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Author: John David Elder
Publisher:
ISBN: 9780494393710
Category : Aerospace engineering
Languages : en
Pages : 155
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Book Description
In 2003 and 2005 13CH4 puffing experiments were conducted on DIII-D [1] in L and ELMy H mode plasmas respectively. The motivation for these experiments was to develop a greater understanding of impurity creation, transport and deposition for hydrocarbons which are produced at the walls of DIII-D by chemical sputtering. In both experiments, tiles from around the vessel were removed after the experiment was complete and the distribution of the 13C deposition was measured using nuclear reaction analysis. During each of these experiments the plasma conditions and emissions were monitored by a number of direct and spectroscopic diagnostics including Langmuir probes, Thomson scattering, the multichord divertor spectrometer, filterscopes, reciprocating probes and others. These diagnostic measurements are used in the thesis to develop a background plasma solution for the experiments through the procedure of empirical plasma reconstruction. These background plasma solutions are used as the basis for modeling the emissions, transport and deposition of the 13C resulting from the breakup of 13CH4 using the OEDGE code. OEDGE was enhanced by the addition of improved methane breakup kinetics models, improved peripheral particle transport, improved support for line profile modeling as well as many other features. The modeling successfully reproduces most of the spectroscopic measurements as well as the observed 13C deposition patterns in both distribution and magnitude. In order to match the experimental results, fast parallel transport in the SOL had to be imposed on the carbon ions. In addition, a radial pinch was required in the SOL for both the L and H mode experiments to move the carbon closer to the separatrix so that it could deposit where it was measured experimentally. Without both of these flows the simulations were unable to replicate the experimental observations. The effects of radial variation in the parallel flow and erosion of deposited 13C were also both investigated. It was found that neither of these processes by itself appears to be capable of replicating the experimental results.
Author: John David Elder
Publisher:
ISBN: 9780494393710
Category : Aerospace engineering
Languages : en
Pages : 155
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Book Description
In 2003 and 2005 13CH4 puffing experiments were conducted on DIII-D [1] in L and ELMy H mode plasmas respectively. The motivation for these experiments was to develop a greater understanding of impurity creation, transport and deposition for hydrocarbons which are produced at the walls of DIII-D by chemical sputtering. In both experiments, tiles from around the vessel were removed after the experiment was complete and the distribution of the 13C deposition was measured using nuclear reaction analysis. During each of these experiments the plasma conditions and emissions were monitored by a number of direct and spectroscopic diagnostics including Langmuir probes, Thomson scattering, the multichord divertor spectrometer, filterscopes, reciprocating probes and others. These diagnostic measurements are used in the thesis to develop a background plasma solution for the experiments through the procedure of empirical plasma reconstruction. These background plasma solutions are used as the basis for modeling the emissions, transport and deposition of the 13C resulting from the breakup of 13CH4 using the OEDGE code. OEDGE was enhanced by the addition of improved methane breakup kinetics models, improved peripheral particle transport, improved support for line profile modeling as well as many other features. The modeling successfully reproduces most of the spectroscopic measurements as well as the observed 13C deposition patterns in both distribution and magnitude. In order to match the experimental results, fast parallel transport in the SOL had to be imposed on the carbon ions. In addition, a radial pinch was required in the SOL for both the L and H mode experiments to move the carbon closer to the separatrix so that it could deposit where it was measured experimentally. Without both of these flows the simulations were unable to replicate the experimental observations. The effects of radial variation in the parallel flow and erosion of deposited 13C were also both investigated. It was found that neither of these processes by itself appears to be capable of replicating the experimental results.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 17
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Book Description
Experiments are described which examine the transport and deposition of carbon entering the main plasma scrape-off layer in DIII-D. 13CH4 was injected from a toroidally symmetric source into the crown of lower single-null detached ELMy H-mode plasmas. 13C deposition, mapped by nuclear reaction analysis of tiles, was high at the inner divertor but absent at the outer divertor, as found previously for low density L-mode plasmas. This asymmetry indicates that ionized carbon is swept towards the inner divertor by a fast flow in the scrape-off layer. In the private flux region between inner and outer strike points, carbon deposition was low for L-mode but high for the H-mode plasmas. OEDGE modeling reproduces observed deposition patterns and indicates that neutral carbon dominates deposition in the divertor from detached H-mode plasmas.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 2
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Book Description
Use of carbon in tokamaks leads to a major tritium retention issue due to co-deposition. To investigate this process a low power (no beams) L-mode experiment was performed on DIII-D in which 13CH4 was puffed into the main vessel through the toroidally-symmetric pumping plenum at the top of lower single-null discharges. Subsequently, the 13C content of tiles taken from the vessel wall was measured. The interpretive OEDGE code was used to model the results. It was found that the 13C deposition pattern is controlled by: (a) source strength of 13C, (b) radial location of the 13C source, (c) D{sub {perpendicular}}, (d) M{sub {parallel}}, the scrape-off layer parallel Mach number. Best agreement was found for (a) (almost equal to)50% conversion efficiency 13CH4 --> 13C+, (b) 13C+ source (almost equal to)3.5 cm outboard of separatrix near 13CH4 injection location, (c)D{sub {perpendicular}} (almost equal to) 0.3 m2s−1, (d) M{sub {parallel}} (almost equal to) 0.4 toward inside.
Author: S. Allen
Publisher:
ISBN:
Category :
Languages : en
Pages : 2
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Book Description
Use of carbon in tokamaks leads to a major tritium retention issue due to co-deposition. To investigate this process a low power (no beams) L-mode experiment was performed on DIII-D in which {sup 13}CH{sub 4} was puffed into the main vessel through the toroidally-symmetric pumping plenum at the top of lower single-null discharges. Subsequently, the {sup 13}C content of tiles taken from the vessel wall was measured. The interpretive OEDGE code was used to model the results. It was found that the {sup 13}C deposition pattern is controlled by: (a) source strength of {sup 13}C{sup +}, (b) radial location of the {sup 13}C{sup +} source, (c) D{sub {perpendicular}}, (d) M{sub {parallel}}, the scrape-off layer parallel Mach number. Best agreement was found for (a) {approx}50% conversion efficiency {sup 13}CH{sub 4} {yields} {sup 13}C{sup +}, (b) {sup 13}C{sup +} source {approx}3.5 cm outboard of separatrix near {sup 13}CH{sub 4} injection location, (c)D{sub {perpendicular}} {approx} 0.3 m{sup 2}s{sup -1}, (d) M{sub {parallel}} {approx} 0.4 toward inside.
Author: S. Allen
Publisher:
ISBN:
Category :
Languages : en
Pages : 51
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Book Description
Trace {sup 13}CH{sub 4} injection experiments into the main scrape-off layer of low density L-mode and high-density H-mode plasmas have been performed in the DIII-D tokamak [Luxon{_}NF02] to mimic the transport and deposition of carbon arising from a main chamber sputtering source. These experiments indicated entrainment of the injected carbon in plasma flow in the main SOL, and transport toward the inner divertor. Ex-situ surface analysis showed enhanced {sup 13}C surface concentration at the corner formed by the divertor floor and the angled target plate of the inner divertor in L-mode; in H-mode, both at the corner and along the surface bounding the private flux region inboard of the outer strike point. Interpretative modeling was made consistent with these experimental results by imposing a parallel carbon ion flow in the main SOL toward the inner target, and a radial pinch toward the separatrix. Predictive modeling carried out to better understand the underlying plasma transport processes suggests that the deuterium flow in the main SOL is related to the degree of detachment of the inner divertor leg. These simulations show that carbon ions are entrained with the deuteron flow in the main SOL via frictional coupling, but higher charge state carbon ions may be suspended upstream of the inner divertor X-point region due to balance of the friction force and the ion temperature gradient.
Author:
Publisher:
ISBN:
Category : Dissertations, Academic
Languages : en
Pages : 800
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Book Description
Author: J. Watkins
Publisher:
ISBN:
Category :
Languages : en
Pages : 17
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Book Description
This report demonstrates a computer simulation model for single-null diverted plasma configurations that include simultaneous interaction of the scrape-off layer (SOL) plasma with toroidally symmetric main-chamber limiter surfaces and divertor plate surfaces. The simulations use the UEDGE code which treats the SOL plasma and recycled neutrals as two-dimensional toroidally symmetric fluids. The spatial domain can include field lines that intersect main chamber surfaces in the far scrape-off layer, which allows the model to include simultaneous plasma contact with both divertor and main chamber targets. Steady-state simulation results for low-density L-mode plasma discharges in DIII-D show that total core fueling increases by about 70 percent when the separatrix-baffle gap is reduced from 6 cm to 3 cm. The additional core fueling is due to neutrals which originate from the ion particle flux incident on the upper outer divertor baffle.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 18
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Book Description
Use of carbon in tokamaks leads to a serious tritium retention issue due to co-deposition. To further investigate the processes involved, a detached ELMy H-mode (6.5 MW NBI) experiment was performed on DIII-D in which 13CH4 was puffed into the main vessel through the toroidally symmetric pumping plenum at the top of lower single-null discharges. Subsequently, the 13C content of tiles taken from the vessel wall was measured. The interpretive OEDGE code was used to model the results. The 13C deposition pattern could be reproduced, in general shape and magnitude, by assuming in the code the existence of a parallel flow and a radial pinch in the scrape-off layer. Parallel flows of Mach (almost equal to) 0.3 toward the inner divertor and a radial pinch (almost equal to)10 to 20 m/s (+ R-direction) were found to yield 13C deposition comparable to the experiment.
Author: S. L. Allen
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
As part of a study of carbon-tritium co-deposition, we carried out an experiment on DIII-D involving a toroidally symmetric injection of {sup 13}CH{sub 4} at the top of a LSN discharge. A Monte Carlo code, DIVIMP-HC, which includes molecular breakup of hydrocarbons, was used to model the region near the puff. The interpretive analysis indicates a parallel flow in the SOL of M{sub l} {approx} 0.4 directed toward the inner divertor. The CH{sub 4} is ionized in the periphery of the SOL and so the particle confinement time, {tau}{sub c}, is not high, only {approx}5 ms, and about 4X lower than if the CH{sub 4} were ionized at the separatrix. For such a wall injection location, however, most of the CH{sub 4} gets ionized to C{sup +}, C{sup ++}, etc., and is efficiently transported along the SOL to the inner divertor, trapping hydrogen by co-deposition there.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
As part of a study of carbon-tritium co-deposition, we carried out an experiment on DIII-D involving a toroidally symmetric injection of [sup 13]CH[sub 4] at the top of a LSN discharge. A Monte Carlo code, DIVIMP-HC, which includes molecular breakup of hydrocarbons, was used to model the region near the puff. The interpretive analysis indicates a parallel flow in the SOL of M[sub l] [approx] 0.4 directed toward the inner divertor. The CH[sub 4] is ionized in the periphery of the SOL and so the particle confinement time, [tau][sub c], is not high, only [approx]5 ms, and about 4X lower than if the CH[sub 4] were ionized at the separatrix. For such a wall injection location, however, most of the CH[sub 4] gets ionized to C[sup +], C[sup ++], etc., and is efficiently transported along the SOL to the inner divertor, trapping hydrogen by co-deposition there.
