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At least 1,081 records · Page 60
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Performance of the CMS muon trigger system in proton-proton collisions at $\sqrt{s} =$ 13 TeV

The muon trigger system of the CMS experiment uses a combination of hardware and software to identify events containing a muon. During Run 2 (covering 2015-2018) the LHC achieved instantaneous luminosities as high as 2 $\times$ 10$^{34}$cm$^{-2}$s$^{-1}$ while delivering proton-proton collisions at $\sqrt{s} =$ 13 TeV. The challenge for the trigger system of the CMS experiment is to reduce the registered event rate from about 40 MHz to about 1 kHz. Significant improvements important for the success of the CMS physics program have been made to the muon trigger system via improved muon reconstruction and identification algorithms since the end of Run 1 and throughout the Run 2 data-taking period. The new algorithms maintain the acceptance of the muon triggers at the same or even lower rate throughout the data-taking period despite the increasing number of additional proton-proton interactions in each LHC bunch crossing. In this paper, the algorithms used in 2015 and 2016 and their improvements throughout 2017 and 2018 are described. Measurements of the CMS muon trigger performance for this data-taking period are presented, including efficiencies, transverse momentum resolution, trigger rates, and the purity of the selected muon sample. This paper focuses on the single- and double-muon triggers with the lowest sustainable transverse momentum thresholds used by CMS. The efficiency is measured in a transverse momentum range from 8 to several hundred GeV.

Trigger detectors↗
DOE OSTI2016

Off-equilibrium sphaleron transitions in the Glasma

We perform the first, to our knowledge, classical-statistical real time lattice simulations of topological transitions in the nonequilibrium glasma of weakly coupled but highly occupied gauge fields created immediately after the collision of ultrarelativistic nuclei. Simplifying our description by employing SU(2) gauge fields, and neglecting their longitudinal expansion, we find that the rate of topological transitions is initially strongly enhanced relative to the thermal sphaleron transition rate and decays with time during the thermalization process. Qualitative features of the time dependence of this nonequilibrium transition rate can be understood when expressed in terms of the magnetic screening length, which we also extract nonperturbatively. Furthermore, a detailed investigation of auto-correlation functions of the Chern-Simons number (N CS ) reveals non-Markovian features of the evolution distinct from previous simulations of non-Abelian plasmas in thermal equilibrium.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2024

Combination of Searches for Higgs Boson Pair Production in pp Collisions at $\sqrt{s}$ = 13 TeV with the ATLAS Detector

This Letter presents results from a combination of searches for Higgs boson pair production using 126–140 fb−1 of proton-proton collision data at √𝑠 =13 TeV recorded with the ATLAS detector. At 95% confidence level (CL), the upper limit on the production rate is 2.9 times the standard model (SM) prediction, with an expected limit of 2.4 assuming no Higgs boson pair production. Constraints on the Higgs boson self-coupling modifier 𝜅 𝜆 = 𝜆 𝐻⁡𝐻⁡𝐻 /𝜆$^{SM}_{𝐻⁡𝐻⁡𝐻}$, and the quartic 𝐻⁡𝐻⁡𝑉⁢𝑉 coupling modifier 𝜅 2⁢𝑉 = 𝑔 𝐻⁡𝐻⁡𝑉⁢𝑉⁡ /𝑔$^{SM}_{𝐻⁡𝐻⁡𝑉⁢𝑉}$, are derived individually, fixing the other parameter to its SM value. The observed 95% CL intervals are −1.2<𝜅 𝜆 < 7.2 and 0.6<𝜅 2⁢𝑉 < 1.5, respectively, while the expected intervals are −1.6<𝜅 𝜆 < 7.2 and 0.4<𝜅 2⁢𝑉 < 1.6 in the SM case. Constraints obtained for several interaction parameters within Higgs effective field theory are the strongest to date, offering insights into potential deviations from SM predictions.

Hadron colliders↗
DOE OSTI2021

Observation of microwave shielding of ultracold molecules

Harnessing the potential wide-ranging quantum science applications of molecules will require control of their interactions. Here, we used microwave radiation to directly engineer and tune the interaction potentials between ultracold calcium monofluoride (CaF) molecules. By merging two optical tweezers, each containing a single molecule, we probed collisions in three dimensions. The correct combination of microwave frequency and power created an effective repulsive shield, which suppressed the inelastic loss rate by a factor of six, in agreement with theoretical calculations. The demonstrated microwave shielding shows a general route to the creation of long-lived, dense samples of ultracold polar molecules and evaporative cooling.

Anderegg, Loïc↗
DOE OSTI2017

Study of runaway electrons using the conditional average sampling method in the Damavand tokamak

Some experiments for studying the runaway electron (RE) effects have been performed using the poloidal magnetic probes system installed around the plasma column in the Damavand tokamak. In these experiments, the so-called runaway-dominated discharges were considered in which the main part of the plasma current is carried by REs. The induced magnetic effects on the poloidal pickup coils signals are observed simultaneously with the Parail–Pogutse instability moments for REs and hard X-ray bursts. The output signals of all diagnostic systems enter the data acquisition system with 2 Msample/(s channel) sampling rate. The temporal evolution of the diagnostic signals is analyzed by the conditional average sampling (CAS) technique. The CASed profiles indicate RE collisions with the high-field-side plasma facing components at the instability moments. The investigation has been carried out for two discharge modes—low-toroidal-field (LTF) and high-toroidal-field (HTF) ones—related to both up and down limits of the toroidal magnetic field in the Damavand tokamak and their comparison has shown that the RE confinement is better in HTF discharges.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

Electron Ion Collider Strong Hadron Cooling Injector and ERL

Intra-beam Scattering (IBS) and other diffusion mechanisms in the EIC Hadron Storage Ring (HSR) degrade the beam emittances during a store, with growth times of about 2 hours at the nominal proton energies of 275GeV, 100 GeV, and 41 GeV. Strong Hadron Cooling (SHC) can maintain good hadron beam quality and high luminosity during long collision stores. A novel cooling method ’ Coherent electron Cooling (CeC) ’ is chosen as the baseline SHC method, due to its high cooling rates. An Energy Recovery Linac (ERL) is used to deliver an intense high-quality electron beam for cooling. In this paper, we discuss the beam requirements for SHC-CeC and describe the current status of the injector and ERL designs. Two designs of injector and ERL will be presented: one for dedicated SHC and another one for SHC with precooler.

Wang, E.↗
DOE OSTI2018

Star Formation Rate Distribution in the Galaxy NGC 1232

NGC 1232 is a face-on spiral galaxy and a great laboratory for the study of star formation due to its proximity. We obtained high spatial resolution Hα images of this galaxy, with adaptive optics, using the SAM instrument at the SOAR telescope, and used these images to study its H ii regions. These observations allowed us to produce the most complete H ii region catalog for it to date, with a total of 976 sources. This doubles the number of H ii regions previously found for this object. We used these data to construct the H ii luminosity function, and obtained a power-law index lower than the typical values found for Sc galaxies. This shallower slope is related to the presence of a significant number of high-luminosity H ii regions (log L > 39 dex). We also constructed the size distribution function, verifying that, as for most galaxies, NGC 1232 follows an exponential law. We also used the Hα luminosity to calculate the star formation rate. An extremely interesting fact about this galaxy is that X-ray diffuse observations suggest that NGC 1232 recently suffered a collision with a dwarf galaxy. We found an absence of star formation around the region where the X-ray emission is more intense, which we interpret as a star formation quenching due to the collision. Along with that, we found an excess of star-forming regions in the northeast part of the galaxy, where the X-ray emission is less intense.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

The Effect of Spatially Varying Collision Frequency on the Development of the Rayleigh–Taylor Instability

Abstract The Rayleigh–Taylor (RT) instability is ubiquitously observed, yet has traditionally been studied using ideal fluid models. Collisionality can vary strongly across the fluid interface, and previous work demonstrates the necessity of kinetic models to completely capture dynamics in certain collisional regimes. Where previous kinetic simulations used spatially and temporally constant collision frequency, this work presents five-dimensional (two spatial, three velocity dimensions) continuum-kinetic simulations of the RT instability using a more realistic spatially varying collision frequency. Three cases of collisional variation are explored for two Atwood numbers: low to intermediate, intermediate to high, and low to high. The low-to-intermediate case exhibits no RT instability growth, while the intermediate-to-high case is similar to a fluid-limit kinetic case with interface widening biased toward the lower-collisionality region. A novel contribution of this work is the low-to-high collisionality case that shows significantly altered instability growth through an upward movement of the interface and damped spike growth due to increased free-streaming particle diffusion in the lower region. Contributions to the energy flux from the non-Maxwellian portions of the distribution function are not accessible to fluid models and are greatest in magnitude in the spike and regions of low collisionality. Increasing the Atwood number results in greater RT instability growth and reduced upward interface movement. Deviation of the distribution function from Maxwellian is inversely proportional to collision frequency and concentrated around the fluid interface. The linear phase of RT instability growth is well described by theoretical linear growth rates accounting for viscosity and diffusion.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1989

Angular motion of a PAH molecule in interstellar environment

Polycyclic aromatic hydrocarbon (PAH) molecules have recently been proposed as an important and hitherto undetected component of the Interstellar Medium (ISM). The theory was based on an explanation of the Unidentified IR Emission Bands by Leger et al. It has already led to a verified prediction on extended galactic and extragalactic emissions measured by IRAS, or by a recent balloon borne experiment. The physics that rules the motion of such molecules in the ISM was studied, taking into account their coupling with the ambient gas, the radiation field (absorption and emission) and the static magnetic field. This is important for many implications of the PAH theory such as the radio emission by these molecules or the expected polarization of their IR emission. A reflection nebulae is considered where the situation is rather well known. Every day life of a mean PAH molecule in such a region is as follows: every 3 hrs a UV photon is absorbed heating the molecule to a thousand degs; the temperature decay due to cooling by IR emission follows then within a few seconds. A collision with a molecule of gas occurs typically once a week, while an H atom is ejected or captured at the same rate. A typical cooling cycle after a heat impulse is given. The PAH molecules studied as representative of the family has typically 50 atoms, a radius of 4.5 A, is circular and has a molecular mass of M = 300; its permanent dipole moment is 3 Debye.

Rouan, D.↗
DOE OSTI2013

Study of collisional deactivation of O{sub 2}(b{sup 1}{Sigma}{sub g}{sup +}) molecules in a hydrogen-oxygen mixture at high temperatures using laser-induced gratings

Collisional deactivation of O{sub 2}(b{sup 1}{Sigma}{sub g}{sup +}) molecules resonantly excited by a 10 ns pulse of laser radiation with a wavelength of 762 nm in H{sub 2}/O{sub 2} mixtures is experimentally studied. The radiation intensity and hence the molecule excitation efficiency have a spatially periodic modulation that leads to the formation of laser-induced gratings (LIGs) of the refractive index. The study of LIG temporal evolution allows collisional relaxation rates of molecular excited states and gas temperature to be determined. In this work, the b{sup 1}{Sigma}{sub g}{sup +} state of O{sub 2} molecules deactivation rates are measured in a 4.3 vol % H{sub 2} mixture at the number density of 2 amg in the temperature range 291-850 K. The physical deactivation is shown to dominate in the collisions of H{sub 2} with O{sub 2}(b{sup 1}{Sigma}{sub g}{sup +}) and O{sub 2}(a{sup 1}{Delta}{sub g}) up to temperatures of 780-790 K at time delays up to 10 {mu}s after the excitation pulse. The parameters of the obtained temperature dependence of the (b{sup 1}{Sigma}{sub g}{sup +} state deactivation rate agree well with the data of independent measurements performed earlier at lower temperatures (200-400 K). Tunable diode laser absorption spectroscopy is used to measure the temperature dependence of the number density of the H{sub 2}O molecules which appear as the mixture, as the result of the dark gross reaction with O{sub 2} molecules in the ground state, O{sub 2} + 2H{sub 2} {yields} 2H{sub 2}O. The measurements show that this reaction results in complete transformation of H{sub 2} into H{sub 2}O at temperatures of 790-810 K.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2013

Quenching of krypton atoms in the metastable 5s ({sup 3}P{sub 2}) state in collisions with krypton and helium atoms

We have used the absorption probe method to study the processes of collisional quenching of the metastable 5s [3/2]{sup o}{sub 2}({sup 3}P{sub 2}) state of the krypton atom in electron-beam-excited high-pressure He – Kr mixtures with a low content of krypton. The rate constants of plasma-chemical reactions Kr* + Kr + He → Kr*{sub 2}+He [(2.88 ± 0.29) × 10{sup -33} cm{sup 6} s{sup -1}], Kr* + 2He → HeKr* + He [(4.6 ± 1.3) × 10{sup -36} cm{sup 6} s{sup -1}] and Kr* + He → products + He [(1.51 ± 0.15) × 10{sup -15} cm{sup 3} s{sup -1}] are measured for the first time. The rate constants of similar reactions in the Ar – Kr mixture are refined. (active media)

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2013

Poloidal flow damping inside transport barriers in a tokamak

The poloidal flow in a tokamak is damped by collisions. Thus, the poloidal damping can be described by the neoclassical theory. The effective poloidal Mach number, M{sub p}, can be of the order of one or higher inside transport barriers in a tokamak. It is found that the poloidal damping rate decreases exponentially as the effective poloidal Mach number increases. The poloidal damping rate is reduced by one order of magnitude in the presence of sonic M{sub p}. We also found that the ion plasma viscosity becomes negligible compared with the electron plasma viscosity when M{sub p}>1.5. In this case, the poloidal flow is damped by electron collisions rather than ion collisions.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

A test of star formation laws in disk galaxies. II. Dependence on dynamical properties

We use the observed radial profiles of the mass surface densities of total, Σ {sub g}, and molecular, Σ{sub H2}, gas, rotation velocity, and star formation rate (SFR) surface density, Σ{sub sfr}, of the molecular-rich (Σ{sub H2} ≥ Σ{sub HI}/2) regions of 16 nearby disk galaxies to test several star formation (SF) laws: a 'Kennicutt-Schmidt (K-S)' law, Σ{sub sfr}=A{sub g}Σ{sub g,2}{sup 1.5}; a 'Constant Molecular' law, Σ{sub sfr} = A {sub H2}Σ{sub H2,2}; the turbulence-regulated laws of Krumholz and McKee (KM05) and Krumholz, McKee, and Tumlinson (KMT09); a 'Gas-Ω' law, Σ{sub sfr}=B{sub Ω}Σ{sub g}Ω; and a shear-driven 'giant molecular cloud (GMC) Collision' law, Σ{sub sfr} = B {sub CC}Σ {sub g}Ω(1-0.7β), where β ≡ d ln v {sub circ}/d ln r. If allowed one free normalization parameter for each galaxy, these laws predict the SFR with rms errors of factors of 1.4-1.8. If a single normalization parameter is used by each law for the entire galaxy sample, then rms errors range from factors of 1.5-2.1. Although the Constant Molecular law gives the smallest rms errors, the improvement over the KMT, K-S, and GMC Collision laws is not especially significant, particularly given the different observational inputs that the laws utilize and the scope of included physics, which ranges from empirical relations to detailed treatment of interstellar medium processes. We next search for systematic variation of SF law parameters with local and global galactic dynamical properties of disk shear rate (related to β), rotation speed, and presence of a bar. We demonstrate with high significance that higher shear rates enhance SF efficiency per local orbital time. Such a trend is expected if GMC collisions play an important role in SF, while an opposite trend would be expected if the development of disk gravitational instabilities is the controlling physics.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

A Rate Theory Model of Radiation-Induced Swelling in an Austenitic Stainless Steel

Many rate theory models of cavity (void) swelling have been published over the past 50 years, all having the same, or similar, structures. A rigorous validation of the models has not been possible because of the dearth of information concerning the microstructures that correspond with the swelling data. Whereas the lack of microstructure information is still an issue for historical swelling data, in the past 10–20 years data have been published on the evolution of the microstructure (point defect yields from collision cascades, cavity number densities, and dislocation densities/yield strengths) allowing certain gaps in information to be filled when considering historic swelling data. With reasonable estimates of key microstructure parameters, a standard rate theory model can be applied, and the model parameter space explored, in connection with historical swelling data. By using published data on: (i) yield strength as a function of dose and temperature (to establish an empirical expression for dislocation density evolution); (ii) cavity number densities as a function of temperature; and (iii) freely migrating defect (FMD) production as a function of primary knock-on atom (PKA) spectrum, the necessary parameter and microstructure inputs that were previously unknown can be used in model development. This paper describes a rate-theory model for void swelling of 316 stainless steel irradiated in the EBR-2 reactor as a function of irradiation temperature and neutron dose.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Computational study of collisions between O({sup 3}P) and NO({sup 2}Π) at temperatures relevant to the hypersonic flight regime

Reactions involving N and O atoms dominate the energetics of the reactive air flow around spacecraft when reentering the atmosphere in the hypersonic flight regime. For this reason, the thermal rate coefficients for reactive processes involving O({sup 3}P) and NO({sup 2}Π) are relevant over a wide range of temperatures. For this purpose, a potential energy surface (PES) for the ground state of the NO{sub 2} molecule is constructed based on high-level ab initio calculations. These ab initio energies are represented using the reproducible kernel Hilbert space method and Legendre polynomials. The global PES of NO{sub 2} in the ground state is constructed by smoothly connecting the surfaces of the grids of various channels around the equilibrium NO{sub 2} geometry by a distance-dependent weighting function. The rate coefficients were calculated using Monte Carlo integration. The results indicate that at high temperatures only the lowest A-symmetry PES is relevant. At the highest temperatures investigated (20 000 K), the rate coefficient for the “O1O2+N” channel becomes comparable (to within a factor of around three) to the rate coefficient of the oxygen exchange reaction. A state resolved analysis shows that the smaller the vibrational quantum number of NO in the reactants, the higher the relative translational energy required to open it and conversely with higher vibrational quantum number, less translational energy is required. This is in accordance with Polanyi's rules. However, the oxygen exchange channel (NO2+O1) is accessible at any collision energy. Finally, this work introduces an efficient computational protocol for the investigation of three-atom collisions in general.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Explosive Ice Multiplication Induced by Multiplicative-Noise Fluctuation of Mechanical Breakup in Ice–Ice Collisions

The number of ice fragments generated by breakup of large graupel in collisions with small graupel fluctuates randomly owing to fluctuations in relative sizes and densities of colliding graupel particles and the stochastic nature of fracture propagation. This paper investigates the impact of the stochasticity of breakup on ice multiplication. When both the rate of generation of primary ice and the initial number concentration of ice crystals are low, the system most likely loses all the initial ice and graupel owing to a lack of sustaining sources. Even randomness does not change this mean evolution of the system in its phase space. However, a fluctuation of ice breakup number gives a small but finite chance that substantial ice crystal fragments are generated by breakup of large graupel. That, in turn, generates more large graupel. This multiplicative process due to fluctuations potentially leads to a small but finite chance of explosive growth of ice number.A rigorous stochastic analysis demonstrates this point quantitatively. The randomness considered here belongs to a particular category called ‘‘multiplicative’’ noise, because the noise amplitude is proportional to a given physical state. To contrast the multiplicative-noise nature of ice breakup with a standard ‘‘additive’’ noise process, fluctuation of the primary ice generation rate is also considered as an example of the latter. These processes are examined by taking the Fokker–Planck equation that explicitly describes the evolution of the probability distribution with time. As an important conclusion, stability in the phase space of the cloud microphysical system of breakup in ice–ice collisions is substantially altered by the multiplicative noise.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2025

Electrochemical loading enhances deuterium fusion rates in a metal target

Nuclear fusion research for energy applications aims to create conditions that release more energy than required to initiate the fusion process1. To generate meaningful amounts of energy, fuels such as deuterium need to be spatially confined to increase the collision probability of particles2, 3–4. We therefore set out to investigate whether electrochemically loading a metal lattice with deuterium fuel could increase the probability of nuclear fusion events. Here we report a benchtop fusion reactor that enabled us to bombard a palladium metal target with deuterium ions. These deuterium ions undergo deuterium–deuterium fusion reactions within the palladium metal. We showed that the in situ electrochemical loading of deuterium into the palladium target resulted in a 15(2)% increase in deuterium–deuterium fusion rates. This experiment shows how the electrochemical loading of a metal target at the electronvolt energy scale can affect nuclear reactions at the megaelectronvolt energy scale.

Chen, Kuo-Yi↗
NASA NTRS1996

A Detailed Level Kinetics Model of NO Vibrational Energy Distributions

Several contemporary problems have pointed to the desirability of a detailed level kinetics approach to modeling the distribution of vibrational energy in NO. Such a model is necessary when vibrational redistribution reactions are insufficient to maintain a Boltzmann distribution over the vibrational energy states. Recent calculations of the rate constant for the first reaction of the Zeldovich mechanism (N2 + O (goes to) NO + N) have suggested that the product NO is formed in high vibrational states. In shock layer flowfields, the product NO molecules may experience an insufficient number of collisions to establish a Boltzmann distribution over vibrational states, thus necessitating a level kinetics model. In other flows, such as expansions of high temperature air, fast, near-resonance vibrational energy exchanges with N2 and O2 may also require a level specific model for NO because of the relative rates of vibrational exchange and redistribution. The proposed report will integrate computational and experimental components to construct such a model for the NO molecule.

Sharma, Surendra P.↗