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Physics And Application Of Impurity Plume Dispersal As An Edge Plasma Flow Diagnostic On The Alcator C Mod Tokamak
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Book Synopsis Physics and Application of Impurity Plume Dispersal as an Edge Plasma Flow Diagnostic on the Alcator C-Mod Tokamak by : Sanjay Gangadhara
Download or read book Physics and Application of Impurity Plume Dispersal as an Edge Plasma Flow Diagnostic on the Alcator C-Mod Tokamak written by Sanjay Gangadhara and published by . This book was released on 2003 with total page 273 pages. Available in PDF, EPUB and Kindle. Book excerpt: (Cont.) A Monte Carlo impurity transport code (LIM) was used to simulate the plumes. Results indicate that contributions to the emission from sputtering explain the cross-field plume width, and that the parallel extent of emission generated in the far SOL is well-described using a sputter launch-energy distribution for the impurities. In the near SOL, the presence of a localized parallel electric field arising from background ion recycling off the probe surface is necessary to explain the parallel extent of emission generated in this region. This electric field accelerates impurity ions formed near the probe tip away from the probe, causing jet-like behavior. LIM was also used to investigate causes for the vertical elongation of the impurity emission. Results suggest the existence of a probe-induced E x B drift, of order ca. 1000 m/s in the near SOL. This drift may be responsible for the transport of both impurity and bulk plasma ions down the probe axis. Values for vII in the far SOL and Er in the near SOL have been extracted from the plume structure. A comparison between plume and probe results for Er suggests that calculations which employ a probe-sheath model may be in error, and that measurement of the poloidal propagation velocity of edge plasma fluctuations may be a more reliable means of inferring Er from probe data. Comparisons between plume- and probe-inferred values for the parallel Mach number suggest that the probe over-estimates parallel flow to the divertor in the far SOL, where effects of short field line connection to the divertor are important ...
Book Synopsis Impurity Plume Experiments in the Edge Plasma of the Alcator C-Mod Tokamak by : Sanjay Gangadhara
Download or read book Impurity Plume Experiments in the Edge Plasma of the Alcator C-Mod Tokamak written by Sanjay Gangadhara and published by . This book was released on 2003 with total page 86 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Book Synopsis Flow Measurements in the Scrape-off Layer of Alcator C-Mod Using Impurity Plumes by : Sanjay Gangadhara
Download or read book Flow Measurements in the Scrape-off Layer of Alcator C-Mod Using Impurity Plumes written by Sanjay Gangadhara and published by . This book was released on 2002 with total page 20 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Book Synopsis Dissertation Abstracts International by :
Download or read book Dissertation Abstracts International written by and published by . This book was released on 2004 with total page 858 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Local Gas Injection as a Scrape-off Layer Diagnostic on the Alcator C-Mod Tokamak by :
Download or read book Local Gas Injection as a Scrape-off Layer Diagnostic on the Alcator C-Mod Tokamak written by and published by . This book was released on 1996 with total page 190 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Book Synopsis Impurity Transport Experiments in the Edge Plasma of Alcator C-Mod Using Gas Injection Plumes by : Sanjay Gangadhara
Download or read book Impurity Transport Experiments in the Edge Plasma of Alcator C-Mod Using Gas Injection Plumes written by Sanjay Gangadhara and published by . This book was released on 2000 with total page 10 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Impurity Transport Studies in Tokamak Edge Plasmas Using Visibe Imaging by : Sanjay Gangadhara
Download or read book Impurity Transport Studies in Tokamak Edge Plasmas Using Visibe Imaging written by Sanjay Gangadhara and published by . This book was released on 2001 with total page 6 pages. Available in PDF, EPUB and Kindle. Book excerpt: Understanding impurity transport in the scrape-off layer (SOL) of tokamak plasmas is a necessary piece of developing the physics basis for designing next-generation reactors. A system for inferring impurity transport parallel and perpendicular to local magnetic field lines has been developed on Alcator C-Mod using gas-injection "plumes". In this system, impurity gas is injected at a fixed position in the SOL via a reciprocating fast-scanning probe, and the resulting emission is imaged. In this paper visible light emission patterns from C+1 and C+2 ions are presented.
Book Synopsis Impurity Transport Studies on Alcator C-Mod Tokamak Using Charge Exchange Recombination Spectroscopy by : Igor Olegovich Bespamyatnov
Download or read book Impurity Transport Studies on Alcator C-Mod Tokamak Using Charge Exchange Recombination Spectroscopy written by Igor Olegovich Bespamyatnov and published by . This book was released on 2008 with total page 322 pages. Available in PDF, EPUB and Kindle. Book excerpt: A Charge-Exchange Recombination Spectroscopy (CXRS) diagnostic has been installed on Alcator C-Mod to study the transport of light impurities in plasma. The system provides spatially (1 cm) and temporally (12.5 msec) resolved measurements of the impurity density, temperature and flow velocities of the particular impurity. Two optical arrays: poloidal (19 channels) and toroidal (10 channels), collect the light emitted from excited impurity ion populated by charge exchange process from the Diagnostic Neutral Beam (DNB) particle. The attention of this dissertation is focused on the B4 (n = 7 [-->] 6) spectral line emitted by B4 ion formed in the following charge exchange reaction (H0 + B5+ [-->] H+ + B4+*). A complex spectral model was developed to simulate emission. The high magnetic fields of C-Mod result in broad Zeeman patterns which must be taken into account for the interpretation of the line shift and broadening in terms of impurity ion velocity and temperature. After the spectral line fitting and careful identification of the charge exchange component, the calculated Doppler broadening and shifts of the spectral line profile yield information on the ion temperature and rotation. Together with the calculation of the beam density, the absolute calibration of the CXRS optical system provides us with B5+ density measurement capabilities. One of the main objectives of this work was to use the acquired impurity density, temperature and flow velocity profiles to investigate plasma transport behavior and infer the radial electric field E[subscript R] from plasma force balance equation. The focus here was placed on the region of the Internal Transport Barrier (ITB) formation 0.35
Book Synopsis Edge Plasma Phenomena in the Alcator C-Mod Tokamak Measured by High Resolution X-ray Imaging Diagnostics by :
Download or read book Edge Plasma Phenomena in the Alcator C-Mod Tokamak Measured by High Resolution X-ray Imaging Diagnostics written by and published by . This book was released on 2000 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: By Thomas Sunn Pedersen.
Book Synopsis Local Impurity Puffing as a Scrape-off Layer Diagnostic on the Alcator C-Mod Tokamak by : David F. Jablonski
Download or read book Local Impurity Puffing as a Scrape-off Layer Diagnostic on the Alcator C-Mod Tokamak written by David F. Jablonski and published by . This book was released on 1996 with total page 13 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Tokamak Plasma Diagnosis by Surface Physics Techniques by :
Download or read book Tokamak Plasma Diagnosis by Surface Physics Techniques written by and published by . This book was released on 1978 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The utilization of elementally-sensitive surface techniques as plasma diagnostics is discussed with emphasis on measuring impurity fluxes, charge states, and energy distributions in the plasma edge. A model of plasma flow to the probe is presented and applied to the interpretation of data. Limits on time and energy resolution, and sensitivity are given. The overlap of these techniques with conventional plasma diagnostics is described.
Book Synopsis Impurity Asymmetries in the Pedestal Region of the Alcator C-Mod Tokamak by : Randy Michael Churchill
Download or read book Impurity Asymmetries in the Pedestal Region of the Alcator C-Mod Tokamak written by Randy Michael Churchill and published by . This book was released on 2014 with total page 216 pages. Available in PDF, EPUB and Kindle. Book excerpt: In an effort to illuminate the effects of the strong plasma gradients in the pedestal region on impurity transport, research was conducted to measure complete sets of impurity density, poloidal and parallel velocity, and temperature at two separate poloidal locations in the pedestal region of the Alcator C-Mod tokamak. To this end, the diagnostic technique gas puff-CXRS was refined and expanded on, allowing for the first time in a tokamak complete measurements of impurities at the high-field side (HFS). Large in-out B5+ impurity density asymmetries were measured in H-mode plasmas with strong boundary electron density gradients, with a build-up of impurity density at the HFS. Impurity temperatures were also found to be asymmetric in the pedestal region, with larger temperatures at the low-field side (LFS). Such temperature asymmetries suggest a significant asymmetry in electron density near the separatrix. In contrast to these H-mode results, plasmas with low boundary electron density gradients, such as L-mode and I-mode, exhibit constant impurity density on a flux surface, even if strong electron temperature gradients are present. Mechanisms which could drive such poloidal asymmetries are explored. Experiments provide evidence against localized impurity sources and fluctuation-induced transport as primary causes. Particle transport timescales are compared, showing that the radial transport becomes comparable to or faster than the parallel transport in the pedestal region. Additionally, modelling of impurity transport using conventional, one-dimensional neoclassical physics fails to correctly reproduce the measured flux-surface averaged impurity density, suggesting along with the timescale estimates that a more complete two-dimensional treatment of impurity particle transport is required. The measured impurity velocities at the LFS and HFS are compared to the canonical form for particle flow velocity within the flux surface of a tokamak. Within the error bars of the measurement, agreement is found with the canonical form. The implications of exact matches to the canonical form are low radial transport, and the E x B drift dominating the perpendicular impurity flow. Further work is motivated into more precise velocity measurements to determine if the velocities exactly match this canonical form.
Book Synopsis Impurity Screening Studies in the Alcator C-mod Tokamak by : G. M. McCracken
Download or read book Impurity Screening Studies in the Alcator C-mod Tokamak written by G. M. McCracken and published by . This book was released on 1996 with total page 9 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Edge Turbulence Imaging in the Alcator C-Mod Tokamak by : S. J. Zweben
Download or read book Edge Turbulence Imaging in the Alcator C-Mod Tokamak written by S. J. Zweben and published by . This book was released on 2001 with total page 9 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Fast Photodiode Diagnostic on Alcator C-Mod Tokamak to Study the Plasma Edge/SOL Structure by : Baʹlint Vetoʺ
Download or read book Fast Photodiode Diagnostic on Alcator C-Mod Tokamak to Study the Plasma Edge/SOL Structure written by Baʹlint Vetoʺ and published by . This book was released on 2005 with total page 176 pages. Available in PDF, EPUB and Kindle. Book excerpt: (Cont.) For the first time, the poloidal measurements of the plasma edge brightness with and without the D2 neutral gas puff yielded an estimate for the vertical extent of the neutral gas puff. The steady state inboard and outboard D, brightness profiles are also compared during two consecutive periods of L and H mode operation. The time lagged cross correlation calculated for neighboring views revealed quickly propagating local brightness maxima (blobs). The phase velocity of these systematically moving brightness perturbations ranges from -1 to 1 km/s inside the separatrix and becomes uniform outside the separatrix at 0.5 km/s where the positive velocity indicates radially outward motion. Downward propagating perturbations are also observed in the outboard SOL.
Book Synopsis Turbulence and Transport Measurements in Alcator C-Mod and Comparisons with Gyrokinetic Simulations by : Paul Chappell Ennever
Download or read book Turbulence and Transport Measurements in Alcator C-Mod and Comparisons with Gyrokinetic Simulations written by Paul Chappell Ennever and published by . This book was released on 2016 with total page 139 pages. Available in PDF, EPUB and Kindle. Book excerpt: Turbulence in tokamak plasmas is the primary means by which energy is transported from the core of the plasma to the edge, where it is lost, and is therefore the main limitation of tokamak plasma performance. Dilution of the main-ion species was found to have a stabilizing effect on ion gyroradius scale turbulence in tokamak plasmas. Dilution of deuterium tokamak plasmas is the reduction of the ratio of the deuterium ion density to the electron density, nD=ne, to less than 1.0 through the introduction of low-Z impurity species into the plasma. Controlled dilution experiments were performed on Alcator C-Mod wherein plasmas at a range of electron density and plasma current were seeded with nitrogen while a cryopump held the electron density fixed. The electron density fluctuations due to turbulence were monitored using a phase contrast imaging (PCI) diagnostic, an absolutely calibrated diagnostic that measures the line-integral of the electron density fluctuations along 32 vertical chords. In these experiments the seeding reduced the PCI density fluctuations, and had a stabilizing effect on the ion energy transport. The seeding also reversed the direction of intrinsic rotation in certain cases. Nonlinear simulations using the gyrokinetic turbulence code GYRO were performed using measured kinetic profiles from the dilution experiments both before and after the nitrogen seeding. The GYRO simulations reproduced the observed reduction in the turbulent ion energy transport with the nitrogen seeding. The GYRO simulated turbulent density fluctuations were compared to the PCI measurements using a synthetic diagnostic, and they were found to be consistent. GYRO simulations were also performed varying only the main ion dilution to explore the theoretical effects of the dilution on energy transport. Through this it was found that the dilution reduced the turbulent ion energy transport in a wide variety of cases, but primarily increased the critical gradient at low densities, and primarily reduced the stiffness of the transport at high densities. This dilution effect is related to observations of reductions in energy transport from seeding on other tokamaks, and will likely have an impact on ITER and future fusion reactors.
Book Synopsis A Comparison of Impurity Screening Between Limiter and Divertor Plasmas in the Alcator C-Mod Tokamak by : Robert Seth Granetz
Download or read book A Comparison of Impurity Screening Between Limiter and Divertor Plasmas in the Alcator C-Mod Tokamak written by Robert Seth Granetz and published by . This book was released on 1996 with total page 14 pages. Available in PDF, EPUB and Kindle. Book excerpt:
