Download or read book Effect of Applied Resonant Magnetic Fields on the Measured MHD Mode Structure in a Tokamak Plasma written by Qingjun Xiao and published by . This book was released on 1998 with total page 216 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book High Resolution MHD Spectroscopy of External Kinks in a Tokamak Plasma written by Daisuke Shiraki and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: By adjusting the helicity of the magnetic field applied by the control coils, the driven plasma response is shown to be predominantly resonant field amplification. When the amplitude of the applied field is not too large, the driven resonant response appears linear, independent of the presence of background MHD phenomena and consistent with the predictions of single-helicity modeling of kink mode dynamics. The spatial structures of both the naturally rotating kink mode and the externally driven response are observed to be identical, while the temporal evolutions are approximately independent. The phase-flip driven plasma response is measured as a function of edge safety factor, plasma rotation, and the amplitude of the applied magnetic perturbation. As the RMP amplitude increases, the plasma response is shown to be linear, saturated, and ultimately, disruptive.

Download or read book Modelling and Measurement of 3d Fields in Stellarators and Tokamaks written by Shaun Robert Haskey and published by . This book was released on 2015 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis presents advances in the modelling, analysis, and measurement of 3D fields, which have significantly improved the diagnosis and understanding of Alfven waves in the H-1NF stellarator and the role of non-axisymmetric magnetic perturbations (MPs) in edge localised mode (ELM) suppression on the DIII-D tokamak. Alfven waves and MPs impact on the performance of stellarators and tokamaks; consequently, improved measurement and understanding of these effects is critical to optimising the operation of these devices and the success of magnetic confinement fusion. To further understand the plasma fluctuations in H-1NF, a sixteen former, tri-axis helical Mirnov array (HMA) was designed and installed. The new array complements two existing poloidal Mirnov arrays by providing polarisation information, higher frequency response, and much improved toroidal resolution for spontaneously excited H-1NF fluctuations. The quantity and complexity of the data obtained from this new array led to the development of a periodic datamining algorithm which has been used to extract distinct plasma fluctuations in multi-channel oscillatory timeseries data. A state of the art synchronous imaging technique which overcomes frame rate and readout noise limitations of cameras is described and demonstrated on longer-lived H-1NF fluctuations. This technique can be used to image modes in the kHz - MHz range, opening up the possibility of high resolution imaging of high frequency MHD instabilities, which play an important role in stability and particle transport on both tokamaks and stellarators. In order to make the most of the data from the synchronous imaging technique, a 3D tomographic reconstruction technique which uses magnetic coordinates was developed for inversion of a set of high-resolution 2D visible light emission projections. Information about the modes, which was obtained using these diagnostic systems and analysis techniques is compared with calculations of the H-1NF continuum gap structure and several discrete normal modes within the framework of linearised ideal compressible MHD, using the CONTI and CAS3D codes. The observations have good agreement with modes where compressibility (beta induced Alfven eigenmodes) or interaction with sound modes is important (beta-induced Alfven-acoustic eigenmodes), in terms of their dominant mode numbers, radial structure, and polarisation. In tokamaks, an outstanding issue is the plasma response to externally applied 3D magnetic field perturbations and how the response leads to ELM suppression. Extensive modelling using the single fluid linear MHD code, MARS-F, shows the ability to tailor the plasma response through careful control of the applied MP field. Metrics are described, which allow the identification of regions of parameter space where the MP directly couples to the pitch-resonant harmonics or the kink mode. Several important parameteric dependencies such as [dollar]q_•[dollar], toroidal rotation, resistivity, and [dollar] beta_N[dollar] are also discussed. Finally, recent experiments on DIII-D using the modelling presented here show the importance of coupling to the kink mode in order to maximise the residual pitch-resonant harmonics and achieve ELM suppression. This finding critically influences the way that MPs are optimised to achieve the vital goal of ELM suppression on tokamaks.

Download or read book Mitigating Edge localized Modes on the Mega Ampere Spherical Tokamak Using Resonant Magnetic Perturbations written by Peter Denner and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Type-I ELMy H-mode is planned to be the reference inductive operational scenario for ITER. However, unmitigated type-I ELMs would cause unacceptable damage to ITER's divertor, so a way of mitigating their effect must be found. This thesis focuses on the ergodization of the plasma edge using RMPs as a means of ELM control, and on related topics relevant to ergodic magnetic fields in MAST. Chapter 1 provides an introduction to nuclear fusion and chapter 2 provides an overview of ELMs. In chapter 3, the effect of ergodic fields on L-mode temperature profiles is calculated. It is found that no flattening of the temperature profile should be expected in MAST plasmas, which is in agreement with experimental results. In chapter 4, various metrics characterizing the degree of ergodicity in both L- and H-mode plasmas are calculated using vacuum modelling and compared with the amount of density pump-out observed experimentally in the those plasmas during the application of RMPs. The only parameter to show a correlation with the amount of density pump-out is the width of the laminar region. However, plasma response modelling provides a robust criterion for the occurrence of density pump-out that applies both to L- and H-mode plasmas. In chapter 5, the results of lower single-null H-mode ELM mitigation experiments using n=4 and n=6 RMPs are presented. ELM mitigation is achieved and refuelling of plasmas that had begun to undergo pump-out is successfully demonstrated. Both ELM frequency and density pump-out are found to increase with ELM coil current above a certain threshold. An analysis of an ergodic magnetic field formed by a current sheet on a rational surface is presented in chapter 6. Various properties of this ergodic field are calculated and compared with experimental effects observed in the plasma. Some agreement is found between the experimental data and the modelling. Finally, a summary of the thesis is given in chapter 7.

Download or read book Scientific and Technical Aerospace Reports written by and published by . This book was released on 1995 with total page 692 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 1994-04 with total page 526 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Resistive MHD Mode Structures in a Tokamak written by Hwan-Young Che and published by . This book was released on 1993 with total page 282 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Magnetohydrodynamic Stability of Tokamaks written by Hartmut Zohm and published by John Wiley & Sons. This book was released on 2015-02-09 with total page 254 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book bridges the gap between general plasma physics lectures and the real world problems in MHD stability. In order to support the understanding of concepts and their implication, it refers to real world problems such as toroidal mode coupling or nonlinear evolution in a conceptual and phenomenological approach. Detailed mathematical treatment will involve classical linear stability analysis and an outline of more recent concepts such as the ballooning formalism. The book is based on lectures that the author has given to Master and PhD students in Fusion Plasma Physics. Due its strong link to experimental results in MHD instabilities, the book is also of use to senior researchers in the field, i.e. experimental physicists and engineers in fusion reactor science. The volume is organized in three parts. It starts with an introduction to the MHD equations, a section on toroidal equilibrium (tokamak and stellarator), and on linear stability analysis. Starting from there, the ideal MHD stability of the tokamak configuration will be treated in the second part which is subdivided into current driven and pressure driven MHD. This includes many examples with reference to experimental results for important MHD instabilities such as kinks and their transformation to RWMs, infernal modes, peeling modes, ballooning modes and their relation to ELMs. Finally the coverage is completed by a chapter on resistive stability explaining reconnection and island formation. Again, examples from recent tokamak MHD such as sawteeth, CTMs, NTMs and their relation to disruptions are extensively discussed.

Download or read book Nuclear Science Abstracts written by and published by . This book was released on 1975 with total page 1090 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Fusion Energy Update written by and published by . This book was released on 1979 with total page 104 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Plasma Physics Index written by and published by . This book was released on 1979 with total page 752 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Physics Briefs written by and published by . This book was released on 1994 with total page 1162 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Nuclear Science Abstracts written by and published by . This book was released on 1975-11 with total page 960 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 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.

Download or read book Current Programs written by and published by . This book was released on 1977 with total page 506 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book MHD Effects of a Ferritic Wall on Tokamak Plasmas written by Paul Ernest Hughes and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The development, assembly, installation, and testing of this wall as a modular upgrade is described, and the effect of the wall on machine performance is characterized. Comparative studies of plasma dynamics with the ferritic wall close-fitting against similar plasmas with the ferritic wall retracted demonstrate substantial effects on plasma stability. Resonant magnetic perturbations (RMPs) are applied, demonstrating a 50% increase in n = 1 plasma response amplitude when the ferritic wall is near the plasma. Susceptibility of plasmas to disruption events increases by a factor of 2 or more with the ferritic wall inserted, as disruptions are observed earlier with greater frequency. Growth rates of external kink instabilities are observed to be twice as large in the presence of a close-fitting ferritic wall. Initial studies are made of the influence of mode rotation frequency on the ferritic effect, as well as observations of the effect of the ferritic wall on disruption halo currents.

Download or read book ERDA Energy Research Abstracts written by United States. Energy Research and Development Administration and published by . This book was released on 1977 with total page 906 pages. Available in PDF, EPUB and Kindle. Book excerpt: