Bayesian inference and calibration of magnetic diagnostics.

The magnetic diagnostics across TAE Technologies' compact toroid fusion device include 28 internal and 45 external flux loops that measure poloidal flux and axial field strength, 64 three-axis (radial, toroidal, and axial) Mirnov probes, and 22 internal and external, axial-only Mirnov probes. Imperfect construction, installation, and physical constraints required a Bayesian approach for the calibration process to best account for errors in signals. These errors included flux loops not fitted to a perfect circle due to spatial constraints, Mirnov probes not perfectly aligned against their respective axes, and flux pickup that occurred within the insert (feedthrough) of the Mirnov probes. Our model-based calibration is derived from magnetostatic theory and the circuitry of the sensors. These models predicted outputs that were compared against experimental data. Using a simple least-squares optimization, we were able to predict flux loop data within 1% of relative error. For the Mirnov probes, we utilized Bayesian inference to determine three rotation angles and three amplifier gains. The results of this work not only gave our diagnostic measurements physical meaning, but also act as a safeguard to spot when instruments have malfunctioned, or when there is an error in database maintenance. This paper will go into the details of our calibration procedure, our Bayesian modeling, and the accuracy of our results compared to experimental data.

Age norms for grating acuity and contrast sensitivity in children using eye tracking technology.

KEY MESSAGES: Visual acuity is the most used method to assess visual function in children. Contrast sensitivity complements the information provided for visual acuity, but it is not commonly used in clinical practice. Digital devices are increasingly used as a method to evaluate visual function, due to multiple advantages. Testing with these devices can improve the evaluation of visual development in children from a few months of age. Visual acuity and contrast sensitivity tests, using eye tracking technology, are able to measure visual function in children across a wide range of ages, objectively, quickly and without need of an experienced examiner. PURPOSE: To report age-normative values for grating visual acuity and contrast sensitivity in healthy children using a digital device with eye tracking technology and to validate the grating acuity test. METHODS: In the first project of the study, we examined healthy children aged between 6 months and 7 years with normal ophthalmological assessment. Grating visual acuity (VA) and contrast sensitivity (CS) were assessed using a preferential gaze paradigm with a DIVE (Device for an Integral Visual Examination) assisted with eye tracking technology to provide age norms. For the validation project, we compared LEA grating test (LGT) with DIVE VA in a group of children aged between 6 months and 4 years with normal and abnormal visual development. RESULTS: Fifty-seven children (2.86 ± 1.55 years) were examined with DIVE VA test and 44 successfully completed DIVE CS test (3.06 ± 1.41 years). Both, VA and CS values increased with age, mainly along the first two years of life. Sixty-nine patients (1.34 ± 0.61 years) were included in the DIVE VA test validation. The mean difference between LGT and DIVE VA was - 1.05 ± 4.54 cpd with 95% limits of agreement (LoA) of - 9.95-7.84 cpd. Agreement between the two tests was higher in children younger than 1 year with a mean difference of - 0.19 ± 4.02 cpd. CONCLUSIONS: DIVE is an automatic, objective and reliable tool to assess several visual function parameters in children, and it has good agreement with classical VA tests, especially for the first stage of life.

Development of a Langmuir probe array for radial potential profile measurement in the collisional merging formation FRC.

The radial electric field in a field-reversed configuration (FRC) plasma plays an important role in the global stability and confinement properties. Herein, we developed a new Langmuir probe array named "Skewered probe" employed in measuring the radial potential profile in the collisional merging formation of an FRC in the FAT-CM (FRC Amplification via Translation - Collisional Merging) device. Because an FRC has a strong toroidal flow, the skewered probe consists of alternately skewered ring electrodes and ceramic beads on a thin stainless-steel tube to neutralize the effect of plasma flow. The developed array has nine electrodes, one every 2 cm from r = 9-25 cm, and it measures the FRC boundary in the case when the radius of the excluded flux ranges from 10 to 20 cm. The skewered probe also has one additional electrode that measures the potential near the chamber wall as a reference for the other electrodes. The radial potential profile of the FRC formed by the collisional merging method in the FAT-CM device was measured using the probe, and the results showed that the region of negative potential gradually changed to a positive potential after merging the FRCs. It was also shown that a strong outward electric field is formed near the separatrix at n = 2 rotational instability.

MHD mode identification by higher order singular value decomposition of C-2W Mirnov probe data.

The C-2W device (also known as "Norman") at TAE Technologies has proven successful at generating stable, long-lived field-reversed configuration (FRC) plasmas with record temperatures. The largest Mirnov probe array in C-2W measures three components of the magnetic field just inside the vessel wall at 64 locations distributed approximately evenly in the cylindrical vessel's azimuthal and axial dimensions. This nearly rectangular array of probes creates a unique opportunity to apply higher order singular value decomposition (HOSVD) to efficiently analyze the external magnetic field data for the purposes of reconstructing the magnetohydrodynamic mode structures in the FRC. In the first application of this method for this purpose, HOSVD is shown to quickly and effectively detect and separate toroidal modes while indicating longitudinal dependence of mode phases and amplitudes, enhancing the coherence and utility of the vast quantity of data produced by this array. Analysis of the data from the entire array at once via HOSVD proves not only computationally more efficient than methods that separately analyze groups of probes at different axial locations but also leads to improved mode resolution at axial locations where these modes are weaker.

The integrated diagnostic suite of the C-2W experimental field-reversed configuration device and its applications.

In the current experimental device of TAE Technologies, C-2W (also called "Norman"), record breaking advanced beam-driven field-reversed configuration (FRC) plasmas are produced and sustained in steady state utilizing variable energy neutral beams (15-40 keV, total power up to 20 MW), advanced divertors, bias electrodes, and an active plasma control system. This fully operational experiment is coupled with a fully operational suite of advanced diagnostic systems. The suite consists of 60+ individual systems spanning 20 categories, including magnetic sensors, Thomson scattering, interferometry/polarimetry, spectroscopy, fast imaging, bolometry, reflectometry, charged and neutral particle analysis, fusion product detection, and electric probes. Recently, measurements of main ion temperatures via a diagnostic neutral beam, axial profiles of energy flux from an array of bolometers, and divertor and edge plasma parameters via an extensive set of electric probes, interferometers, and spectrometers have all been made available. All the diagnostics work together to provide a complete picture of the FRC, fast-ion inventory, and edge plasma details enabling tomographic reconstruction of plasma parameter profiles and real-time plasma control.

The Haemostasis Traffic Light, a user-centred coagulation management tool for acute bleeding situations: a simulation-based randomised dual-centre trial.

The Haemostasis Traffic Light is a cognitive aid with a user-centred design to enhance and simplify situation awareness and decision-making during peri-operative bleeding. Its structure helps to prioritise therapeutic interventions according to the pathophysiology and the severity of the bleeding. This investigator-initiated, randomised, prospective, international, dual-centre study aimed to validate the Haemostasis Traffic Light by adapting it to the local coagulation protocols of two university hospitals. Between 9 January and 12 May 2020, we recruited 84 participants at the University Hospital Zurich, Switzerland, and the Italian Hospital of Buenos Aires, Argentina. Each centre included 21 resident and 21 staff anaesthetists. Participants were randomly allocated to either the text-based algorithm or the Haemostasis Traffic Light. All participants managed six bleeding scenarios using the same algorithm. In simulated bleeding scenarios, the design of the Haemostasis Traffic Light algorithm enabled more correctly solved cases, OR (95%CI) 7.23 (3.82-13.68), p < 0.001, and faster therapeutic decisions, HR (95%CI) 1.97 (1.18-3.29, p = 0.010). In addition, the tool improved therapeutic confidence, OR (95%CI) 4.31 (1.67-11.11, p = 0.003), and reduced perceived work-load coefficient (95%CI) -6.1 (-10.98 to -1.22), p = 0.020). This study provides empirical evidence for the importance of user-centred design in the development of haemostatic management protocols.

Magnetic diagnostic suite of the C-2W field-reversed configuration experiment.

A fundamental component of any magnetically confined fusion experiment is a firm understanding of the magnetic field. The increased complexity of the C-2W machine warrants an equally enhanced diagnostic capability. C-2W is outfitted with over 700 magnetic field probes of various types. They are both internal and external to the vacuum vessel. Inside, a linear array of innovative in-vacuum annular flux loop/B-dot combination probes provide information about plasma shape, size, pressure, energy, temperature, and trapped flux when coupled with established theoretical interpretations. A linear array of B-dot probes complement the azimuthally averaged measurements. A Mirnov array of 64 3D probes, with both low and high frequency resolution, detail plasma motion and MHD modal content via singular value decomposition analysis. Internal Rogowski probes measure axial currents flowing in the plasma jet. Outside, every feed-through for an internal probe has an external axial field probe. There are many external loops that measure the plasma formation dynamics and the total external magnetic flux. The external measurements are primarily used to characterize eddy currents in the vessel during a plasma shot. Details of these probes and the data derived from their signals are described.

Internal magnetic field measurements of translated and merged field-reversed configuration plasmas in the FAT-CM device.

Field-reversed configuration (FRC) Amplification via Translation-Collisional Merging (FAT-CM) experiments have recently commenced to study physics phenomena of colliding and merged FRC plasma states. Two independently formed FRCs are translated into the confinement region of the FAT-CM device, collided near the mid-plane of the device with a relative speed of up to ∼400 km/s, and a final merged FRC plasma state is achieved. To measure internal magnetic field profiles of the translated and merged FRC plasmas as well as to understand its collisional-merging process, an internal magnetic probe array, developed by TAE Technologies, has been installed in the mid-plane of the FAT-CM device. Initial magnetic field measurements indicate that both the translated and the merged FRC plasma states exhibit a clear field-reversed structure, which is qualitatively in good agreement with 2D MHD simulation. It is found and verified that a sufficient mirror field in the confinement region is required for colliding FRCs to be fully merged into a single FRC plasma state.

Fast-framing camera based observations of spheromak-like plasmoid collision and merging process using two magnetized coaxial plasma guns.

We have been conducting compact toroid (CT) collision and merging experiments by using two magnetized coaxial plasma guns. As is well known, an actual CT/plasmoid moves macroscopically in a confining magnetic field. Therefore, three-dimensional measurements are important in understanding the behavior of the CTs. To observe the macroscopic process, we adopted a fast-framing camera (ULTRA Cam HS-106E) developed by NAC Image Technology. The characteristics of this camera are as follows: a CCD color sensor, capable of capturing 120 images during one sequence with a frame rate of up to 1.25 MHz. Using this camera, we captured the global motion of a CT inside the magnetic field and the collision of two CTs at the mid-plane of the experimental device. Additionally, by using a color sensor, we captured the global change in the plasma emission of visible light during the CT collision/merging process. As a result of these measurements, we determined the CT's global motion and the changes in the CT's shape and visible emission. The detailed system setup and experimental results are presented and discussed.

Inference of field reversed configuration topology and dynamics during Alfvenic transients.

Active control of field reversed configuration (FRC) devices requires a method to determine the flux surface geometry and dynamic properties of the plasma during both transient and steady-state conditions. The current tomography (CT) method uses Bayesian inference to determine the plasma current density distribution using both the information from magnetic measurements and a physics model in the prior. Here we show that, from the inferred current sources, the FRC topology and its axial stability properties are readily obtained. When Gaussian process priors are used and the forward model is linear, the CT solution involves non-iterative matrix operations and is then ideally suited for deterministic real-time applications. Because no equilibrium assumptions are used in this case, inference of plasma topology and dynamics up to Alfvenic frequencies then becomes possible. Inference results for the C-2U device exhibit self-consistency of motions and forces during Alfvenic transients, as well as good agreement with plasma imaging diagnostics.

Face recognition impairment in small for gestational age and preterm children.

BACKGROUND: Infants born prematurely or with low birth weight are at increased risk of visual perceptual impairment. Face recognition is a high-order visual ability important for social development, which has been rarely assessed in premature or low birth weight children. AIMS: To evaluate the influence of prematurity and low birth weight on face recognition skills. METHODS: Seventy-seven children were evaluated as part of a prospective cohort study. They were divided into premature and term birth cohorts. Children with a birth weight below the 10th centile were considered small for gestational age. All children underwent a full ophthalmologic assessment and evaluation of face recognition skills using the Facial Memory subtest from the Test of Memory and Learning. RESULTS: Premature infants scored worse on immediate face recognition compared to term infants. However, after adjusting for birth weight, prematurity was not associated with worse outcomes. Independent of gestational age, outcomes of low birth weight children were worse than those of appropriate birth weight children, for immediate face recognition (odds ratio [OR], 5.14; 95% confidence interval [CI], 1.32-21.74) and for face memory (OR, 4.48; 95% CI, 1.14-16.95). CONCLUSIONS: Being born small for gestational age is associated with suboptimal face recognition skills, even in children without major neurodevelopmental problems.

Characterization of compact-toroid injection during formation, translation, and field penetration.

We have developed a compact toroid (CT) injector system for particle refueling of the advanced beam-driven C-2U field-reversed configuration (FRC) plasma. The CT injector is a magnetized coaxial plasma gun (MCPG), and the produced CT must cross the perpendicular magnetic field surrounding the FRC for the refueling of C-2U. To simulate this environment, an experimental test stand has been constructed. A transverse magnetic field of ∼1 kG is established, which is comparable to the C-2U axial magnetic field in the confinement section, and CTs are fired across it. On the test stand we have been characterizing and studying CT formation, ejection/translation from the MCPG, and penetration into transverse magnetic fields.

Jet outflow and open field line measurements on the C-2U advanced beam-driven field-reversed configuration plasma experiment.

Knowledge and control of the axial outflow of plasma particles and energy along open-magnetic-field lines are of crucial importance to the stability and longevity of the advanced beam-driven field-reversed configuration plasma. An overview of the diagnostic methods used to perform measurements on the open field line plasma on C-2U is presented, including passive Doppler impurity spectroscopy, microwave interferometry, and triple Langmuir probe measurements. Results of these measurements provide the jet ion temperature and axial velocity, electron density, and high frequency density fluctuations.

Enhanced magnetic field probe array for improved excluded flux calculations on the C-2U advanced beam-driven field-reversed configuration plasma experiment.

External flux conserving coils were installed onto the exterior of the C-2U [M. W. Binderbauer et al., Phys. Plasmas 22, 056110 (2015)] confinement vessel to increase the flux confinement time of the system. The 0.5 in. stainless steel vessel wall has a skin time of ∼5 ms. The addition of the external copper coils effectively increases this time to ∼7 ms. This led to better-confined/longer-lived field-reversed configuration (FRC) plasmas. The fringing fields generated by the external coils have the side effect of rendering external field measurements invalid. Such measurements were key to the previous method of excluded flux calculation [M. C. Thompson et al., Rev. Sci. Instrum. 83, 10D709 (2012)]. A new array of B-dot probes and Rogowski coils were installed to better determine the amount of flux leaked out of the system and ultimately provide a more robust measurement of plasma parameters related to pressure balance including the excluded flux radius. The B-dot probes are surface mountable chip inductors with inductance of 33 µH capable of measuring the DC magnetic field and transient field, due to resistive current decay in the wall/coils, when coupled with active integrators. The Rogowski coils measure the total change in current in each external coil (150 A/2 ms). Currents were also actively driven in the external coils. This renders the assumption of total flux conservation invalid which further complicates the analysis process. The ultimate solution to these issues and the record breaking resultant FRC lifetimes will be presented.

Effect of prematurity and low birth weight in visual abilities and school performance.

BACKGROUND: Prematurity and low birth weight are known risk factors for cognitive and developmental impairments, and school failure. Visual perceptual and visual motor skills seem to be among the most affected cognitive domains in these children. AIMS: To assess the influence of prematurity and low birth weight in visual cognitive skills and school performance. METHODS: We performed a prospective cohort study, which included 80 boys and girls in an age range from 5 to 13. Subjects were grouped by gestational age at birth (preterm, <37 weeks; term, 37-42 weeks) and birth weight (small for gestational age (SGA), <10th centile; appropriate weight for gestational age (AGA), ≥10th centile). Each child underwent full ophthalmologic assessment and standardized testing of visual cognitive abilities (Test of Visual Perceptual Skills and Test of Visual Analysis Skills). Parents completed a questionnaire on school performance in children. RESULTS: Figure-ground skill and visual motor integration were significantly decreased in the preterm birth group, compared with term control subjects (figure-ground: 45.7 vs 66.5, p=0.012; visual motor integration, TVAS: (9.9 vs 11.8, p=0.018), while outcomes of visual memory (29.0 vs 47.7, p=0.012), form constancy (33.3 vs 52.8, p=0.019), figure-ground (37.4 vs 65.6, p=0.001), and visual closure (43.7 vs 62.6 p=0.016) testing were lower in the SGA (vs AGA) group. Visual cognitive difficulties corresponded with worse performance in mathematics (r=0.414, p=0.004) and reading (r=0.343, p=0.018). CONCLUSION: Specific patterns of visual perceptual and visual motor deficits are displayed by children born preterm or SGA, which hinder mathematics and reading performance.

Development of a magnetized coaxial plasma gun for compact toroid injection into the C-2 field-reversed configuration device.

A compact toroid (CT) injector was developed for the C-2 device, primarily for refueling of field-reversed configurations. The CTs are formed by a magnetized coaxial plasma gun (MCPG), which consists of coaxial cylindrical electrodes and a bias coil for creating a magnetic field. First, a plasma ring is generated by a discharge between the electrodes and is accelerated by Lorenz self-force. Then, the plasma ring is captured by an interlinkage flux (poloidal flux). Finally, the fully formed CT is ejected from the MCPG. The MCPG described herein has two gas injection ports that are arranged tangentially on the outer electrode. A tungsten-coated inner electrode has a head which can be replaced with a longer one to extend the length of the acceleration region for the CT. The developed MCPG has achieved supersonic CT velocities of ∼100 km/s. Plasma parameters for electron density, electron temperature, and the number of particles are ∼5 × 10(21) m(-3), ∼40 eV, and 0.5-1.0 × 10(19), respectively.

An International Multicenter Review of the Malignancy Rate of Excised Papillomatous Breast Lesions.

BACKGROUND: Papillary lesions of the breast are a relatively rare, but heterogeneous group ranging from benign to atypical and malignant. Debate exists regarding the optimal management of these lesions. In the absence of more accurate risk-stratification models, traditional management guidelines recommend surgical excision, despite the majority of lesions proving benign. This study sought to determine the rate of malignancy in excised breast papillomas and to elucidate whether there exists a population in which surgical excision may be unnecessary. METHODS: A multicenter international retrospective review of core biopsy diagnosed breast papillomas and papillary lesions was performed between 2009 and 2013, following institutional ethical approval. Patient demographics, histopathological, and radiological findings were recorded. All data was tabulated, and statistical analysis performed using Stata. RESULTS: A total of 238 patients were included in the final analysis. The age profile of those with benign pathology was significantly younger than those with malignant pathology (p < 0.001). Atypia on core needle biopsy was significantly associated with a final pathological diagnosis of malignancy (OR = 2.73). The upgrade rate from benign core needle biopsy to malignancy on the final pathological sample was 14.4 %; however, only 3.7 % had invasive cancer. CONCLUSIONS: This international dataset is one of the largest in the published literature relating to breast papillomas. The overall risk of malignancy is significantly associated with older age and the presence of atypia on core needle biopsy. It may be possible to stratify higher-risk patients according to age and core needle biopsy findings, thereby avoiding surgery on low-risk patients.

Achieving a long-lived high-beta plasma state by energetic beam injection.

Developing a stable plasma state with high-beta (ratio of plasma to magnetic pressures) is of critical importance for an economic magnetic fusion reactor. At the forefront of this endeavour is the field-reversed configuration. Here we demonstrate the kinetic stabilizing effect of fast ions on a disruptive magneto-hydrodynamic instability, known as a tilt mode, which poses a central obstacle to further field-reversed configuration development, by energetic beam injection. This technique, combined with the synergistic effect of active plasma boundary control, enables a fully stable ultra-high-beta (approaching 100%) plasma with a long lifetime.

Langmuir probe diagnostic suite in the C-2 field-reversed configuration.

Several in situ probes have been designed and implemented into the diagnostic array of the C-2 field-reversed configuration (FRC) at Tri Alpha Energy [M. Tuszewski et al. (the TAE Team), Phys. Rev. Lett. 108, 255008 (2012)]. The probes are all variations on the traditional Langmuir probe. They include linear arrays of triple probes, linear arrays of single-tipped swept probes, a multi-faced Gundestrup probe, and an ion-sensitive probe. The probes vary from 5 to 7 mm diameter in size to minimize plasma perturbations. They also have boron nitride outer casings that prevent unwanted electrical breakdown and reduce the introduction of impurities. The probes are mounted on motorized linear-actuators allowing for programmatic scans of the various plasma parameters over the course of several shots. Each probe has a custom set of electronics that allows for measurement of the desired signals. High frequency ( > 5MHz) analog optical-isolators ensure that plasma parameters can be measured at sub-microsecond time scales while providing electrical isolation between machine and data acquisition systems. With these probes time-resolved plasma parameters (temperature, density, spatial potential, flow, and electric field) can be directly/locally measured in the FRC jet and edge/scrape-off layer.

Tomographic imaging system for measuring impurity line emission in a field-reversed configuration.

A 16 chord optical tomography system has been developed and implemented in the flux coil generated-field reversed configuration (FRC). The chords are arranged in two fans of eight, which cover ~35% of the vessel area at the midplane. Each illuminate separate photomultiplier tubes (PMTs) which are fitted with narrow band-pass filters. In this case, filters are centered at 434.8 nm to measure emission from singly ionized argon. PMT crosstalk is negligible. Background noise due to electron radiation and H(γ) line radiation is <10% of argon emission. The spatial resolution of the reconstruction is 1.5 cm. Argon is introduced using a puff valve and tube designed to impart the gas into the system as the FRC is forming. Reconstruction of experimental data results in time-dependent, 2D emissivity profiles of the impurity ions. Analysis of these data show radial, cross-field diffusion to be in the range of 10-10(3) m(2)∕s during FRC equilibrium.