Download or read book Empirical Study of Ne in H Mode Pedestal in DIII D written by and published by . This book was released on 2005 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: There is compelling empirical [1] and theoretical [2] evidence that the global confinement of H-mode discharges increases as the pedestal pressure or temperature increases. Therefore, confidence in the performance of future machines requires an ability to predict the pedestal conditions in those machines. At this time, both the theoretical and empirical understanding of transport in the pedestal are incomplete and are inadequate to predict pedestal conditions in present or future machines. Recent empirical results might be evidence of a fundamental relation between the electron temperature T{sub e} and electron density n{sub e} profiles in the pedestal. A data set from the ASDEX-Upgrade tokamak has shown that [eta]{sub e}, the ratio between the scale lengths of the n{sub e} and T{sub e} profiles, exhibits a value of about 2 throughout the pedestal, despite a large range of the actual density and temperature values [3]. Data from the DIII-D tokamak show that over a wide range of pedestal density, the width of the steep gradient region for the T{sub e} profile is about 1-2 times the corresponding width for the n{sub e} profile, where both widths are measured from the plasma edge [4]. Thus, the barrier in the density might form a lower limit for the barrier in the electron temperature.

Download or read book Empirical Study of Ne in H Mode Pedestal in DIII D written by D. M. Thomas and published by . This book was released on 2004 with total page 6 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Comprehensive Dynamic Analysis of the H Mode Pedestal in DIII D written by Andrew Oakleigh Nelson and published by . This book was released on 2021 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: The H-mode pedestal, characterized by steep gradients and reduced transport, is an essential feature of tokamak plasmas that couples the cold Scrape-Off-Layer (SOL) to the hot, fusion-relevant core. Though existing magnetohydrodynamic models yield some insight into the pedestal, they are (due to the complexity of interaction between the pedestal and the rest of the plasma) unable to fully predict pedestal behavior from generalized plasma conditions. To progress towards a more comprehensive understanding of pedestal dynamics, a larger context must be considered. Using state-of-the-art modeling and perturbative experimental techniques on DIII-D, this thesis develops a broader empirical understanding of dynamic pedestal behavior that will inform future modeling efforts.The pedestal obeys the physics of the continuity equation, which is set by the sourcing of particles, inter-ELM transport, and boundary conditions. In this light, three phenomena are selected for in-depth study: fueling, transport, and SOL interactions. First, the effect of particle sources on the pedestal structure is examined through a series of dedicated experiments on DIII-D. Gas and pellet fueling techniques are applied to change the neutral ionization profile at similar plasma conditions, showing that the structure of the pedestal can vary significantly with changes to the neutral source profile. Second, a novel experimental technique is used to probe the nature of inter-ELM turbulence, which is linked to the evolution and recovery of the pedestal structure. Additional current is induced in the pedestal region of several DIII-D plasmas, providing a first-of-its-kind experimental demonstration of microtearing modes (MTMs) in the tokamak edge. MTMs may contribute strongly to intense heat fluxes through the pedestal region, potentially providing the groundwork for an entirely physics-based predictive model of pedestal behavior. Finally, to develop a physics understanding of how the SOL boundary condition couples with the pedestal over the course of an entire plasma discharge, detailed modeling work is performed with the UEDGE code as a function of pedestal and ELM conditions. In this section, we establish a dynamic connection between the pedestal structure and divertor behavior, highlighting the need for a comprehensive approach to pedestal physics.

Download or read book OVERVIEW OF H MODE PEDESTAL RESEARCH ON DIII D written by and published by . This book was released on 2001 with total page 7 pages. Available in PDF, EPUB and Kindle. Book excerpt: Developing an understanding of the processes that control the H-mode transport barrier is motivated by the significant impact this small region (typically

Download or read book Structure Stability and ELM Dynamics of the H mode Pedestal in DIII D written by M. E. Fenstermacher and published by . This book was released on 2005 with total page 14 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Exploration of the Super H mode Regime on DIII D and Potential Advantages for Burning Plasma Devices written by and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: In a new high pedestal regime ("Super H-mode") we predicted and accessed DIII-D. Super H-mode was first achieved on DIII-D using a quiescent H-mode edge, enabling a smooth trajectory through pedestal parameter space. By exploiting Super H-mode, it has been possible to access high pedestal pressures at high normalized densities. And while elimination of Edge localized modes (ELMs) is beneficial for Super H-mode, it may not be a requirement, as recent experiments have maintained high pedestals with ELMs triggered by lithium granule injection. Simulations using TGLF for core transport and the EPED model for the pedestal find that ITER can benefit from the improved performance associated with Super H-mode, with increased values of fusion power and gain possible. In similar studies demonstrate that the Super H-mode pedestal can be advantageous for a steady-state power plant, by providing a path to increasing the bootstrap current while simultaneously reducing the demands on the core physics performance.

Download or read book The Effect of Plasma Shape on H Mode Pedestal Characteristics on DIII D written by and published by . This book was released on 1999 with total page 21 pages. Available in PDF, EPUB and Kindle. Book excerpt: The characteristics of the H-mode are studied in discharges with varying triangularity and squareness. The pressure at the top of the H-mode pedestal increases strongly with triangularity primarily due to an increase in the margin by which the edge pressure gradient exceeds the ideal ballooning mode first stability limit. Two models are considered for how the edge may exceed the ballooning mode limit. In one model [1], access to the ballooning mode second stable regime allows the edge pressure gradient and associated bootstrap current to continue to increase until an edge localized, low toroidal mode number, ideal kink mode is destabilized. In the second model [2], the finite width of the H-mode transport barrier, and diamagnetic effects raise the pressure gradient limit above the ballooning mode limit. We observe a weak inverse dependence of the width of the H-mode transport barrier, [Delta], on triangularity relative to the previously obtained [3] scaling [Delta] ∞ ([beta]{sub P}{sup PED})12. The energy loss for Type I ELMs increases with triangularity in proportion to the pedestal energy increase. The temperature profile is found to respond stiffly to changes in T{sup PED} at low temperature, while at high temperature the response is additive. The response of the density profile is also found to play a role in the response of the total stored energy to changes in the W{sup PED}.

Download or read book Structure Stability and Elm Dynamics of the H Mode Pedestal in DIII D written by and published by . This book was released on 2005 with total page 37 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Progress in Quantifying the Edge Physics of H Mode Regime in DIII D written by and published by . This book was released on 2000 with total page 8 pages. Available in PDF, EPUB and Kindle. Book excerpt: Edge conditions in DIII-D are being quantified in order to provide insight into the physics of the H-mode regime. Electron temperature is not the key parameter that controls the L-H transition. Gradients of edge temperature and pressure are much more promising candidates for such parameters. The quality of H-mode confinement is strongly correlated with the height of the H-mode pedestal for the pressure. The gradient of the pressure appears to be controlled by MHD modes, in particular by kink-ballooning modes with finite mode number n. For a wide variety of discharges, the width of the barrier is well described with a relationship that is proportional to ([beta]{sub p}{sup ped})12. An attractive regime of confinement has been discovered which provides steady-state operation with no ELMs, low impurity content and normal H-mode confinement. A coherent edge MHD-mode evidently provides adequate particle transport to control the plasma density and impurity content while permitting the pressure pedestal to remain almost identical to that observed in ELMing discharges.

Download or read book Characteristics of the H mode Pedestal in Improved Confinement Scenarios in ASDEX Upgrade DIII D JET and JT 60U written by C. F. Maggi and published by . This book was released on 2006 with total page 30 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Study of H mode Threshold Conditions in DIII D written by and published by . This book was released on 1996 with total page 8 pages. Available in PDF, EPUB and Kindle. Book excerpt: Studies have been conducted in DIII-D to determine the dependence of the power threshold P{sub lh} for the transition to the H-mode regime and the threshold P{sub hl} for the transition from H-mode to L-mode as functions of external parameters. There is a value of the line-averaged density n{sub e} at which P{sub lh} has a minimum and P{sub lh} tends to increase for lower and higher values of n{sub e}. Experiments conducted to separate the effect of the neutral density n0 from the plasma density n{sub e} give evidence of a strong coupling between n0 and n{sub e}. The separate effect of neutrals on the transition has not been determined. Coordinated experiments with JET made in the ITER shape show that P{sub lh} increases approximately as S{sup 0.5} where S is the plasma surface area. For these discharges, the power threshold in DIII-D was high by normal standards, thus suggesting that effects other than plasma size may have affected the experiment. Studies of H-L transitions have been initiated and hysteresis of order 40% has been observed. Studies have also been done of the dependence of the L-H transition on local edge parameters. Characterization of the edge within a few ms prior to the transition shows that the range of edge temperatures at which the transition has been observed is more restrictive than the range of densities at which it occurs. These results suggest that some temperature function is important for controlling the transition.

Download or read book Fusion Science and Technology written by and published by . This book was released on 2007 with total page 890 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Enhanced H mode Pedestals with Lithium Injection in DIII D written by and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Proceedings of the Fourteenth Topical Meeting on the Technology of Fusion Energy October 15 19 2000 Park City Utah written by and published by . This book was released on 2001 with total page 906 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Edge Pedestal Control in Quiescent H Mode Discharges in DIII D Using Co Plus Counter Neutral Beam Injection written by and published by . This book was released on 2008 with total page 10 pages. Available in PDF, EPUB and Kindle. Book excerpt: We have made two significant discoveries in our recent studies of quiescent H-mode (QH-mode) plasmas in DIII-D. First, we have found that we can control the edge pedestal density and pressure by altering the edge particle transport through changes in the edge toroidal rotation. This allows us to adjust the edge operating point to be close to, but below the ELM stability boundary, maintaining the ELM-free state while allowing up to a factor of two increase in edge pressure. The ELM boundary is significantly higher in more strongly shaped plasmas, which broadens the operating space available for QH-mode and leads to improved core performance. Second, for the first time on any tokamak, we have created QH-mode plasmas with strong edge co-rotation; previous QH-modes in all tokamaks had edge counter rotation. This result demonstrates that counter NBI and edge counter rotation are not essential conditions for QH-mode. Both these investigations benefited from the edge stability predictions based on peeling-ballooning mode theory. The broadening of the ELM-stable region with plasma shaping is predicted by that theory. The theory has also been extended to provide a model for the edge harmonic oscillation (EHO) that regulates edge transport in the QH-mode. Many of the features of that theory agree with the experimental results reported either previously or in the present paper. One notable example is the prediction that co-rotating QH-mode is possible provided sufficient shear in the edge rotation can be created.

Download or read book A 0 D Scaling Approach to the DIII D L H Power Threshold in the Presence of Resonant Magnetic Perturbations written by Michael Hanson and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: We report a DIII-D database study of the H-mode power threshold over a wide range of plasma conditions and in the presence of resonant magnetic perturbations (RMPs). This database consisting of global (i.e. averaged) quantities is first compared to the 2008 ITPA database and the resulting L-H power scaling [38]. Since ELM control is critical for ITER, and applied 3D fields will likely be present prior to the transition into the H-mode, this study is important for assessing the impact of RMP ELM suppression on the L-H power threshold. The L-H transition has been studied extensively and is dependent on the physical and magnetic divertor geometry, shear flows, and drifts, among other parameters, some of which are altered by RMP fields. In order to understand the effects of RMPs on the L-H threshold, we attempt to make a robust empirical model, using only DIII-D data, that includes magnitudes and the toroidal modes of various resonant and non-resonant 3D fields. In addition, we assess the validity of previous assumptions about fast ion losses, as well as the usefulness of 0-D database regressions for extrapolation to ITER. Results from this database study show the standard 0-D parameters to be insufficient for capturing the complex L-H transition physics at a level high enough to provide an extrapolation to ITER with reasonable certainty.

Download or read book written by and published by . This book was released on 1967 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: