126 research outputs found
A method for computing driving and detuning beam coupling impedances of an asymmetric cavity using eigenmode simulations
We propose a method for numerical calculation of driving and detuning
transverse beam coupling impedances of an asymmetric cavity. The method relies
on eigenmode simulations and can be viewed as an alternative to time domain
wakefield simulations. A similar procedure is well-established for symmetric
cavities, and this paper extends it to the case of an asymmetric cavity. The
method is benchmarked with time-domain wakefield simulations and its practical
implementation is discussed
Spreading widths of giant resonances in spherical nuclei: damped transient response
We propose the universal approach to describe spreading widths of monopole,
dipole and quadrupole giant resonances in heavy and superheavy spherical
nuclei. Our approach is based on the ideas of the random matrix distribution of
the coupling between one-phonon and two-phonon states generated in the random
phase approximation. We use the Skyrme interaction SLy4 as our model
Hamiltonian to create a single-particle spectrum and to analyze excited states
of the doubly magic nuclei Sn, Pb and 126. Our results
demonstrate that the universal approach enables to describe gross structure of
the spreading widths of the considered giant resonances.Comment: 6 pages, 2 figure
Two-phonon structures for beta-decay theory
The -decay rates of Ca have been studied within a microscopic
model, which is based on the Skyrme interaction T45 to construct
single-particle and phonon spaces. We observe a redistribution of the
Gamow-Teller strength due to the phonon-phonon coupling, considered in the
model. For Sc, the spin-parity of the ground state is found to be .
We predict that the half-life of Ca is 0.3 ms, while the total
probability of the emission is 6.1%. Additionally, the random
matrix theory has been applied to analyse the statistical properties of the
spectrum populated in the -decay to elucidate the obtained
results.Comment: 4 pages, 1 figure, proceedings of International Conference on Nuclear
Structure and Related Topics (NSRT18), June 3-9 2018, Burgas, Bulgari
First beam test of Laser Engineered Surface Structures (LESS) at cryogenic temperature in CERN SPS accelerator
Electron cloud mitigation is an essential requirement for accelerators of positive particles with high intensity beams to guarantee beam stability and limited heat load in cryogenic systems. Laser Engineered Surface Structures (LESS) are being considered, within the High Luminosity upgrade of the LHC collider at CERN (HL-LHC), as an option to reduce the Secondary Electron Yield (SEY) of the surfaces facing the beam, thus suppressing the elec-tron cloud phenomenon. As part of this study, a 2.2 m long Beam Screen (BS) with LESS has been tested at cryogenic temperature in the COLD bore EXperiment (COLDEX) facility in the SPS accelerator at CERN. In this paper, we describe the manufacturing procedure of the beam screen, the employed laser treatment technique and discuss our first observations in COLDEX confirming electron cloud suppression.Electron cloud mitigation is an essential requirement for accelerators of positive particles with high intensity beams to guarantee beam stability and limited heat load in cryogenic systems. Laser Engineered Surface Structures (LESS) are being considered, within the High Luminosity upgrade of the LHC collider at CERN (HL-LHC), as an option to reduce the Secondary Electron Yield (SEY) of the surfaces facing the beam, thus suppressing the electron cloud phenomenon. As part of this study, a 2.2 m long Beam Screen (BS) with LESS has been tested at cryogenic temperature in the COLD bore EXperiment (COLDEX) facility in the SPS accelerator at CERN. In this paper, we describe the manufacturing procedure of the beam screen, the employed laser treatment technique and discuss our first observations in COLDEX confirming electron cloud suppression
Building the impedance model of a real machine
A reliable impedance model of a particle accelerator can be built by combining the beam coupling impedances of all the components. This is a necessary step to be able to evaluate the machine performance limitations, identify the main contributors in case an impedance reduction is required, and study the interaction with other mechanisms such as optics nonlinearities, transverse damper, noise, space charge, electron cloud, beam-beam (in a collider).
The main phases to create a realistic impedance model, and verify it experimentally, will be reviewed, highlighting the main challenges. Some examples will be presented revealing the levels of precision of machine impedance models that have been achieved
Fine structure of the isoscalar giant monopole resonance in Ni, Zr, Sn and Pb
Over the past two decades high energy-resolution inelastic proton scattering
studies were used to gain an understanding of the origin of fine structure
observed in the isoscalar giant quadrupole resonance (ISGQR) and the isovector
giant dipole resonance (IVGDR). Recently, the isoscalar giant monopole
resonance (ISGMR) in Ni, Zr, Sn and Pb was
studied at the iThemba Laboratory for Accelerator Based Sciences (iThemba LABS)
by means of inelastic -particle scattering at very forward scattering
angles (including ). The good energy resolution of the measurement
revealed significant fine structure of the ISGMR.~To extract scales by means of
wavelet analysis characterizing the observed fine structure of the ISGMR in
order to investigate the role of different mechanisms contributing to its decay
width. Characteristic energy scales are extracted from the fine structure using
continuous wavelet transforms. The experimental energy scales are compared to
different theoretical approaches performed in the framework of quasiparticle
random phase approximation (QRPA) and beyond-QRPA including complex
configurations using both non-relativistic and relativistic density functional
theory. All models highlight the role of Landau fragmentation for the damping
of the ISGMR especially in the medium-mass region. Models which include the
coupling between one particle-one hole (1p-1h) and two particle-two hole
(2p-2h) configurations modify the strength distributions and wavelet scales
indicating the importance of the spreading width. The effect becomes more
pronounced with increasing mass number. Wavelet scales remain a sensitive
measure of the interplay between Landau fragmentation and the spreading width
in the description of the fine structure of giant resonances.Comment: 13 pages,7 figures, regular articl
Recommended from our members
HE-LHC: The High-Energy Large Hadron Collider: Future Circular Collider Conceptual Design Report Volume 4
Abstract: In response to the 2013 Update of the European Strategy for Particle Physics (EPPSU), the Future Circular Collider (FCC) study was launched as a world-wide international collaboration hosted by CERN. The FCC study covered an energy-frontier hadron collider (FCC-hh), a highest-luminosity high-energy lepton collider (FCC-ee), the corresponding 100 km tunnel infrastructure, as well as the physics opportunities of these two colliders, and a high-energy LHC, based on FCC-hh technology. This document constitutes the third volume of the FCC Conceptual Design Report, devoted to the hadron collider FCC-hh. It summarizes the FCC-hh physics discovery opportunities, presents the FCC-hh accelerator design, performance reach, and staged operation plan, discusses the underlying technologies, the civil engineering and technical infrastructure, and also sketches a possible implementation. Combining ingredients from the Large Hadron Collider (LHC), the high-luminosity LHC upgrade and adding novel technologies and approaches, the FCC-hh design aims at significantly extending the energy frontier to 100 TeV. Its unprecedented centre-of-mass collision energy will make the FCC-hh a unique instrument to explore physics beyond the Standard Model, offering great direct sensitivity to new physics and discoveries
HE-LHC: The High-Energy Large Hadron Collider – Future Circular Collider Conceptual Design Report Volume 4
In response to the 2013 Update of the European Strategy for Particle Physics (EPPSU), the Future Circular Collider (FCC) study was launched as a world-wide international collaboration hosted by CERN. The FCC study covered an energy-frontier hadron collider (FCC-hh), a highest-luminosity high-energy lepton collider (FCC-ee), the corresponding 100 km tunnel infrastructure, as well as the physics opportunities of these two colliders, and a high-energy LHC, based on FCC-hh technology. This document constitutes the third volume of the FCC Conceptual Design Report, devoted to the hadron collider FCC-hh. It summarizes the FCC-hh physics discovery opportunities, presents the FCC-hh accelerator design, performance reach, and staged operation plan, discusses the underlying technologies, the civil engineering and technical infrastructure, and also sketches a possible implementation. Combining ingredients from the Large Hadron Collider (LHC), the high-luminosity LHC upgrade and adding novel technologies and approaches, the FCC-hh design aims at significantly extending the energy frontier to 100 TeV. Its unprecedented centre-of-mass collision energy will make the FCC-hh a unique instrument to explore physics beyond the Standard Model, offering great direct sensitivity to new physics and discoveries
- …