Single Line Of Sight Research Articles

Characterization of the upgraded single-line-of-sight time-resolved x-ray imager using short-pulse visible and UV lasers.

The single-line-of-sight time-resolved x-ray imager (SLOS-TRXI), a fast-gated x-ray imager used for capturing x-ray self-emission in inertial confinement fusion experiments on OMEGA, has been upgraded and characterized. SLOS-TRXI combines an electron-dilation imager and a hybrid complementary metal-oxide-semiconductor (hCMOS) sensor to capture multiple gated frames on a single line of sight with a temporal resolution of ∼40ps and a spatial resolution of 10 µm. The original hCMOS sensor with four frames was replaced with a newer-generation hCMOS sensor having eight frames. Gate characterizations of both the sensor and the entire SLOS-TRXI diagnostic were performed using ∼10-ps FWHM visible (2ω) and UV (4ω) short-pulse lasers, respectively. A stepped echelon was used to generate a train of five UV laser pulses having an interpulse separation of 30 ± 3ps. Characterization results of the hCMOS gating (2.28 ± 0.02-ns FWHM on average) and a temporal resolution of the upgraded SLOS-TRXI (34 ± 4-ps FWHM on average) are presented. A temporal magnification for the electron-dilation imager between 40 and 60 was inferred from the characterization results. The spatial resolution of the upgraded SLOS-TRXI remains the same in light of this work.

Time-resolved X-ray diffraction diagnostic development for the National Ignition Facility.

We present the development of an experimental platform that can collect four frames of x-ray diffraction data along a single line of sight during laser-driven, dynamic-compression experiments at the National Ignition Facility. The platform is comprised of a diagnostic imager built around ultrafast sensors with a 2-ns integration time, a custom target assembly that serves also to shield the imager, and a 10-ns duration, quasi-monochromatic x-ray source produced by laser-generated plasma. We demonstrate the performance with diffraction data for Pb ramp compressed to 150GPa and illuminated by a Ge x-ray source that produces ∼7 × 1011, 10.25-keV photons/ns at the 400μm diameter sample.

An Experimental Study Measuring the Image Field Angle of an Electron Beam Using a Streak Tube

The final stage of an inertial confinement fusion (ICF) experiment requires the diagnostic instruments to have the ability to obtain multiple images with high spatiotemporal resolution due to its extremely short duration. However, the influence of field curvature in the streak tube may lead to resolution differences between each image from single line-of-sight (SLOS) technology. In order to achieve high-precision adaptive adjustments, the direction and depth of adjustment should be determined rapidly, which means that the diagnostic instrument must work within the image depth of field of its detector imaging system, requiring it to measure the image field angle of the electron beam. Here, a method based on the streak tube using the combination of planar and spherical fluorescent screens to directly calculate the image field angle of the electron beam from the rear image quality has been proposed for the first time, and its effectiveness has been proved by experiments. It is expected to provide a basis for the diagnostic equipment in ICF experiments to achieve adaptive high-precision adjustment of the focusing voltage to obtain a series of high-resolution images.

Cosmic metal invaders: Intergalactic O VII as a tracer of the warm-hot intergalactic medium within cosmic filaments in the EAGLE simulation

Context. The current observational status of the hot (log T(K) > 5.5) intergalactic medium (IGM) remains incomplete. While recent X-ray emission and Sunyaev-Zeldovich effect observations from stacking large numbers of Cosmic Web filaments have yielded statistically significant detections of this phase, direct statistically significant measurements of single objects remain scarce. The lack of such a sample currently prevents a robust analysis of the cosmic baryon content composed of the hot IGM, which would potentially help solve the cosmological missing baryons problem. Aims. In order to improve the observationally challenging search for the missing baryons, we utilise the theoretical avenue afforded by the EAGLE simulations. Our aim is to get insights into the metal enrichment of the Cosmic Web and the distribution of highly ionised metals in the IGM. Our goal is to aid in the planning of future X-ray observations of the hot intergalactic plasma. Methods. We detected the filamentary network by applying the Bisous formalism to galaxies in the EAGLE simulation. We characterised the spatial distributions of oxygen and O VII and studied their mass and volume filling fractions in the filaments. Since oxygen is formed in and expelled from galaxies, we also studied the surroundings of haloes. We used this information to construct maps of the O VII column density and determine the feasibility of detecting it via absorption with Athena X-IFU. Results. Within EAGLE, the oxygen and O VII number densities drop dramatically beyond the virial radii of haloes. In the most favourable scenario, the median extent of O VII above the Athena X-IFU detection limit is ≈700 kpc. Since galaxies are relatively far apart from one another, only ∼1% of the filament volumes are filled with O VII at high enough column densities to be detectable by X-IFU. The highly non-homogeneous distribution of the detectable O VII complicates the usage of the measurements of the intergalactic O VII absorbers for tracing the missing baryons and estimating their contribution to the cosmic baryon budget. Instead, the detectable volumes form narrow and dense envelopes around haloes, while the rest of the O VII is diluted at low densities within the full filament volumes. This localised nature, in turn, results in a low chance (∼10−20% per sight line) of detecting intergalactic O VII with Athena X-IFU within the observational SDSS catalogue of nearby filaments. Fortunately, with deeper filament samples, such as those provided via the future 4MOST 4HS survey, the chances of intercepting an absorbing system are expected to increase up to a comfortable level of ∼50% per sight line. Conclusions. Based on EAGLE results, targeting the Cosmic Web with Athena may only result in tip-of-the-iceberg detections of the intergalactic O VII, which is located in the galaxy outskirts. This would not be enough to conclusively solve the missing baryon problem. However, the projection of many filaments into a single line of sight will enable a useful X-ray observation strategy with Athena X-IFU for the hot cosmic baryon gas, reducing the amount of baryons still missing by up to ∼25%.

TriWaSp: a multi-faceted visible spectroscopy diagnostic on the ST40 tokamak

We present a new state-of-the-art Triple Wavelength Spectrometer (TriWaSp), recently deployed on ST40, a high field low aspect ratio spherical tokamak. The TriWaSp has a range of possible applications due to its flexible design; the current configuration focuses on charge exchange recombination spectroscopy from carbon and neon impurities in the ST40 plasma. This paper discusses the detailed setup of the system and presents initial charge exchange ion temperature measurements using a single line of sight, which show good agreement with other ion temperature diagnostics. Building on these commissioning results and forward modelling of the system, a new observation geometry has been implemented for the next experimental campaign which will considerably improve the localisation of ion temperature and velocity profile measurements.

Machine learning for detection of 3D features using sparse x-ray tomographic reconstruction.

In many inertial confinement fusion (ICF) experiments, the neutron yield and other parameters cannot be completely accounted for with one and two dimensional models. This discrepancy suggests that there are three dimensional effects that may be significant. Sources of these effects include defects in the shells and defects in shell interfaces, the fill tube of the capsule, and the joint feature in double shell targets. Due to their ability to penetrate materials, x rays are used to capture the internal structure of objects. Methods such as computational tomography use x-ray radiographs from hundreds of projections, in order to reconstruct a three dimensional model of the object. In experimental environments, such as the National Ignition Facility and Omega-60, the availability of these views is scarce, and in many cases only consists of a single line of sight. Mathematical reconstruction of a 3D object from sparse views is an ill-posed inverse problem. These types of problems are typically solved by utilizing prior information. Neural networks have been used for the task of 3D reconstruction as they are capable of encoding and leveraging this prior information. We utilize half a dozen, different convolutional neural networks to produce different 3D representations of ICF implosions from the experimental data. Deep supervision is utilized to train a neural network to produce high-resolution reconstructions. These representations are used to track 3D features of the capsules, such as the ablator, inner shell, and the joint between shell hemispheres. Machine learning, supplemented by different priors, is a promising method for 3D reconstructions in ICF and x-ray radiography, in general.

Characterizing line-of-sight variability of polarized dust emission with future CMB experiments

ABSTRACT While Galactic dust emission is often accounted for in cosmic microwave background (CMB) analyses by fitting a two-parameter modified blackbody (MBB) model in each pixel, typically a number of such clouds are found along each line of sight and within each angular pixel, resulting in a superposition of their spectra. We study the effects of this superposition on pixel-based foreground fitting strategies by modeling the spectral energy distribution (SED) in each pixel as the integral of individual MBB spectra over various physically motivated statistical distributions of dust cloud properties. We show that fitting these SEDs with the two-parameter MBB model generally results in unbiased estimates of the CMB Stokes Q and U amplitudes per pixel, unless there are significant changes in both the dust SED and polarization angle along the line of sight, in which case significant (>10σ) biases are observed in an illustrative model. We find that the best-fitting values of the dust temperature, Td, and spectral index, βd, are significantly biased from the mean/median of the corresponding statistical distributions when the distributions are broad, suggesting that MBB model fits can give an unrepresentative picture of the physical properties of dust at microwave wavelengths if not interpreted carefully. Using Fisher matrix analysis, we determine the experimental sensitivity required to recover the parameters of the Td and βd distributions by fitting a probabilistic MBB model, finding that only the parameters of broad distributions can be measured by SED fitting on a single line of sight.

X-ray-imaging spectrometer (XRIS) for studies of residual kinetic energy and low-mode asymmetries in inertial confinement fusion implosions at OMEGA (invited).

A system of x-ray imaging spectrometer (XRIS) has been implemented at the OMEGA Laser Facility and is capable of spatially and spectrally resolving x-ray self-emission from 5 to 40keV. The system consists of three independent imagers with nearly orthogonal lines of sight for 3D reconstructions of the x-ray emission region. The distinct advantage of the XRIS system is its large dynamic range, which is enabled by the use of tantalum apertures with radii ranging from 50 μm to 1mm, magnifications of 4 to 35×, and image plates with any filtration level. In addition, XRIS is capable of recording 1-100's images along a single line of sight, facilitating advanced statistical inference on the detailed structure of the x-ray emitting regions. Properties such as P0 and P2 of an implosion are measured to 1% and 10% precision, respectively. Furthermore, Te can be determined with 5% accuracy.

Augmented reality in minimally invasive spine surgery: early efficiency and complications of percutaneous pedicle screw instrumentation

Augmented reality (AR) employs an optical projection directly onto the user's retina, allowing complex image overlay on the natural visual field. In general, pedicle screw accuracy rates have improved with increasingly use of technology, with navigation-based instrumentation described as accurate in 89%-100% of cases. Emerging AR technology in spine surgery builds upon current spinal navigation to provide 3-dimensional imaging of the spine and powerfully reduce the impact of inherent ergonomic and efficiency difficulties. This publication describes the first known series of in vivo pedicle screws placed percutaneously using AR technology for MIS applications. After IRB approval, 3 senior surgeons at 2 institutions contributed cases from June, 2020 - March, 2022. 164 total MIS cases in which AR used for placement of percutaneous pedicle screw instrumentation with spinal navigation were identified prospectively. 155 (94.5%) were performed for degenerative pathology, 6 (3.6%) for tumor and 3 (1.8%) for spinal deformity. These cases amounted to a total of 606 pedicle screws; 590 (97.3%) were placed in the lumbar spine, with 16 (2.7%) thoracic screws placed. Patient demographics and surgical metrics including total posterior construct time (defined as time elapsed from preincision instrument registration to final screw placement), clinical complications and instrumentation revision rates were recorded in a secure and de-identified database. The AR system used features a wireless headset with transparent near-eye display which projects intra-operative 3D imaging directly onto the surgeon's retina. After patient positioning, 1 percuntaneous and 1 superficial reference marker are placed. Intra-operative CT data is processed to the headset and integrates into the surgeon's visual field creating a "see-through" 3D effect in addition to 2D standard navigation images. MIS pedicle screw placement is then carried out percutaneously through single line of sight using navigated instruments. Time elapsed from registration and percutaneous approach to final screw placement averaged 3 minutes and 54 seconds per screw. Analysis of the learning curve revealed similar surgical times in the early cases compared to the cases performed with more experience with the system. No instrumentation was revised for clinical or radiographic complication at final available follow-up ranging from 6-24 months. A total of 3 screws (0.49%) were replaced intra-operatively. No clinical effects via radiculopathy or neurologic deficit postoperatively were noted. This is the first report of the use of AR for placement of spinal pedicle screws using minimally invasive techniques. This series of 164 cases confirmed efficiency and safety of screw placement with the inherent advantages of AR technologies over legacy enabling technologies.

216. The arrival of augmented reality in MIS: initial results of use for percutaneous pedicle screw instrumentation

<h3>BACKGROUND CONTEXT</h3> Augmented reality (AR) employs computer-generated sensory inputs to enhance the user's perception of his or her environment. Pedicle screw instrumentation has become a mainstay of spinal stabilization. In general, pedicle screw accuracy rates have improved with increasing use of technology; navigation-based instrumentation have been described as accurate in 89-100% of cases. Some inherent difficulties persist with regards to ergonomics and efficiency of spinal navigation. Traditional navigation requires removing focus from the surgical field to interpret and coordinate input of external visual data. Line-of-sight disturbance and attention-shift has known impact on cognitive load and optimization of workflow in surgery. Emerging AR technology in spine surgery aims to reduce the impact of these pitfalls. <h3>PURPOSE</h3> To describe the first known series of in vivo pedicle screws placed percutaneously using AR technology for minimally invasive surgery (MIS) applications. <h3>STUDY DESIGN/SETTING</h3> After IRB approval, three senior surgeons at two institutions collected cases from June, 2020 - October, 2021, in which AR was used for placement of percutaneous pedicle screw instrumentation. <h3>PATIENT SAMPLE</h3> A total of 148 total MIS cases were studied; the average patient age was 59.7 ±13.84 and average BMI was 30.8 ±7.2. <h3>OUTCOME MEASURES</h3> Patient demographics and surgical metrics including total posterior construct time (defined as time elapsed from pre-incision instrument registration, percutaneous posterior fusion and final screw placement) were recorded. Screw revision intraoperatively after fluoroscopic evaluation and revision rates postoperatively were recorded. <h3>METHODS</h3> The xvision^TM (Augmedics Inc., Arlington Heights, IL, USA) system features a wireless headset with transparent near-eye display which projects intraoperative 3D imaging directly onto the surgeon's retina. After patient positioning, one percuntaneous and one superficial reference marker are placed. Intra-operative CT data is processed to the headset and integrates into the surgeon's visual field creating a "see-through" 3D effect in addition to 2D standard navigation images. MIS pedicle screw placement is then carried out percutaneously through single line of sight using navigated instruments. <h3>RESULTS</h3> Of the 148 cases, 139 (93.9%) were performed for degenerative pathology, 6 (4.1%) for tumor and 3 (2.0%) for spinal deformity. A total of 535 pedicle screws were placed; 519 (97.0%) lumbar and 16 (3.0%) thoracic. Eighty-four (58.8%) cases were 1-level, 42 (28.4%) were 2-level, 16 (10.8%) were 3-level and 6 (4.1%) were 4-level, equating to an average of 3.51 screws per case. A total of one screw (0.20%) was replaced intraoperatively after examining position with fluoroscopy. No instrumentation was revised postoperatively at final available follow-up ranging from 3-18 months. The mean total posterior construct time was 5 minutes and 56 seconds per screw overall; cases later in the learning curve achieved total posterior construct mean time of 2 minutes and 51 seconds per screw. <h3>CONCLUSIONS</h3> This study represents the first report of the use of AR to place MIS pedicle screws. These data support an exceedingly low rate of complications with screw placement and confirms a rapid learning curve with a high level of surgical efficiency demonstrated. These advances are achieved with an image- and implant-agnostic system which requires no physical footprint in the operating room. <h3>FDA DEVICE/DRUG STATUS</h3> xvision^TM (Augmedics Inc., Arlington Heights, IL, USA) (Approved for this indication)

Understanding the spatial variation of Mg ii and ionizing photon escape in a local LyC leaker

ABSTRACT Ionizing photons must have escaped from high-redshift galaxies, but the neutral high-redshift intergalactic medium makes it unlikely to directly detect these photons during the Epoch of Reionization. Indirect methods of studying ionizing photon escape fractions present a way to infer how the first galaxies may have reionized the Universe. Here, we use HET/LRS2 observations of J0919 + 4906, a confirmed z≈ 0.4 emitter of ionizing photons to achieve spatially resolved (12.5 kpc in diameter) spectroscopy of Mg iiλ2796, Mg iiλ2803, [O ii]λλ3727, 3729, [Ne iii]λ3869, H γ, [O iiI]λ4363, H β, [O iii]λ4959, [O iii]λ5007, and H α. From these data, we measure Mg ii emission, which is a promising indirect tracer of ionizing photons, along with nebular ionization and dust attenuation in multiple spatially resolved apertures. We find that J0919 + 4906 has significant spatial variation in its Mg ii escape and thus ionizing photon escape fraction. Combining our observations with photoionization models, we find that the regions with the largest relative Mg ii emission and Mg ii escape fractions have the highest ionization and lowest dust attenuation. Some regions have an escape fraction that matches that required by models to reionize the early Universe, while other regions do not. We observe a factor of 36 spatial variation in the inferred LyC escape fraction, which is similar to recently observed statistical samples of indirect tracers of ionizing photon escape fractions. These observations suggest that spatial variations in neutral gas properties lead to large variations in the measured LyC escape fractions. Our results suggest that single sightline observations may not trace the volume-averaged escape fraction of ionizing photons.

Beam and Channel Tracking for 5G Communication Systems Using Adaptive Filtering Techniques: A Comparison Study

In this paper, we study the problem of beam tracking of a multipath channel in millimeter-wave massive MIMO communication system using adaptive filters. We focus on the performance of least-mean-square filter (LMS) and recursive least-squares filter (RLS) algorithms, compared to a reference extended Kalman filter (EKF), in scenarios where the wireless channel is dominated by a single line of sight (LOS) path or a small number of strong paths. The signal direction and channel coefficients are tracked and updated using these filters. Our results recommend that beamforming systems at millimeter-wave bands should consider variable number of paths rather than a single dominant LOS path. Furthermore, we show that the mean squared-error (MSE) of the innovation process gives a better overall view of the tracking performance than the MSE of the state parameters.

Novel designfor a polarizing DUV spectrometer using a Wollaston prism and its application as a diagnostic for measuring Thomson scattering data in the presence of strong self-emission backgrounds.

We present a novel designfor an optical spectrometer for use in ultraviolet Thomson scattering measurements of plasma parameters in high energy density (HED) inertial confinement fusion experiments on large-scale high-energy laser facilities. In experiments investigating high-Z plasmas, the fidelity of measurements is commonly limited by signal/background ratios approaching or exceeding unity. An alpha barium borate Wollaston prism can provide both spectral dispersion and polarization channel separation, allowing simultaneous measurement of both the Thomson scattering signal and plasma self-emission along a single line of sight and in a single experiment, which should greatly improve data quality and reduce the opportunity cost of taking high quality measurements. We present a basic discussion of the designand a worked example of an instrument designed to take fourth harmonic electron plasma wave measurements in HED experiments at the OMEGA laser facility.

A new lidar design for operational atmospheric wind and cloud/aerosol survey from space

Abstract. Global wind profile measurement has, for a long time, been a first priority for numerical weather prediction. The demonstration, from ground-based observations, that a double-edge Fabry–Pérot interferometer could be efficiently used for deriving wind profiles from the molecular scattered signal in a very large atmospheric vertical domain has led to the choice of the direct detection technique in space and the selection of the Atmospheric Dynamics Mission (ADM)-Aeolus by the European Space Agency (ESA) in 1999. ADM-Aeolus was successfully launched in 2018, after the technical issues raised by the lidar development had been solved, providing the first global wind profiles from space in the whole troposphere. Simulated and real-time assimilation of the projected horizontal wind information was able to confirm the expected improvements in the forecast score, validating the concept of a wind profiler using a single line-of-sight lidar from space. The question is raised here about consolidating the results gained from ADM-Aeolus mission with a potential operational follow-on instrument. Maintaining the configuration of the instrument as close as possible to the one achieved (UV emission lidar with a single line of sight), we revisit the concept of the receiver by replacing the arrangement of the Fizeau and Fabry–Pérot interferometers with a unique quadri-channel Mach–Zehnder (QMZ) interferometer, which relaxes the system's operational constraints and extends the observation capabilities to recover the radiative properties of clouds. This ability to profile wind and cloud/aerosol radiative properties enables the meeting of the two highest priorities of the meteorological forecasting community regarding atmospheric dynamics and radiation. We discuss the optimization of the key parameters necessary in the selection of a high-performance system, as based on previous work and development of our airborne QMZ lidar. The selected optical path difference (3.2 cm) of the QMZ leads to a very compact design, allowing the realization of a high-quality interferometer and offering a large field angle acceptance. Performance simulation of horizontal wind speed measurements with different backscatter profiles shows results in agreement with the targeted ADM-Aeolus random errors, using an optimal 45∘ line-of-sight angle. The Doppler measurement is, in principle, unbiased by the atmospheric conditions (temperature, pressure, and particle scattering) and only weakly affected by the instrument calibration errors. The study of the errors arising from the uncertainties in the instrumental calibration and in the modeled atmospheric parameters used for the backscattered signal analysis shows a limited impact under realistic conditions. The particle backscatter coefficients can be retrieved with uncertainties better than a few percent when the scattering ratio exceeds 2, such as in the boundary layer and in semi-transparent clouds. Extinction coefficients can be derived accordingly. The chosen design further allows the addition of a dedicated channel for aerosol and cloud polarization analysis.

Stellar Rotation in the K2 Sample: Evidence for Modified Spin-down

Abstract We analyze light curves of 284,834 unique K2 targets using a Gaussian process model with a quasi-periodic kernel function. By cross-matching K2 stars to observations from Gaia Data Release 2, we have identified 69,627 likely main-sequence stars. From these we select a subsample of 8977 stars on the main sequence with highly precise rotation period measurements. With this sample we recover the gap in the rotation period−color diagram first reported by McQuillan et al. While the gap was tentatively detected in Reinhold &amp; Hekker, this work represents the first robust detection of the gap in K2 data for field stars. This is significant because K2 observed along many lines of sight at wide angular separation, in contrast to Kepler’s single line of sight. Together with recent results for rotation in open clusters, we interpret this gap as evidence for a departure from the t −1/2 Skumanich spin-down law, rather than an indication of a bimodal star formation history. We provide maximum likelihood estimates and uncertainties for all parameters of the quasi-periodic light-curve model for each of the 284,834 stars in our sample.

Evidence for line-of-sight frequency decorrelation of polarized dust emission in Planck data

If a single line of sight (LOS) intercepts multiple dust clouds with different spectral energy distributions and magnetic field orientations, then the frequency scaling of each of the Stokes Q and U parameters of the thermal dust emission may be different, a phenomenon we refer to as LOS frequency decorrelation. We present first evidence for LOS frequency decorrelation in Planck data using independent measurements of neutral-hydrogen (HI) emission to probe the 3D structure of the magnetized interstellar medium (ISM). We use HI-based measurements of the number of clouds per LOS and the magnetic field orientation in each cloud to select two sets of sightlines: (i) a target sample of pixels that are likely to exhibit LOS frequency decorrelation and (ii) a control sample of pixels that lack complex LOS structure. We test the null hypothesis that LOS frequency decorrelation is not detectable in Planck 353 and 217 GHz polarization data at high Galactic latitudes. We reject the null hypothesis at high significance based on data that show that the combined effect of polarization angle variation with frequency and depolarization are detected in the target sample. This detection is robust against the choice of cosmic microwave background (CMB) map and map-making pipeline. The observed change in polarization angle due to LOS frequency decorrelation is detectable above the Planck noise level. The probability that the detected effect is due to noise alone ranges from 5 × 10−2 to 4 × 10−7, depending on the CMB subtraction algorithm and treatment of residual systematic errors; correcting for residual systematic errors consistently increases the significance of the effect. Within the target sample, the LOS decorrelation effect is stronger for sightlines with more misaligned magnetic fields, as expected. With our sample, we estimate that an intrinsic variation of ~15% in the ratio of 353 to 217 GHz polarized emission between clouds is sufficient to reproduce the measured effect. Our finding underlines the importance of ongoing studies to map the three-dimensional structure of the magnetized and dusty ISM that could ultimately help component separation methods to account for frequency decorrelation effects in CMB polarization studies.

Spatially resolved measurements of RF accelerated deuterons at JET

An understanding of fast (supra-thermal) ion behavior is of great importance in tokamak physics and is a subject studied from both theoretical and experimental perspectives. This paper investigates the spatial energy and density distributions of RF accelerated deuterons using the neutron camera at the tokamak JET. Using the 19 liquid scintillator detectors available in the neutron camera system, we obtain spatial information that cannot be accessed with a single sightline. We present a spectroscopic analysis method in which a spatially resolved model of the fast ion distribution is fitted to the pulse height spectra from all 19 detectors simultaneously. The fast ion distribution is parameterized in such a way that the density, energy, and pitch-angle parts are uncoupled. The energy part is composed of a Maxwellian distribution, characterized by an ‘RF tail temperature,’ and the spatial dependence is modeled as a two-dimensional Gaussian distribution on the poloidal plane of the tokamak. From this parameterized model, we can calculate the spectrum of fusion born neutrons originating from reactions involving RF accelerated deuterons, and by fitting this model to the measured neutron camera pulse height spectra, we obtain an estimate of the spatially resolved distribution of the fast deuterons. The method has been applied to three JET pulses using different RF heating schemes and is shown to identify several features of the fast ion distribution produced in the various scenarios. Hence, this method is able to provide quantitative information about the fast ion distribution resulting from different heating schemes, and can also be useful, e.g., to validate simulation results from RF modeling codes.

VLA Measurements of Faraday Rotation Through a Coronal Mass Ejection Using Multiple Lines of Sight

Coronal mass ejections (CMEs) are large eruptions of magnetized plasma from the Sun that play an important role in space weather. The key to understanding the fundamental physics of a CME is measurement of the plasma properties within heliocentric distances of $< 20~\mathrm{R}_{\odot }$ . Faraday rotation, a radioastronomical propagation measurement, is an extremely valuable diagnostic for studying CMEs. Faraday rotation measurements [RM] contain information on the magnetic field in the medium causing the Faraday rotation. Recent observations of CME-induced Faraday rotation (e.g., Howard et al. in Astrophys. J. 831, 208, 2016; Kooi et al. in Solar Phys. 292, 56, 2017; Bisi et al. in EGU General Assembly Conference Abstracts, 13243, 2017) have all been restricted to a single line of sight (LOS) and, therefore, limited to providing estimates of the magnetic field strength. Modeling by Liu et al. (Astrophys. J. 665, 1439, 2007) and Jensen and Russell (Geophys. Res. Lett. 35, L02103, 2008) demonstrated that multiple LOS are necessary to recover the magnetic field strength and structure of the observed CME. We report the first successful observations of Faraday rotation through a CME using multiple lines of sight: 13 LOS across seven target radio fields. We made these radio observations using the Karl G. Jansky Very Large Array (VLA) at $1-2$ GHz frequencies in the triggered operation mode on 31 July 2015, using a constellation of cosmic radio sources through the solar corona at heliocentric distances of $8.2-19.5~\mathrm{R}_{\odot }$ . For LOS within $10~\mathrm{R}_{\odot }$ , the CME’s contribution to the measured RM was $\approx 0$ to −20 rad m−2, a significant enhancement over the coronal contribution. We assumed a force-free flux-rope structure for the CME’s magnetic field and explored three separate models for the CME’s plasma density: constant density, thin shell, and thick shell. The plasma densities and axial magnetic field strengths for the three models ranged over $5.4-6.4\times 10^{3}$ cm−3 and $26-35$ mG, respectively. Further, using all 13 LOS, we successfully determined the CME’s orientation and helicity.

Detecting multiple DLAs per spectrum in SDSS DR12 with Gaussian processes

ABSTRACT We present a revised version of our automated technique using Gaussian processes (GPs) to detect damped Lyman α absorbers (DLAs) along quasar (QSO) sightlines. The main improvement is to allow our GP pipeline to detect multiple DLAs along a single sightline. Our DLA detections are regularized by an improved model for the absorption from the Lyman α forest that improves performance at high redshift. We also introduce a model for unresolved sub-DLAs that reduces misclassifications of absorbers without detectable damping wings. We compare our results to those of two different large-scale DLA catalogues and provide a catalogue of the processed results of our GP pipeline using 158 825 Lyman α spectra from SDSS data release 12. We present updated estimates for the statistical properties of DLAs, including the column density distribution function, line density (dN/dX), and neutral hydrogen density (ΩDLA).

Measurement of cryogenic target position and implosion core offsets on OMEGA

Cryogenic target implosions currently performed on the University of Rochester's OMEGA Laser System [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)] are of deuterium–tritium-filled polystyrene shells held at near the triple point temperature (∼20 K) inside a cooled shroud that must be retracted from around the target just before the target is illuminated by OMEGA. As a consequence, impulses may be imparted to the target stalk, causing the target to depart from its ideal position centered at the aim point of the laser beams. The positions of cryogenic targets at the start of the laser pulse are determined in this work by comparing the positions of images of the cryogenic target implosion to that of a non-cryogenic target implosion that is accurately centered on the aim point of the beams. Images are taken from an array of up to five digitally recorded, x-ray pinhole cameras. Positions of the resultant implosion cores are determined along a single line of sight from x-ray images of these cores taken with an x-ray microscope operating in the time-integrated mode. The offsets of the cryogenic-target cores relative to the non-cryogenic-target cores are found to have a magnitude and direction consistent with the core forming in the direction of the target offset at the start of the laser pulse. The inferred offsets are therefore consistent with each other within errors. Neutron yields are seen to be affected by the target offset although with considerable scatter.