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Author: Sanjay Gangadhara Publisher: ISBN: Category : Languages : en Pages : 20
Book Description
Accurate measurements of plasma flows in the scrape-off layer (SOL) are a necessary requirement for understanding the physics of tokamak edge plasmas. A system is being developed on Alcator C-Mod for inferring flows parallel (v) and perpendicular (vE x B) to local magnetic field lines from impurity emission patterns ("plumes") generated by local gas injection. Carbon plumes are generated at variable location in the SOL by puffing deuterated ethylene gas (C2D4) through the end of a reciprocating fast-scanning probe. Two intensified CCD cameras are used to record C+1 and C+2 emission patterns simultaneously from near-perpendicular views. Plumes are modeled using a Monte Carlo impurity transport code, from which values for the background flows may be extracted. The sensitivity of the plume structure is investigated for a number of code inputs, including radial electric field (Er) and the neutral launch dynamics. Initial modeling results indicate discrepancies between values of v and Er extracted from the plumes and measurements obtained from probe data. Key words: Alcator C-Mod; Scrape-Off Layer Flows; Plumes.
Author: Sanjay Gangadhara Publisher: ISBN: Category : Languages : en Pages : 20
Book Description
Accurate measurements of plasma flows in the scrape-off layer (SOL) are a necessary requirement for understanding the physics of tokamak edge plasmas. A system is being developed on Alcator C-Mod for inferring flows parallel (v) and perpendicular (vE x B) to local magnetic field lines from impurity emission patterns ("plumes") generated by local gas injection. Carbon plumes are generated at variable location in the SOL by puffing deuterated ethylene gas (C2D4) through the end of a reciprocating fast-scanning probe. Two intensified CCD cameras are used to record C+1 and C+2 emission patterns simultaneously from near-perpendicular views. Plumes are modeled using a Monte Carlo impurity transport code, from which values for the background flows may be extracted. The sensitivity of the plume structure is investigated for a number of code inputs, including radial electric field (Er) and the neutral launch dynamics. Initial modeling results indicate discrepancies between values of v and Er extracted from the plumes and measurements obtained from probe data. Key words: Alcator C-Mod; Scrape-Off Layer Flows; Plumes.
Author: Sanjay Gangadhara Publisher: ISBN: Category : Languages : en Pages : 86
Book Description
The physics of impurity transport in response to a local gas injection in the scrape-off-layer (SOL) of Alcator C-Mod is investigated. Carbon "plumes'' are formed at variable locations in the SOL -- up to the separatrix -- by puffing deuterated ethylene gas (C2D4) through the end of a reciprocating fast-scanning probe. CCD cameras are used to simultaneously record C+1 and C+2 emission patterns from two near-perpendicular views. The plume dispersal patterns are found to yield direct qualitative information about plasma flow, including the direction of VExB near the separatrix. Impurity transport and plasma-surface interaction physics implicit in the 3-D plume structure is explored in detail using a Monte Carlo impurity transport code, with the aim of extracting background plasma-flow quantities. A number of important local effects involving plasma-probe interaction have been identified: a vertical ExB drift near the probe surface, a parallel electric field above the probe tip arising from plasma recycling off the probe surface, and sputtering of a carbon layer that dynamically forms on the probe surface. The emission patterns are also found to yield important information on flows in the SOL: radial electric field (Er) in the near SOL and volume-averaged values of the parallel Mach number in the far SOL. Er values obtained from plume data compare favorably with estimates of Er based on the poloidal propagation velocity of edge plasma fluctuations measured by the scanning probe. Comparisons between parallel Mach numbers obtained from the plume data and probe measurements indicate that the probe over-estimates the parallel flow towards the divertor in the far SOL. This result supports the picture of particle balance in the SOL of Alcator C-Mod being dominated by main-chamber recycling, with weak plasma flow into the divertor.
Author: Publisher: ISBN: Category : Languages : en Pages : 190
Book Description
A capillary puffing array has been installed on Alcator C-Mod which allows localized introduction of gaseous species in the scrape-off layer. This system has been utilized in experiments to elucidate both global and local properties of edge transport. Deuterium fueling and recycling impurity screening are observed to be characterized by non-dimensional screening efficiencies which are independent of the location of introduction. In contrast, the behavior of non-recycling impurities is seen to be characterized by a screening time which is dependent on puff location. The work of this thesis has focused on the use of the capillary array with a camera system which can view impurity line emission plumes formed in the region of an injection location. The ionic plumes observed extend along the magnetic field line with a comet-like asymmetry, indicative of background plasma ion flow. The flow is observed to be towards the nearest strike-point, independent of x-point location, magnetic field direction, and other plasma parameters. While the axes of the plumes are generally along the field line, deviations are seen which indicate cross-field ion drifts. A quasi-two dimensional fluid model has been constructed to use the plume shapes of the first charge state impurity ions to extract information about the local background plasma, specifically the temperature, parallel flow velocity, and radial electric field. Through comparisons of model results with those of a three dimensional Monte Carlo code, and comparisons of plume extracted parameters with scanning probe measurements, the efficacy of the model is demonstrated. Plume analysis not only leads to understandings of local edge impurity transport, but also presents a novel diagnostic technique.
Author: Taekyun Chung Publisher: ISBN: Category : Languages : en Pages : 26
Book Description
We report on impurity transport modeling using the DIVIMP code which is able to qualitatively reproduce the poloidal variation of non-recycling impurity penetration factor (PFNR) found in C-Mod experiments: a lower PFNR is computed at the inboard (3.6 %) and divertor target locations (0.7 %) than at the outboard (11 %). By artificially increasing the modeled inner SOL plasma flow to correspond to measured values, a better quantitative agreement between modeled and measured PFs is achieved. We have also roughly reproduced the observed penetration factor for recycling impurities both in time dependence and magnitude. The model has shown that under attached conditions, the majority of recycling impurity ions flow into the confined plasma through the outboard side separatrix. For detached conditions the impurity influx across the separatrix is more concentrated near the divertor.
Author: P.C Stangeby Publisher: CRC Press ISBN: 9780750305594 Category : Science Languages : en Pages : 738
Book Description
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.
Author: National Academies of Sciences Engineering and Medicine Publisher: ISBN: 9780309685382 Category : Languages : en Pages :
Book Description
Fusion energy offers the prospect of addressing the nation's energy needs and contributing to the transition to a low-carbon emission electrical generation infrastructure. Technology and research results from U.S. investments in the major fusion burning plasma experiment known as ITER, coupled with a strong foundation of research funded by the Department of Energy (DOE), position the United States to begin planning for its first fusion pilot plant. Strong interest from the private sector is an additional motivating factor, as the process of decarbonizing and modernizing the nation's electric infrastructure accelerates and companies seek to lead the way. At the request of DOE, Bringing Fusion to the U.S. Grid builds upon the work of the 2019 report Final Report of the Committee on a Strategic Plan for U.S. Burning Plasma Research to identify the key goals and innovations - independent of confinement concept - that are needed to support the development of a U.S. fusion pilot plant that can serve as a model for producing electricity at the lowest possible capital cost.
Author: Sanjay Gangadhara
Author: Sanjay Gangadhara
Author: Sanjay Gangadhara
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Author: 
Author: Taekyun Chung
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Author: 
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Author: P.C Stangeby
Author: National Academies of Sciences Engineering and Medicine