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At least 487 records · Page 27
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Laser spectroscopy of indium Rydberg atom bunches by electric field ionization

This work reports on the application of a novel electric field-ionization setup for high-resolution laser spectroscopy measurements on bunched fast atomic beams in a collinear geometry. In combination with multi-step resonant excitation to Rydberg states using pulsed lasers, the field ionization technique demonstrates increased sensitivity for isotope separation and measurement of atomic parameters over previous non-resonant laser ionization methods. The setup was tested at the Collinear Resonance Ionization Spectroscopy experiment at ISOLDE-CERN to perform high-resolution measurements of transitions in the indium atom from the 5s 2 5d 2 D 5/2 and 5s 2 5d 2 D 3/2 states to 5s 2 np 2 P and 5s 2 nf 2 F Rydberg states, up to a principal quantum number of n=72 . The extracted Rydberg level energies were used to re-evaluate the ionization potential of the indium atom to be 46,670.107(4)cm -1 . The nuclear magnetic dipole and nuclear electric quadrupole hyperfine structure constants and level isotope shifts of the 5s 2 5d 2 D 5/2 and 5s 2 5d 2 D 3/2 states were determined for 113,115 In. The results are compared to calculations using relativistic coupled-cluster theory. A good agreement is found with the ionization potential and isotope shifts, while disagreement of hyperfine structure constants indicates an increased importance of electron correlations in these excited atomic states. With the aim of further increasing the detection sensitivity for measurements on exotic isotopes, a systematic study of the field-ionization arrangement implemented in the work was performed at the same time and an improved design was simulated and is presented. The improved design offers increased background suppression independent of the distance from field ionization to ion detection.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2024

Conditional guided generative diffusion for particle accelerator beam diagnostics

Abstract Advanced accelerator-based light sources such as free electron lasers (FEL) accelerate highly relativistic electron beams to generate incredibly short (10s of femtoseconds) coherent flashes of light for dynamic imaging, whose brightness exceeds that of traditional synchrotron-based light sources by orders of magnitude. FEL operation requires precise control of the shape and energy of the extremely short electron bunches whose characteristics directly translate into the properties of the produced light. Control of short intense beams is difficult due to beam characteristics drifting with time and complex collective effects such as space charge and coherent synchrotron radiation. Detailed diagnostics of beam properties are therefore essential for precise beam control. Such measurements typically rely on a destructive approach based on a combination of a transverse deflecting resonant cavity followed by a dipole magnet in order to measure a beam’s 2D time vs energy longitudinal phase-space distribution. In this paper, we develop a non-invasive virtual diagnostic of an electron beam’s longitudinal phase space at megapixel resolution (1024 × 1024) based on a generative conditional diffusion model. We demonstrate the model’s generative ability on experimental data from the European X-ray FEL.

43 PARTICLE ACCELERATORS↗
DOE OSTI2025

Deployment and validation of predictive 6-dimensional beam diagnostics through generative reconstruction with standard accelerator elements

Understanding the 6-dimensional phase space distribution of particle beams is essential for optimizing accelerator performance. Conventional diagnostics such as use of transverse deflecting cavities offer detailed characterization but require dedicated hardware and space. Generative phase space reconstruction (GPSR) methods have shown promise in beam diagnostics, yet prior implementations still rely on such components. Here we present the first experimental implementation and validation of the GPSR methodology, realized by the use of standard accelerator elements including accelerating cavities and dipole magnets, to achieve complete 6-dimensional phase space reconstruction. Through simulations and experiments at the Pohang Accelerator Laboratory X-ray Free Electron Laser facility, we successfully reconstruct complex, nonlinear beam structures. Furthermore, we validate the methodology by predicting independent downstream measurements excluded from training, revealing the reconstruction closely resembling ground truth. This advancement establishes a pathway for predictive diagnostics across beamline segments while reducing hardware requirements and expanding applicability to various accelerator facilities.

Kim, Seongyeol [Pohang Univ. of Science and Techno↗
DOE OSTI2024

Collective excitations and low-energy ionization signatures of relativistic particles in silicon detectors

Abstract Solid-state detectors with a low energy threshold have several applications, including searches of non-relativistic halo dark-matter particles with sub-GeV masses. When searching for relativistic, beyond-the-Standard-Model particles with enhanced cross sections for small energy transfers, a small detector with a low energy threshold may have better sensitivity than a larger detector with a higher energy threshold. In this paper, we calculate the low-energy ionization spectrum from high-velocity particles scattering in a dielectric material. We consider the full material response including the excitation of bulk plasmons. We generalize the energy-loss function to relativistic kinematics, and benchmark existing tools used for halo dark-matter scattering against electron energy-loss spectroscopy data. Compared to calculations commonly used in the literature, such as the Photo-Absorption-Ionization model or the free-electron model, including collective effects shifts the recoil ionization spectrum towards higher energies, typically peaking around 4–6 electron-hole pairs. We apply our results to the three benchmark examples: millicharged particles produced in a beam, neutrinos with a magnetic dipole moment produced in a reactor, and upscattered dark-matter particles. Our results show that the proper inclusion of collective effects typically enhances a detector’s sensitivity to these particles, since detector backgrounds, such as dark counts, peak at lower energies.

Physics↗
DOE OSTI2020

An intriguing intermediate state as a bridge between antiferroelectric and ferroelectric perovskites

The configuration of electric or magnetic dipoles embedded into a crystal lattice gives rise to the defining physical properties of a functional material. The prevailing antiferroelectric materials have so far been allusively assumed to be in a strict antiparallel electric polarization configuration, although they have shown huge potential applications for use in electronic devices. Herein, we have revealed for the first time the complex crystal structure of an intermediate state between the two conventional antiferroelectric (AFE) and ferroelectric (FE) states in PbZrO 3 -based perovskites by employing a combination of advanced synchrotron X-ray, neutron and three-dimensional (3D) electron diffraction techniques. We found that the intermediate state displays an intriguing flexible configuration of a sinusoidal wave functional with imbalanced polarization, different to the commonly believed antiparallel and balanced polarization. Such an intermediate state was concluded to act as a bridge between the conventional AFE and FE states. Our observations offer new insight into the AFE state and its transformation into the FE state. Such an intermediate state with a unique polarization configuration is believed to be a common feature that occurs in high-performance AFE perovskite materials.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Application of saturation absorption spectroscopy to study the hyperfine structure of 235U and accurate 235U/238U isotope ratio determinations at 861.031 nm

The uranium transition 5f 3 6d7s 2 ( 5 L 6 ) → 5f 3 7s 2 7p ( 5 K 5 ) at 861.031 nm was studied using saturation absorption spectroscopy. The hyperfine structure of the 235 U isotope was determined by measuring the Doppler-suppressed absorption spectrum, and the hyperfine structure constants were obtained by employing transition-specific line strength theory and spectral fitting. The magnetic-dipole and electric-quadrupole constants were determined to be A = -3.2887 ± 0.1957 mK and B = 31.8712 ± 8.0789 mK for the upper state 5f 3 7s 2 7p ( 5 K 5 ). A theoretical calculation for the hyperfine structure constants of the 235 U isotope was also carried out by the relativistic configuration-interaction (RCI) method, and the obtained values were found to be in agreement with the measured values. In addition, the line profile of 238 U was experimentally investigated for different excitation intensities and modeled using the RCI method for estimating the transition probability and oscillator strength, with various residual broadening mechanisms considered beyond the radiative decay. Finally, we show that these results allow us to make improvements on the precision of spectral measurements using our previously developed technique for isotope ratio determinations in atomic beams.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Planck intermediate results: XVII. Emission of dust in the diffuse interstellar medium from the far-infrared to microwave frequencies

The dust-Hi correlation is used to characterize the emission properties of dust in the diffuse interstellar medium (ISM) from far infrared wavelengths to microwave frequencies. The field of this encompasses the part of the southern sky best suited to study the cosmic infrared and microwave backgrounds. We cross-correlate sky maps from Planck , the Wilkinson Microwave Anisotropy Probe ( WMAP ), and the diffuse infrared background experiment ( DIRBE ), at 17 frequencies from 23 to 3000 GHz, with the Parkes survey of the 21 cm line emission of neutral atomic hydrogen, over a contiguous area of 7500 deg 2 centred on the southern Galactic pole. We present a general methodology to study the dust-Hi correlation over the sky, including simulations to quantify uncertainties. Our analysis yields four specific results. (1) We map the temperature, submillimetre emissivity, and opacity of the dust per H-atom. The dust temperature is observed to be anti-correlated with the dust emissivity and opacity. We interpret this result as evidence of dust evolution within the diffuse ISM. The mean dust opacity is measured to be (7.1 ± 0.6) × 10 -27 cm 2 H -1 × (v/353 GHz) 1.53 ± 0.03 for 100 ≤ v ≤ 353 GHz. This is a reference value to estimate hydrogen column densities from dust emission at submillimetre and millimetre wavelengths. (2) We map the spectral index β mm of dust emission at millimetre wavelengths (defined here as v ≤ 353 GHz), and find it to be remarkably constant at β mm = 1.51 ± 0.13. We compare it with the far infrared spectral index β FIR derived from greybody fits at higher frequencies, and find a systematic difference, β mm -β FIR = -0.15, which suggests that the dust spectral energy distribution (SED) flattens at v ≤ 353 GHz. (3) We present spectral fits of the microwave emission correlated with Hi from 23 to 353 GHz, which separate dust and anomalous microwave emission (AME). We show that the flattening of the dust SED can be accounted for with an additional component with a blackbody spectrum. This additional component, which accounts for (26 ± 6)% of the dust emission at 100GHz, could represent magnetic dipole emission. Alternatively, it could account for an increasing contribution of carbon dust, or a flattening of the emissivity of amorphous silicates, at millimetre wavelengths. These interpretations make different predictions for the dust polarization SED. (4) We analyse the residuals of the dust-Hi correlation. We identify a Galactic contribution to these residuals, which we model with variations of the dust emissivity on angular scales smaller than that of our correlation analysis. This model of the residuals is used to quantify uncertainties of the CIB power spectrum in a companion Planck paper.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

The Heavy Photon Search (HPS) Software Environment

The Heavy Photon Search (HPS) is an experiment at the Thomas Jefferson National Accelerator Facility (JLab) designed to search for a hidden sector photon (A’) in fixed-target electro-production. It uses a silicon microstrip tracking and vertexing detector placed inside a dipole magnet to measure charged particle trajectories and a fast lead-tungstate crystal calorimeter located just downstream of the magnet to provide a trigger and to identify electromagnetic showers. The HPS experiment uses both invariant mass and secondary vertex signatures to search for the A’. The experimental collaboration is small and quite heterogeneous: it is composed of members of the nuclear physics as well as particle physics communities, from universities and national labs from around the US and Europe. Enabling such a disparate group to concentrate on the physics aspects of the experiment required that the software be easy to install and use, and having such limited manpower meant that existing solutions had to be exploited. HPS has successfully completed two engineering runs and completed its first physics run in the summer of 2019. We begin with an overview of the physics goals of the experiment followed by a short description of the detector design. We then describe the software tools used to design the detector layout and simulate the expected detector performance. Event reconstruction involving track, cluster and vertex finding and fitting for both simulated and real data was, to first order, adopted from existing software originally developed for Linear Collider studies. Bringing it all together into a cohesive whole involved the use of multiple software solutions with common interfaces.

Graf, Norman↗
DOE OSTI2014

Synchronization of spin torque nano-oscillators through dipolar interactions

In an array of spin-torque nano-oscillators (STNOs) that combine a perpendicular polarized fixed layer with strong in-plane anisotropy in the free layers, magnetic dipolar interactions can effectively phase-lock the array, thus further enhancing the power of the output microwave signals. We perform a qualitative analysis of the synchronization of an array based on the Landau-Lifshitz-Gilbert equation, with a spin-transfer torque that assumes strong in-plane anisotropy. Finally, we present the numerical results for four coupled STNOs to provide further evidence for the proposed theory.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2020

A compact, high resolution energy, and emittance diagnostic for electron beams using active plasma lenses

High-resolution (sub-%), single-shot energy distribution, and emittance measurements of GeV-class electron beams generated by laser plasma accelerators (LPAs) have been enabled through the use of an active plasma lens combined with relatively short dipole magnets. This setup, with only 60 cm between the LPA source and the final diagnostic screen, was facilitated through the use of a replenishable ∼20–40 nm thick liquid crystal plasma mirror to separate remnant laser radiation from the electron beam without emittance degradation. As LPAs capable of generating GeV-class electron beams at cm-scale distances become increasingly ubiquitous, there is a need to supplement these compact accelerators with equally compact diagnostics.

Barber, S. K. (ORCID:0000000172518755)↗
DOE OSTI2024

Current potential patches

A novel form of the current potential, a mathematical tool for the design of stellarators and stellarator coils, is developed. Specifically, these are current potentials with a finite-element basis, called current potential patches. Current potential patches leverage the relationship between distributions of magnetic dipoles and current potentials to explore limits of the access properties of stellarator coil sets. An example calculation is shown using the Helically Symmetric Experiment (HSX) equilibrium, demonstrating the method's use in coil design and understanding the limits of the access properties of coil sets. Current potential patches have additional desirable properties such as of promoting sparse current sheet solutions and identifying crucial locations of shaping current placement. A result is found for the HSX equilibrium that shaping currents covering only 22% of the winding surface are sufficient to produce the equilibrium to a good accuracy, provided a toroidal field is generated by an exterior coil set.

Elder, Todd↗
DOE OSTI2016

Frustration by design

Geometrical frustration is a condition that occurs when a material’s lattice geometry precludes minimizing the energy of all the interactions among pairs of neighbors simultaneously. Moreover, the simplest example is three antiferromagnetically coupled Ising spins, pointing up or down, on the corners of an equilateral triangle: It is also impossible to arrange the spins so that each pair is antiparallel. In more complex magnetic lattices, the frustrated state can arise from the combination of lattice geometry and the strength and sign of the interactions among the magnetic dipole moments.1 (See the article by Roderich Moessner and Art Ramirez, Physics Today, February 2006, page 24.) A wide variety of exotic and collective phenomena sometimes arises from the competing interactions. One prime example is spin liquids, materials in which the local atomic moments fluctuate down to the lowest accessible temperatures and never settle into a static ground-state configuration.

36 MATERIALS SCIENCE↗
DOE OSTI2014

NuSTAR discovery of a young, energetic pulsar associated with the luminous gamma-ray source HESS J1640–465

We report the discovery of a 206 ms pulsar associated with the TeV γ-ray source HESS J1640–465 using the Nuclear Spectroscopic Telescope Array (NuSTAR) X-ray observatory. PSR J1640–4631 lies within the shell-type supernova remnant (SNR) G338.3–0.0, and coincides with an X-ray point source and putative pulsar wind nebula (PWN) previously identified in XMM-Newton and Chandra images. It is spinning down rapidly with period derivative P-dot = 9.758(44) × 10{sup –13}, yielding a spin-down luminosity E-dot = 4.4 × 10{sup 36} erg s{sup –1}, characteristic age τ{sub c}≡P/2 P-dot = 3350 yr, and surface dipole magnetic field strength B{sub s} = 1.4 × 10{sup 13} G. For the measured distance of 12 kpc to G338.3–0.0, the 0.2-10 TeV luminosity of HESS J1640–465 is 6% of the pulsar's present E-dot . The Fermi source 1FHL J1640.5–4634 is marginally coincident with PSR J1640–4631, but we find no γ-ray pulsations in a search using five years of Fermi Large Area Telescope (LAT) data. The pulsar energetics support an evolutionary PWN model for the broadband spectrum of HESS J1640–465, provided that the pulsar's braking index is n ≈ 2, and that its initial spin period was P {sub 0} ∼ 15 ms.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Proper motion and timing of two unusual pulsars: Calvera and 1E 1207.4—5209

Using pairs of images from the Chandra High Resolution Camera we examine the proper motion of the central compact object (CCO) 1E 1207.4−5209 in the supernova remnant (SNR) PKS 1209−51/52, and the unusual pulsar Calvera that is possibly a CCO descendant. For 1E 1207.4−5209, an insignificant proper motion of μ=15±7 mas yr{sup −1} is measured, corresponding to a corrected tangential velocity of v{sub ⊥,c}<180 km s{sup −1} at the distance of 2 kpc. This proves that the previously noted large offset of the pulsar from the apparent geometric center of the SNR is not due to high proper motion; evidently the symmetry of the remnant does not indicate its center of expansion. Calvera has a marginally significant proper motion of μ=69±26 mas yr{sup −1}, corresponding to v{sub ⊥,c}=86±33 km s{sup −1} for a hypothetical distance of 0.3 kpc. Notably, its vector is away from the Galactic plane, although its high Galactic latitude of b=+37{sup ∘} may be more a consequence of its proximity than its velocity. We also provide updated timing solutions for each pulsar. Spanning 14.5 years, the ephemeris of 1E 1207.4−5209 has a small and steady frequency derivative that, because of the negligible proper motion, requires no kinematic correction. The derived surface dipole magnetic field strength of 1E 1207.4−5209 thus remains B{sub s}=9.8×10{sup 10} G. Calvera has B{sub s}=4.4×10{sup 11} G, intermediate between those of ordinary young pulsars and CCOs, suggesting that it may be on a trajectory of field growth that could account for the absence of descendants in the neighborhood of CCOs in the P− P-dot diagram.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Intrinsic operators for the translationally-invariant many-body problem

Abstract The need to enforce fermionic antisymmetry in the nuclear many-body problem commonly requires use of single-particle coordinates, defined relative to some fixed origin. To obtain physical operators which nonetheless act on the nuclear many-body system in a Galilean-invariant fashion, thereby avoiding spurious center-of-mass contributions to observables, it is necessary to express these operators with respect to the translational intrinsic frame. Several commonly-encountered operators in nuclear many-body calculations, including the magnetic dipole and electric quadrupole operators (in the impulse approximation) and generators of U(3) and Sp ( 3 , R ) symmetry groups, are bilinear in the coordinates and momenta of the nucleons and, when expressed in intrinsic form, become two-body operators. To work with such operators in a second-quantized many-body calculation, it is necessary to relate three distinct forms: the defining intrinsic-frame expression, an explicitly two-body expression in terms of two-particle relative coordinates, and a decomposition into one-body and separable two-body parts. We establish the relations between these forms, for general (non-scalar and non-isoscalar) operators bilinear in coordinates and momenta.

Physics↗
DOE OSTI2018

Controlling Cu–Sn mixing so as to enable higher critical current densities in RRP ® Nb 3 Sn wires

Dipole magnets for the proposed Future Circular Collider (FCC) demand specifications significantly beyond the limits of all existing Nb 3 Sn wires, in particular a critical current density (J c ) of more than 1500 A mm -2 at 16 T and 4.2 K with an effective filament diameter (D eff ) of less than 20 μm. The restacked-rod-process (RRP ® ) is the technology closest to meeting these demands, with a J c (16 T) of up to 1400 A mm -2 , residual resistivity ratio > 100, for a sub-element size D s of 58 μm (which in RRP ® wires is essentially the same as D eff ). An important present limitation of RRP ® is that reducing the sub-element size degrades J c to as low as 900 A mm -2 at 16 T for D s = 35 μm. To gain an understanding of the sources of this J c degradation, we have made a detailed study of the phase evolution during the Cu–Sn 'mixing' stages of the wire heat treatment that occur prior to Nb 3 Sn formation. Using extensive microstructural quantification, we have identified in this paper the critical role that the Sn–Nb–Cu ternary phase (Nausite) can play. The Nausite forms as a well-defined ring between the Sn source and the Cu/Nb filament pack, and acts as an osmotic membrane in the 300 °C–400 °C range—greatly inhibiting Sn diffusion into the Cu/Nb filament pack while supporting a strong Cu counter-diffusion from the filament pack into the Sn core. This converts the Sn core into a mixture of the low melting point (408 °C) η phase (Cu 6 Sn 5 ) and the more desirable ε phase (Cu 3 Sn), which decomposes at 676 °C. After the mixing stages, when heated above 408 °C towards the Nb 3 Sn reaction, any residual η liquefies to form additional irregular Nausite on the inside of the membrane. All Nausite decomposes into NbSn 2 on further heating, and ultimately transforms into coarse-grain (and often disconnected) Nb 3 Sn which has little contribution to current transport. Understanding this critical Nausite reaction pathway has allowed us to simplify the mixing heat treatment to only one stage at 350 °C for 400 h which minimizes Nausite formation while encouraging the formation of the higher melting point ε phase through better Cu–Sn mixing. Finally, at a D s of 41 μm, the Nausite control heat treatment increases the J c at 16 T by 36%, reaching 1300 A mm -2 (i.e. 2980 A mm -2 at 12 T), and moving RRP ® closer to the FCC targets.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Beneficial influence of Hf and Zr additions to Nb4at%Ta on the vortex pinning of Nb 3 Sn with and without an O source

In this paper we show that addition of Hf to Nb4Ta can significantly improve the high field performance of Nb 3 Sn, making it suitable for dipole magnets for a machine like the 100 TeV Future Circular Collider (FCC). A big challenge of the FCC is that the desired non-Cu critical current density (J c ) target of 1500 A mm –2 (16 T, 4.2 K) is substantially above the best present Nb 3 Sn conductors doped with Ti or Ta (~1300 A mm –2 in the very best sample of the very best commercial wire). Recent success with internal oxidation of Nb–Zr precursor has shown significant improvement in the layer J c of Nb 3 Sn wires, albeit with the complication of providing an internal oxygen diffusion pathway and avoiding degradation of the irreversibility field H Irr . We here extend the Nb1Zr oxidation approach by comparing Zr and Hf additions to the standard Nb4Ta alloy of maximum H c2 and H Irr . Nb4Ta rods with 1Zr or 1Hf were made into monofilament wires with and without SnO 2 and their properties measured over the entire superconducting range at fields up to 31 T. We found that Group IV alloying of Nb4Ta does raise H Irr , though O 2 addition still slightly degrades it. As noted in earlier Nb1Zr work with an O source, the pinning force density F p is strongly enhanced and its peak value shifted to higher field by internal oxidation. A surprising result of this work is that we found better properties in Nb4Ta1Hf without SnO 2 , F pMax achieving 2.35 times that of the standard Nb4Ta alloy, while the oxidized Nb4Ta1Zr alloy achieved 1.54 times that of the Nb4Ta alloy. The highest layer J c (16 T, 4.2 K) of 3700 A mm –2 was found in the SnO 2 -free wire made with Nb4Ta1Hf alloy. Using a standard A15 cross-section fraction of 60% for modern powder-in-tube and rod restack process wires, we estimated that a non-Cu J c of 2200 A mm –2 is obtainable in modern conductors, well above the 1500 A mm –2 FCC specification. Moreover, since the best properties were obtained without SnO 2 , the Nb4Ta1Hf alloy appears to open a straightforward route to enhanced properties in Nb 3 Sn wires manufactured by virtually all the presently used commercial routes employed today.

36 MATERIALS SCIENCE↗
DOE OSTI2022

A very high energy hadron collider on the Moon

Abstract The long-term prospect of building a hadron collider around the circumference of a great circle of the Moon is sketched. A circular collider on the Moon (CCM) of ∼11 000 km in circumference could reach a proton–proton center-of-mass collision energy of 14 PeV—a thousand times higher than the Large Hadron Collider at CERN—optimistically assuming a dipole magnetic field of 20 T. Several aspects of such a project are presented, including siting, construction, availability of necessary materials on the Moon, and powering, as well as a discussion of future studies and further information needed to determine the more concrete feasibility of each. Machine parameters and vacuum requirements are explored, and an injection scheme is delineated. Other unknowns are set down. Due to the strong interest from multiple organizations in establishing a permanent Moon presence, a CCM could be the (next-to-) next-to-next-generation discovery machine for high-energy particle physics and a natural successor to next-generation machines, such as the proposed future circular collider at CERN or a super proton–proton collider in China, and other future machines, such as a collider in the Sea, in the Gulf of Mexico. A CCM would serve as an important stepping stone toward a Planck-scale collider sited in our Solar System.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗