First measurements of p11B fusion in a magnetically confined plasma.

Proton-boron (p11B) fusion is an attractive potential energy source but technically challenging to implement. Developing techniques to realize its potential requires first developing the experimental capability to produce p11B fusion in the magnetically-confined, thermonuclear plasma environment. Here we report clear experimental measurements supported by simulation of p11B fusion with high-energy neutral beams and boron powder injection in a high-temperature fusion plasma (the Large Helical Device) that have resulted in diagnostically significant levels of alpha particle emission. The injection of boron powder into the plasma edge results in boron accumulation in the core. Three 2 MW, 160 kV hydrogen neutral beam injectors create a large population of well-confined, high -energy protons to react with the boron plasma. The fusion products, MeV alpha particles, are measured with a custom designed particle detector which gives a fusion rate in very good relative agreement with calculations of the global rate. This is the first such realization of p11B fusion in a magnetically confined plasma.

Fiber Bragg grating sensor array for detecting heat flux in vacuum.

In TAE Technologies' current experimental device, C-2W (also called "Norman"), record-breaking, advanced beam-driven field-reversed configuration plasmas are produced and sustained in steady state utilizing variable energy neutral beams, advanced divertors, edge-biasing electrodes, and an active plasma control system [Gota et al., Nucl. Fusion 61, 106039 (2021)]. A novel diagnostic has been developed by TAE Technologies to leverage an industrial fiber Bragg grating (FBG) sensor array to detect heat flux along the wall of the vacuum vessel from a plasma discharge. The system consists of an optical fiber with FBG sensors distributed along its length, housed in a pressurized steel sheath. Each FBG sensor is constructed to reflect a different wavelength, the exact value of which is sensitive to the strain and temperature at the location of the grating in the fiber. The fiber is illuminated with broadband light, and the data acquisition system analyzes the spectrum of reflected light to determine the temperature at the location of each FBG. We have installed four of these vacuum-rated FBG sensor arrays on the C-2W experiment, each with 30 individual FBG sensors spaced at 0.15 m intervals along the 5 m fiber, with a 100 Hz acquisition rate. The measurement of temperature change due to a plasma discharge provides a single data point at each sensor location, creating a 120-point heat map of the vacuum vessel.

A novel technique for in situ calibration of the C-2W electromagnetic neutral particle analyzer utilizing machine learning.

In TAE Technologies' current experimental device, C-2W, neutral beam injection creates a large fast ion population that sustains a field-reversed configuration (FRC) plasma. Diagnosis of these fast ions is therefore critical for understanding the behavior of the FRC. Neutral Particle Analyzers (NPAs) are used to measure the energy spectrum of fast ions that charge exchange on background or beam neutrals and are lost from the plasma. To ensure correct diagnosis of the fast ion population, a calibration check of the NPAs was performed. A novel, generally applicable method for an in situ relative calibration of diagnostics on an unknown source with a small dataset was developed. The method utilizes a machine learning technique, Generalized Additive Models (GAMs), to reconstruct the diagnostic source distribution, and Stochastic Gradient Descent (SGD) to determine the NPA channel calibration factors. The results on both synthetic and experimental datasets are presented.

Secondary electron emission detectors for neutral beam characterization on C-2W.

Heating, current drive, and partial fueling from neutral beam injection are essential to sustainment of C-2W field-reversed configuration plasmas. C-2W has eight 2.1 MW neutral beams (16.8 MW of total electrical power), capable of providing a beam of 15 keV hydrogen neutrals for 30 ms. To maximize the effectiveness of neutral beam injection, duct losses must be minimized by maintaining beam alignment and optimizing beam current for minimum divergence. Each beam terminates on a vertical and horizontal array of secondary electron emission detectors (nine in the vertical, seven in the horizontal, and sharing one in the middle). The molybdenum detectors are spatially separated to characterize the beam size and alignment. With knowledge of the geometry of the vacuum ducts and horizontal and vertical beam profiles from test stand measurements, the focal length, divergence, and power loss were calculated. Through characterization, the set of neutral beams are optimized to inject up to 12 MW of power into the confinement vessel throughout the plasma discharge.

Measuring dynamic fast ion spatial profiles with fusion protons in the Madison Symmetric Torus.

Neutral beam injected fast ions play a dominant role in both the field reversed configuration (FRC) at TAE Technologies and the Madison Symmetric Torus (MST) reversed field pinch (RFP), making fast ion diagnosis a major pillar of both research programs. And as strongly self-organized plasmas, the FRC and RFP similarly exhibit dynamic relaxation events which can redistribute fast ions. Recently, a collaboration between TAE Technologies and the University of Wisconsin was conducted to develop a method for measuring a fast changing fast ion spatial profile with a fusion proton detector and to investigate commonalities between the two plasmas. The steerable detector was designed and built at TAE and installed on MST. The fusion proton emission profile resulting from injection of a 25 kV deuterium neutral beam is measured with better than 5 cm spatial resolution and 100 µs temporal resolution over the course of several 10s of shots. The fast ion density profile, forward modeled by tracing the orbits of the 3 MeV protons through a reconstructed magnetic equilibrium, is observed to flatten during global magnetic tearing mode activity, dropping by 30% in the core and increasing by a similar amount at the edge. The equilibrium profile is observed to be consistent with measurements made with a collimated neutron detector.

Absolute calibration of neutron detectors on the C-2U advanced beam-driven FRC.

In the C-2U fusion energy experiment, high power neutral beam injection creates a large fast ion population that sustains a field-reversed configuration (FRC) plasma. The diagnosis of the fast ion pressure in these high-performance plasmas is therefore critical, and the measurement of the flux of neutrons from the deuterium-deuterium (D-D) fusion reaction is well suited to the task. Here we describe the absolute, in situ calibration of scintillation neutron detectors via two independent methods: firing deuterium beams into a high density gas target and calibration with a 2 × 107 n/s AmBe source. The practical issues of each method are discussed and the resulting calibration factors are shown to be in good agreement. Finally, the calibration factor is applied to C-2U experimental data where the measured neutron rate is found to exceed the classical expectation.

Fusion proton diagnostic for the C-2 field reversed configuration.

Measurements of the flux of fusion products from high temperature plasmas provide valuable insights into the ion energy distribution, as the fusion reaction rate is a very sensitive function of ion energy. In C-2, where field reversed configuration plasmas are formed by the collision of two compact toroids and partially sustained by high power neutral beam injection [M. Binderbauer et al., Phys. Rev. Lett. 105, 045003 (2010); M. Tuszewski et al., Phys. Rev. Lett. 108, 255008 (2012)], measurements of DD fusion neutron flux are used to diagnose ion temperature and study fast ion confinement and dynamics. In this paper, we will describe the development of a new 3 MeV proton detector that will complement existing neutron detectors. The detector is a large area (50 cm(2)), partially depleted, ion implanted silicon diode operated in a pulse counting regime. While the scintillator-based neutron detectors allow for high time resolution measurements (∼100 kHz), they have no spatial or energy resolution. The proton detector will provide 10 cm spatial resolution, allowing us to determine if the axial distribution of fast ions is consistent with classical fast ion theory or whether anomalous scattering mechanisms are active. We will describe in detail the diagnostic design and present initial data from a neutral beam test chamber.

A two photon absorption laser induced fluorescence diagnostic for fusion plasmas.

The quality of plasma produced in a magnetic confinement fusion device is influenced to a large extent by the neutral gas surrounding the plasma. The plasma is fueled by the ionization of neutrals, and charge exchange interactions between edge neutrals and plasma ions are a sink of energy and momentum. Here we describe a diagnostic capable of measuring the spatial distribution of neutral gas in a magnetically confined fusion plasma. A high intensity (5 MW/cm(2)), narrow bandwidth (0.1 cm(-1)) laser is injected into a hydrogen plasma to excite the Lyman ß transition via the simultaneous absorption of two 205 nm photons. The absorption rate, determined by measurement of subsequent Balmer α emission, is proportional to the number of particles with a given velocity. Calibration is performed in situ by filling the chamber to a known pressure of neutral krypton and exciting a transition close in wavelength to that used in hydrogen. We present details of the calibration procedure, including a technique for identifying saturation broadening, measurements of the neutral density profile in a hydrogen helicon plasma, and discuss the application of the diagnostic to plasmas in the DIII-D tokamak.

Classical impurity ion confinement in a toroidal magnetized fusion plasma.

High-resolution measurements of impurity ion dynamics provide first-time evidence of classical ion confinement in a toroidal, magnetically confined plasma. The density profile evolution of fully stripped carbon is measured in MST reversed-field pinch plasmas with reduced magnetic turbulence to assess Coulomb-collisional transport without the neoclassical enhancement from particle drift effects. The impurity density profile evolves to a hollow shape, consistent with the temperature screening mechanism of classical transport. Corroborating methane pellet injection experiments expose the sensitivity of the impurity particle confinement time to the residual magnetic fluctuation amplitude.

Anisotropic ion heating and tail generation during tearing mode magnetic reconnection in a high-temperature plasma.

Complementary measurements of ion energy distributions in a magnetically confined high-temperature plasma show that magnetic reconnection results in both anisotropic ion heating and the generation of suprathermal ions. The anisotropy, observed in the C(+6) impurity ions, is such that the temperature perpendicular to the magnetic field is larger than the temperature parallel to the magnetic field. The suprathermal tail appears in the majority ion distribution and is well described by a power law to energies 10 times the thermal energy. These observations may offer insight into the energization process.

Toroidal charge exchange recombination spectroscopy measurements on MST.

Charge exchange recombination spectroscopy measurements of the poloidal component of the C(+6) temperature and flow in the Madison Symmetric Torus have been vital in advancing the understanding of the ion dynamics in the reversed field pinch. Recent work has expanded the diagnostic capability to include toroidal measurements. A new toroidal view overcomes a small signal-to-background ratio (5%-15%) to make the first localized measurements of the parallel component of the impurity ion temperature in the core of the reversed field pinch. The measurement is made possible through maximal light collection in the optical design and extensive atomic modeling in the fitting routine. An absolute calibration of the system allowed the effect of Poisson noise in the signal on line fitting to be quantified. The measurement is made by stimulating emission with a recently upgraded 50 keV hydrogen diagnostic neutral beam. Radial localization is ∼4 cm(2), and good temporal resolution (100 µs) is achieved by making simultaneous emission and background measurements with a high-throughput double-grating spectrometer.

Observation of weak impact of a stochastic magnetic field on fast-ion confinement.

Fast ions are observed to be very well confined in the Madison Symmetric Torus reversed field pinch despite the presence of stochastic magnetic field. The fast-ion energy loss is consistent with the classical slowing down rate, and their confinement time is longer than expected by stochastic estimates. Fast-ion confinement is measured from the decay of d-d neutrons following a short pulse of a 20 keV atomic deuterium beam. Ion confinement agrees with computation of particle trajectories in the stochastic magnetic field, and is understood through consideration of ion guiding center islands.

Clinicopathological correlation of epiretinal membranes and posterior lens opacification following perfluorohexyloctane tamponade.

BACKGROUND/AIMS: Epiretinal and retrolental proliferation may occur during prolonged use of the novel tamponade agent perfluorohexyloctane (F(6)H(8)). This study aims to determine whether there is any histological evidence that F(6)H(8) has a role in the formation of these membranes. METHODS: Eight epiretinal membranes and three opaque posterior lens capsules were excised from patients in whom F(6)H(8) had been used as a long term retinal tamponade agent. The membranes and capsules were examined employing light microscopic methods, including immunohistochemistry. RESULTS: The epiretinal membranes showed histological features typical of proliferative vitreoretinopathy (PVR) epiretinal membranes, but they also exhibited a dense macrophagic infiltration. In addition, three of the membranes contained multinucleated cells. Macrophages represented up to 30% of the cells present and appeared to contain large intracytoplasmic vacuoles. Similar cells were seen on the back of the posterior lens capsule in one specimen and all three capsules had posterior migration of lens epithelium. CONCLUSION: The pathological findings are not simply those of PVR. The macrophage infiltration suggests that there may be a biological reaction to F(6)H(8) which could reflect its surmised propensity to emulsify. Further investigations concerning the cellular response to this promising tamponade agent are warranted.

Synthesis of osteonectin by human retinal pigment epithelial cells is modulated by cell density.

PURPOSE: To determine whether human retinal pigment epithelial (HRPE) cells are able to synthesize the antiadhesive protein osteonectin, also known as secreted protein, acidic and rich in cysteine (SPARC). Additionally, because locally produced SPARC may modulate cellular behavior during tissue repair, to ascertain whether HRPE SPARC production and HRPE proliferation, migration, and/or differentiation are associated, in a simple HRPE wound-healing model. METHODS: Immunohistochemical and Western blot analyses of SPARC protein expression by low- and high-density cultured HRPE cells were undertaken. Total RNA extracted from cultures was studied by reverse transcription-polymerase chain reaction (RT-PCR) and Northern blot analysis. Western and Northern blot analyses were evaluated by densitometry. Experiments were repeated with HRPE cells cultured in the presence of 1, 10, or 100 microM of the differentiating agents butyric acid (BA) and retinoic acid (RA). RESULTS: HRPE cell cultures exhibited SPARC immunoreactivity. Western blot analysis of cell lysates and conditioned media showed a 43-kDa protein. RT-PCR and Northern blot analysis confirmed the presence of SPARC mRNA (with transcripts at 2.2 and 3.0 kb). Protein and mRNA transcript band densitometry revealed a higher proportion of SPARC protein and mRNA in high-density HRPE cell culture than in low-density culture. Neither BA nor RA (at the concentrations assessed) had a significant effect on SPARC production by HRPE cells in high- or low-density culture. CONCLUSIONS: HRPE can synthesize SPARC. Although the findings do not support an invariable association between SPARC production by HRPE and HRPE proliferation, migration, or differentiation, they demonstrate that synthesis of SPARC by HRPE is modulated by cell density.

Matrix and the retinal pigment epithelium in proliferative retinal disease.

In their normal state, RPE cell are strongly adherent to Bruch's membrane. Certain pathological conditions such as retinal detachment cause an injury-type response (probably augmented or induced by the local accumulation of a variety of substances which modulate cell behaviour) in which RPE begin to dissociate from the membrane. This RPE-Bruch's membrane separation may be mediated by proteins with counter-adhesive properties and proteolytic enzymes, partly derived from the RPE themselves. Concomitant with the RPE disassociation, the cells begin to lose tertiary differentiation characteristics and gain macrophage-like features. When the "free" RPE arrive at the surface of the neuroretina, they may attach to or create a provisional matrix. Some of the cells adopt a fibroblast-like phenotype. This phenotype is similar to that of the dermal fibroblast during cutaneous wound repair and the fibroblastic RPE synthesise the types of matrix components found in healing skin wounds. Many of these molecules in turn further modulate the activities of the cells via several families of cell surface receptors, while the RPE continue to remodel the new matrix with a range of proteolytic enzymes. The resulting tissue (or membrane) has many of the features of a contractile scar and is the hallmark of the condition known as proliferative vitreoretinopathy (PVR). Thus the development of PVR, and the resulting tractional distortion of the neuroretina, appears to be dependent on RPE-matrix interactions. The interactions present a number of potential therapeutic targets for the management of the disorder.

Identification of free and conjugated ecdysteroids in cercariae of the schistosome Trichobilharzia ocellata.

Extracts of cercariae of the avian schistosome Trichobilharzia ocellata were analysed for the presence of ecdysteroids by radioimmunoassay, high-performance liquid chromatography monitoring fractions by radioimmunoassay, and gas chromatography/mass spectrometry (selected ion monitoring). Both free ecdysteroids and polar conjugated ecdysteroids were detected in the cercarial extracts. The free ecdysteroid fraction, as well as the hydrolysed polar conjugated ecdysteroid fraction, contained both ecdysone and 20-hydroxyecdysone in approximately equal amounts. The amount of ecdysteroids detected is comparable to those found in other platyhelminths. A possible role for the ecdysteroids in the development of the parasite and/or the interactions between the parasite and its intermediate host, the freshwater snail Lymnaea stagnalis, is discussed.

Quantification and partial characterisation of regulatory peptides in the liver fluke, Fasciola hepatica, from different mammalian hosts.

1. Extracts of the liver fluke, Fasciola hepatica from three different hosts (cow, sheep, rat) have been subjected to radioimmunoassay using antisera to 6 mammalian regulatory peptides. 2. Immunoreactivity was measured to pancreatic polypeptide, substance P, peptide histidine isoleucine and gastrin-releasing peptide. Levels of each peptide varied considerably in flukes from different hosts. 3. Reverse-phase HPLC of rat and sheep fluke extracts revealed three molecular forms of tachykinin immunoreactivity and single peaks of pancreatic polypeptide and peptide histidine isoleucine immunoreactivity. No GRP-immunoreactivity was detected by RIA of HPLC fractions.

Isolation and partial sequencing of a pancreatic polypeptide-like neuropeptide from the liver fluke, Fasciola hepatica.

1. A pancreatic polypeptide (PP)-immunoreactive neuropeptide has been isolated and partially sequenced from the liver fluke, Fasciola hepatica. 2. Gel permeation chromatography of an acid ethanol extract of cattle flukes showed that the peptide is similar in size to mammalian (bovine) PP. 3. The Fasciola peptide was purified to homogeneity by means of reverse-phase HPLC, employing different column chemistries. 4. The purified peptide was sequenced using automated gas-phase Edman degradation and the first 24 amino acid residues determined.