85 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
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
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
Characterization of inverted coaxial Ge detectors in GERDA for future double- decay experiments
Neutrinoless double- decay of Ge is searched for with germanium
detectors where source and detector of the decay are identical. For the success
of future experiments it is important to increase the mass of the detectors. We
report here on the characterization and testing of five prototype detectors
manufactured in inverted coaxial (IC) geometry from material enriched to 88% in
Ge. IC detectors combine the large mass of the traditional semi-coaxial
Ge detectors with the superior resolution and pulse shape discrimination power
of point contact detectors which exhibited so far much lower mass. Their
performance has been found to be satisfactory both when operated in vacuum
cryostat and bare in liquid argon within the GERDA setup. The measured
resolutions at the Q-value for double- decay of Ge
(Q = 2039 keV) are about 2.1 keV full width at half maximum in
vacuum cryostat. After 18 months of operation within the ultra-low background
environment of the GERmanium Detector Array (GERDA) experiment and an
accumulated exposure of 8.5 kgyr, the background index after analysis
cuts is measured to be counts
/(keVkgyr) around Q. This work confirms the
feasibility of IC detectors for the next-generation experiment LEGEND.Comment: 13 pages, 12 figures, submitted to EPJ
Pulse shape analysis in Gerda Phase II
The GERmanium Detector Array (Gerda) collaboration searched for neutrinoless double-β decay in 76Ge 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 228Th 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 Qββ=2039 keV, while preserving (81±3)% of the signal. In addition, an exhaustive list of parameters is provided which were used in the final data analysis
Final Results of GERDA on the Two-Neutrino Double- Decay Half-Life of Ge
We present the measurement of the two-neutrino double- decay rate of
Ge performed with the GERDA Phase II experiment. With a subset of the
entire GERDA exposure, 11.8 kgyr, the half-life of the process has been
determined: yr. This is the most precise determination of the
Ge two-neutrino double- decay half-life and one of the most
precise measurements of a double- decay process. The relevant nuclear
matrix element can be extracted: Comment: 7 pages, 4 figures, 2 table
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