Download or read book Effects of Magnetic Shear on Toroidal Rotation in Tokamak Plasmas with LHCD written by John E. Rice and published by . This book was released on 2014 with total page 7 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Sheared Rotation Effects on Kinetic Stability in Enhanced Confinement Tokamak Plasmas and Nonlinear Dynamics of Fluctuations and Flows in Axisymmetric Plasmas written by G. Rewoldt and published by . This book was released on 1997 with total page 23 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Investigation of the Effect of Large Core Changes in Toroidal Plasma Rotation and Radial Electric Field on Confinement in H mode Discharges in the DIII D Tokamak written by and published by . This book was released on 1992 with total page 4 pages. Available in PDF, EPUB and Kindle. Book excerpt: The plasma toroidal rotation and the radial electric field in the core ([rho]{approx lt}0.9) of H-mode discharges in DIII-D are greatly altered by the drag produced by application of static, resonant magnetic field perturbations from an external coil (the n = 1 coil''). Transport loss due to turbulent fluctuations can in theory be reduced by E{sub r} shear stabilization or suppression. This is tested experimentally in DIII-D by using the magnetic breaking'' of rotation (with concomitant change in E{sub r}) as an independent control. The magnetic braking produces reversal of the core radial electric field, E{sub r}, and E{sub r} shear. However, the plasma maintains a negative edge ([rho]{approx lt}0.95) E{sub r} and E{sub r} shear and remains in H-mode with insignificant changes in global confinement, density profile and temperature profiles. The H-mode confinement is remarkably robust to the increasing error fields and the slowed toroidal rotation up to the onset of a locked mode which induces a transition to L-mode, the virtual cessation of plasma rotation and large reconnected islands.
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 Turbulent Transport in Rotating Tokamak Plasmas written by Francis James Casson and published by . This book was released on 2011 with total page 294 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Effects of ExB Velocity Shear and Magnetic Shear in the Formation of Core Transport Barriers in the DIII D Tokamak written by and published by . This book was released on 1997 with total page 22 pages. Available in PDF, EPUB and Kindle. Book excerpt: Core transport barriers can be reliably formed in DIII-D by tailoring the evolution of the current density profile. This paper reports studies of the relative role of magnetic and ExB shear in creating core transport barriers in the DIII-D tokamak and considers the detailed dynamics of the barrier formation. The core barriers seen in DIII-D negative shear discharges form in a stepwise fashion during the initial current ramp. The reasons for the stepwise formation is not known; these steps do not correlate with integer values of q(O) or minimum q. The data from DIII-D is consistent with previous results that negative magnetic shear facilitates the formation of core transport barriers in the ion channel but is not necessary. However, strongly negative magnetic shear does allow formation of transport barriers in particle, electron thermal, ion thermal and angular momentum transport channels. Shots with strong negative magnetic shear have produced the steepest ion temperature and toroidal rotation profiles seen yet in DIII-D. In addition, the ExB shearing rates seen in these shots exceed the previous DIII-D record value by a factor of four.
Download or read book Transport Physics in Reversed Shear Plasmas written by and published by . This book was released on 1997 with total page 17 pages. Available in PDF, EPUB and Kindle. Book excerpt: Reversed magnetic shear is considered a good candidate for improving the tokamak concept because it has the potential to stabilize MHD instabilities and reduce particle and energy transport. With reduced transport the high pressure gradient would generate a strong off-axis bootstrap current and could sustain a hollow current density profile. Such a combination of favorable conditions could lead to an attractive steady-state tokamak configuration. Indeed, a new tokamak confinement regime with reversed magnetic shear has been observed on the Tokamak Fusion Test Reactor (TFTR) where the particle, momentum, and ion thermal diffusivities drop precipitously, by over an order of magnitude. The particle diffusivity drops to the neoclassical level and the ion thermal diffusivity drops to much less than the neoclassical value in the region with reversed shear. This enhanced reversed shear (ERS) confinement mode is characterized by an abrupt transition with a large rate of rise of the density in the reversed shear region during neutral beam injection, resulting in nearly a factor of three increase in the central density to 1.2 X 10(exp 20) cube m. At the same time the density fluctuation level in the reversed shear region dramatically decreases. The ion and electron temperatures, which are about 20 keV and 7 keV respectively, change little during the ERS mode. The transport and transition into and out of the ERS mode have been studied on TFTR with plasma currents in the range 0.9-2.2 MA, with a toroidal magnetic field of 2.7-4.6 T, and the radius of the q(r) minimum, q{sub min}, has been varied from r/a = 0.35 to 0.55. Toroidal field and co/counter neutral beam injection toroidal rotation variations have been used to elucidate the underlying physics of the transition mechanism and power threshold of the ERS mode.
Download or read book 2 written by and published by . This book was released on 1930 with total page 100 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Rotation Generation and Transport in Tokamak Plasmas written by Yuri Anatoly Podpaly and published by . This book was released on 2012 with total page 201 pages. Available in PDF, EPUB and Kindle. Book excerpt: Plasma toroidal rotation is a factor important for plasma stability and transport, but it is still a fairly poorly understood area of physics. This thesis focuses on three aspects of rotation: momentum transport, Ohmic rotation reversals, and LHCD induced rotation. Momentum transport is approached in a semi-empirical method through the development of the "Toy Model." The "Toy Model" assumes that the toroidal momentum is transported via diffusive and convective profiles, and, using assumptions about the diffusive and convective terms, it can generate the profiles of the residual stress or source as a function of space and time. Several resultant source profile calculations are shown for SSEP sweeps, rotation reversals, H-modes, and I-modes. Generally, it is observed that the convective profiles do not greatly improve the fits to the data, and that source profiles have peaks around the steep core rotation gradient region of the plasma. Rotation reversals, spontaneous reversals of the rotation direction during the Ohmic phase, are also described in this work. It is seen that they are related to the Linear Ohmic Confinement (LOC) to Saturated Ohmic Confinement (SOC) regime changeover. This relation is supported through linear gyrokinetic simulations that show that the co- to counter- reversal coincides with a change from marginally electron to ion diamagnetic direction most unstable modes which is believed to play a role in the LOC to SOC explanation as well. Lower Hybrid Current Drive (LHCD) induced rotation is also described, including the first experimental observations of bi-directional rotation on a single tokamak. These observations help to explain differences in rotation seen among the various devices running lower hybrid. The LHCD rotation reverses direction as a function of plasma current, and this occurs in a similar parameter space as the Ohmic rotation reversal; it also has turbulence changes that are reminiscent of the Ohmic reversal as well. This suggests that LHCD is, in fact, causing the plasma to transition from the ITG dominated regime to the TEM dominated regime, which explains the rotation differences. These experiments and models provide new tools to understand rotation transport and generation in tokamaks.
Download or read book Sheared Rotation Effects on Kinetic Stability in Enhanced Confinement Tokamak Plasmas and Nonlinear Dynamics of Fluctuations and Flows in Axisymmetric Plasmas written by G. Rewoldt and published by . This book was released on 1997 with total page 23 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Shear Flow Effects on Ion Thermal Transport in Tokamaks written by and published by . This book was released on 1995 with total page 41 pages. Available in PDF, EPUB and Kindle. Book excerpt: From various laboratory and numerical experiments, there is clear evidence that under certain conditions the presence of sheared flows in a tokamak plasma can significantly reduce the ion thermal transport. In the presence of plasma fluctuations driven by the ion temperature gradient, the flows of energy and momentum parallel and perpendicular to the magnetic field are coupled with each other. This coupling manifests itself as significant off-diagonal coupling coefficients that give rise to new terms for anomalous transport. The authors derive from the gyrokinetic equation a set of velocity moment equations that describe the interaction among plasma turbulent fluctuations, the temperature gradient, the toroidal velocity shear, and the poloidal flow in a tokamak plasma. Four coupled equations for the amplitudes of the state variables radially extended over the transport region by toroidicity induced coupling are derived. The equations show bifurcations from the low confinement mode without sheared flows to high confinement mode with substantially reduced transport due to strong shear flows. Also discussed is the reduced version with three state variables. In the presence of sheared flows, the radially extended coupled toroidal modes driven by the ion temperature gradient disintegrate into smaller, less elongated vortices. Such a transition to smaller spatial correlation lengths changes the transport from Bohm-like to gyrobohm-like. The properties of these equations are analyzed. The conditions for the improved confined regime are obtained as a function of the momentum-energy deposition rates and profiles. The appearance of a transport barrier is a consequence of the present theory.
Download or read book Co current Toroidal Rotation driven and Turbulent Stresses with Resonant Magnetic Perturbations in the Edge Plasmas of the J TEXT Tokamak written by and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Core Transport Reduction in Tokamak Plasmas with Modified Magnetic Shear written by M. G. Bell and published by . This book was released on 1998 with total page 18 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Summary Record of the 1st Part of the 20th Meeting Held at the Palais Des Nations Geneva on Monday 12 February 1990 written by and published by . This book was released on 1990 with total page 21 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 1994-06 with total page 544 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Effects of Low Magnetic Shear on Ideal MHD Modes of Tokamak Plasma with Elongated Cross section written by and published by . This book was released on 1987 with total page 13 pages. Available in PDF, EPUB and Kindle. Book excerpt:
