Power Balance in the ITER Plasma and Divertor

It is planned to use atomic processes to spread out most of the heating power over the first wall and side walls to reduce the heat loads on the plasma facing components in ITER to ~ 50 MW. Calculations indicate that there will be 100 MW in bremstrahlung radiation from the plasma center, 50 MW of radiation from the plasma edge inside the separatrix and 100 MW of radiation from the scrape-off layer and divertor plasma, leaving 50 MW of power to be deposited on the divertor plates. The radiation losses are enhanced by the injection of impurities such as Neon or Argon at acceptably low levels (~0.1 % Argon, etc.)Comment: Preprint for the Plasma Edge Theory Conference, Monterey, Dec.4-6, 1995, 5 pages, gzipped postscrip

Real-time depth sectioning: Isolating the effect of stress on structure development in pressure-driven flow

Transient structure development at a specific distance from the channel wall in a pressure-driven flow is obtained from a set of real-time measurements that integrate contributions throughout the thickness of a rectangular channel. This “depth sectioning method” retains the advantages of pressure-driven flow while revealing flow-induced structures as a function of stress. The method is illustrated by applying it to isothermal shear-induced crystallization of an isotactic polypropylene using both synchrotron x-ray scattering and optical retardance. Real-time, depth-resolved information about the development of oriented precursors reveals features that cannot be extracted from ex-situ observation of the final morphology and that are obscured in the depth-averaged in-situ measurements. For example, at 137 °C and at the highest shear stress examined (65 kPa), oriented thread-like nuclei formed rapidly, saturated within the first 7 s of flow, developed significant crystalline overgrowth during flow and did not relax after cessation of shear. At lower stresses, threads formed later and increased at a slower rate. The depth sectioning method can be applied to the flow-induced structure development in diverse complex fluids, including block copolymers, colloidal systems, and liquid-crystalline polymers

Molecular Simulation of Flow-Enhanced Nucleation in n-Eicosane Melts Under Steady Shear and Uniaxial Extension

Non-equilibrium molecular dynamics is used to study crystal nucleation of n-eicosane under planar shear and, for the first time, uniaxial extension. A method of analysis based on the mean first-passage time is applied to the simulation results in order to determine the effect of the applied flow field type and strain rate on the steady-state nucleation rate and a characteristic growth rate, as well as the effects on kinetic parameters associated with nucleation: the free energy barrier, critical nucleus size, and monomer attachment pre-factor. The onset of flow-enhanced nucleation (FEN) occurs at a smaller critical strain rate in extension as compared to shear. For strain rates larger than the critical rate, a rapid increase in the nucleation rate is accompanied by decreases in the free energy barrier and critical nucleus size, as well as an increase in chain extension. These observations accord with a mechanism in which FEN is caused by an increase in the driving force for crystallization due to flow-induced entropy reduction. At high applied strain rates, the free energy barrier, critical nucleus size, and degree of stretching saturate, while the monomer attachment pre-factor and degree of orientational order increase steadily. This trend is indicative of a significant diffusive contribution to the nucleation rate under intense flows that is correlated with the degree of global orientational order in a nucleating system. Both flow fields give similar results for all kinetic quantities with respect to the reduced strain rate, which we define as the ratio of the applied strain rate to the critical rate. The characteristic growth rate increases with increasing strain rate, and shows a correspondence with the nucleation rate that does not depend on the type of flow field applied. Additionally, a structural analysis of the crystalline clusters indicates that the flow field suppresses the compaction and crystalline ordering of clusters, leading to the formation of large articulated clusters under strong flow fields, and compact well-ordered clusters under weak flow fields

A Review of Recent Developments in Atomic Processes for Divertors and Edge Plasmas

The most promising concepts for power and particle control in tokamaks and other fusion experiments rely upon atomic processes to transfer the power and momentum from the edge plasma to the plasma chamber walls. This places a new emphasis on processes at low temperatures (1-200 eV) and high densities (10^20-10^22 m^-3). The most important atomic processes are impurity and hydrogen radiation, ionization, excitation, recombination, charge exchange, radiation transport, molecular collisions, and elastic scattering of atoms, molecules and ions. Important new developments have occurred in each of these areas. The best available data for these processes and an assessment of their role in plasma wall interactions are summarized, and the major areas where improved data are needed are reviewed.Comment: Preprint for the 11th PSI meeting, postscript with 22 figures, 40 page

ELM triggering conditions for the integrated modeling of H-mode plasmas

Recent advances in the integrated modeling of ELMy H-mode plasmas are presented. A model for the H-mode pedestal and for the triggering of ELMs predicts the height, width, and shape of the H-mode pedestal and the frequency and width of ELMs. Formation of the pedestal and the L-H transition is the direct result of ExB flow shear suppression of anomalous transport. The periodic ELM crashes are triggered by either the ballooning or peeling MHD instabilities. The BALOO, DCON, and ELITE ideal MHD stability codes are used to derive a new parametric expression for the peeling-ballooning threshold. The new dependence for the peeling-ballooning threshold is implemented in the ASTRA transport code. Results of integrated modeling of DIII-D like discharges are presented and compared with experimental observations. The results from the ideal MHD stability codes are compared with results from the resistive MHD stability code NIMROD.Comment: 12th International Congress on Plasma Physics, 25-29 October 2004, Nice (France

Applications of shear-induced polarized light imaging (SIPLI) technique for mechano-optical rheology of polymers and soft matter materials

A new experimental method for studying the mechano-optical rheology of polymeric liquids and soft matter materials is presented. The method is based on a combination of rotational rheology and a recently developed optical technique—shear-induced polarized light imaging (SIPLI). The method provides a unique opportunity to monitor a complete sample view during rheological measurements in plate–plate and cone-and-plate geometry. Applications of the method are presented including simultaneous SIPLI and the rheology of the oriented lamellar phase of block copolymers and liquid crystals as well as a study of the thermally induced reversible transformation of worm-like micelles to spherical micelles. In addition, a direct relation between the shish formation and the polymer melt viscosity upturn during flow-induced crystallization of semi-crystalline polymers is demonstrated. An application of SIPLI for quantitative birefringence measurements is also shown

Structural assessment of the gripper interlock of the DEMO breeding blanket transporter

The maintenance of the DEMO Breeding Blanket (BB) remotely is a crucial aspect in development of the DEMO power plant. It is a challenge due to the huge mass of the BB segment of about 180 tons. A new concept for the BB transporter has recently been developed. To properly grip and manipulate each BB segment, the BB transporter has been equipped with a gripper interlock. Due to the geometry of the BB and the vacuum vessel, the attachment point on the BB segment is not aligned with its center of gravity. Hence in addition to the vertical lifting load, large moments about the horizontal axes need to be reacted.The work discussed here concerns the structural analysis conducted on the gripper interlock; its structural integrity has been checked against the most severe load conditions that include also seismic loads according to the EN13001. Elastic analyses were performed using a finite element model in accordance with EN 13001-3-1:2012 + A2:2018, Cranes - General Design - Part 3-1: Limit States and proof competence of steel structure. The effect of the gap sizes at the contact surfaces between gripper interlock and BB after engagement as well as the effect of different friction coefficients on the sliding areas were assessed. The improvements of the design based on the structural analysis are presented, too

A Spatial Five-Bar Linkage as a Tilting Joint of the Breeding Blanket Transporter for the Remote Maintenance of EU DEMO

The future fusion power plant EU DEMO will generate its own tritium fuel through the use of segmented breeding blankets (BBs), which must be replaced from time to time due to material damage caused by high-energy neutrons from the plasma. A vertical maintenance architecture has been proposed, using a robotic remote handling tool (transporter) to disengage the 180 t and 125 t outboard and inboard segments and manipulate them through an upper port. Safe disengagement without damaging the support structures requires the use of high-capacity tilting joints in the transporter. The trolley tilting mechanism (TTM) is proposed as a novel, compact, high-capacity robotic joint consisting of a five-bar spatial mechanism integrated in the BB transporter trolley link. A kinematic model of the TTM is established, and the analytical input–output relationships, including the position-dependent transmission ratio, are derived and used to guide the design and optimization of the mechanism. The model predictions are compared to an ADAMS multibody simulation and to the results of an experiment conducted on a down-scaled prototype, both of which validate the model accuracy