Engineering topics

Tomas, R.

Publications and source records attributed to Tomas, R..

4 records

DOE OSTI2024

Impact of beam–beam effects on absolute luminosity calibrations at the CERN Large Hadron Collider

At the Large Hadron Collider (LHC), absolute luminosity calibrations obtained by the van der Meer (vdM) method are affected by the mutual electromagnetic interaction of the two beams. The colliding bunches experience relative orbit shifts, as well as optical distortions akin to the dynamic-β effect, that both depend on the transverse beam separation and must therefore be corrected for when deriving the absolute luminosity scale. In the vdM regime, the beam–beam parameter is small enough that the orbit shift can be calculated analytically. The dynamic-β corrections to the luminometer calibrations, however, had until the end of Run 2 been estimated in the linear approximation only. In this report, the influence of beam–beam effects on the vdM-based luminosity scale is quantified, together with the associated systematic uncertainties, by means of simulations that fully take into account the non-linearity of the beam–beam force, as well as the resulting non-Gaussian distortions of the transverse beam distributions. Two independent multiparticle simulations, one limited to the weak-strong approximation and one that models strong-strong effects in a self-consistent manner, are found in excellent agreement; both predict a percent-level shift of the absolute pp-luminosity values with respect to those assumed until recently in the physics publications of the LHC experiments. These results also provide guidance regarding further studies aimed at reducing the beam–beam-related systematic uncertainty on beam–beam corrections to absolute luminosity calibrations by the van der Meer method.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2021

Nonlinear Optics Measurements in IOTA

Nonlinear integrable optics is a recently proposed accelerator lattice design approach which allows to generate an amplitude dependent tune shift which is needed in high brightness accelerators to mitigate fast coherent instabilities. Whereas usually octupoles are used to achieve this task, this concept allows doing so without exciting any resonances, in turn preventing any particle loss. The concept is based around a special magnet design, together with specific constraints on the optics of the accelerator. To study such a system, the Integrable Optics Test Accelerator (IOTA) was recently constructed and commissioned at Fermilab. For the assessment of the performance of this concept, good knowledge of the optics and the (non-)linear dynamics without the special magnet is of key importance. As such, measurements were conducted in the IOTA ring, using the captured turn-by-turn data by the beam position monitors after excitation to infer quantities such as amplitude detuning and resonance driving terms. In this note, first results of these measurements are presented.

43 PARTICLE ACCELERATORS↗

NASA NTRS2019

Volcanic Eruption Signatures in the Isotope Enabled Last Millennium Ensemble

Explosive volcanic eruptions are one of the largest natural climate perturbations, but few observational constraints exist on either the climate responses to eruptions or the properties (size, hemispheric aerosol distribution, etc.) of the eruptions themselves. Paleoclimate records are thus important sources of information on past eruptions, often through the measurement of oxygen isotopic ratios (𝛿18O) in natural archives. However, since many processes affect 𝛿18O, the dynamical interpretation of these records can be quite complex. Here we present results from new, isotope-enabled members of the Community Earth System Model Last Millennium Ensemble, documenting eruption-induced 𝛿18O variations throughout the climate system. Eruptions create significant perturbations in the 𝛿18O of precipitation and soil moisture in central/eastern North America, via excitation of the Atlantic Multidecadal Oscillation. Monsoon Asia and Australia also exhibit strong precipitation and soil 𝛿18O anomalies; in these cases, 𝛿18O may reflect changes to El Niño-Southern Oscillation phase following eruptions. Salinity and seawater 𝛿18O patterns demonstrate the importance of both local hydrologic shifts and the phasing of the El Niño-Southern Oscillation response, both along the equator and in the subtropics. In all cases, the responses are highly sensitive to eruption latitude, which points to the utility of isotopic records in constraining aerosol distribution patterns associated with past eruptions. This is most effective using precipitation 𝛿18O; all Southern eruptions and the majority (66%) of Northern eruptions can be correctly identified. This work thus serves as a starting point for new, quantitative uses of isotopic records for understanding volcanic impacts on climate.

Stevenson, S.↗

NASA NTRS2019

The Connected Isotopic Water Cycle in the Community Earth System Model Version 1

Because of the pervasive role of water in the Earth system, the relative abundances of stable isotopologues of water are valuable for understanding atmospheric, oceanic, and biospheric processes, and for interpreting paleoclimate proxy reconstructions. Isotopologues are transported by both largescale and turbulent flows, and the ratio of heavy to light isotopologues changes due to fractionation that can accompany condensation and evaporation processes. Correctly predicting the isotopic distributions requires resolving the relationships between largescale ocean and atmospheric circulation and smallerscale hydrological processes, which can be accomplished within a coupled climate modeling framework. Here we present the water isotopeenabled version of the Community Earth System Model version 1 (iCESM1), which simulates global variations in water isotopic ratios in the atmosphere, land, ocean, and sea ice. In a transient Last Millennium simulation covering the 850-2005 period, iCESM1 correctly captures the latetwentiethcentury structure of δ(exp 18)O and δD over the global oceans, with more limited accuracy over land. The relationship between salinity and seawater δ(exp 18)O is also well represented over the observational period, including interbasin variations. We illustrate the utility of coupled, isotopeenabled simulations using both Last Millennium simulations and freshwater hosing experiments with iCESM1. Closing the isotopic mass balance between all components of the coupled model provides new confidence in the underlying depiction of the water cycle in CESM, while also highlighting areas where the underlying hydrologic balance can be improved. The iCESM1 is poised to be a vital community resource for ongoing model development with both modern and paleoclimate applications.

Brady, E.↗