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Models Of Sol Transport And Their Relation To Scaling Of The Divertor Heat Flux Width In Diii D
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Book Synopsis Models of SOL Transport and Their Relation to Scaling of the Divertor Heat Flux Width in DIII-D. by :
Download or read book Models of SOL Transport and Their Relation to Scaling of the Divertor Heat Flux Width in DIII-D. written by and published by . This book was released on 2014 with total page 6 pages. Available in PDF, EPUB and Kindle. Book excerpt: Strong support for the critical pressure gradient model for the heat flux width has been obtained, in that the measured separatrix pressure gradient lies below and scales similarly to the pressure gradient limit obtained from the ideal, infinite-n stability codes, BALOO and 2DX, in all cases that have been examined. Predictions of a heuristic drift model for the heat flux width are also in qualitative agreement with the measurements. We obtained these results by using an improved high rep-rate and higher edge spatial resolution Thomson scattering system on DIII-D to measure the upstream electron temperature and density profiles. In order to compare theory and experiment, profiles of density, temperature, and pressure for both electrons and ions are needed as well values of these quantitities at the separatrix. We also developed a simple method to identify a proxy for the separatrix.
Book Synopsis Scaling of Divertor Heat Flux Profile Widths in DIII-D. by :
Download or read book Scaling of Divertor Heat Flux Profile Widths in DIII-D. written by and published by . This book was released on 2009 with total page 6 pages. Available in PDF, EPUB and Kindle. Book excerpt: The width of the divertor heat flux profile w{sub q, div} is of great interest in future large tokamaks as well as many present devices. Previous studies examining the parametric dependence of w{sub q, div} have arrived at diverse scalings in JET, ASDEX-Upgrade, JT60-U, DIII-D, and NSTX with results somewhat at variance with each other. We attempt here to perform a new series of experiments in DIII-D under controlled conditions to obtain scaling of the divertor heat flux peak value, profile width, and divertor plate power as a function of plasma input parameters, with the maximum number of divertor and scrape-off-layer (SOL) diagnostics brought to bear. We performed measurements in lower single-null edge localized mode (ELM) H-mode diverted configurations that were not strongly pumped due to the strike-point positions. We varied the plasma current I{sub p} at constant toroidal field (B{sub T}) and line-averaged density {bar n}{sub e} at constant I{sub p} and B{sub T}. The neutral beam injected power P{sub inj} was changed at constant I{sub p} and BT, B{sub T} at constant I{sub p}, and B{sub T}/I{sub p} at constant q95. The divertor heat flux was calculated from infrared camera measurements using a new high-resolution fast-framing IR camera. The IR camera recorded divertor plate surface thermal emission at many-kilohertz frame rates through the whole discharge, so that time-averaged data as well as rapid changes due to ELMs were obtained. The heat flux at each position in the radial profile was calculated at each of the times steps using the THEODOR 2D heat flux analysis code. We show scaling of the divertor peak heat flux and profile width as a function of the parameters varied, and compare with published results from other devices.
Book Synopsis Radiative and SOL Experiments in Open and Baffled Divertors on DIII-D. by :
Download or read book Radiative and SOL Experiments in Open and Baffled Divertors on DIII-D. written by and published by . This book was released on 1998 with total page 28 pages. Available in PDF, EPUB and Kindle. Book excerpt: The authors present recent progress towards an understanding of the physical processes in the divertor and scrape-off-layer (SOL) plasmas in DIII-D. This has been made possible by a combination of new diagnostics, improved computational models, and changes in divertor geometry. They have focused primarily on ELMing H-mode discharges. The physics of Partially Detached Divertor (PDD) plasmas, with divertor heat flux reduction by divertor radiation enhancement using D2 puffing, has been studied in 2-D, and a model of the heat and particle transport has been developed that includes conduction, convection, ionization, recombination, and flows. Plasma and impurity particle flows have been measured with Mach probes and spectroscopy and these flows have been compared with the UEDGE model. The model now includes self-consistent calculations of carbon impurities. Impurity radiation has been increased in the divertor and SOL with puff and pump techniques using SOL D2 puffing, divertor cryopumping, and argon puffing. The important physical processes in plasma-wall interactions have been examined with a DiMES probe, plasma characterization near the divertor plate, and the REDEP code. Experiments comparing single-null (SN) plasma operation in baffled and open divertors have demonstrated a change in the edge plasma profiles. These results are consistent with a reduction in the core ionization source calculated with UEDGE. Divertor particle control in ELMing H-mode with pumping and baffling has resulted in reduction in H-mode core densities to n{sub e}/n{sub gw} (almost equal to) 0.25. Divertor particle exhaust and heat flux has been studied as the plasma shape was varied from a lower SN, to a balanced double null (DN), and finally to an upper SN.
Book Synopsis Transport of Elm Energy and Particles Into the Sol and Divertor of DIII-D. by :
Download or read book Transport of Elm Energy and Particles Into the Sol and Divertor of DIII-D. written by and published by . This book was released on 2002 with total page 19 pages. Available in PDF, EPUB and Kindle. Book excerpt: We report on DIII-D data that reveal the underlying processes responsible for transport of energy and particles from the edge pedestal to the divertor target during edge-localized modes (ELMs). The separate convective and conductive transport of energy due to an ELM is determined by Thomson scattering measurements of electron density and temperature in the pedestal. Conductive transport is measured as a drop in pedestal temperature and decreases with increasing density. The convective transport of energy, measured as a loss of density from the pedestal, however, remains constant as a function of density. From the SOL ELM energy is quickly carried to the divertor target. An expected sheath limit to the ELM heat flux set by the slower arrival of pedestal ions is overcome by additional ionization of neutrals generated from the divertor target as evidenced by a fast, ≈100 [mu]s, rise in divertor density. A large in/out asymmetry of the divertor ELM heat flux is observed at high density, but becomes nearly symmetric at low density.
Book Synopsis DIII-D Data for Modeling the Scrape-off-layer Plasma by :
Download or read book DIII-D Data for Modeling the Scrape-off-layer Plasma written by and published by . This book was released on 1989 with total page 48 pages. Available in PDF, EPUB and Kindle. Book excerpt: We are in the process of assembling a database of edge and divertor plasma parameters suitable for use in benchmarking tious 2D models of the scrape-off- layer (SOL) plasma. Also, we are using the Braams B2 code to derive transport coefficients for the edge plssma. In parallel, work is starting on an upgrade to the B2 code that includes padlel current flow and EXB drifts. These efforts are directed at increasing the confidence level of models of the tokamak edge plasma so that we can predict the effect of planned upgrades to DIII-D (e.g., the Advanced Divertor Program) and the performance of next generation machines such as CIT or ITER, where initial design studies show that plasma conditions at the divertor targets can have a large impact on the lifetime and cost of the machine. This report summarizes our recent progress in characterizing the DIII-D SOL plasma and in modeling these data with the the B2 code. Section I contains a brief description of the diagnostics available for characterizing the SOL plasma. In Section II we present our measurements of the SOL parameters for H-mode plasmas. This includes data showing how the divertor plasma parameters (n{sub e}(r), T{sub e}(r), and Q(r)) vary from ohmic to L-mode to H-mode, and power balance for quasi-stationary H-mode plasmas. Section III covers divertor-target heat-flux asymmetries for double and single null operation with forward and reversed toroidal field. In Section IV we show the scaling of L-mode parameters with neutral beam power, and Section V concludes with a summary of the results obtained from the Braams B2 SOL simulation code.
Book Synopsis Scaling and Profiles of Heat Flux During Partial Detachment in DIII-D. by :
Download or read book Scaling and Profiles of Heat Flux During Partial Detachment in DIII-D. written by and published by . This book was released on 1998 with total page 18 pages. Available in PDF, EPUB and Kindle. Book excerpt: The authors examine the scaling of the peak divertor heat flux and total divertor plate power in partially detached divertor (PDD) discharges in DIII-D, as a function of input power and radiated power. The peak divertor heat flux in the attached plasma increases linearly with input power, but saturates in the detached cases. The total divertor plate power remains linear with input power in both the attached and detached plasmas. This is consistent with the fact that the heat flux peak is reduced from the attached case but other areas receive increased radiant heating from the detached plasma. The divertor plate radiant heating is linear with input power because the total radiated power from the entire plasma is a linear function of input power in both attached and detached plasma. In the private flux region, radiated heat flux absorbed on the target plate calculated from bolometer data is enough to account for the measured plate heating. Approximately half of the overall plate heating power in detached plasma is due to absorbed radiation. By mapping the divertor heat flux before and during the PDD to flux coordinates, and comparing with a flux mapping of inserted bolometer and tangential TV data, they have verified that the radiated power is emitted from the same flux surfaces on which heat flux is reduced.
Book Synopsis Modeling and Analysis of the DIII-D Tokamak Scrape-off Layer and Divertor by : Quang Thanh Nguyen
Download or read book Modeling and Analysis of the DIII-D Tokamak Scrape-off Layer and Divertor written by Quang Thanh Nguyen and published by . This book was released on 1995 with total page 238 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis The Plasma Boundary of Magnetic Fusion Devices by : P.C Stangeby
Download or read book The Plasma Boundary of Magnetic Fusion Devices written by P.C Stangeby and published by CRC Press. This book was released on 2000-01-01 with total page 738 pages. Available in PDF, EPUB and Kindle. Book excerpt: The Plasma Boundary of Magnetic Fusion Devices introduces the physics of the plasma boundary region, including plasma-surface interactions, with an emphasis on those occurring in magnetically confined fusion plasmas. The book covers plasma-surface interaction, Debye sheaths, sputtering, scrape-off layers, plasma impurities, recycling and control, 1D and 2D fluid and kinetic modeling of particle transport, plasma properties at the edge, diverter and limiter physics, and control of the plasma boundary. Divided into three parts, the book begins with Part 1, an introduction to the plasma boundary. The derivations are heuristic and worked problems help crystallize physical intuition, which is emphasized throughout. Part 2 provides an introduction to methods of modeling the plasma edge region and for interpreting computer code results. Part 3 presents a collection of essays on currently active research hot topics. With an extensive bibliography and index, this book is an invaluable first port-of-call for researchers interested in plasma-surface interactions.
Book Synopsis Advanced Diagnostics for Magnetic and Inertial Fusion by : Peter E. Stott
Download or read book Advanced Diagnostics for Magnetic and Inertial Fusion written by Peter E. Stott and published by Springer Science & Business Media. This book was released on 2011-06-28 with total page 449 pages. Available in PDF, EPUB and Kindle. Book excerpt: Proceedings of the International Conference on Advanced Diagnostics for Magnetic and Inertial Fusion, held September 3-7, 2001 at Villa Monastero, Varenna, Italy. This volume focuses on future diagnostic requirements for fusion energy research emphasizing advanced diagnostics, new techniques and areas where further progress is required.
Book Synopsis Radiative Divertor Plasmas with Convection in DIII-D. by :
Download or read book Radiative Divertor Plasmas with Convection in DIII-D. written by and published by . This book was released on 1998 with total page 34 pages. Available in PDF, EPUB and Kindle. Book excerpt: The radiation of divertor heat flux on DIII-D is shown to greatly exceed the limits imposed by assumptions of energy transport dominated by electron thermal conduction parallel to the magnetic field. Approximately 90% of the power flowing into the divertor is dissipated through low Z radiation and plasma recombination. The dissipation is made possible by an extended region of low electron temperature in the divertor. A one-dimensional analysis of the parallel heat flux finds that the electron temperature profile is incompatible with conduction dominated parallel transport. Plasma flow at up to the ion acoustic speed, produced by upstream ionization, can account for the parallel heat flux. Modeling with the two-dimensional fluid code UEDGE has reproduced many of the observed experimental features.
Book Synopsis Plasma Surface Interactions in Controlled Fusion Devices by :
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:
Book Synopsis Scientific and Technical Aerospace Reports by :
Download or read book Scientific and Technical Aerospace Reports written by and published by . This book was released on 1995 with total page 464 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Measurements of Divertor Target Plate Conditions and Their Relationship to Scrape-off Layer Transport by : Adam QingYang Kuang
Download or read book Measurements of Divertor Target Plate Conditions and Their Relationship to Scrape-off Layer Transport written by Adam QingYang Kuang and published by . This book was released on 2019 with total page 232 pages. Available in PDF, EPUB and Kindle. Book excerpt: Cross-field filamentary transport in the scrape-off layer (SOL) is important for controlling SOL profiles, main-chamber recycling fluxes, and divertor operation. However, questions remain about the extent to which divertor target conditions play a role in setting transport levels. The Alcator C-Mod SOL is well diagnosed and extensively characterized, making it an ideal platform to assess the impact of divertor target conditions on SOL filamentary transport and the resultant upstream profiles, in particular, density shoulder formation. To facilitate the investigation, a set of high heat flux handling, flush-mounted rail Langmuir probes were designed for the Alcator C-Mod divertor. They were validated and proved to be robust, reliable diagnostics. Main chamber SOL fluctuations and density profiles were observed and found to be strongly correlated with divertor target conditions when the core plasma Greenwald fraction was increased. However, no trend was observed when local changes to near SOL divertor conditions were made using N2 impurity seeding. To understand these results, a numerical model for filament transport was constructed that includes realistic magnetic geometry effects (e.g. magnetic shear) and collisionality profiles, both of which have been identified by theory to be important parameters. In validating the numerical model, a discrepancy was highlighted: experimental observations find fluctuation timescales in the SOL to be independent of location, whereas theories assume that timescales are set by local parameters—not accounting for the nonlocal effect of filaments being formed in the near SOL and propagating outwards. The numerical model reveals that strong distortions to the magnetic geometry in the near SOL, due to proximity to the X-point, electrically disconnect the main chamber SOL from divertor target conditions, offering an explanation for the experimental observations, and further suggesting that divertor heat flux mitigation may be optimized without direct impact on main chamber plasma profiles. When the divertor is electrically connected to the main chamber SOL, simulations indicate that increasing divertor collisionality causes a decrease to filament velocity, contrary to published literature. In summary, the combined impact of SOL collisionality and magnetic geometry effects were found to be strong controlling parameters on cross-field filamentary transport consistent with theoretical expectations, providing strong motivation for including these effects in SOL transport simulations and in interpreting experimental results.
Book Synopsis Divertor Plasma Studies on DIII-D by :
Download or read book Divertor Plasma Studies on DIII-D written by and published by . This book was released on 1996 with total page 33 pages. Available in PDF, EPUB and Kindle. Book excerpt: In a magnetically diverted tokamak, the scrape-off layer (SOL) and divertor plasma provides separation between the first wall and the core plasma, intercepting impurities generated at the wall before they reach the core plasma. The divertor plasma can also serve to spread the heat and particle flux over a large area of divertor structure wall using impurity radiation and neutral charge exchange, thus reducing peak heat and particle fluxes at the divertor strike plate. Such a reduction will be required in the next generation of tokamaks, for without it, the divertor engineering requirements are very demanding. To successfully demonstrate a radiative divertor, a highly radiative condition with significant volume recombination must be achieved in the divertor, while maintaining a low impurity content in the core plasma. Divertor plasma properties are determined by a complex interaction of classical parallel transport, anomalous perpendicular transport, impurity transport and radiation, and plasma wall interaction. In this paper the authors describe a set of experiments on DIII-D designed to provide detailed two dimensional documentation of the divertor and SOL plasma. Measurements have been made in operating modes where the plasma is attached to the divertor strike plate and in highly radiating cases where the plasma is detached from the divertor strike plate. They also discuss the results of experiments designed to influence the distribution of impurities in the plasma using enhanced SOL plasma flow. Extensive modeling efforts will be described which are successfully reproducing attached plasma conditions and are helping to elucidate the important plasma and atomic physics involved in the detachment process.
Download or read book Fusion Technology written by and published by . This book was released on 1992 with total page 1414 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Analysis of Particle Flow in the DIII-D SOL and Divertor by :
Download or read book Analysis of Particle Flow in the DIII-D SOL and Divertor written by and published by . This book was released on 1995 with total page 6 pages. Available in PDF, EPUB and Kindle. Book excerpt: The scrape-off layer (SOL) and divertor plasma in the DEEI-D tokamak has been modeled using the 2-D fluid code UEDGE. The resulting simulated plasmas are compared in detail with the numerous diagnostics available on the device. Good agreement is obtained between the experimental measurements and the simulations when relatively small values of the assumed anomalous perpendicular transport coefficients are used. We use a purely diffusive model for perpendicular transport, with transport coefficients which are constant in space. The value of each of these transport coefficients is varied in the simulation to match the measured upstream density and temperature profiles. The resulting plasma parameters are then compared with all other diagnostics which measure parameters at various poloidal locations in the SOL.
Book Synopsis Development of a Radiative Divertor for DIII-D. by :
Download or read book Development of a Radiative Divertor for 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: We have used experiments and modeling to develop a new radiative divertor configuration for DIII-D. Gas puffing experiments with the existing open divertor have shown the creation of a localized ([approximately]10 cm diameter) radiation zone which results in substantial reduction (3--10) in the divertor heat flux while [delta][sub E] remains [approximately]2 times ITER-89P scaling. However, ne increases with D[sub 2] puffing, and Z[sub eff] increases with neon puffing. Divertor structures are required to minimize the effects on the core plasma. The UEDGE fluid code, benchmarked with DIII-D data, and the DEGAS neutrals transport code are used to estimate the effectiveness of divertor configurations; slots reduce the core ionization more than baffles. The overall divertor shape is set by confinement studies which indicate that high triangularity ([delta] [approximately]0.8) is important for high [tau][sub E] VH-modes. Results from engineering feasibility studies, including diagnostic access, will be presented.
