian, the collision probability is much higher for particles in the core of
the beam than in the tails. When small-amplitude particles are removed, the
remaining ones therefore have a larger transverse emittance. This effect,
called core depletion, may cause a decrease in luminosity. An approximate
analytic model is developed to study the effect and benchmarked against a
multiparticle tracking simulation. Finally, the time evolution of the intensity
and emittances of a Pb bunch in the Large Hadron Collider (LHC) at CERN is
calculated, taking into account also other processes than collisions. The
results show that integrated luminosity drops by 3--4% if core depletion is
taken into account. It is also found that core depletion causes the transverse
emittance to be larger when more experiments are active. This observation could
be checked against experimental data once the LHC is operational.Comment: 20 pages, 5 figure
Performance of the diamond active target prototype for the PADME experiment at the DANE BTF
The PADME experiment at the DANE Beam-Test Facility (BTF) is designed
to search for the gauge boson of a new interaction in the process
ee+, using the intense positron beam hitting a
light target. The , usually referred as dark photon, is assumed to
decay into invisible particles of a secluded sector and it can be observed by
searching for an anomalous peak in the spectrum of the missing mass measured in
events with a single photon in the final state. The measurement requires the
determination of the 4-momentum of the recoil photon, performed by a
homogeneous, highly segmented BGO crystals calorimeter. A significant
improvement of the missing mass resolution is possible using an active target
capable to determine the average position of the positron bunch with a
resolution of less than 1 mm. This report presents the performance of a real
size PADME active target made of a thin (50 m) diamond
sensor, with graphitic strips produced via laser irradiation on both sides. The
measurements are based on data collected in a beam test at the BTF in November
2015.Comment: 7 pages, 10 figure
Superconducting elliptical cavities
We give a brief overview of the history, state of the art, and future for
elliptical superconducting cavities. Principles of the cell shape optimization,
criteria for multi-cell structures design, HOM damping schemes and other
features are discussed along with examples of superconducting structures for
various applications.Comment: 25 pages, contribution to the CAS - CERN Accelerator School:
Specialised Course on RF for Accelerators; 8 - 17 Jun 2010, Ebeltoft, Denmar
Resonant and random excitations on the proton beam in the Large Hadron Collider for active halo control with pulsed hollow electron lenses
We present the results of numerical simulations and experimental studies
about the effects of resonant and random excitations on proton losses,
emittances, and beam distributions in the Large Hadron Collider (LHC). In
addition to shedding light on complex nonlinear effects, these studies are
applied to the design of hollow electron lenses (HEL) for active beam halo
control. In the High-Luminosity Large Hadron Collider (HL-LHC), a considerable
amount of energy will be stored in the beam tails. To control and clean the
beam halo, the installation of two hollow electron lenses, one per beam, is
being considered. In standard electron-lens operation, a proton bunch sees the
same electron current at every revolution. Pulsed electron beam operation
(i.e., different currents for different turns) is also considered, because it
can widen the range of achievable halo removal rates. For an axially symmetric
electron beam, only protons in the halo are excited. If a residual field is
present at the location of the beam core, these particles are exposed to
time-dependent transverse kicks and to noise. We discuss the numerical
simulations and the experiments conducted in 2016 and 2017 at injection energy
in the LHC. The excitation patterns were generated by the transverse feedback
and damping system, which acted as a flexible source of dipole kicks. Proton
beam losses, emittances, and transverse distributions were recorded as a
function of excitation patterns and strengths. The resonant excitations induced
rich dynamical effects and nontrivial changes of the beam distributions, which,
to our knowledge, have not previously been observed and studied in this detail.
We conclude with a discussion of the tolerable and achievable residual fields
and proposals for further studies.Comment: 33 pages, 32 figures, 46 references. Revised manuscript submitted to
Phys. Rev. Accel. Beam
Fel Oscillators with Tapered Undulators: Inclusion of Harmonic Generation and Pulse Propagation
We review the theory of FEL oscillators operating with tapered undulators. We
consider the case of a uniform tapering and introduce a parameter which
characterizes the effect of the tapering on the gain and on the saturation
intensity. We analyze the effect of the tapering on the FEL dynamics by
including the pulse propagation effects too. We analyze the importance of
tapering as a tool to model the optical pulse shapes and to control the higher
harmonic intensities
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