113 research outputs found
Simulation of instability at transition energy with a new impedance model for CERN PS
Instabilities driven by the transverse impedance are proven to be one of the limitations for the high intensity reach of the CERN PS. Since several years, fast single bunch vertical instability at transition energy has been observed with the high intensity bunch serving the neutron Time-of-Flight facility (n-ToF). In order to better understand the instability mechanism, a dedicated measurement campaign took place. The results were compared with macro-particle simulations with PyHEADTAIL based on the new impedance model developed for the PS. Instability threshold and growth rate for different longitudinal emittances and beam intensities were studied
Impedance measurements and simulations on the TCT and TDI LHC collimators
The LHC collimation system is a critical element for
the safe operation of the LHC machine and it is subject
to continuous performance monitoring, hardware upgrade
and optimization. In this work we will address the impact
on impedance of the upgrades performed on the injection
protection target dump (TDI), where the absorber material
has been changed to mitigate the device heating observed
in machine operation, and on selected secondary (TCS) and
tertiary (TCT) collimators, where beam position monitors
(BPM) have been embedded for faster jaw alignment. Con-
cerning the TDI, we will present the RF measurements per-
formed before and after the upgrade, comparing the result
to heating and tune shift beam measurements. For the TCTs,
we will study how the higher order modes (HOM) intro-
duced by the BPM addition have been cured by means of
ferrite placement in the device. The impedance mitigation
campaign has been supported by RF measurements whose
results are in good agreement with GdfidL and CST simula-
tions. The presence of undamped low frequency modes is
proved not to be detrimental to the safe LHC operation
Design, construction, and beam tests of a rotatable collimator prototype for high-intensity and high-energy hadron accelerators
A rotatable-jaw collimator design was conceived as a solution to recover from catastrophic beam impacts which would damage a collimator at the Large Hadron Collider (LHC) or its High-Luminosity upgrade (HL-LHC). One such rotatable collimator prototype was designed and built at SLAC and delivered to CERN for tests with LHC-type circulating beams in the Super Proton Synchrotron (SPS). This was followed by destructive tests at the dedicated High Radiation to Materials (HiRadMat) facility to validate the design and rotation functionality. An overview of the collimator design, together with results from tests without and with beam are presented
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
Pulse shape analysis in Gerda Phase II
The GERmanium Detector Array (Gerda) collaboration searched for neutrinoless double- decay in Ge using isotopically enriched high purity germanium detectors at the Laboratori Nazionali del Gran Sasso of INFN. After Phase I (2011–2013), the experiment benefited from several upgrades, including an additional active veto based on LAr instrumentation and a significant increase of mass by point-contact germanium detectors that improved the half-life sensitivity of Phase II (2015–2019) by an order of magnitude. At the core of the background mitigation strategy, the analysis of the time profile of individual pulses provides a powerful topological discrimination of signal-like and background-like events. Data from regular Th calibrations and physics data were both considered in the evaluation of the pulse shape discrimination performance. In this work, we describe the various methods applied to the data collected in Gerda Phase II corresponding to an exposure of 103.7 kg year. These methods suppress the background by a factor of about 5 in the region of interest around  keV, while preserving % of the signal. In addition, an exhaustive list of parameters is provided which were used in the final data analysis
Search for tri-nucleon decays of Ge76 in GERDA
We search for tri-nucleon decays of Ge in the dataset from the GERmanium Detector Array (GERDA) experiment. Decays that populate excited levels of the daughter nucleus above the threshold for particle emission lead to disintegration and are not considered. The ppp-, ppn-, and pnn-decays lead to Cu, Zn, and Ga nuclei, respectively. These nuclei are unstable and eventually proceed by the beta decay of Ga to Ge (stable). We search for the Ga decay exploiting the fact that it dominantly populates the 66.7 keV Ga state with half-life of 0.5 s. The nnn-decays of Ge that proceed via Ge are also included in our analysis. We find no signal candidate and place a limit on the sum of the decay widths of the inclusive tri-nucleon decays that corresponds to a lower lifetime limit of 1.210 yr  (90% credible interval). This result improves previous limits for tri-nucleon decays by one to three orders of magnitude
Machine layout and performance
The Large Hadron Collider (LHC) is one of the largest scientific instruments ever built. Since opening up a new
energy frontier for exploration in 2010, it has gathered a global user community of about 7,000 scientists working
in fundamental particle physics and the physics of hadronic matter at extreme temperature and density. To sustain
and extend its discovery potential, the LHC will need a major upgrade in the 2020s. This will increase its luminosity
(rate of collisions) by a factor of five beyond the original design value and the integrated luminosity (total
collisions created) by a factor ten. The LHC is already a highly complex and exquisitely optimised machine so this
upgrade must be carefully conceived and will require about ten years to implement. The new configuration, known
as High Luminosity LHC (HL-LHC), will rely on a number of key innovations that push accelerator technology
beyond its present limits. Among these are cutting-edge 11-12 tesla superconducting magnets, compact superconducting
cavities for beam rotation with ultra-precise phase control, new technology and physical processes
for beam collimation and 300 metre-long high-power superconducting links with negligible energy dissipation.
The present document describes the technologies and components that will be used to realise the project and is
intended to serve as the basis for the detailed engineering design of HL-LHC
Calibration of the Gerda experiment
The GERmanium Detector Array (Gerda) collaboration searched for neutrinoless double-β decay in 76Ge with an array of about 40 high-purity isotopically-enriched germanium detectors. The experimental signature of the decay is a monoenergetic signal at Qββ= 2039.061 (7) keV in the measured summed energy spectrum of the two emitted electrons. Both the energy reconstruction and resolution of the germanium detectors are crucial to separate a potential signal from various backgrounds, such as neutrino-accompanied double-β decays allowed by the Standard Model. The energy resolution and stability were determined and monitored as a function of time using data from regular 228Th calibrations. In this work, we describe the calibration process and associated data analysis of the full Gerda dataset, tailored to preserve the excellent resolution of the individual germanium detectors when combining data over several years
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