58 research outputs found
Trapped modes in a dummy extraction septum for CERN Proton Synchrotron
The term trapped mode is usually referred to a mode that can
not propagate in the beam pipe, but is localized in a particular region inside the device, producing narrow resonances peaks in the coupling impedance. They can be
excited by the presence of discontinuities inside different devices of an accelerator, producing unwanted beam instabilities. It is therefore important to identify trapped
modes, especially for new elements to be installed in a high-intensity accelerator. We present a recent study of the coupling impedance due to trapped modes in a new extraction septum that will be installed in the CERN Proton Synchrotron in the framework of PS Multi-turn extraction (MTE) commissioning. Simulation and theoretical calculations were performed in order to understand performance limitations of the machine, to find cures to reduce the instabilities, and to evaluate beam-induced heating
Chromaticity dependence of the transverse effective impedance in the CERN Proton Synchrotron
The current knowledge of the transverse beam coupling impedance of the CERN Proton Synchrotron (PS) has been established with beam-based measurements at different energies. The transverse coherent tune shift as a function of the beam intensity has been measured in order to evaluate the total effective imaginary part of the transverse impedance in the accelerator at the energies of 7, 13 and 25 GeV. Measurements have been performed changing the vertical chromaticity
for each vertical tune scan with intensity. The data analysis revealed an increase of impedance with chromaticity for all the considered energies. The transverse impedance
can be compared with the previously evaluated theoretical impedance budget taking into account the individual contribution of several machine devices
CVD-based techniques for the synthesis of nanographites and nanodiamonds
We report about some Chemical Vapor Deposition approaches used
to produce a variety of C-sp2 and C-sp3 crystalline nanostructures. The methodologies
developed in our laboratories provide custom-made solutions for the fabrication
of specific carbon nanomaterials with properties tailored for applications in the field
of nanotechnology
Weak localization and dimensional crossover in carbon nanotube systems
We investigate the effects of magnetic and electric fields on electron wavefunction
interactions in single walled carbon nanotube bundles. The magnetoresistance measurements
performed at 4.2Â K and the dependence of the data upon the electric field reveal good
agreement with weak localization theory. An electrical field conditioned characteristic
length is associated to ohmic-non ohmic transition, observed below 85Â K, in current
voltage characteristics. This length results equal to the average bundles diameter just at
T ≅ 85 K, indicating that 2D-3D crossover is responsible for the
observed conductance transition
Detonation nanodiamonds tailor the structural oeder of PEDOT chains in conductive coating layers of hybrid nanoparticles
Solid layers of PEDOT–detonation nanodiamond based nanoparticles with an exceptional structural order
were produced by means of a template-free polymerization technique. As an efficient multifunctional filler,
the nanocrystalline diamond has been shown to possess a high catalytic activity on the monomer
polymerization rate as well as to play a fundamental role as a 3D arrangement-directing agent of the
PEDOT chains at the micro- and nano-scale. SEM, TEM and TED analyses highlighted the mutual
organization between PEDOT oligomers and nanodiamond grains, and the produced hierarchical effects
on the arrangement of the backbones of the final polymer. Optical and Raman spectroscopy, used
together with XRD diffraction to study the molecular structure and crystallographic features of the hybrid
materials, pointed out that the adopted synthetic strategy enables highly conjugated and doped hybrid
systems to be generated. The spatial distribution of the filler inside the polymeric matrix and the mutual
connectivity of nanodiamond crystals and PEDOT segments are found to strongly improve the functional
properties of the host polymer. Mechanical characterizations by advanced AFM-based techniques
revealed that both indentation modulus and hardness of PEDOT/nanodiamond materials are 3 times
higher than the pure PEDOT polymer, while electrical characterizations by a 4-probe method gave sheet
resistance values of 1 106 U sq 1 for the nanocomposite particle
Tuning procedure for traveling wave structures and its application to the C-Band cavities for SPARC photo injector energy upgrade
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A First Search for Cosmogenic Neutrinos with the ARIANNA Hexagonal Radio Array
The ARIANNA experiment seeks to observe the diffuse flux of neutrinos in the
10^8 - 10^10 GeV energy range using a grid of radio detectors at the surface of
the Ross Ice Shelf of Antarctica. The detector measures the coherent Cherenkov
radiation produced at radio frequencies, from about 100 MHz to 1 GHz, by
charged particle showers generated by neutrino interactions in the ice. The
ARIANNA Hexagonal Radio Array (HRA) is being constructed as a prototype for the
full array. During the 2013-14 austral summer, three HRA stations collected
radio data which was wirelessly transmitted off site in nearly real-time. The
performance of these stations is described and a simple analysis to search for
neutrino signals is presented. The analysis employs a set of three cuts that
reject background triggers while preserving 90% of simulated cosmogenic
neutrino triggers. No neutrino candidates are found in the data and a
model-independent 90% confidence level Neyman upper limit is placed on the all
flavor neutrino+antineutrino flux in a sliding decade-wide energy bin. The
limit reaches a minimum of 1.9x10^-23 GeV^-1 cm^-2 s^-1 sr^-1 in the 10^8.5 -
10^9.5 GeV energy bin. Simulations of the performance of the full detector are
also described. The sensitivity of the full ARIANNA experiment is presented and
compared with current neutrino flux models.Comment: 22 pages, 22 figures. Published in Astroparticle Physic
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