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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 847 records · Page 47
All sourcesNASA NTRSDOE OSTI
DOE OSTI2011

Commissioning of Photon Beams of a Flattening Filter-Free Linear Accelerator and the Accuracy of Beam Modeling Using an Anisotropic Analytical Algorithm;TrueBeam; Flattening filter free; Commissioning; Anisotropic analytical algorithm

Purpose: To investigate dosimetric characteristics of a new linear accelerator designed to deliver flattened, as well as flattening filter-free (FFF), beams. To evaluate the accuracy of beam modeling under physical conditions using an anisotropic analytical algorithm. Methods and Materials: Dosimetric data including depth dose curves, profiles, surface dose, penumbra, out-of-field dose, output, total and scatter factors were examined for four beams (X6, X6FFF, X10, and X10FFF) of Varian's TrueBeam machine. Beams modeled by anisotropic analytical algorithm were compared with measured dataset. Results: FFF beams have lower mean energy (tissue-phantom ratio at the depths of 20 and 10 cm (TPR 20/10): X6, 0.667; X6FFF, 0.631; X10, 0.738; X10FFF, 0.692); maximum dose is located closer to the surface; and surface dose increases by 10%. FFF profiles have sharper but faster diverging penumbra. For small fields and shallow depths, dose outside a field is lower for FFF beams; however, the advantage fades with increasing phantom scatter. Output increases 2.26 times for X6FFF and 4.03 times for X10FFF and is less variable with field size; collimator exchange effect is reduced. A good agreement between modeled and measured data is observed. Criteria of 2% depth-dose and 2-mm distance-to-agreement are always met. Conclusion: Reference dosimetric characteristics of TrueBeam photon bundles were obtained, and successful modeling of the beams was achieved.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2015

Future beam experiments in the magnetosphere with plasma contactors: How do we get the charge off the spacecraft?

Abstract The idea of using a high‐voltage electron beam with substantial current to actively probe magnetic field line connectivity in space has been discussed since the 1970s. However, its experimental realization onboard a magnetospheric spacecraft has never been accomplished because the tenuous magnetospheric plasma cannot provide the return current necessary to keep spacecraft charging under control. In this work, we perform Particle‐In‐Cell simulations to investigate the conditions under which a high‐voltage electron beam can be emitted from a spacecraft and explore solutions that can mitigate spacecraft charging. The electron beam cannot simply be compensated for by an ion beam of equal current, because the Child‐Langmuir space charge limit is violated under conditions of interest. On the other hand, releasing a high‐density neutral contactor plasma prior and during beam emission is critical in aiding beam emission. We show that after an initial transient controlled by the size of the contactor cloud where the spacecraft potential rises, the spacecraft potential can settle into conditions that allow for electron beam emission. A physical explanation of this result in terms of ion emission into spherical geometry from the surface of the plasma cloud is presented, together with scaling laws of the peak spacecraft potential varying the ion mass and beam current. These results suggest that a strategy where the contactor plasma and the electron beam operate simultaneously might offer a pathway to perform beam experiments in the magnetosphere.

Delzanno, G. L.↗
DOE OSTI2011

Uniform Beam Distributions Of Charged Particle Beams

The use of octupole elements was originally suggested [1] to transform the transverse Gaussian distribution of a charged particle beam into a uniform beam distribution having rectangular cross section. The first experimental realization of this concept was materialized at the Radiation Effects Facility (REF) of the Brookhaven National Laboratory (BNL)[2] where the transverse Gaussian distribution of a 200 MeV H{sup -} beam was transformed into a rectangular uniform distribution. Later, the beam line of the NASA Space Radiation Laboratory (NSRL) facility [3,4] built at BNL, was specifically designed to generate uniform beam distributions with rectangular cross sections, in both, the horizontal and vertical directions, at the location of the target. The NSRL facility generates uniform beam distributions of various nuclear species, which may vary in energy, and also vary in size of the uniform beam distribution. We will present an overview of the method to generate uniform beam distributions, show some results from the NSRL facility, and suggest other possibilities for generating such beam distributions.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2016

Measurement of the branching ratios for the standard model Higgs decays into muon pairs and into Z boson pairs at a 1.4 TeV CLIC

The measurement of the Higgs production cross-section times the branching ratios for its decays into μ{sup +}μ{sup −} and ZZ* pairs at a 1.4 TeV CLIC collider is investigated in this paper. The Standard Model Higgs boson with a mass of 126 GeV is dominantly produced via WW fusion in e{sup +}e{sup −} collisions at 1.4 TeV centre-of-mass energy. Analyses of both decay channels are based on a full simulation of the CLIC-ILD detector. All relevant physics and beam-induced background processes are taken into account. An integrated luminosity of 1.5 ab{sup −1} and unpolarised beams are assumed. For the H→ZZ* decay, the purely hadronic final state (ZZ* → qq̄qq̄) is considered as well as ZZ* decays into two jets and two leptons (ZZ* → qql{sup +}l{sup −}). It is shown that the branching ratio for the Higgs decay into a muon pair times the Higgs production cross-section can be measured with 38% statistical uncertainty. It is also shown that the statistical uncertainty of the Higgs branching ratio for decay into a Z boson pair times the Higgs production cross-section can be measured with a precision of 18.3% and 5.6% for the hadronic and semi-leptonic ZZ* decays, respectively.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Three dimensional analysis of longitudinal plasma oscillations in a thermal relativistic electron beam

In this paper, we develop a three-dimensional kinetic theory of longitudinal plasma oscillations in a relativistic electron beam. Our analysis includes the effects of betatron motion, finite emittance, and energy spread as well as edge effects due to the finite size of the beam. The consequences of these effects are shown to be of significant interest, as they give rise to several distinct new phenomena. These include an emittance induced anisotropy between backward and forward propagating plasma waves as well as a beatwave effect between plasma and betatron oscillations caused by the coupling of betatron motion to the transverse structure of the charge perturbation. The experimental implications of these new results and their relevance to the beam and radiation physics of advanced light sources, such as free-electron lasers, are also discussed.

43 PARTICLE ACCELERATORS↗
DOE OSTI2016

WE-AB-207A-01: BEST IN PHYSICS (IMAGING): High-Resolution Cone-Beam CT of the Extremities and Cancellous Bone Architecture with a CMOS Detector

Purpose: Extremity cone-beam CT (CBCT) with an amorphous silicon (aSi) flat-panel detector (FPD) provides low-dose volumetric imaging with high spatial resolution. We investigate the performance of the newer complementary metal-oxide semiconductor (CMOS) detectors to enhance resolution of extremities CBCT to ∼0.1 mm, enabling morphological analysis of trabecular bone. Quantitative in-vivo imaging of bone microarchitecture could present an important advance for osteoporosis and osteoarthritis diagnosis and therapy assessment. Methods: Cascaded systems models of CMOS- and FPD-based extremities CBCT were implemented. Performance was compared for a range of pixel sizes (0.05–0.4 mm), focal spot sizes (0.3–0.6 FS), and x-ray techniques (0.05–0.8 mAs/projection) using detectability of high-, low-, and all-frequency tasks for a nonprewhitening observer. Test-bench implementation of CMOS-based extremity CBCT involved a Teledyne DALSA Xineos3030HR detector with 0.099 mm pixels and a compact rotating anode x-ray source with 0.3 FS (IMD RTM37). Metrics of bone morphology obtained using CMOS-based CBCT were compared in cadaveric specimens to FPD-based system using a Varian PaxScan4030 (0.194 mm pixels). Results: Finer pixel size and reduced electronic noise for CMOS (136 e compared to 2000 e for FPD) resulted in ∼1.9× increase in detectability for high-frequency tasks and ∼1.1× increase for all-frequency tasks. Incorporation of the new x-ray source with reduced focal spot size (0.3 FS vs. 0.5 FS used on current extremities CBCT) improved detectability for CMOS-based CBCT by ∼1.7× for high-frequency tasks. Compared to FPD CBCT, the CMOS detector yielded improved agreement with micro-CT in measurements of trabecular thickness (∼1.7× reduction in relative error), bone volume (∼1.5× reduction), and trabecular spacing (∼3.5× reduction). Conclusion: Imaging performance modelling and experimentation indicate substantial improvements for high-frequency imaging tasks through adoption of the CMOS detector and small FS x-ray source, motivating the use of these components in a new system for quantitative in-vivo imaging of trabecular bone. Financial Support: US NIH grant R01EB018896. Qian Cao is a Howard Hughes Medical Institute International Student Research Fellow. Disclosures: W Zbijewski, J Siewerdsen and A Sisniega receive research funding from Carestream Health.

60 APPLIED LIFE SCIENCES↗
NASA NTRS1974

Physical conditions for conducting radiobiological experiments in beams of accelerated particles with high linear energy transfer

The design and construction of an accelerator to conduct radiobiological experiments is reported that uses aluminum filters to control the accelerated ion beam while preserving its stability, and a vacuum chamber to conduct the ion beam with the help of a collector through a lavsan exit port to the target. Depth distribution of the absorbed dose from a monodirectional ion beam is practically completely represented by the change in the energy spectrum of the biological object.

Kudryashov, Y. I.↗
DOE OSTI2019

Multi-stream instability of a single long electron bunch in a storage ring

A multistream instability is observed experimentally during the longitudinal expansion of an electron beam in a storage ring. The instability is observed when the beam expands in length to several times the circumference of the ring so that portions of the beam overlap. While portions of the beam overlap in physical space, they form multiple streams and remain separate in velocity space. The streams become unstable as their number increases and their separation in velocity decreases. An analytical theory predicts the onset of the instability, in agreement with simulations and measurements, over a wide range of peak line-charge densities (10.3 pC/m–1.8 nC/m) and bunch lengths. Finally, this work extends previous calculations to include the dynamic nonlinear elongation of the bunch, with a given initial length, and defines an onset criterion for the filament velocity separation for the beam to be unstable.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Conceptual Design Report -- eSPS

The design of a primary electron beam facility at CERN is described. It re-enables the SPS as an electron accelerator, and leverages the development invested in CLIC technology for its injector and as accelerator R&D infrastructure. The facility would be relevant for several of the key priorities in the 2020 update of the European Strategy for Particle Physics, such as an electron-positron(e-p) Higgs factory, accelerator R&D, dark sector physics, and neutrino physics. In addition, it could serve experiments in nuclear physics. The electron beam delivered by this facility would provide access to light dark matter production significantly beyond the targets predicted by a thermal dark matter origin, and for natures of dark matter particles that are not accessible by direct detection experiments. It would also enable electro-nuclear measurements crucial for precise modelling the energy dependence of neutrino-nucleus interactions, which is needed to precisely measure neutrino oscillations as a function of energy. The implementation of the facility is the natural next step in the development of X-band high-gradient acceleration technology, a key technology for compact and cost-effective electron/positron linacs. It would also become the only facility with multi-GeV drive bunches and truly independent electron witness bunches for plasma wakefield acceleration. The facility would be used for the development and studies of a large number of components and phenomena for a future e-p Higgs and electroweak factory as the first stage of a next circular collider at CERN, and its cavities in the SPS would be the same type as foreseen for such a future collider. The operation of the SPS with electrons would train a new generation of scientists. The facility could be made operational in about five years and would operate in parallel and without interference with Run 4 at the LHC.

43 PARTICLE ACCELERATORS↗
DOE OSTI2014

New light weakly-coupled particle searches in a neutrino detector

Neutrino detectors at the accelerator machines of the Intensity Frontier in particle physics are becoming commonplace. As their capabilities are being understood, they seem to have the potential for studies beyond the neutrino oscillations measurements. Besides these primary neutrino physics goals, a number of exotic searches can be done with such detectors in general, and the NOvA detectors that we present here, as a particular example. Specifically, we focus on simulating signatures in NOvA experiment's Near-Detector (300 ton, 900 m from the NuMI target of Fermilab) that correspond to beam-generated new physics states from hidden sectors, dark sectors, axion-like particles, heavy or sterile neutrinos, and heavy photons. As there are no physics generators that can inherently include such states, along with the mainstream production branches, we present here the initial stages of an effort to incorporate these signatures manually in the overall simulation framework of the NOvA experiment. For this, we discuss examples and examine the potential and challenges for detecting such signatures.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2019

Preparation for the Beam Energy Scan II at RHIC in 2020

RHIC will provide Au-Au collisions at beam energies of 5.75, 4.59 GeV/nucleon for physics program in 2020, and at beam energy of 3.85 GeV/nucleon for physics program in 2021 as part of the BeamEnergy Scan II (BES-II). The oper- ational experience gained in the first year (2019) of BES-II operation will be applied toward operations in the coming years. This article will present some technical details and the outlook of the BES-II operations in the coming years.

43 PARTICLE ACCELERATORS↗
DOE OSTI2013

High intensity neutrino oscillation facilities in Europe

The EUROnu project has studied three possible options for future, high intensity neutrino oscillation facilities in Europe. The first is a Super Beam, in which the neutrinos come from the decay of pions created by bombarding targets with a 4 MW proton beam from the CERN High Power Superconducting Proton Linac. The far detector for this facility is the 500 kt MEMPHYS water Cherenkov, located in the Fréjus tunnel. The second facility is the Neutrino Factory, in which the neutrinos come from the decay of μ + and μ – beams in a storage ring. The far detector in this case is a 100 kt magnetized iron neutrino detector at a baseline of 2000 km. The third option is a Beta Beam, in which the neutrinos come from the decay of beta emitting isotopes, in particular 6 He and 18 Ne, also stored in a ring. The far detector is also the MEMPHYS detector in the Fréjus tunnel. EUROnu has undertaken conceptual designs of these facilities and studied the performance of the detectors. Based on this, it has determined the physics reach of each facility, in particular for the measurement of CP violation in the lepton sector, and estimated the cost of construction. These have demonstrated that the best facility to build is the Neutrino Factory. Furthermore, if a powerful proton driver is constructed for another purpose or if the MEMPHYS detector is built for astroparticle physics, the Super Beam also becomes very attractive.

43 PARTICLE ACCELERATORS↗
DOE OSTI2021

Dimensionality-Induced Change in Topological Order in Multiferroic Oxide Superlattices

We construct ferroelectric (LuFeO 3 ) m /(LuFe 2 O 4 ) superlattices with varying index m to study the effect of confinement on topological defects. We observe a thickness-dependent transition from neutral to charged domain walls and the emergence of fractional vortices. In thin LuFeO 3 layers, the volume fraction of domain walls grows, lowering the symmetry from P6 3 cm to P3c1 before reaching the nonpolar P6 3 /mmc state, analogous to the group-subgroup sequence observed at the high-temperature ferroelectric to paraelectric transition. Our study shows how dimensional confinement stabilizes textures beyond those in bulk ferroelectric systems.

36 MATERIALS SCIENCE↗