Download or read book H mode Pedestal Characteristics and MHD Stability of the Edge Plasma in Alcator C Mod written by Dmitri A. Mossessian and published by . This book was released on 2002 with total page 32 pages. Available in PDF, EPUB and Kindle. Book excerpt: Under most operational conditions of Alcator C-Mod the dominant type of H-mode is the steady state enhanced Da mode (EDA), characterized by good energy confinement, continuously degraded impurity confinement and absence of regular ELMs. In this regime a quasicoherent (QC) electromagnetic mode ... is observed, localized in the region of the density pedestal. Experimental evidence suggests that the mode is responsible for enhancement of particle transport. It is shown experimentally that the QC mode can exist in a well defined region in edge temperature-safety factor space, favoring high edge q values ... and requiring moderate pedestal temperatureTeped ... As edge temperature and pressure gradient increase, the quasicoherent mode is replaced by broadband low frequency fluctuations (f
Download or read book Pedestal Structure and Stability in High performance Plasmas on Alcator C Mod written by John Reel Walk (Jr.) and published by . This book was released on 2014 with total page 225 pages. Available in PDF, EPUB and Kindle. Book excerpt: High-performance operation in tokamaks is characterized by the formation of a pedestal, a region of suppressed transport and steep gradients in density, temperature, and pressure near the plasma edge. The pedestal height is strongly correlated with overall fusion performance, as a substantial pedestal supports the elevated core pressure necessary for the desired fusion reaction rate and power density. However, stationary operation requires some relaxation of the particle transport barrier, to avoid the accumulation of impurities (e. g., helium "fusion ash," plasmafacing surface materials) in the plasma. Moreover, the formation of the pedestal introduces an additional constraint: the steep gradients act as a source of free energy for Edge-Localized Mode (ELM) instabilities, which on ITER- or reactor-scale devices can drive large, explosive bursts of particle and energy transport leading to unacceptable levels of heat loading and erosion damage to plasma-facing materials. As such, the suppression, mitigation, or avoidance of large ELMs is the subject of much current research. In light of this, a firm physical understanding of the pedestal structure and stability against the ELM trigger is essential for the extrapolation of high-performance regimes to large-scale operation, particularly in operating scenarios lacking large, deleterious ELMs. This thesis focuses on the I-mode, a novel high-performance regime pioneered on the Alcator C-Mod tokamak. I-mode is unique among high-performance regimes in that it appears to decouple energy and particle transport, reaching H-mode levels of energy confinement with the accompanying temperature pedestal while maintaining a L-mode-like density profile and particle transport. I-mode exhibits three attractive properties for a reactor regime: (1) I-mode appears to be inherently free of large ELMs, avoiding the need for externally-applied ELM control. (2) The lack of a particle transport barrier maintains the desired level of impurity flushing from the plasma, avoiding excessive radiative losses. (3) Energy confinement in I-mode presents minimal degradation with input heating power, contrary to that found in H-mode. This thesis presents the results from a combined empirical and computational study of the pedestal on C-Mod. Analysis methods are first implemented in ELMy H-mode base cases on CMod -- in particular, the EPED model based on the combined constraints from peeling-ballooning MHD instability and kinetic-ballooning turbulence is tested on C-Mod. Empirical results in ELMy H-mode are consistent with the physics assumptions used in EPED, with the pedestal pressure gradient constrained by [delta]p ~ I2/p expected from the ballooning stability limit. To lowestorder approximation, ELMy H-mode pedestals are limited in [beta]p,ped, with the attainable beta set by shaping -- within this limit, an inverse relationship between pedestal density and temperature is seen. The pedestal width is found to be described by the scaling [delta][psi] = G[beta] 1/2 / p.ped expected from the KBM limit, where G([nu],[epsilon], ...) is a weakly varying function with hGi = 0.0857. No systematic secondary scalings with field, gyroradius, shaping, or collisionality are observed. The EPED model, based on these assumptions, correctly predicts the pressure pedestal width and height to within a systematic ~20% uncertainty. Empirical scalings in I-mode highlight the operational differences from conventional H-modes. The temperature and pressure pedestal exhibit a positive trend with current, similar to H-mode (although I-mode pedestal temperature typically exceeds that found in comparable H-modes) -- however, the temperature and pressure respond significantly more strongly to heating power, with Te ... The I-mode density profile is set largely independently of the temperature pedestal (unlike ELMy H-mode), controlled by operator fueling. Given sufficient heating power to maintain a consistent ..., temperature pedestals are matched across a range of fueling levels. This indicates a path to readier access and increased performance in Imode, with the mode accessed at moderate density and power, after which the pedestal pressure is elevated with matched increases in fueling and heating power. Global performance metrics in I-mode are competitive with H-mode results on C-Mod, and are consistent with the weak degradation of energy confinement with heating power. I-mode pedestals are also examined against the physics basis for the EPED model. Peelingballooning MHD stability is calculated using the ELITE code, finding the I-mode pedestal to be strongly stable to the MHD modes associated with the ELM trigger. Similarly, modeling of the KBM using the infinite-n ballooning mode calculated in BALOO as a surrogate for the threshold indicates that the I-mode pedestal is stable to kinetic-ballooning turbulence, consistent with the observed lack of a trend in the pedestal width with [beta]p,ped. This is found to be the case even in I-modes exhibiting small, transient ELM-like events. The majority of these events are triggered by the sawtooth heat pulse reaching the edge, and do not negatively perturb the temperature pedestal -- it is proposed, then, that these events are not true peeling-ballooning-driven ELMs, but rather are an ionization front in the SOL driven by the sawtooth heat pulse. There are transient ELM events showing the characteristic temperature pedestal crash indicating a true ELM -- the steady I-mode pedestals around these isolated events are also modeled to be P-B and KBM stable, although more detailed modeling of these events is ongoing.
Download or read book H mode Edge Stability of Alcator C mod Plasmas written by Dmitri A. Mossessian and published by . This book was released on 2002 with total page 34 pages. Available in PDF, EPUB and Kindle. Book excerpt: For steady state H-mode operation, a relaxation mechanism is required to limit build-up of the edge gradient and impurity content. C-Mod sees two such mechanisms - EDA and grassy ELMs, but not large type I ELMs. In EDA the edge relaxation is provided by an edge localized quasicoherent electromagnetic mode that exists at moderate pedestal temperature T400 eV, high pedestal density and high edge safety factor ...3.5, and does not limit the build up of the edge pressure gradient. The q boundary of the operational space of the mode depends on plasma shape, with the q95 limit moving down with increasing plasma triangularity. At high edge pressure gradients and temperatures the mode is replaced by broadband fluctuations (f
Download or read book Pedestal Characteristics and MHD Stability of H mode Plasmas in TCV written by Andreas Pitzschke and published by . This book was released on 2011 with total page 211 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Magnetic Fusion Energy written by George Neilson and published by Woodhead Publishing. This book was released on 2016-06-02 with total page 634 pages. Available in PDF, EPUB and Kindle. Book excerpt: Magnetic Fusion Energy: From Experiments to Power Plants is a timely exploration of the field, giving readers an understanding of the experiments that brought us to the threshold of the ITER era, as well as the physics and technology research needed to take us beyond ITER to commercial fusion power plants. With the start of ITER construction, the world’s magnetic fusion energy (MFE) enterprise has begun a new era. The ITER scientific and technical (S&T) basis is the result of research on many fusion plasma physics experiments over a period of decades. Besides ITER, the scope of fusion research must be broadened to create the S&T basis for practical fusion power plants, systems that will continuously convert the energy released from a burning plasma to usable electricity, operating for years with only occasional interruptions for scheduled maintenance. Provides researchers in academia and industry with an authoritative overview of the significant fusion energy experiments Considers the pathway towards future development of magnetic fusion energy power plants Contains experts contributions from editors and others who are well known in the field
Download or read book Active Control of Magneto hydrodynamic Instabilities in Hot Plasmas written by Valentin Igochine and published by Springer. This book was released on 2014-09-15 with total page 350 pages. Available in PDF, EPUB and Kindle. Book excerpt: During the past century, world-wide energy consumption has risen dramatically, which leads to a quest for new energy sources. Fusion of hydrogen atoms in hot plasmas is an attractive approach to solve the energy problem, with abundant fuel, inherent safety and no long-lived radioactivity. However, one of the limits on plasma performance is due to the various classes of magneto-hydrodynamic instabilities that may occur. The physics and control of these instabilities in modern magnetic confinement fusion devices is the subject of this book. Written by foremost experts, the contributions will provide valuable reference and up-to-date research reviews for "old hands" and newcomers alike.
Download or read book Measurements of the H mode Pedestal Region on Alcator C Mod written by Amanda E. Hubbard and published by . This book was released on 1997 with total page 21 pages. Available in PDF, EPUB and Kindle. Book excerpt:
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 Observations and Empirical Scalings of the High confinement Mode Pedestal on Alcator C Mod written by J. W. Hughes and published by . This book was released on 2002 with total page 50 pages. Available in PDF, EPUB and Kindle. Book excerpt: On the Alcator C-Mod tokamak [Phys. Plasmas 1, 1511, (1994)], radial profiles of electron temperature (Te) and density (ne) are measured at the plasma edge with millimeter resolution Thomson scattering [Rev. Sci. Instrum. 72, 1107 (2001)]. Edge transport barriers in the high confinement regime (H-mode) exhibit Te, ne pedestals with typical widths of 2-6 mm, with the Te pedestal on average slightly wider than and inside the ne pedestal. Measurements at both the top and the base of the pedestal are consistent with profiles obtained using other diagnostics. The two primary H-mode regimes on C-Mod, enhanced Da (EDA) and edge-localized mode free (ELM-free), have been examined for differences in pedestals. EDA operation is favored by high edge collisionality n*, in addition to high edge safety factor q95. Scaling studies at fixed shape yield little systematic variation of pedestal widths with plasma parameters, though higher triangularity is seen to increase the ne pedestal width dramatically. Pedestal heights and gradients show the clearest dependencies on plasma control parameters. Pedestal ne and Te both scale linearly with plasma current IP, while pedestal Te depends strongly on power flowing from the core plasma into the scrape-off layer PSOL. The electron pressure (pe) pedestal and pe gradient both scale with IP2 PSOL1/2. Plasma stored energy WP scales with pedestal pe, implying that pedestal scalings may in large part determine global confinement scalings.
Download or read book Mainzer Stadtanssichten aus f nf Jahrhunderten written by and published by . This book was released on 1980 with total page 20 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Edge Dimensionless Identity Experiment on DIII D and Alcator C Mod written by Dmitri A. Mossessian and published by . This book was released on 2002 with total page 38 pages. Available in PDF, EPUB and Kindle. Book excerpt: Experiments were carried out to study the similarity of H-mode (High confinement mode) physics on the Alcator C-Mod and DIII-D tokamaks comparing plasmas with matched local edge dimensionless parameters ... and shape ... It was observed that matching local values of the dimensionless parameters on top of the H-mode pedestals produces similar Te and ne profiles across the entire pedestal region, with pedestal width scaling linearly with the machine size. Furthermore, in H-modes with matched pedestals, similar edge fluctuations were observed. Discharges in DIII-D with scaled pedestal parameters similar to those of C-Mod EDA (Enhanced D-alpha) H-mode showed a quasicoherent mode localized to the outer half of the pedestal, similar to the C-Mod quasicoherent mode (QC mode). The wavenumber of the mode observed on DIII-D matches the wavenumber of the C-Mod QC mode if scaled with the machine size. For higher pedestal temperatures and pressures, small high frequency ELMs (Edge Localized Modes) appear in both machines. Keywords: edge plasmas; H-mode; tokamaks; fluctuations; transport phenonmena.
Download or read book H mode Pedestal Studies in Alcataor C Mod written by Dmitri A. Mossessian and published by . This book was released on 2000 with total page 9 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book High Power Density H modes in Alcator C Mod written by Yuichi Takase and published by . This book was released on 1996 with total page 9 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Local Plasma Parameters and H mode Threshold in Alcator C mod written by Amanda E. Hubbard and published by . This book was released on 1996 with total page 6 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book The L to H mode Transition and Momentum Confinement in Alcator C Mod Plasmas written by John Reel Walk (Jr.) and published by . This book was released on 2010 with total page 64 pages. Available in PDF, EPUB and Kindle. Book excerpt: Using a spatially-resolving x-ray spectrometer system, toroidal impurity rotation in Alcator C-Mod plasmas was measured. The propagation of the rotational velocity from the edge to the core of the plasma column was measured during the L- to H-mode transition. Momentum transport was measured in both Ohmic and ICRF-heated discharges, which produced EDA and ELM-free H-modes. The momentum transport was modeled by a simplified diffusion model, in which momentum diffusivity was substantially higher than neoclassically predicted values.
Download or read book H modes on Alcator C mod written by Joseph Allan Snipes and published by . This book was released on 1995 with total page 10 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Plasma Surface Interactions in Controlled Fusion Devices written by and published by . This book was released on 1978 with total page 658 pages. Available in PDF, EPUB and Kindle. Book excerpt:
