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At least 865 records · Page 48
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Realization of a gas puff imaging system on the Wendelstein 7-X stellarator

A system for studying the spatiotemporal dynamics of fluctuations in the boundary of the W7-X plasma using the “Gas-Puff Imaging” (GPI) technique has been designed, constructed, installed, and operated. This GPI system addresses a number of challenges specific to long-pulse superconducting devices, such as W7-X, including the long distance between the plasma and the vacuum vessel wall, the long distance between the plasma and diagnostic ports, the range of last closed flux surface (LCFS) locations for different magnetic configurations in W7-X, and management of heat loads on the system’s plasma-facing components. The system features a pair of “converging–diverging” nozzles for partially collimating the gas puffed locally ≈135 mm radially outboard of the plasma boundary, a pop-up turning mirror for viewing the gas puff emission from the side (which also acts as a shutter for the re-entrant vacuum window), and a high-throughput optical system that collects visible emission resulting from the interaction between the puffed gas and the plasma and directs it along a water-cooled re-entrant tube directly onto the 8 × 16 pixel detector array of the fast camera. The DEGAS 2 neutral code was used to simulate the Hα (656 nm) and HeI (587 nm) line emission expected from well-characterized gas-puffs of H2 and He and excited within typical edge plasma profiles in W7-X, thereby predicting line brightnesses used to reduce the risks associated with system sensitivity and placement of the field of view. Operation of GPI on W7-X shows excellent signal-to-noise ratios (>100 at 2 Mframes/s) over the field of view for minimally perturbing gas puffs. The GPI system provides detailed measurements of the two-dimensional (radial and poloidal) dynamics of plasma fluctuations in the W7-X edge and scrape-off layer and in and around the magnetic islands outside the LCFS that make up the island divertor configuration employed on W7-X.

Instruments & Instrumentation↗
DOE OSTI2024

Upgrade of the Lyman-alpha diagnostic system on DIII-D for main chamber edge neutral studies

The LLAMA (Lyman Alpha Measurement Apparatus) pinhole camera diagnostic had previously been deployed on DIII-D to measure radial profiles of the Lyman-α (Ly-α) deuterium neutral line brightness across the plasma boundary in the lower chamber to infer neutral deuterium density and ionization rate profiles. This system has recently been upgraded with a new diagnostic head, named ALPACA, that also encloses two pinhole cameras and duplicates the LLAMA views in the upper chamber. Similar to LLAMA, ALPACA provides two times 20 lines of sight, viewing the plasma edge on the inboard and outboard sides with a radial resolution of ~2.5 cm (FWHM) and an effective time resolution of ~1 ms that allows for the investigation of inter-ELM dynamics. The extended Ly-α system provides better coverage to study neutrals in experiments with various plasma shapes utilizing both the upper and lower divertors. Furthermore, post-campaign calibration of the LLAMA diagnostic has successfully been demonstrated for the first time. This was facilitated by various upgrades to the calibration set-up and detailed measurements of the emissivity distribution of the Ly-α calibration source using a pinhole collimator. It was found that the sensitivity of the inboard LLAMA pinhole camera was reduced by a factor of 2.0 ± 0.2 over the course of six months of plasma operation in 2021. In conclusion, the upgraded Ly-α system, equipped with improved absolute calibration, will provide key input for neutral fueling and pedestal particle transport studies and for 2D edge transport code validation on the DIII-D tokamak.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

An atomic beam of titanium for ultracold atom experiments

Here we generate an atomic beam of titanium (Ti) using a “Ti-ball” Ti-sublimation pump, which is a common getter pump used in ultrahigh vacuum systems. We show that the sublimated atomic beam can be optically pumped into the metastable 3d 3 ( 4 F)4s a 5 F 5 state, which is the lower energy level in a cycling optical transition that can be used for laser cooling. We measure the atomic density and transverse and longitudinal velocity distributions of the beam through laser fluorescence spectroscopy. We find a metastable atomic flux density of 4.3(2) × 10 9 s -1 cm -2 with a mean forward velocity of 773(8) m/s at 2.55 cm directly downstream of the center of the Ti-ball. Owing to the details of optical pumping, the beam is highly collimated along the transverse axis parallel to the optical pumping beam and the flux density falls off as 1/r. We discuss how this source can be used to load atoms into a magneto-optical trap.

47 OTHER INSTRUMENTATION↗
DOE OSTI2024

Dephasing of ion beams as magnetic vortex acceleration regime transitions into a bubble-like field structure

The interaction of an ultra-intense laser pulse with a near critical density target results in the formation of a plasma channel, a strong azimuthal magnetic field and moving vortices. An application of this is the generation of energetic and collimated ion beams via magnetic vortex acceleration. The optimized regime of magnetic vortex acceleration is becoming experimentally accessible with new high intensity laser beamlines coming online and advances made in near critical density target fabrication. The robustness of the acceleration mechanism with realistic experimental conditions is examined with three-dimensional simulations. Of particular interest is the acceleration performance with different laser temporal contrast conditions, in some cases leading to pre-expanded target profiles prior to the arrival of the main pulse. Preplasma effects on the structure of the accelerating fields are explored, including a detailed analysis of the ion beam properties and the efficiency of the process. Improved scaling laws for the magnetic vortex acceleration mechanism, including the laser focal spot size effects, are presented.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

An experimental platform for investigating astrophysically relevant magnetized plasma jets on the COBRA facility

A new platform has been developed for the 1-MA COBRA generator to investigate the physical processes affecting the formation, collimation, and stability of high-speed outflows in magnetically driven laboratory plasma jets. Such experiments serve as diagnostically accessible surrogates for astrophysical jets under the assumption that the underlying dynamics are scale invariant. In contrast to previous current driven high energy density laboratory jet experiments that use radial/conical wire arrays or foils, the platform described here uses azimuthally symmetric gas-puff injection. This avoids the ablation phase from a solid target, allowing the jets to develop earlier and be driven longer without depleting their mass source and disrupting. A permanent magnet provides an initial poloidal magnetic field, which links the two concentric electrodes and mimics the boundary conditions of a star-accretion disk system. Extended magnetohydrodynamic effects can be assessed using a polarity convolute, which allows for reversal of the electrode bias. The resulting plasma jets exhibit remarkable stability, persisting for hundreds of nanoseconds and achieving aspect ratios ≳30:1.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2026

Nozzle geometry optimization for high-current aluminum ion beam acceleration via direct plasma injection scheme

We report the generation of a record aluminum ion beam current exceeding 58 mA at the Al 11+ charge state, accelerated to an energy of 5.5 MeV using the direct plasma injection scheme, which integrates a laser ion source (LIS) with a radio frequency quadrupole (RFQ) accelerator. The effect of nozzle geometry on beam extraction was systematically investigated using 8 and 12 mm tapered designs and an 18 mm cylindrical configuration. The 18 mm nozzle achieved the highest Al 11+ beam current, while the 12 mm aperture provided a favorable balance between beam intensity and current density. Beam extraction simulations confirmed effective RFQ matching across multiple charge states, and solenoidal field tuning further enhanced plasma collimation. This work not only establishes a new benchmark for high-current ion beam generation but also provides a fundamental understanding of plasma–beam interface dynamics crucial for the next generation of high-intensity particle accelerators, particularly those employing LIS-RFQ systems.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2015

Investigation of optical properties of multilayer dielectric structures using prism-coupling technique

A method based on resonant excitation of waveguide modes with a prism coupler is proposed for measuring the thickness and refractive index of thin-film layers in multilayer dielectric structures. The peculiarities of reflection of TE- and TM-polarised light beams from a structure comprising eleven alternating layers of zinc sulfide (ZnS) and magnesium barium fluoride (MgBaF{sub 4}), whose thicknesses are much less than the wavelength of light, are investigated. Using the mathematical model developed, we have calculated the coefficients of reflection of collimated TE and TM light beams from a multilayer structure and determined the optical constants and thicknesses of the structure layers. The refractive indices of the layers, obtained for TE and TM polarisation of incident light, are in good agreement. The thicknesses of ZnS and MgBaF{sub 4} layers, found for different polarisations, coincide with an accuracy of ±1%. Thus, we have demonstrated for the first time that the prism-coupling technique allows one to determine the optical properties of thin-film structures when the number of layers in the structure exceeds ten layers. (integrated optics)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

Laboratory reflectometer for the investigation of optical elements in a wavelength range of 5–50 nm: description and testing results

We describe a laboratory reflectometer developed at the IPM RAS for precision measurements of spectral and angular dependences of the reflection and transmission coefficients of optical elements in a wavelength range of 5–50 nm. The radiation is monochromatised using a high-resolution Czerny–Turner spectrometer with a plane diffraction grating and two spherical collimating mirrors. A toroidal mirror focuses the probe monochromatic beam on a sample. The X-ray source is a highly ionised plasma produced in the interaction of a high-power laser beam with a solid target at an intensity of 10{sup 11}–10{sup 12} W cm{sup –2}. To stabilise the emission characteristics, the target executes translatory and rotary motions in such a way that every pulse irradiates a new spot. The short-focus lens is protected from contamination by erosion products with the use of a specially designed electromagnetic system. The samples under study are mounted on a goniometer is accommodated in a dedicated chamber, which provides five degrees of freedom for samples up to 500 mm in diameter and two degrees of freedom for a detector. The sample mass may range up to 10 kg. The X-ray radiation is recorded with a detector composed of a CsI photocathode and two microchannel plates. A similar detector monitors the probe beam intensity. The spectral reflectometer resolution is equal to 0.030 nm with the use of ruled gratings with a density of 900 lines mm{sup –1} (spectral range: 5–20 nm) and to 0.067 nm for holographic gratings with a density of 400 lines mm{sup –1} (spectral range: 10–50 nm). We analyse the contribution of higher diffraction orders to the probe signal intensity and the ways of taking it into account in the measurements. Examples are given which serve to illustrate the reflectometer application to the study of multilayer mirrors and filters. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Design and analysis of logic NOR, NAND and XNOR gates based on interference effect

We have developed and analysed logic NOR, NAND and XNOR gates based on two dimensional (2D) photonic crystals at a wavelength of 1.55 μm. The interference and self-collimation effects are used to design logic gates, which control the output by adjusting the phase difference to achieve constructive or destructive interference. The splitter is a line defect of the photonic crystal with a row of periodically arranged air rods. The radius of the defect rods depends on the function of the logic element. The use of these logic gates can reduce the size of logic devices. (optical logic elements)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2025

Suppression of pair beam instabilities in a laboratory analogue of blazar pair cascades

The generation of dense electron–positron pair beams in the laboratory can enable direct tests of theoretical models of γ-ray bursts and active galactic nuclei. We have successfully achieved this using ultrarelativistic protons accelerated by the Super Proton Synchrotron at (CERN). In the first application of this experimental platform, the stability of the pair beam is studied as it propagates through a meter-length plasma, analogous to TeV γ-ray-induced pair cascades in the intergalactic medium. It has been argued that pair beam instabilities disrupt the cascade, thus accounting for the observed lack of reprocessed GeV emission from TeV blazars. If true, this would remove the need for a moderate strength intergalactic magnetic field to explain the observations. We find that the pair beam instability is suppressed if the beam is not perfectly collimated or monochromatic, hence the lower limit to the intergalactic magnetic field inferred from γ-ray observations of blazars is robust.

blazar jets↗
DOE OSTI2026

New developments in structure-property and amorphous materials research at the upgraded 16-BM-B Paris-Edinburgh press station at HPCAT

Beamline 16-BM-B of the High-Pressure Collaborative Access Team (HPCAT) at the Advanced Photon Source (APS) provides a Paris-Edinburgh press program to probe the structure and properties of crystalline and amorphous materials up to 12 GPa at room temperature or 7 GPa at 2000°C. During the recent APS upgrade, 16-BM-B undertook major improvements to its instrumentation and measurement techniques. The upgrade includes the addition of a 1.2 m horizontal “condenser” mirror and a new variable-sized collimation system, the combination of which decreases the acquisition time for energy dispersive X-ray diffraction measurements by a factor of 10 when compared to pre-upgrade measurements. The addition of a new Ge energy-sensitive detector and DANTE (XGLab) digital pulse processor allows for processing the increased diffraction counts with minimal deadtime. In addition to upgraded beamline components, new techniques are being developed for eventual release to the user community, including electrical resistivity and tomography measurements.

APS upgrade↗
DOE OSTI2017

Design and Fabrication of Opacity Targets for the National Ignition Facility

Accurate models for opacity of partially ionized atoms are important for modeling and understanding stellar interiors and other high-energy-density phenomena such as inertial confinement fusion. Lawrence Livermore National Laboratory is leading a multilaboratory effort to conduct experiments on the National Ignition Facility (NIF) to try to reproduce recent opacity tests at the Sandia National Laboratory Z-facility. Since 2015, the NIF effort has evolved several hohlraum designs that consist of multiple pieces joined together. The target also has three components attached to the main stalk over a long distance with high tolerances that have resulted in several design iterations. The target has made use of rapid prototyped features to attach a capsule and collimator under the hohlraum while avoiding interference with the beams. Here, this paper discusses the evolution of the hohlraum and overall target design and the challenges involved with fabricating and assembling these targets.

47 OTHER INSTRUMENTATION↗
DOE OSTI2017

Evolution of the Design and Fabrication of Astrophysics Targets for Turbulent Dynamo (TDYNO) Experiments on OMEGA

Although the overall function of a campaign’s primary target design may remain unchanged, the components and structure often evolve from one shot day to the next to better meet experimental goals. The target fabrication engineer’s involvement in this evolution can be important for advising modifications in order to improve and simplify assembly at the same time. Highly complex targets are constructed by General Atomics (GA) for astrophysics experiments conducted by the University of Chicago at the OMEGA laser facility. Several novel target components are fabricated, precision-assembled, and extensively measured in support of this campaign, and have evolved over the last three years to improve both the science and assembly. Examples include unique laser machined polyimide grids to enhance plasma mixing at target center, precision micromachined cylindrical shields that also act as component spacers, drawn glass target supports to suspend physics packages at critical distances, and tilted pinholes for collimated proton radiography. Target component fabrication and evolution details for this turbulent dynamics (TDYNO) campaign are presented, along with precision-assembly techniques, metrology methods, and considerations for future TDYNO experiments on OMEGA.

42 ENGINEERING↗
DOE OSTI2015

THE COMPLEX NORTH TRANSITION REGION OF CENTAURUS A: RADIO STRUCTURE

We present deep radio images of the inner ∼50 kpc of Centaurus A, taken with the Karl G. Jansky Very Large Array at 90 cm. We focus on the Transition Regions between the inner galaxy—including the active nucleus, inner radio lobes, and star-forming disk—and the outer radio lobes. We detect previously unknown extended emission around the Inner Lobes, including radio emission from the star-forming disk. We find that the radio-loud part of the North Transition Region (NTR), known as the North Middle Lobe, is significantly overpressured relative to the surrounding interstellar medium. We see no evidence for a collimated flow from the active galactic nucleus through this region. Our images show that the structure identified by Morganti et al. as a possible large-scale jet appears to be part of a narrow ridge of emission within the broader, diffuse, radio-loud region. This knotty radio ridge is coincident with other striking phenomena: compact X-ray knots, ionized gas filaments, and streams of young stars. Several short-lived phenomena in the NTR, as well as the frequent re-energization required by the Outer Lobes, suggest that energy must be flowing through both Transition Regions at the present epoch. We suggest that the energy flow is in the form of a galactic wind.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

FRAGMENTATION OF MOLECULAR CLUMPS AND FORMATION OF A PROTOCLUSTER

Sufficiently massive clumps of molecular gas collapse under self-gravity and fragment to spawn a cluster of stars that have a range of masses. We investigate observationally the early stages of formation of a stellar cluster in a massive filamentary infrared dark cloud, G28.34+0.06 P1, in the 1.3 mm continuum and spectral line emission using the Atacama Large Millimeter/Submillimeter Array. Sensitive continuum data reveal further fragmentation in five dusty cores at a resolution of several 10{sup 3} AU. Spectral line emission from C{sup 18}O, CH{sub 3}OH, {sup 13}CS, H{sub 2}CO, and N{sub 2}D{sup +} is detected for the first time toward these dense cores. We found that three cores are chemically more evolved as compared with the other two; interestingly, though, all of them are associated with collimated outflows as suggested by evidence from the CO, SiO, CH{sub 3}OH, H{sub 2}CO, and SO emission. The parsec-scale kinematics in exhibit velocity gradients along the filament, consistent with accretion flows toward the clumps and cores. The moderate luminosity and the chemical signatures indicate that the five cores harbor low- to intermediate-mass protostars that likely become massive ones at the end of the accretion. Despite the fact that the mass limit reached by the dust continuum sensitivity is 30 times lower than the thermal Jeans mass, there is a lack of a distributed low-mass protostellar population in the clump. Our observations indicate that in a protocluster, low-mass stars form at a later stage after the birth of more massive protostars.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Jet motion, internal working surfaces, and nested shells in the protostellar system HH 212

HH 212 is a nearby (400 pc) highly collimated protostellar jet powered by a Class 0 source in Orion. We have mapped the inner 80″ (∼0.16 pc) of the jet in SiO (J=8−7) and CO (J=3−2) simultaneously at ∼ 0.″ 5 resolution with the Atacama Millimeter/Submillimeter Array (SMA) at unprecedented sensitivity. The jet consists of a chain of knots and bow shocks with sinuous structures in between. Compared to what we saw in our previous observations with the SMA, the jet appears to be more continuous, especially in the northern part. Some of the knots are now observed to be associated with small bow shocks, with their bow wings curving back to the jet axis, as seen in pulsed jet simulations. Two of the knots are reasonably resolved, showing kinematics consistent with sideways ejection, possibly tracing the internal working surfaces formed by a temporal variation in the jet velocity. In addition, nested shells are seen in CO around the jet axis connecting to the knots and bow shocks, driven by them. The proper motion of the jet is estimated to be ∼115 ± 50 km s{sup −1}, comparing with our previous observations. The jet has a small semi-periodical wiggle with a period of ∼93 yr. The amplitude of the wiggle first increases with the distance from the central source and then stays roughly constant. One possible origin of the wiggle could be the kink instability in a magnetized jet.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Time-dependent modeling of gamma-ray flares in blazar PKS1510–089

Here we present a new approach for constraining luminous blazars, incorporating fully time-dependent and self-consistent modeling of bright γ-ray flares of PKS 1510–089, resolved with Fermi-LAT, in the framework of the internal shock scenario. The results of our modeling imply the location of the γ-ray flaring zone to be outside of the broad-line region, namely around ≃0.3 pc from the core for a free-expanding jet with the opening angle Γ θ{sub jet}≃1 (where Γ is the jet bulk Lorentz factor), up to ≃3 pc for a collimated outflow with Γ θ{sub jet}≃0.1. Moreover, under the Γ θ{sub jet}≃1 condition, our modeling indicates the maximum efficiency of the jet production during the flares, with the total jet energy flux strongly dominated by protons and exceeding the available accretion power in the source. This is in contrast to the quiescence states of the blazar, characterized by lower jet kinetic power and an approximate energy equipartition between different plasma constituents. We demostrate how strictly simultaneous observations of flaring PKS 1510–089 at optical, X-ray, and GeV photon energies, on hourly timescales, augmented by extensive simulations as presented in this paper, may help to impose further precise constraints on the magnetization and opening angle of the emitting region. In addition, our detailed modeling implies that a non-uniformity of the Doppler factor across the jet, caused by the radial expansion of the outflow, may lead to a pronounced time distortion in the observed γ-ray light curves, resulting, in particular, in asymmetric flux profiles with substantially extended decay phases.

79 ASTRONOMY AND ASTROPHYSICS↗