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An efficient neutron transport-based multiphysics coupling algorithm is developed to model fast-burst reactor dynamics. It extends the previously developed tightly coupled implicit-explicit (IMEX) multiphysics algorithm based on neutron diffusion and linear mechanics to follow the dynamic time scale of the problem. The diffusion model is not expected to adequately represent the neutronic behavior of the system due its small size. The transport effects are incorporated using the moment-based acceleration concept. This concept enables us to isolate the angular flux from the coupled multiphysics system by using a consistently discretized lower-order system for the scalar flux in the coupling equations, thus helping to mitigate the increased numerical burden associated with a neutron transport model. Solution of a representative slab model demonstrates the difference between diffusion and transport models and also demonstrates second-order convergence in the coupled simulation with the combination of the mome...

A powerful multidimensional fuels performance capability, applicable to both steady and transient fuel behavior, is developed based on enhancements to the commercially available ABAQUS general-purpose thermomechanics code. Enhanced capabilities are described, including: UO2 temperature and burnup dependent thermal properties, solid and gaseous fission product swelling, fuel densification, fission gas release, cladding thermal and irradiation creep, cladding irradiation growth , gap heat transfer, and gap/plenum gas behavior during irradiation. The various modeling capabilities are demonstrated using a 2D axisymmetric analysis of the upper section of a simplified multi-pellet fuel rod, during both steady and transient operation. Computational results demonstrate the importance of a multidimensional fully-coupled thermomechanics treatment. Interestingly, many of the inherent deficiencies in existing fuel performance codes (e.g., 1D thermomechanics, loose thermo-mechanical coupling, separate steady and transient analysis, cumbersome pre- and post-processing) are, in fact, ABAQUS strengths.

Usually, tokamak core scaling laws are written in terms of dimensionless geometrical quantities and parameters corresponding to Coulomb collisionality, gyro-motion, and plasma beta. However, Lackner [K. Lackner, Comments Plasma Phys. Controlled Fusion 15, 359 (1994)] observed that the temperature profiles also must be the same to obtain the same atomic physics in the divertor region of similar discharges. He obtained a scaling indicating that none of the present tokamaks could be made similar to the International Thermonuclear Experimental Reactor (ITER) [G. Janeschitz et al., J. Nucl. Mater. 220–222, 73 (1995)], but implicitly retained only two body interactions. Subsequent work [P. J. Catto et al., Phys. Plasmas 3, 3191 (1996)] demonstrated that non-two-body effects (multistep radiation, excitation, and ionization processes as well as three body recombination) cannot be ignored for plasma densities above 1019 m−3; the regime in which the ITER divertor must operate. In this reactor relevant regime, scali...

We study the application of enhanced nonlinear iterative methods to the steady-state solution of a system of two-dimensional convection-diffusion-reaction partial differential equations that describe the partially ionized plasma flow in the boundary layer of a tokamak fusion reactor. This system of equations is characterized by multiple time and spatial scales and contains highly anisotropic transport coefficients due to a strong imposed magnetic field. We use Newton's method to linearize the nonlinear system of equations resulting from an implicit, finite volume discretization of the governing partial differential equations, on a staggered Cartesian mesh. The resulting linear systems are neither symmetric nor positive definite, and are poorly conditioned. Preconditioned Krylov iterative techniques are employed to solve these linear systems. We investigate both a modified and a matrix-free Newton--Krylov implementation, with the goal of reducing CPU cost associated with the numerical formation of the Jacobian. A combination of a damped iteration, mesh sequencing, and a pseudotransient continuation technique is used to enhance global nonlinear convergence and CPU efficiency. GMRES is employed as the Krylov method with incomplete lower-upper (ILU) factorization preconditioning. The goal is to construct a combination of nonlinear and linear iterative techniques for this complex physical problem that optimizes trade-offs between robustness, CPU time, memory requirements, and code complexity. It is shown that a mesh sequencing implementation provides significant CPU savings for fine grid calculations. Performance comparisons of modified Newton--Krylov and matrix-free Newton--Krylov algorithms will be presented.

Analysis of the experimental data from tokamaks and linear divertor simulators leads to the conclusion that plasma recombination is a crucial element of plasma detachment. Different mechanisms of plasma recombination relevant to the experimental conditions of the tokamak scrape-off layer (SOL) and divertor simulators are considered. The physics of Molecular Activated Recombination (MAR) involving vibrationally excited molecular hydrogen are discussed. Although conventional Electron–Ion Recombination (EIR) alone can strongly alter the plasma parameters, MAR impact can be substantial for both tokamak SOL plasma and divertor simulators. Investigation of the effects of EIR on the plasma flow in divertor simulators shows that due to the balances of (a) energy transport and electron cooling, and (b) the plasma flow and recombination, that EIR extinguishes the simulator plasma at an electron temperature about 0.15 eV.

The breakdown of two body scaling laws is illustrated by using the two dimensional plasma code UEDGE coupled to an advanced Navier-Stokes neutrals transport package to model attached and detached regimes in a simplified geometry. Two body similarity scalings are used as benchmarks for runs retaining non-two body modifications due to the effects of (i) multi-step processes altering ionization and radiation via the excited states of atomic hydrogen and (ii) three body recombination. Preliminary investigations indicate that two body scaling interpretations of experimental data fail due to (i) multi-step processes when a significant region of the plasma exceeds a plasma density of 1019 m−3, or (ii) three body recombination when there is a significant region in which the temperature is ≤ 1 eV while the plasma density is ≥ 1020 m−3. These studies demonstrate that two body scaling arguments are often inappropriate in the divertor and the first results for alternate scalings are presented.

Understanding the physics of divertor detachment is important since detached operation in ITER could reduce the target heat flux drastically, while aiding helium ash removal. In order to model detachment properly we have incorporated a parallel Navier-Stokes neutral model in UEDGE. In simulations of Alcator C-Mod we reproduce the partial detachment observed in experiments. A bifurcation to a MARFE has been found, similar to experiments. Volume recombination is a very important effect in removing the ion current to the target and we observe strong plasma flux detachment. Similar results have been found for ITER, with an order of magnitude decrease of the peak heat flux and a strong reduction of the target ion flux. Detachment has been induced with both neon and carbon.

A combined edge plasma/Navier–Stokes neutral transport model is used to characterize divertor plasma detachment, in the collisional limit for neutrals, on a simplified two‐dimensional slab geometry with Alcator‐C‐MOD‐like plasma conditions [I. H. Hutchinson et al., Phys. Plasmas 1, 1511 (1994)]. The neutral model contains three momentum equations which are coupled to the plasma through ionization, recombination, and ion–neutral elastic collisions. The neutral transport coefficients are evaluated including both ion–neutral and neutral–neutral collisions. Detachment is brought about via impurity radiation using a fixed fraction impurity model. The transport model is shown to reproduce all salient features of experimentally observed detachment, such as large drops in ion saturation current and plasma heat flux at the divertor plate. The solutions are also shown to be sensitive to volume recombination. A region of relatively high toroidal neutral Mach number is observed upon detachment. Due to the high neutra...

We have simulated detachment in Alcator C-Mod, using an improved neutral fluid model. It features a parallel neutral momentum equation, fully coupled to the ions, allowing parallel plasma momentum to be converted into neutral momentum, which is dispersed to the material walls due to the high neutral viscosity. The simulations reproduce the pervasive experimental feature that the plasma detaches gradually, starting at the strike point, while always remaining attached above the nose of the divertor channel. The strike point heat flux and current drop by an order of magnitude as 0.5% of carbon is introduced to induce partial detachment. The plate temperature remains at or above about 1 eV all the way out to the divertor nose, in agreement with the experimental data.

A combined edge plasma / Navier-Stokes neutral transport model is used to simulate dissipative divertor plasmas in the collisional limit for neutrals on a simplified two-dimensional slab geometry with ITER-like plasma conditions and scale lengths. The neutral model contains three momentum equations which are coupled to the plasma through ionization, recombination, and ion-neutral elastic collisions. The neutral transport coefficients are evaluated including both ion-neutral and neutral-neutral collisions.

We have simulated detachment in ITER, with the UEDGE code coupled to a Navier-Stokes neutral model, for realistic toroidal geometry and plasma parameters, with a heat flux of 100 MW into the outboard SOL. For a fixed fraction of carbon, corresponding to Zeff2.5 in the SOL, the power to the outer plate is reduced by more than 90%, the peak plate temperature is reduced to about 1 eV, and the total ion saturation current drops by 85%. Volume recombination plays an important role in removing the current. Bifurcated solutions and marfe-like structures below the X-point have been found under certain conditions.

Two-dimensional numerical models of divertors contain large numbers of dimensionless parameters that must be varied to investigate all operating regimes of interest. To simplify the task and gain insight into divertor operation, we employ similarity techniques to investigate whether model systems of equations plus boundary conditions in the steady state admit scaling transformations that lead to useful divertor similarity scaling laws. A short mean free path neutral-plasma model of the divertor region below the x-point is adopted in which all perpendicular transport is due to the neutrals. We illustrate how the results can be used to benchmark large computer simulations by employing a modified version of UEDGE which contains a neutral fluid model.

We consider the effect of perpendicular energy transport in the low temperature divertor region on impurity radiation loss from the SOL plasma. We show that the perpendicular energy transport results in enlargement of the volume with relatively low temperature and a very high density of the plasma. High plasma density causes a strong energy loss due to impurity radiation peak in this low temperature region. For low Z impurity the energy transport due to plasma convection and neutrals also can strongly influence the volume of low temperature region.

A two‐dimensional combined edge plasma Navier–Stokes neutral transport model is presented for the simulation of dense recombining divertor plasmas. This model includes ions, electrons, and neutral atoms which undergo Coulomb collisions, electron impact ionization, ion–neutral elastic collisions, three‐body and radiative recombination, and neutral–neutral collisions. The advanced fully implicit solution algorithm is briefly described and a variety of results on a model geometry are presented. It is shown that interesting neutral flow patterns can exist and that these flows can convect significant energy. A solution that ignores neutral–neutral collisions is shown to be quantitatively different from one that includes neutral–neutral collisions. Solutions are also shown to be sensitive to the plasma opacity for Lyman α radiation.

This paper describes recent development of the UEDGE code in three important areas. (1) Non-orthogonal grids allow accurate treatment of experimental geometries in which divertor plates intersect flux surfaces at oblique angles. (2) Radating impurities are included by means of one or more continuity equations that describe transport and sources, and sinks due to ionization and recombination processes. (3) Advanced iterative methods that reduce storage and execution time allow us to find fully converged solutions of larger problems (i.e., finer grids). Sample calculations are presented to illustrate these development.

We have used experiments and modeling to develop a new radiative divertor configuration for DIII-D. Gas puffing experiments with the existing open divertor have shown the creation of a localized (∼ 10 cm diameter) radiation zone which results in substantial reduction (3–10) in the divertor heat flux while τ E remains ∼ 2 times ITER-89P scaling. However, n e increases with D 2 puffing, and Z eff increases with neon puffing. Divertor structures are required to minimize the effects on the core plasma. The UEDGE fluid code, benchmarked with DIII-D data, and the DEGAS neutrals transport code are used to estimate the effectiveness of divertor configurations; slots reduce the core ionization more than baffles. The overall divertor shape is set by confinement studies which indicate that high triangularity (δ ≈ 0.8) is important for high τ E VH-modes. Results from engineering feasibility studies, including diagnostic access, will be presented.

The features of the fully implicit 2-D fluid code UEDGE are described. The utility of the code is demonstrated by showing bifurcations or multiple solutions of the tokamak edge plasma for both deuterium and impurity injection in the divertor.

The transport of either intrinsic or injected impurities will play a crucial role in the energy loss mechanisms in the ITER gaseous/cold plasma target divertor. Both 1-D and 2-D multi-charge state fluid codes are used to model the transport of beryllium in the ITER SOL. Our major conclusion is that in order to model the containment of impurities, the background flow field must be known in detail. Comparing 1-D and 2-D solutions, hydrogen flow reversal plays an important role in the entrainment process. Further, the flow of particles from the core plasma also has a strong impact on the resultant entrainment of the impurities in both 1-D and 2-D. It is imperative that those components of poloidal velocity due to ExB and diamagnetic drifts be included in the models.

Newton's method, finite volume discretization, and a staggered grid are used to compute the steady state profiles of the two-dimensional two-fluid Tokamak edge plasma fluid equations. In this set of fluid equations, the transport coefficients are highly nonlinear functions of the dependent variables, and mass and energy transfer due to atomic reactions is included. The techniques of an adaptive damped iteration, mesh sequencing, and reduced factorization are combined to increase the radius of convergence and to accelerate convergence. These techniques are illustrated through a model problem.

Scaling laws found under the assumption that two‐body collisions dominate can be effectively used to benchmark complex multi‐dimensional codes dedicated to investigating tokamak edge plasmas. The applicability of such scaling laws to the interpretation of experimental data, however, is found to be restricted to the relatively low plasma densities (

Detailed studies on the synthesis and processing of bulk (Hg,A)Ba2Ca2Cu3Oy (A=Bi, Pb) were conducted to understand the role of heat treatment, precursor phase assembly, and Hg-pressure during synthesis. An additional lower temperature annealing stage after high temperature reaction is shown to improve the microstructural characteristics of Hg1223 samples. BaCaCuO precursor powders containing free CaO allows formation of liquid phase and assists in grain growth and texture development. Control of Hg-pressure during the reaction by using an external Hg-source, in sealed tubes, improves the density of Hg1223 products. Chemical nature of external Hg-source changes Hg-pressure and influences melting characteristics and grain growth. CaHgO2 is shown to be a very effective external Hg-source for producing dense Hg1223 materials with improved grain growth and texture. Phase purity and microstructural characteristics are correlated with high field magnetization measurements.

Objective—The objective of this study was to determine the effectiveness of a 5–minute surgical scrub using either a one-brush or a two-brush technique in clean and dirty surgical procedures, and to compare the efficacy of povidone iodine with chlorhexidine as surgical scrub solutions. Study Design—Prospective clinical trial. Methods—Nine veterinarians scrubbed their hands on eight separate occasions using either povidone iodine or chlorhexidine gluconate. A 5-minute scrub and either a one-brush or two-brush technique used in both clean and dirty operations were evaluated by taking glove juice samples before scrubbing, immediately after scrubbing, and 30, 60, 90, and 120 minutes after scrubbing. Glove juice samples were cultured and the colonies were counted. Percent reductions of bacterial forming units were calculated for all eight scrub procedures. Results—All scrub procedures provided an adequate percent reduction in colony forming units (CFU) during the 2–hour sampling period. The number of CFU immediately after scrubbing were significantly lower than prescrub. At 120 minutes, there were significantly fewer CFUs than presecrub, but there were more than immediately after scrubbing. No significant difference in reduction in CFUs were detected between one-brush and two-brush techniques. Both chlorhexidine and povidone iodine scrub solutions adequately reduced bacterial colony counts for 120 minutes after scrubbing regardless of the amount of contamination before skin preparation. Conclusions—Bacterial counts after a hand scrub procedure using a one-brush technique were not significantly different than after a procedure that used a two-brush technique. Povidone iodine and chlorhexidine are equally effectively in decreasing bacterial numbers on the skin, given a variety of contamination levels present before the scrub procedure. Clinical Relevance—Surgeons may use either chlorhexidine or povidone iodine for antiseptic preparation of their hands before surgery. A two-brush technique is not necessary.

Micelles and vesicles coexist in native bile. Mixed micelles are composed of bile salt, phospholipid, and cholesterol. Micellar bile salt is in equilibrium with the aqueous phase bile salt (intermicellar bile salt), and mixed micelles can be converted to cholesterol-phospholipid vesicles by depletion of bile salt. To determine the amount of cholesterol carried in vesicles and micelles, these two populations must be separated without altering the relative proportion of each. Based on the size difference between micelles and vesicles, gel filtration chromatography has been used to accomplish this separation. We reasoned that to maintain the proportion of micelles and vesicles in bile, the column must be equilibrated and eluted with buffer containing the intermicellar bile salt concentration (IMBC) and species. To test this hypothesis we created a model bile composed exclusively of micelles, a solution containing micelles and vesicles, and a model bile containing all vesicles, as demonstrated by quasielastic light scattering. Gel filtration on Sepharose 4B demonstrated that model vesicles and micelles could be separated on a column eluted with buffer containing bile salt at the IMBC. However, a modest decrease in the buffer bile salt concentration (less than 1 mmol/L) resulted in complete conversion of micelles to vesicles. A comparable increase in the buffer bile salt concentration converted vesicles to micelles. Using only taurocholate in the eluting buffer at the IMBC caused a complete shift of micelles to vesicles, whereas using only taurochenodeoxycholate resulted in conversion of vesicles to micelles. An initial collection of rat bile separated on a column equilibrated with the measured IMBC demonstrated that 94% of the cholesterol was in the micellar fractions.(ABSTRACT TRUNCATED AT 250 WORDS)

The coalescence of magnetic islands in the high Lundquist number regime is studied. Within the resistive magnetohydrodynamics model, the coalescence rate is known to stall (sloshing) in the limit of high Lundquist number. Previously, this stalling has been associated with the presence of a secondary tearing mode. Here it is shown that this stalling results from high magnetic pressure gradients, which result from thin current sheets at high Lundquist number. This phenomenon is frequently referred to as the “pressure problem” in flux pile-up reconnection studies. Sensitivity of the dynamic solution is presented, over a wide range of resistivities.

After a short introduction of the subject “proton transfer in ice” and some background information on previous polarization measurements, the growing and preparation of our single crystals and the instrumentation for a–c measurements from 105–8 × 10−3 Hz, 0 to − 180°C, are briefly described. By rigorous control of error limits and an improved computerized evaluation procedure it was possible to resolve the dielectric spectrum of these “pure” ice single crystals into several significant components: the intrinsic Debye spectrum, two weak spectra preceding it at a high frequency, and “space‐charge‐polarization” spectra. Important characteristics of these spectra and inherent difficulties in quoting their “accurate” parameters are presented. The interpretation of these data requires new molecular models; they are developed in Part II; the analysis of polarization data is resumed in Part III in conjunction with new transconductance measurements.

This paper keynotes the "Infrared Automatic Target Recognition" session. Its thesis is that: 1) To win in the battlefield of the future against a numerically superior enemy equipped with weapons of unprecedented capabilities, we must have the "force multiplier" promised by technology 2) Automatic target recognition (ATR) is one such technology with attributes that provide this leverage 3) ATR can provide this enhanced performance for several current, specific, combat missions 4) ATR can be applied to broader applications if several technical challenges can be met 5) DoD is recognizing the potential of ATR to provide "the winning edge."

We present the status of comprehensive two-dimensional (2-D) transport modeling for the tokamak scrape-off layer (SOL) using the UEDGE and B2.5 codes. These codes are now able to integrate a variety of physics, including coupling of plasma and neutral transport leading to detachment, complicated divertor-plate geometries, multispecies impurities, and currents and E x B drifts. These new models are outlined and the capabilities are illustrated by a number of examples that emphasize the importance of including the 2-D geometry.