Download or read book Plasma Transport in Stochastic Magnetic Field Caused by Vacuum Resonant Magnetic Perturbations at Diverted Tokamak Edge written by and published by . This book was released on 2010 with total page 15 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Electron Transport in the Plasma Edge with Rotating Resonant Magnetic Perturbations at the TEXTOR Tokamak written by Henning Stoschus and published by Forschungszentrum Jülich. This book was released on 2011 with total page 141 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Particle Transport as a Result of Resonant Magnetic Perturbations written by Saskia Mordijck and published by . This book was released on 2011 with total page 97 pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis makes contributes to field of plasma physics with a particular focus on particle transport as a result of resonant magnetic perturbations (RPMs) in magnetic confinement devices (Tokamaks). RPMs have proven to be a useful technique to suppress edge localized modes (ELMs) that under certain conditions can damage the confinement device. In order to suppress ELMs, these magnetic perturbations are created to be be resonant at the edge of the plasma (i.e., by selecting an n=3 spectrum and a q95 = 3.6). However, RMPs lead to a changes in the density profile, not only in the pedestal area, but also deeper in the plasma core, limiting plasma performance. As a first contribution in this thesis we carefully investigate density pump-out, and show that it is the result of a change in particle transport (as opposed to a change in neutral fueling). A second contribution of this work is the introduction of a weighted magnetic diffusion coefficient (D/OFL) that allows us to make quantitative comparisons between experimental datasets from different Tokamak devices. By comparing D/OFL for MAST L-modes and DIII-D H-modes, we find that both machines exhibit a very different density pump-out for similar D/OFL values. Since turbulent particle transport is very different for L and H-modes, we investigate, as a third contribution of this work, the influence of RMPs on turbulent particle transport in both MAST and DIII-D. We find that while an increase in turbulent transport on MAST correlates well with density pump-out, no meaningful correlation was found for pedestal density changes in DIII-D. Therefore, as a final contribution in this thesis, we investigate how convective particle transport parallel to the magnetic field alters the density profiles. We compare the increase in convective parallel particle transport and find good agreement with experimental density profiles.

Download or read book Toroidal Phasing of Resonant Magnetic Perturbation Effect on Edge Pedestal Transport in the DIII D Tokamak written by Theresa M. Wilks and published by . This book was released on 2013 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Resonant Magnetic Perturbation (RMP) fields produced by external control coils are considered a viable option for the suppression of Edge Localized Modes (ELMs) in present and future tokamaks. Repeated reversals of the toroidal phase of the I-coil magnetic field in RMP shot 147170 on DIII-D has generated uniquely different edge pedestal profiles, implying different edge transport phenomena. The causes, trends, and implications of RMP toroidal phase reversal on edge transport is analyzed by comparing various parameters at 0 and 60 degree toroidal phases, with an I-coil mode number of n=3. An analysis of diffusive and non-diffusive transport effects of these magnetic perturbations it the plasma edge pedestal for this RMP shot is characterized by interpreting the ion and electron heat diffusivities, angular momentum transport frequencies, ion diffusion coefficients, and pinch velocities for both phases.

Download or read book written by and published by . This book was released on 1997 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Plasma Transport in Stochastic Magnetic Fields I General Considerations and Test Particle Transport written by and published by . This book was released on 1978 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: A systematic theory is developed for the computation of electron transport in stochastic magnetic fields. Small scale magnetic perturbations arising, for example, from finite-.beta. micro-instabilities are assumed to destroy the flux surfaces of a standard tokamak equilibrium. Because the magnetic lines then wander in a volume, electron radial flux is enhanced due to the rapid particle transport along as well as across the lines. By treating the magnetic lines as random variables, it is possible to develop a kinetic equation for the electron distribution function. This is solved approximately to yield the diffusion coefficient.

Download or read book Edge Stability and Transport Control with Resonant Magnetic Perturbations in Collisionless Tokamak Plasmas written by and published by . This book was released on 2006 with total page 26 pages. Available in PDF, EPUB and Kindle. Book excerpt: A critical issue for fusion plasma research is the erosion of the first wall of the experimental device due to impulsive heating from repetitive edge magneto-hydrodynamic (MHD) instabilities known as 'edge-localized modes' (ELMs). Here, we show that the addition of small resonant magnetic field perturbations completely eliminates ELMs while maintaining a steady-state high-confinement (H-mode) plasma. These perturbations induce a chaotic behavior in the magnetic field lines, which reduces the edge pressure gradient below the ELM instability threshold. The pressure gradient reduction results from a reduction in particle content of the plasma, rather than an increase in the electron thermal transport. This is inconsistent with the predictions of stochastic electron heat transport theory. These results provide a first experimental test of stochastic transport theory in a highly rotating, hot, collisionless plasma and demonstrate a promising solution to the critical issue of controlling edge instabilities in fusion plasma devices.

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 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 0 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

Download or read book Plasma Transport in Stochastic Magnetic Fields II written by John A. Krommes and published by . This book was released on 1978 with total page 16 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Theory of Tokamak Plasmas written by R.B. White and published by Elsevier. This book was released on 2017-01-31 with total page 374 pages. Available in PDF, EPUB and Kindle. Book excerpt: This is a graduate textbook on tokamak physics, designed to provide a basic introduction to plasma equilibrium, particle orbits, transport, and those ideal and resistive magnetohydrodynamic instabilities which dominate the behavior of a tokamak discharge, and to develop the mathematical methods necessary for their theoretical analysis.

Download or read book Energy Research Abstracts written by and published by . This book was released on 1993 with total page 762 pages. Available in PDF, EPUB and Kindle. Book excerpt: Semiannual, with semiannual and annual indexes. References to all scientific and technical literature coming from DOE, its laboratories, energy centers, and contractors. Includes all works deriving from DOE, other related government-sponsored information, and foreign nonnuclear information. Arranged under 39 categories, e.g., Biomedical sciences, basic studies; Biomedical sciences, applied studies; Health and safety; and Fusion energy. Entry gives bibliographical information and abstract. Corporate, author, subject, report number indexes.

Download or read book Plasma Transport in Stochastic Magnetic Fields II Principles and Problems of Test Electron Transport written by and published by . This book was released on 1978 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: A model stochastic differential equation is considered which describes guiding center electron motion in a statistically specified spectrum of turbulent magnetic fluctuations. The fluctuation intensity is assumed to satisfy the Chirikov criterion (resonance overlap) for onset of stochasticity. In this limit typical lines diffuse and are adequately described by a quasilinear diffusion coefficient D/sub m/. However, quasilinear theory does not describe an important mechanism for loss of particle correlations: particles collisionally diffuse from one line to an adjacent one which diverges rapidly from the first, carrying the particles away. The scale length L/sub K/ for line divergence is related to the inverse of the Kolmogorov-Sinai entropy. An attempt is made to determine L/sub K/ from a simplified Eulerian vertex renormalization. The exponentiation length which emerges is L/sub K/ approximately L/sub s/(anti k2/sub theta/D''/sub m/L/sub s/)−13, where L/sub s/ is the shear length, k bar/sub theta/ is a typical azimuthal wavenumber, and D''/sub m/ is of order D/sub m/. In a particular limit of weak shear, the particle diffusion coefficient can then be estimated as D approximately DELTA r2?sub c/, where .delta.r2 approximately D/sub m/z(tau/sub c/), z? is the distance traveled along the lines in time tau, and for static fluctuations tau/sub c/ approximately tau(L/sub delta/), where L/sub delta/ is L/sub K/ multiplied by a logarithmic factor involving the perpendicular collisional diffusion coefficient.

Download or read book Partially Ionized Plasma Transport and Line Radiation Interactions as the Tokamak Edge written by Mark Lloyd Adams and published by . This book was released on 2003 with total page 179 pages. Available in PDF, EPUB and Kindle. Book excerpt: Hydrogenic resonance line radiation interacts with the high-density low-temperature plasma at the tokamak edge. As a result, there exists a significant nonlocal plasma energy transport channel, local atomic level populations are altered by global plasma properties, and plasma transport is affected. In this dissertation, new theoretical and computational models of partially ionized plasma transport, which include line radiation interactions, are developed and then applied to the study of plasma phenomena at the tokamak edge. First, to include the effects of an external magnetic field on nonlocal thermodynamic equilibrium (NLTE) mlodels, TotalB, a computationally efficient spectral line shape code that describes the broadening of radiative transitions due to an applied magnetic field, the ion microfield, and electron perturbers, is developed using standard line broadening theory. Second, to enable the study of plasma transport and line radiation interactions, PIP, a partially ionized plasma transport model that includes the charge-exchange coupling of ions with neutral atoms, the transport of potential energy, the effects of resonance line radiation interactions on atomic rates, and the transport of an arbitrary number of atomic levels, is developed and coupled with an existing NLTE radiation transport model. Finally, the combined capabilities model is applied to the simulation of a tokamak divertor and the significant effect of line radiation interactions on plasma transport at the tokamak edge is demonstrated. In addition, since the solution of the radiation field is an integral part of the calculation, several spectroscopic diagnostic techniques are developed.

Download or read book Plasma Transport in Stochastic Magnetic Fields III Kinetics of Test particle Diffusion written by and published by . This book was released on 1982 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: A discussion is given of test particle transport in the presence of specified stochastic magnetic fields, with particular emphasis on the collisional limit. Certain paradoxes and inconsistencies in the literature regarding the form of the scaling laws are resolved by carefully distinguishing a number of physically distinct correlation lengths, and thus by identifying several collisional subregimes. The common procedure of averaging the conventional fluid equations over the statistics of a random field is shown to fail in some important cases because of breakdown of the Chapman-Enskog ordering in the presence of a stochastic field component with short autocorrelation length. A modified perturbation theory is introduced which leads to a Kubo-like formula valid in all collisionality regimes. The direct-interaction approximation is shown to fail in the interesting limit in which the orbit exponentiation length L/sub K/ appears explicitly. A higher order renormalized kinetic theory in which L/sub K/ appears naturally is discussed and used to rederive more systematically the results of the heuristic scaling arguments.

Download or read book Edge Localized Mode Control by Resonant Magnetic Perturbations in Tokamak Plasmas written by Francois Orain and published by . This book was released on 2014 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: The growth of plasma instabilities called Edge Localized Modes (ELMs) in tokamaks results in the quasi-periodic relaxations of the edge plasma, potentially harmful for the divertor in ITER. One of the promising ELM control methods planned in ITER is the application of external resonant magnetic perturbations (RMPs), already efficient for ELM mitigation/suppression in current tokamak experiments. However a better understanding of the interaction between ELMs, RMPs and plasma flows is needed to make reliable predictions for ITER. In this perspective, non-linear modeling of ELMs and RMPs is done with the reduced MHD code JOREK, in realisitic geometry including the X-point and the Scrape-Off Layer. The two-fluid diamagnetic drifts, the neoclassical friction, a source of parallel rotation and RMPs have been implemented to simulate the RMP penetration consistently with the plasma response. As a first step, the plasma response to RMPs (without ELMs) is studied for JET, MAST and ITER realistic plasma parameters and geometry. Then the cyclic dynamics of the ELMs (without RMPs) is modeled for the first time in realistic geometry. After an ELM crash, the diamagnetic rotation is found to be instrumental to stabilize the plasma and to model the cyclic reconstruction and collapse of the plasma pressure profile. Last the ELM mitigation and suppression by RMPs is observed for the first time in modeling. The non-linear coupling of the RMPs with unstable modes is found to induce a continuous MHD activity in place of a large ELM crash, resulting in the mitigation of the ELMs. Over a threshold in magnetic perturbation, the full ELM suppression is also observed.

Download or read book Effects of Magnetic Field Perturbations in the ATF Torsatron written by and published by . This book was released on 1993 with total page 28 pages. Available in PDF, EPUB and Kindle. Book excerpt: The effects of errors in the magnetic fields of tokamaks on the plasma are quite different from those in stellarators. In tokamaks, field errors can cause disruptive locked modes through the non-linear evolution of tearing modes acting on initially small error-induced islands. Scaling predictions for these effects indicate that the critical relative field error which can be tolerated becomes smaller as the tokamak size becomes larger. In stellarators, the effect is more benign, as field errors appear only to cause increased plasma transport in the vicinity of islands. Great care has been taken to minimize magnetic field errors in the most recent generation of stellarator-type magnetic plasma traps. In the past six years, several new and sensitive techniques have been developed to detect and map field errors. These methods all rely on the detection of electrons injected along magnetic field lines. During the commissioning of ATF, flux surfaces were mapped using the fluorescent screen technique. Field errors were discovered and traced to uncompensated dipoles in the helical current feeds. Prior to elimination of these errors, plasma discharges indicated centrally peaked plasma profiles. After correction of the uncompensated dipoles, flux surfaces were mapped a second time, and the island widths were found to be greatly reduced. Field errors were then deliberately introduced using a set of perturbation coils that had been added to ATF, and electron-beam mapping of the flux surfaces showed that islands several centimeters in width could easily be created by these coils. After elimination of the error fields, the measured plasma temperature and density profiles were much broader. The field-perturbation coils were then used to produce magnetic field asymmetries, and the measured plasma profiles were again shown to narrow as a result of islands.