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[en] Fusion devices produce tens of thousands of discharges but only a very limited part of the collected information is analysed. The analysis of physical events requires their identification and temporal location and the generation of specialized databases in relation to these time instants. The automatic determination of precise time instants in which events happen and the automatic search for potential relevant time intervals could be made thanks to classification techniques and regression techniques. Classification and regression techniques have been used for the automatic creation of specialized databases for JET and have allowed the automatic determination of disruptive / non-disruptive character of discharges. The validation of the recognition method has been carried out with 4400 JET discharges and the global success rate has been 99.02 per cent
[en] The Super-X Divertor (SXD), a robust axisymmetric redesign of the divertor magnetic geometry that can allow a fivefold increase in the core power density of toroidal fusion devices, is presented. With small changes in poloidal coils and currents for standard divertors, the SXD allows the largest divertor plate radius inside toroidal field coils. This increases the plasma-wetted area by 2-3 times over all flux-expansion-only methods (e.g., plate near main X point, plate tilting, X divertor, and snowflake), decreases parallel heat flux and hence plasma temperature at plate, and increases connection length by 2-5 times. Examples of high-power-density fusion devices enabled by SXD are discussed; the most promising near-term device is a 100 MW modular compact fusion neutron source 'battery' small enough to fit inside a conventional fission blanket.
[en] A comprehensive analysis of scaling laws for plasma focus devices producing neutrons is presented. Similarities and differences in plasma focus devices working with stored energies ranging from 1 MJ to 0.1 J are found. First, a brief review listing the most important results achieved by the Thermonuclear Plasma Department of the Chilean Nuclear Energy Commission, CCHEN, is presented. The aim of the work at CCHEN has been to characterize the physics of dense plasma foci and also to carry out the design and construction of smaller devices-in terms of both input energy and size-capable of providing dense hot plasmas. Certain scaling rules have been found from this research. These rules combined with other scaling laws have been applied to design and construct plasma focus devices with storage energy in a region never explored before (tens of joules and less than 1 J). Thus, a comprehensive analysis also including results from other groups is presented. In particular, all the devices, from the largest to the smallest, maintain the same value of ion density, magnetic field, plasma sheath velocity, Alfven speed and the quantity of energy per particle. Therefore, fusion reactions are even possible to obtain in ultraminiature devices (driven by generators of 0.1 J for example), as they are in the larger devices (driven by generators of 1 MJ). However, the stability of the plasma pinch highly depends on the size and energy of the device.
[en] Final technical report for research performed by Professor Dalton D. Schnack on SciDAC Cooperative Agreement: Center for Extended MHD Modeling, DE-FC02-06ER54870, for the period 7/1/06 to 2/15/08. Principal results for this period are: 1. Development of a model for computational modeling for the primitive form of the extended MMD equations. This was reported as Phys. Plasmas 13, 058103 (2006). 2. Comparison between the NIMROD and M3D codes for simulation of the nonlinear sawtooth crash in the CDXU tokamak. This was reported in Phys. Plasmas 14, 056105 (2006). 3. Demonstration of 2-fluid and gyroviscous stabilization of interchange modes using computational extended MHD models. This was reported in Phys. Rev. Letters 101, 085005 (2008). Each of these publications is attached as an Appendix of this report. They should be consulted for technical details.
[en] Perturbative experiments are essential to understand the complex transport phenomena in fusion plasmas. The perturbative methods used for transport studies are summarized and the main properties discussed. Based on this approach, transport of particles, heat and momentum has been intensively investigated. The main results obtained for the different channels are described and illustrated with selected examples.
[en] Gridded inertial electrostatic confinement (IEC) devices are of interest to the research community for their multiple near-term applications. The number of applications of an IEC device increases with increasing fusion reaction rate. However, all attempts to improve the fusion reactivity of the IEC device have resulted in a linear or less than linear response with the power supply current. This work is geared toward determining the reasons for the observed response of the IEC device. Such an understanding would help formulate new ways to improve the efficiency of the device. Experiments were conducted with single loop grids built from different materials (Re and W25%Re) to study the electron emission from the cathode in an IEC device. A single loop grid produces a (∼line) cylindrical fusion source and was used to study the electron emission from cathode. Electron emission from the cathode increases non-linearly due to the presence of multiple sources (secondary electron emission, field emission and photoemission), as a result of which the ion current increases in a less than linear fashion with the power supply current. The ion recirculation current equation has been updated to accommodate various electron contributions. Several techniques to mitigate the electron emission from the cathode are suggested in this paper.
[en] So far the models used to study dust grain-plasma interactions in fusion plasmas neglect the effects of dust material vapor, which is always present around dust in rather hot and dense edge plasma environment in fusion devices. However, when the vapor density and/or the amount of ionized vapor atoms become large enough, they can alter the grain-plasma interactions. Somewhat similar processes occur during pellet injection in fusion plasma. In this brief communication the applicability limits of the models ignoring vapor effects in grain-plasma interactions are obtained.
[en] Developments in computer architecture and neutronics code capabilities have enabled high-resolution analysis of complex 3D geometries. Thus, accurately modeling 3D source distributions has become important for nuclear analyses. In this work two methods are described which generate and sample such 3D sources based directly on the plasma parameters of a fusion device and which facilitate the ability to update the neutron source following changes to the plasma physics configuration. The cylindrical mesh method is for toroidally symmetric machines and utilizes data in a standard file format which represents the poloidal magnetic flux on an R-Z grid. The conformal hexahedral mesh method takes plasma physics data generated in an idealized toroidal coordinate system and uses a Jacobian transformation and a functional expansion to generate the source. This work describes each methodology and associated test cases. The cylindrical mesh method was applied to ARIES-RS and the conformal hexahedral mesh method was applied to a uniform torus and ARIES-CS. The results of the test cases indicate that these improved source definitions can have important effects on pertinent engineering parameters, such as neutron wall loading, and should therefore be used for high-resolution nuclear analyses of all toroidal devices.
[en] A fusion plant designed to demonstrate electricity production, known as DEMO, is likely to be very different from existing fusion devices and even from ITER. These differences will be found not only in the technology employed but also in physics areas including, but not confined to, the plasma behaviour. Here, some of the areas where DEMO is expected to be different are highlighted and explored. As a result of the differences between DEMO and existing devices, the fusion community needs to develop a new intuition when considering the design and performance of DEMO.