Download or read book Transport driven Scrape off Layer Flows and the Boundary Conditions Imposed at the Magnetic Separatrix in a Tokamak Plasma written by Brian LaBombard and published by . This book was released on 2004 with total page 110 pages. Available in PDF, EPUB and Kindle. Book excerpt: (Cont.) Experiments suggest that topology-dependent flow boundary conditions may also play a role in the sensitivity of L-H power threshold to x-point location: in a set of otherwise similar discharges, the L-H transition is seen to be coincident with central rotation achieving roughly the same value, independent of magnetic topology. For discharges with BxGradB pointing away from the x-point (i.e., with the SOL flow boundary condition impeding co-current rotation), the same characteristic rotation can only be achieved with higher input power.

Download or read book Driven Rotation Self Generated Flow and Momentum Transport in Tokamak Plasmas written by John Rice and published by Springer Nature. This book was released on 2022-01-13 with total page 158 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book provides a comprehensive look at the state of the art of externally driven and self-generated rotation as well as momentum transport in tokamak plasmas. In addition to recent developments, the book includes a review of rotation measurement techniques, measurements of directly and indirectly driven rotation, momentum sinks, self-generated flow, and momentum transport. These results are presented alongside summaries of prevailing theory and are compared to predictions, bringing together both experimental and theoretical perspectives for a broad look at the field. Both researchers and graduate students in the field of plasma physics will find this book to be a useful reference. Although there is an emphasis on tokamaks, a number of the concepts are also relevant to other configurations.

Download or read book Fusion Physics written by MITSURU KIKUCHI and published by International Atomic Energy. This book was released on 2002-01-01 with total page 1158 pages. Available in PDF, EPUB and Kindle. Book excerpt: Humans do not live by bread alone. Physically we are puny creatures with limited prowess, but with unlimited dreams. We see a mountain and want to move it to carve out a path for ourselves. We see a river and want to tame it so that it irrigates our fields. We see a star and want to fly to its planets to secure a future for our progeny. For all this, we need a genie who will do our bidding at a flip of our fingers. Energy is such a genie. Modern humans need energy and lots of it to live a life of comfort. In fact, the quality of life in different regions of the world can be directly correlated with the per capita use of energy [1.1–1.5]. In this regard, the human development index (HDI) of various countries based on various reports by the United Nations Development Programme (UNDP) [1.6] (Fig. 1.1), which is a parameter measuring the quality of life in a given part of the world, is directly determined by the amount of per capita electricity consumption. Most of the developing world (~5 billion people) is crawling up the UN curve of HDI versus per capita electricity consumption, from abysmally low values of today towards the average of the whole world and eventually towards the average of the developed world. This translates into a massive energy hunger for the globe as a whole. It has been estimated that by the year 2050, the global electricity demand will go up by a factor of up to 3 in a high growth scenario [1.7–1.9]. The requirements beyond 2050 go up even higher.

Download or read book Turbulent Transport In Magnetized Plasmas Second Edition written by C Wendell Horton, Jr and published by #N/A. This book was released on 2017-07-21 with total page 522 pages. Available in PDF, EPUB and Kindle. Book excerpt: For a few seconds with large machines, scientists and engineers have now created the fusion power of the stars in the laboratory and at the same time find the rich range of complex turbulent electromagnetic waves that transport the plasma confinement systems. The turbulent transport mechanisms created in the laboratory are explained in detail in the second edition of 'Turbulent Transport in Magnetized Plasmas' by Professor Horton.The principles and properties of the major plasma confinement machines are explored with basic physics to the extent currently understood. For the observational laws that are not understood — the empirical confinement laws — offering challenges to the next generation of plasma students and researchers — are explained in detail. An example, is the confinement regime — called the 'I-mode' — currently a hot topic — is explored.Numerous important problems and puzzles for the next generation of plasma scientists are explained. There is growing demand for new simulation codes utilizing the massively parallel computers with MPI and GPU methods. When the 20 billion dollar ITER machine is tested in the 2020ies, new theories and faster/smarter computer simulations running in near real-time control systems will be used to control the burning hydrogen plasmas.

Download or read book Nuclear Fusion written by and published by . This book was released on 2009 with total page 324 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Scrape off Layer Flows Magnetic Topology and Influence on the L H Threshold in a Tokamak written by Brian LaBombard and published by . This book was released on 2004 with total page 24 pages. Available in PDF, EPUB and Kindle. Book excerpt: The dependence of L-H power threshold on magnetic topology (upper-, lower-null) in a tokamak is linked to near-sonic plasma flows in the high-field side scrape-off layer. Scrape-off layer flow momentum, coupling across the separatrix, imparts a topology-dependent increment to edge and core toroidal rotation (counter-, co-current). In all topologies, rotation increases in the co-current direction with input power: the L-H transition is seen when co-rotation achieves a characteristic level. Correspondingly, higher power is required to attain H-modes in upper- versus lower-null (with BxGradB down).

Download or read book Electron Temperature Gradient Driven Instability in the Tokamak Boundary Plasma written by and published by . This book was released on 1992 with total page 24 pages. Available in PDF, EPUB and Kindle. Book excerpt: A general method is developed for calculating boundary plasma fluctuations across a magnetic separatrix in a tokamak with a divertor or a limiter. The slab model, which assumes a periodic plasma in the edge reaching the divertor or limiter plate in the scrape-off layer(SOL), should provide a good estimate, if the radial extent of the fluctuation quantities across the separatrix to the edge is small compared to that given by finite particle banana orbit. The Laplace transform is used for solving the initial value problem. The electron temperature gradient(ETG) driven instability is found to grow like t−12e{sup {gamma}mt}.

Download or read book Simulation of the Scrape off Layer Plasma During a Disruption written by and published by . This book was released on 1996 with total page 16 pages. Available in PDF, EPUB and Kindle. Book excerpt: The evolution of the scrape-off layer (SOL) during a disruption in the DIII-D tokamak is modeled using the 2-D UEDGE transport code. The focus is on the thermal quench phase when most of the energy content of the discharge is rapidly transported across the magnetic separatrix where it then flows to material surfaces or is radiated. Comparisons between the simulation and an experiment on the DIII-D tokamak are made with the heat flux to the divertor plate, and temperature and density profiles at the SOL midplane. The temporal response of the separate electron and ion heat-flux components to the divertor plate is calculated. The sensitivity of the solution to assumptions of electron heat-flux models and impurity radiation is investigated.

Download or read book Boundary Conditions for Tokamak Transport Equations from Scrape off Layer Modelling written by Kurt Borrass and published by . This book was released on 1980 with total page 13 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Energy Research Abstracts written by and published by . This book was released on 1994-12 with total page 508 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Scrape Off Layer Flow Studies in Tokamaks written by and published by . This book was released on 2011 with total page 10 pages. Available in PDF, EPUB and Kindle. Book excerpt: A summary is given of the work carried out under the LDRD project 09-ERD-025 entitled Scrape-Off-Layer Flow Studies in Tokamaks. This project has lead to implementation of the new prototype Fourier Transform Spectrometer edge plasma flow diagnostic on the DIII-D National Fusion Facility at General Atomics, acquisition of carbon impurity concentration and flow data, and demonstration that the resulting data compare reasonably well with LLNL's edge plasma transport code UEDGE. Details of the work are contained in attached published papers, while the most recent results that are being written-up for publication are summarized in the report. Boundary plasma flows in tokamak fusion devices are key in determining the distribution of fuel and impurity ions, with tritium build-up in the walls an especially critical operational issue. The intrusion of impurity ions to the hot plasma core region can result in serious energy-loss owing to line radiation. However, flow diagnostic capability has been severely limited in fusion-relevant hot edge plasmas where Langmuir-type probes cannot withstand the high heat flux and traditional Doppler spectroscopy has limited resolution and signal strength. Thus, new edge plasma flow diagnostic capabilities need to be developed that can be used in existing and future devices such as ITER. The understanding of such flows requires simulation with 2-dimensional transport codes owing to the geometrical complexity of the edge region in contact with material surfaces and the large number of interaction physical processes including plasma flow along and across the magnetic field, and coupling between impurity and neutral species. The characteristics of edge plasma flows are substantially affected by cross-magnetic-field drifts (ExB/B2 and BxVB/B2), which are known to introduce substantial convergence difficulty for some cases. It is important that these difficulties be overcome so that drifts can be included in transport models, both for validation with existing data and for projection to future devices.

Download or read book TEMPEST Simulations of the Plasma Transport in a Single Null Tokamak Geometry written by and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: We present edge kinetic ion transport simulations of tokamak plasmas in magnetic divertor geometry using the fully nonlinear (full-f) continuum code TEMPEST. Besides neoclassical transport, a term for divergence of anomalous kinetic radial flux is added to mock up the effect of turbulent transport. In order to study the relative roles of neoclassical and anomalous transport, TEMPEST simulations were carried out for plasma transport and flow dynamics in a single-null tokamak geometry, including the pedestal region that extends across the separatrix into the scrape-off layer and private flux region. In a series of TEMPEST simulations were conducted to investigate the transition of midplane pedestal heat flux and flow from the neoclassical to the turbulent limit and the transition of divertor heat flux and flow from the kinetic to the fluid regime via an anomalous transport scan and a density scan. The TEMPEST simulation results demonstrate that turbulent transport (as modelled by large diffusion) plays a similar role to collisional decorrelation of particle orbits and that the large turbulent transport (large diffusion) leads to an apparent Maxwellianization of the particle distribution. Moreover, we show the transition of parallel heat flux and flow at the entrance to the divertor plates from the fluid to the kinetic regime. For an absorbing divertor plate boundary condition, a non-half-Maxwellian is found due to the balance between upstream radial anomalous transport and energetic ion endloss.

Download or read book Driving Toroidally Asymmetric Current Through the Tokamak Scrape off Layer Part II written by and published by . This book was released on 2009 with total page 41 pages. Available in PDF, EPUB and Kindle. Book excerpt: The structure of the magnetic field perturbations due to non-axisymmetric field-aligned currents in the tokamak scrape-off layer (SOL) are analytically calculated near the X-point. Part I [I. Joseph, et al., submitted to Phys. Plasmas (2008)] demonstrated that biasing divertor target plates in a toroidally asymmetric fashion can generate an appreciable toroidally asymmetric parallel current density in the SOL along the separatrix. Here, the magnetic field perturbation caused by a SOL current channel of finite width and step-wise constant amplitude at the target plate is derived. Flux expansion amplifies the magnetic perturbation near the X-point, while phase interference causes the SOL amplitude to be reduced at large toroidal mode number. Far enough from the current channel, the magnetic field can be approximated as arising from a surface current near the separatrix with differing amplitudes in the SOL and the divertor leg. The perturbation spectrum and resonant components of this field are computed analytically asymptotically close to the separatrix in magnetic flux coordinates. The size of the stochastic layer due to the applied perturbation that would result without self-consistent plasma shielding is also estimated. If enough resonant field is generated, control of the edge pressure gradient may allow stabilization of edge localized modes.

Download or read book Material Migration in Tokamak Plasmas with a Three dimensional Boundary written by Ruth Laengner and published by Forschungszentrum Jülich. This book was released on 2013 with total page 175 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book The Plasma Boundary of Magnetic Fusion Devices written by P.C Stangeby and published by CRC Press. This book was released on 2000-01-01 with total page 738 pages. Available in PDF, EPUB and Kindle. Book excerpt: The Plasma Boundary of Magnetic Fusion Devices introduces the physics of the plasma boundary region, including plasma-surface interactions, with an emphasis on those occurring in magnetically confined fusion plasmas. The book covers plasma-surface interaction, Debye sheaths, sputtering, scrape-off layers, plasma impurities, recycling and control, 1D and 2D fluid and kinetic modeling of particle transport, plasma properties at the edge, diverter and limiter physics, and control of the plasma boundary. Divided into three parts, the book begins with Part 1, an introduction to the plasma boundary. The derivations are heuristic and worked problems help crystallize physical intuition, which is emphasized throughout. Part 2 provides an introduction to methods of modeling the plasma edge region and for interpreting computer code results. Part 3 presents a collection of essays on currently active research hot topics. With an extensive bibliography and index, this book is an invaluable first port-of-call for researchers interested in plasma-surface interactions.

Download or read book Edge Localized Mode Dynamics and Transport in the Scrape Off Layer of the DIII D Tokamak written by and published by . This book was released on 2004 with total page 44 pages. Available in PDF, EPUB and Kindle. Book excerpt: High temporal and spatial resolution measurements in the boundary of the DIII-D tokamak show that edge localized modes (ELMs) are produced in the low field side, are poloidally localized and are composed of fast bursts (≈20 to 40 [mu]s long) of hot, dense plasma on a background of less dense, colder plasma (≈5 x 1018 m{sup {+-}3}, 50 eV) possibly created by the bursts themselves. The ELMs travel radially in the scrapeoff layer (SOL), starting at the separatrix at ≈450 m/s, and slow down to ≈150 m/s near the wall, convecting particles and energy to the SOL and walls. The temperature and density in the ELM plasma initially correspond to those at the top of the density pedestal but quickly decay with radius in the SOL. The temperature decay length (≈1.2 to 1.5 cm) is much shorter than the density decay length (≈3 to 8 cm), and the latter decreases with increasing pedestal (and SOL) density. The local particle and energy flux at the midplane wall during the bursts are 10% to 50% (≈1 to 2 x 1021 m{sup {+-}2} s{sup {+-}1}) and 1% to 2 % (≈20 to 30 kW/m2) respectively of the LCFS average fluxes, indicating that particles are transported radially much more efficiently than heat. Evidence is presented suggesting toroidal rotation of the ELM plasma in the SOL. The ELM plasma density and temperature increase linearly with discharge/pedestal density up to a Greenwald fraction of ≈0.6, and then decrease resulting in more benign (grassier) ELMs.

Download or read book Particle Exhaust and Neutral Fueling in Spherical Tokamaks with Resonant Magnetic Perturbation Fields written by Ian Jacob Waters and published by . This book was released on 2018 with total page 222 pages. Available in PDF, EPUB and Kindle. Book excerpt: Resonant Magnetic Perturbations (RMPs) and Advanced Divertors (ADs) are both promising candidates to be utilized to meet the challenges of power exhaust in future fusion devices. A combination of both approaches is a promising avenue in order to achieve a stable, high performance plasma edge in an integrated way that takes into account divertor heat load limits while allowing for density and impurity control. The latter is of particular importance in spherical tokamaks which feature Edge Localized Mode free high confinement H-mode regimes prone to density rises and core impurity accumulation. The capability to control core densities and particle exhaust in spherical tokamaks needs to be assessed to determine their viability for compact fusion nuclear science facilities. The experimentally observed, density pump-out effect induced by the application of small amplitude RMPs is an important phenomena with respect to density control but its underlying cause is not well understood. One proposed mechanism for this density pump-out is that the opening of formerly confined field lines from the plasma edge enables enhanced parallel exhaust from the core plasma into the scrape-off-layer and to the divertor targets. Further, regions of stochasticity inside the separatrix can lead to enhanced perpendicular transport, even if these field lines do not themselves escape to the wall. Based on magneto-hydrodynamic (MHD) modeling, it has been previously proposed that a particular resonant response to the applied RMP fields--the so called "Edge-Peeling" response--enhances these geometric changes and thus drives enhanced exhaust. How much these mechanisms contribute to the overall pump-out is an open question. Further, how these RMPs impact the fundamental coupling between the plasma core, edge, and scrape-off-layer, through changes to particle fueling and particle exhaust, is the subject of this thesis. The EMC3-EIRENE code is utilized to assess these scenarios on the Mega-Ampere Spherical Tokamak (MAST) and it's upgrade (MAST-U). Initially, work was carried out to validate the theoretical mechanism for enhanced exhaust: that pressure gradients drive flows along open field lines in the plasma edge. Modeling showed that flows generated by local gas puffing are robust to changes in plasma parameters, and ultimately are a fundamental feature that can be experimentally validated. The underlying mechanism of static pressure driven flows was resolved with a 1D model. Modeling was then used to study the impact of RMP fields specifically. The inclusion of plasma response (from a resistive single fluid MHD model) in the RMP fields shows a more moderate response of density and temperature to the RMPs than does a vacuum field approach in MAST lower single null discharges. In this scenario, enhanced exhaust is shown to contribute to the density pump-out, but the modeled confinement changes underpredict the impact expected from analysis of experiments. Applying this same approach in MAST double null discharges--a second test case from experiment--shows that the addition of RMPs with the single fluid Edge-Peeling response does not cause a consistent pump-out signature in the modeling. This numerical finding of no density pump-out is in contrast to experimental observations for such configurations. This is found in spite of the fact that field lines are escaping the confined region, pressure driven flows are formed, and characteristic lobe structures appear in the plasma edge. This study has shown in a consistent manner that pressure driven flows along field lines are a viable mechanism to govern the plasma particle exhaust from the edge reservoir. If 3D magnetic flux bundles generated by RMP fields connect to regions deep inside of the separatrix, the parallel pressure gradient towards divertor targets will drive enhanced particle flux out of the formerly confined region of the plasma. If the length scale of connection is too long such that the parallel pressure gradient can not be maintained, the flow vanishes, and in spite of the nominal 3D structures in the magnetic field, no impact on particle exhaust is seen. This finding is important for the efforts to understand plasma exhaust with RMP fields. The mere existence of the 3D lobes of the separatrix, formed by the RMP fields, is not sufficient to explain the plasma density pump out alone. But for plasma scenarios with short connection length, and magnetic fields characterized by steep radial gradients they are a viable contributor.