Confinement Vessel Research Articles

High-fidelity inference of local impurity profiles in C-2W using Bayesian tomography.

In C-2W (also called "Norman") [1], beam-driven field reversed configuration plasmas embedded in a magnetic mirror are produced and sustained in a steady state. A multi-chord passive Doppler spectroscopy diagnostic provides line-integrated impurity emission measurements near the center plane of the confinement vessel with fast time resolution. The high degree of plasma non-uniformity across optical sightlines can preclude direct fitting of the measured line-integrated spectra. To overcome this challenge, local impurity profiles are inferred using Bayesian tomography, a superior analysis technique based on a complete forward model of the diagnostic. The measured emission of O4+ triplet lines near 278.4nm is modeled assuming two independent populations: thermal and beam ions. Gaussian processes are used to generate and infer local profiles. The inference incorporates details of the geometrical arrangement of the diagnostic, instrument function, intensity calibration, and a noise model. Markov chain Monte Carlo (MCMC) sampling of the posterior distribution of solutions provides high-fidelity uncertainty estimates. The reconstructed O4+ impurity profiles are consistent with data from other diagnostics and show good agreement with expected physics based on previously developed models of biasing circuit and impurity transport.

Crowding-induced morphological changes in synthetic lipid vesicles determined using smFRET.

Lipid vesicles are valuable mesoscale molecular confinement vessels for studying membrane mechanics and lipid-protein interactions, and they have found utility among bio-inspired technologies, including drug delivery vehicles. While vesicle morphology can be modified by changing the lipid composition and introducing fusion or pore-forming proteins and detergents, the influence of extramembrane crowding on vesicle morphology has remained under-explored owing to a lack of experimental tools capable of capturing morphological changes on the nanoscale. Here, we use biocompatible polymers to simulate molecular crowding in vitro, and through combinations of FRET spectroscopy, lifetime analysis, dynamic light scattering, and single-vesicle imaging, we characterize how crowding regulates vesicle morphology. We show that both freely diffusing and surface-tethered vesicles fluorescently tagged with the DiI and DiD FRET pair undergo compaction in response to modest concentrations of sorbitol, polyethylene glycol, and Ficoll. A striking observation is that sorbitol results in irreversible compaction, whereas the influence of high molecular weight PEG-based crowders was found to be reversible. Regulation of molecular crowding allows for precise control of the vesicle architecture in vitro, with vast implications for drug delivery and vesicle trafficking systems. Furthermore, our observations of vesicle compaction may also serve to act as a mechanosensitive readout of extramembrane crowding.

Classification of ablation mode during impact of hot liquid jet on a solid

The ablation consecutive to hot jet impingement is a safety issue for future Sodium Fast Reactors (SFR) core-catcher that can occur during relocation of molten fuel (corium) under severe nuclear accident situation. Much is still unknown on the ablation phenomenon especially explanations on cavity shape are lacking. However, these data are required to specify the core-catchers which will be used in future nuclear reactors’ vessel to prevent the corium from drilling through the confinement vessel during severe accident. To tackle this subject, data from experiments are obtained and analyzed to identify first order physical mechanisms at stake, and their links to geometry of the cavity. Two ablation mechanisms are noticed, the film ablation regime, for which liquid exits the cavity as a liquid film followed by the pool effect for which the cavity is filled with liquid. The analysis of results shows that the cavity shape is fixed during the film ablation regime and translates as ablation proceeds. Modes of liquid exit from the cavity are analyzed as well as the shapes the cavity assumes. Liquid/air interface temperature is also determined, in the film ablation regime. An explanation of cavity shape is presented. Conditions based on dimensionless numbers are put forward to differentiate between different cavity shapes and liquid exit modes. A first model for transition between film and pool effect ablation regimes is presented. It is the first time to the best of our knowledge that such analyses are undertaken. These give new tools for ablation risk assessment.

Measurements of impurity ion temperature and velocity distributions via active charge-exchange recombination spectroscopy in C-2W.

In TAE Technologies' C-2W experiment, electrode biasing is utilized for boundary control of a field-reversed configuration (FRC) plasma embedded in a magnetic mirror. Understanding the underlying physics associated with FRC rotation, stabilization, and heating is crucial for improving machine performance. Impurity ion rotation and temperature are sensitive to biasing effects, and measurements of these quantities can provide insight into important plasma dynamics and overall effectiveness of the biasing system. To this end, a charge-exchange recombination spectroscopy (ChERS) diagnostic was developed and deployed to measure local impurity ion temperature and velocity in the confinement vessel of C-2W. The system utilizes a new diagnostic neutral beam (40 keV, 8.5A) and a fiber-coupled spectrometer with an image-intensified high-speed camera to measure beam-induced spectral line emission at multiple lines-of-sight. Design details and the first experimental results obtained with this new diagnostic are presented and discussed.

Investigation of Hydrogen Glow Discharge Cleaning Side Effects on Tungsten

Hydrogen glow discharge cleaning (H-GDC) is a routine conditioning procedure for the modern tokamaks and the future fusion machines, including ITER. Due to the low energy of hydrogen ions in glow discharge plasmas, the probability of any considerable damage to the plasma-facing components was mainly ignored. In this work, Tungsten, as the primary candidate for the plasma-facing materials in tokamaks, is considered for studies regarding effects of the H-GDC procedure on the material during a routine vacuum vessel conditioning in Damavand tokamak. After performing routine H-GDC using pure hydrogen, the formation of loosely attached nanostructured bundles (NSBs) on the surface of the tungsten samples was observed. The presence of the NSBs, which can be a source of dust, would be significant due to their possible effects on the functionality of the future fusion plasma devices. The NSBs are observed on the tungsten samples with the surface temperature of <370 K after 2.5–4 hours of hydrogen ion bombardment with incident energy of ≈120 eV and fluence of ≈(2–3.5) × 1022 m–2. The surface modifications of specimens exposed to H‑GDC were examined using a material probe experiment and several surface analysis techniques such as SEM, EDX, XRD, and ERDA. Therefore, the formation of loose nanostructures on the wall of plasma confinement vessels due to H-GDC draws attention to probable damaging effects of this phenomenon upon functionality and outcomes of tokamaks.

The effect of the third invariant on the strength and failure of boron carbide and silicon carbide

AbstractThis article presents new test data to assess the effect the third invariant has on the strength and failure of two ceramic materials: boron carbide and silicon carbide. Two experimental techniques are used: the Brazilian test that produces a biaxial state of stress, and a new technique that uses a high‐pressure confinement vessel to load a specially designed dumbbell specimen in triaxial extension. The dumbbell geometry provides two important advantages over the typically used cylindrical specimen: no adhesive is required to bond the specimen to the load cell because the dumbbell geometry naturally takes the specimen into tension, and any loading asymmetries are essentially eliminated due to the axisymmetric geometry. The results show that when the stress state is on the tensile meridian the equivalent stress at failure is constant, independent of the hydrostatic pressure. The average equivalent stress at failure is for boron carbide and for silicon carbide. The Brazilian test was only performed on boron carbide and failed at , much higher than when on the tensile meridian () indicating that the effect of the third invariant is significant (because of the difference in the failure strength) and must be accounted for to accurately predict when failure will occur.

Symmetric ideal magnetofluidostatic equilibria with nonvanishing pressure gradients in asymmetric confinement vessels

We study the possibility of constructing steady magnetic fields satisfying the force balance equation of ideal magnetohydrodynamics with tangential boundary conditions in asymmetric confinement vessels, i.e., bounded regions that are not invariant under continuous Euclidean isometries (translations, rotations, or their combination). This problem is often encountered in the design of next-generation fusion reactors. We show that such configurations are possible if one relaxes the standard assumption that the vessel boundary corresponds to a pressure isosurface. We exhibit a smooth solution that possesses a Euclidean symmetry and yet solves the boundary value problem in an asymmetric ellipsoidal domain while sustaining a nonvanishing pressure gradient. This result provides a definitive answer to the problem of existence of regular ideal magnetofluidostatic equilibria in asymmetric bounded domains. The question remains open whether regular asymmetric solutions of the boundary value problem exist.

Formation of hot, stable, long-lived field-reversed configuration plasmas on the C-2W device

TAE Technologies’ research is devoted to producing high temperature, stable, long-lived field-reversed configuration (FRC) plasmas by neutral-beam injection (NBI) and edge biasing/control. The newly constructed C-2W experimental device (also called ‘Norman’) is the world’s largest compact-toroid (CT) device, which has several key upgrades from the preceding C-2U device such as higher input power and longer pulse duration of the NBI system as well as installation of inner divertors with upgraded electrode biasing systems. Initial C-2W experiments have successfully demonstrated a robust FRC formation and its translation into the confinement vessel through the newly installed inner divertor with adequate guide magnetic field. They also produced dramatically improved initial FRC states with higher plasma temperatures (Te ~ 250 + eV; total electron and ion temperature >1.5 keV, based on pressure balance) and more trapped flux (up to ~15 mWb, based on rigid-rotor model) inside the FRC immediately after the merger of collided two CTs in the confinement section. As for effective edge control on FRC stabilization, a number of edge biasing schemes have been tried via open field-lines, in which concentric electrodes located in both inner and outer divertors as well as end-on plasma guns are electrically biased independently. As a result of effective outer-divertor electrode biasing alone, FRC plasma is well stabilized and diamagnetism duration has reached up to ~9 ms which is equivalent to C-2U plasma duration. Magnetic field flaring/expansion in both inner and outer divertors plays an important role in creating a thermal insulation on open field-lines to reduce a loss rate of electrons, which leads to improvement of the edge and core FRC confinement properties. An experimental campaign with inner-divertor magnetic-field flaring has just commenced and early result indicates that electron temperature of the merged FRC stays relatively high and increases for a short period of time, presumably by NBI and E × B heating.

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.

Design of a custom insertable probe platform for measurements of C-2W inner divertor plasma parameters.

A custom motor controlled probe system has been designed to make spatially resolved measurements of temperature, density, flow, and plasma potential in the C-2W inner divertors. Measurements in the inner divertors, which have a 1.7 m radius and are located on either end of the confinement vessel, are critical in order to gauge exactly how local settings affect the plasma conditions, confinement, and stability in the field-reversed configuration core. The inner Divertor Insertable Probe Platform (iDIPP) system consists of a custom motor controlled linear rack and pinion transporter that has a 1.9 m travel length in order to reach the center of the divertor. Mounted to the end of the transporter is a 1 m long segmented probe shaft made of individually floating stainless steel rings to prevent shorting out the electrode plates, which are biased up to 5 kV/m. A variety of interchangeable probe tips, including a triple Langmuir probe, a baffled probe, and a Gundestrup probe, can plug into the end of the probe shaft. Custom UHV coiled cabling comprised of 9 shielded conductors expands/retracts with the motion of the transporter in/out of the divertor. The physics motivating plasma parameter measurements in the inner divertors and the details of the design of the iDIPP system will be discussed.

Deuterium retention in deposited W layer exposed to EAST deuterium plasma

The deposited W layers formed on the W plate by hydrogen plasma sputtering were exposed to deuterium plasma in EAST together with bare W plate. In TDS measurement, the deuterium release was clearly observed from the deposited W layer in addition to the release of hydrogen which was incorporated during the sputtering-deposition processes. On the other hand, the release of hydrogen isotope was not detected from the bare W plate. This suggests that the formation of deposited W layers increases tritium inventory in the plasma confinement vessel. Although the thermocouple contacting to the backside of the W plate did not indicate a remarkable temperature rise, deuterium release peaks from the W layer were close to that from the W layer irradiated by 2keV D2+ at 573K. It was found by glow discharge optical emission spectrometry analysis that retained deuterium in the W layer has a peak at the depth of 50nm and gradually decreases toward the W substrate. From X-ray photoelectron spectroscopy analysis, it was evaluated that W oxide existed just at the surface and W atoms in the bulk of deposited W layer were not oxidized. These data suggest that hydrogen isotopes are not retained in W oxide but grain boundaries.

Basic creep of concrete-coupling between high stresses and elevated temperatures

The prestressed concrete confinement vessel is the third and last barrier in French Nuclear Power Plants (NPP). In case of a severe accident (loss of cooling agent of the reactor for instance), pressure and temperature will increase in the nuclear vessel (+0,5 MPa and 180 °C during 2 weeks). Due to elevated temperatures, the evolution of basic creep will be accelerated. High compressive stresses would appear and induce higher delayed strains and damage. The modelling of basic creep and its couplings with temperature is then very important for the safety of the structure (tightness of the concrete vessel). Here, we present a model considering the following elements: a coupling between creep and damage is introduced, kinetics of basic creep is affected by temperature by the means of an Arrhenius thermo-activation, damage due to the increase in temperature (under stress or not) is taken into account. The model is compared with the available experimental results. This work is a part of the MACENA project.

Modelling Basic Creep of Concrete at Elevated Temperatures and Stresses

The prestressed concrete confinement vessel is the third and last barrier in Nuclear Power Plants (NPP). In case of a severe accident (loss of cooling agent of the reactor for instance), pressure and temperature will increase in the nuclear vessel (0,5 MPa and 180°C during 2 weeks). Due to elevated temperatures, the evolution of basic creep will be accelerated. In this case, due to internal pressure, some tensile stresses could appear in specific parts of the structure and induce cracking. The modelling of basic creep and its couplings with temperature is very important for the safety of the structure (tightness of the concrete vessel). Here we present a model considering the following elements: a coupling between creep and damage is introduced, kinetics of basic creep is affected by temperature by the means of an Arrhenius thermo-activation, damage due to the increase of temperature is taken into account. The model is compared with the available experimental results. This work is a part of the MACENA project.

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.

Pre-ignition confinement and deflagration violence in LX-10 and PBX 9501

In thermal explosions of the nitramine octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX)-based explosives LX-10 and PBX-9501, the pre-ignition spatial and temporal heating profile defines the ignition location. The ignition location then determines the extent of inertial confinement and the violence of the resulting deflagration. In this work, we present results of experiments in which ∼23 g cylinders of LX-10 and PBX 9501 in thin-walled aluminum confinement vessels were subjected to identical heating profiles but which presented starkly different energy release signatures. Post-explosion LX-10 containment vessels were completely fragmented, while the PBX 9501 vessels were merely ruptured. Flash x-ray radiography images show that the initiation location for the LX-10 is a few mm farther from the end caps of the vessel relative to the initiation location of PBX 9501. This difference increases deflagration confinement for LX-10 at the time of ignition and extends the pressurization time during which the deflagration front propagates in the explosive. The variation in the initiation location, in turn, is determined by the thermal boundary conditions, which differ for these two explosives because of the larger coefficient of thermal expansion and greater thermal stability of the Viton binder in LX-10 relative to the estane and bis(2,2-dinitropropyl) acetal/formal binder of the PBX 9501. The thermal profile and initiation location were modeled for LX-10 using the hydrodynamics and structures code ALE3D; results indicate temperatures in the vicinity of the ignition location in excess of 274 °C near the time of ignition. The conductive burn rates for these two explosives, as determined by flash x-ray radiography, are comparable in the range 0.1–0.2 mm/μs, somewhat faster than rates observed by strand burner experiments for explosives in the temperature range 150–180 °C and pressures up to 100 MPa. The thinnest-wall aluminum containment vessels presented here rupture at lower pressures, in the range 10 MPa, suggesting that moderately higher temperatures and pressures are present near the deflagration front. For these explosives, however the most important property for determining deflagration violence is the degree of inertial confinement.

Ab initio molecular dynamics simulations of water and an excess proton in water confined in carbon nanotubes.

Ab initio molecular dynamics simulations were performed to investigate the effects of nanoscale confinement on the structural and dynamical properties of water and slightly acidic water. Single-walled carbon nanotubes (CNTs) of two different diameters (11.0 and 13.3 Å) were used as confinement vessels, and the inner walls of the CNT were either left bare or fluorinated to explore the influence of the confined environment on the determined properties. The water molecules in the fluorinated nanotubes were found to preferentially localize near the CNT surface and exhibit highly ordered structures while those in the bare CNTs were more randomly distributed. Additionally, weak interactions that resembled hydrogen bonds between the water molecules and the fluorine atoms were observed which occurred at a greater frequency in the smaller diameter CNT indicating an influence of the confinement dimensions on these interactions. This was further pronounced when an excess proton was added where, on average, approximately half of the water molecules in the smaller tube were involved in these interactions. This also led to a structured hydrogen bond network with regular defect sites that hindered proton transfer along the channel axis. Addition of the proton in the larger fluorinated CNT, however, disrupted the structural ordering and proton transfer down the nanotube axis near the surface of the CNT wall readily occurred. Proton transfer through the channel was also observed in the smaller nonfluorinated system, however, the proton was located closer to the center of the CNT, while in the larger nonfluorinated CNT proton transfer exhibited less directional preference indicating an impact of the scale of confinement and nature of the surface on proton transfer.

Rigid-rotor, field-reversed configuration

The radial profiles, n(r), Bz(r), and Er(r), for a Flux-Coil (“inductively driven”), Field-Reversed Configuration (FC-FRC) are measured and compared to the predictions of the Rigid-Rotor Model (RRM), which is an analytic, one-dimensional, time-independent, equilibrium description for the FRC. Injectors mounted on both ends of the confinement vessel provide a pre-fill plasma. Coaxial coils mounted outside the vacuum boundaries of the annular-confinement vessel accelerate the plasma and produce the FRC. The density profile is measured by laser interferometry, the magnetic-field profile using an in-situ probe array, and the electric-field profile using an in-situ, floating-probe array. Free parameters for each profile are measured, which also allow other intrinsic-plasma parameters to be determined, using computer-fit algorithms: null radius, radial thickness, plasma temperature, rotation frequencies, the latter of which are independently verified by spectroscopy. All radial profiles agree with the RRM predictions, for the experimental configuration, parameter regime, and specified-time interval studied here.

Residual Stresses in a Welded Zircaloy Cold Neutron Source Containment Vessel

Zirconium alloys are widely used in the nuclear industry because of their relative high strength, neutron transparency, resistance to high neutron-irradiation environment and corrosion resistance. One application for Zirconium alloy Zr-2.5Nb is the vacuum confinement vessel utilised in the cold neutron source of the OPAL research reactor at ANSTO. Having a total length of more the 3 meters, it is made of two sections joined using electron beam welding. The weld and the nearby regions are critical for the performance and integrity of the component and therefore understanding of the residual stresses development within the weld is important in connection to (i) evolution of fine dual phase α/b microstructure and crystallographic texture (ii) and stress-related radiation induced phenomena, such as grain growth, creep and sub-critical crack growth by delayed hydride cracking. The stresses were measured in and around an electron beam weld produced during the development of this component of the OPAL Cold Neutron Source. The effects of a large grain size in the weld were reduced by taking advantage of rotational symmetry and rotating the sample to increase the swept volume. Due to the heat-treatment after welding, the stresses were very low, less than 10% of the yield strength of the material, in both the hoop and axial directions. As a result of phase transformation effects during the welding process the final stresses are compressive in the weld, which reduces the likelihood of fracture or of hydride formation in this region. The highest stresses are in the parent material adjacent to the weld where the toughness is expected to be higher than in the weld material.

A friction test between steel and a brittle material at high contact pressures and high sliding velocities

Our aim is to characterize the interface behaviour between an aggregate material and steel. This work focuses on contact pressures and sliding velocities reaching 100 MPa and 10 m/s. The set-up consists in a cylindrical sample of the aggregate material which slips into a steel tube. The tube is both a confinement vessel and a sliding surface. Thanks to confinement, the material can be tested under high stresses without failure. The interface pressure is generated by an axial compression. The sample is pressed on a spring, so it can be simultaneously compressed and rubbed on the tube. The set-up has been tested in the case of a quasi-static loading and the 100 MPa pressure has been reached. Then the set-up was mounted on a Split Hopkinson Pressure Bar device in order to reach higher velocities. Numerical simulations have been realized to check the feasibility and the relevance of this dynamic test. These results are analysed and compared to the experimental ones.

Experimental study of the confined behaviour of PMMA under quasi-static and dynamic loadings

This study has investigated the confined behaviour of PMMA under quasi-static loading and at high strain-rates as well. To this goal, quasi-oedometric compression tests have been performed. A cylindrical specimen, tightly enclosed inside a thick confinement vessel which material is either brass or high strength aluminium alloy, is axially compressed. The constitutive law allowing the description of the ring metal being known, a processing method is proposed to deduce the confining pressure accounting for the plastic behaviour of the vessel as well as to calculate the s7hortening of the specimen. Next, the hydrostatic pressure and the Huber-Mises stress may be deduced. Both vessels permit us to explore the behaviour of PMMA under lateral pressure levels rising up to 500 MPa. Based on the proposed method quasi-static and dynamic tests performed in a range of strain-rates from 1E-3/s to 1E3/s are processed and the obtained results are compared to those corresponding to unconfined compression tests. It was found that the compressive strength of PMMA is weakly influenced by the level of pressure and is much more sensitive to strain-rate. Finally, an elastic brittle behaviour is observed at high strain-rates for unconfined as well as confined conditions, whereas an elasto-plastic behaviour followed by a mode II fracturing of the specimen is noticed for quasi-static confined loading.