Download or read book Modeling of Impurity Spectroscopy in the Divertor and SOL of DIII D Using the 1D Multifluid Model NEWT1D written by and published by . This book was released on 1996 with total page 6 pages. Available in PDF, EPUB and Kindle. Book excerpt: NEWT1D, a one dimensional multifluid model of the scrape-off layer and divertor plasma, has been used to model the plasma including the distribution of carbon ionization states in the SOL and divertor of ELMing H-mode at two injected power levels in DIII-D. Comparison of the code predictions to the measured divertor and scrape-off layer (SOL) plasma density and temperature shows good agreement. Comparison of the predicted line emissions to the spectroscopic data suggests that physically sputtered carbon from the strike point is not transported up the flux tube; a distributed source of carbon a few centimeters up the flux tube is required to achieve reasonable agreement.
Download or read book 23rd European Physical Society Conference on Controlled Fusion and Plasma Physics written by and published by . This book was released on 1996 with total page 580 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Experimental Measurements and Modeling of Impurity Transport in the Divertor and Boundary Plasma of DIII D written by and published by . This book was released on 1994 with total page 4 pages. Available in PDF, EPUB and Kindle. Book excerpt: Analysis of trace impurity injection experiments on DIII-D during a beam power scan is presented. Spectroscopic measu- rements indicate that as beam power is increased, and concomitantly ELM frequency and scrape-off-layer thickness increase while energy confinement decreases, the core impurity content decreases only slightly. Modeling of the edge plasma using the UEDGE 2D and NEWT1D plasma fluid codes indicate that as beam power is increased, the parallel forces on an impurity ion increase in the direction from the divertor and toward the core plasma. Experiments using the divertor cryopump to induce higher parallel particle flow toward the divertor demonstrate significant reduction in core impurity content. These results indicate that parallel forces on impurity ions in the scrape off layer are playing a significant role in core impurity content.
Download or read book Impurity Control Studies Using SOL Flow in DIII D written by and published by . This book was released on 2001 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Experiments on DIII-D have demonstrated the efficacy of using induced scrape-off-layer (SOL) flow to preferentially enrich impurities in the divertor plasma. This SOL flow is produced through simultaneous deuterium gas injection at the midplane and divertor exhaust. Using this SOL flow, an improvement in enrichment (defined as the ratio of impurity fraction in the divertor to that in the plasma core) has been observed for all impurities in trace-level experiments (i.e., impurity level is non-perturbative), with the degree of improvement increasing with impurity atomic number. In the case of argon, exhaust gas enrichment using a modest SOL flow is as high as 17. Using this induced SOL flow technique and argon injection, radiative ELMing H-mode plasmas have been produced that combine high radiation losses (P[sub rad]/P[sub input]> 70%), low core fuel dilution (Z[sub eff]1.9), and good core confinement ([tau][sub E] 1.0[tau][sub E], ITER93H).
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.
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.
Download or read book Modeling of DIII D Noble Gas Puff and Pump Experiments written by and published by . This book was released on 1997 with total page 5 pages. Available in PDF, EPUB and Kindle. Book excerpt: Previous DIII-D experiments that induced a D flow in the scrap-off layer (SOL) showed that this flow increased the divertor concentration of extrinsically injected impurities (neon, argon). These impurity fueling and exhaust (or puff and pump) experiments raise a number of modeling issues: the effect of edge-localized modes (ELMs) in regulating impurity core accumulation; the particle balance of the extrinsic impurities; the relation between divertor and plenum enrichment; and the effect of features unique to the present DIII-D Advanced Divertor configuration, specifically, the localized back-conductance of D2 and impurities from the baffle plenum in the outboard divertor region. To aid in understanding the relations between these processes, models have been improved: for core impurity transport to include ELM effects, and for divertor models to treat helium, neon, and argon transport with DIII-D--specific configuration effects. The models have been used to analyze a series of experiments in which neon and argon were first continuously injected (in the divertor private flux region) for 1.5 s, and then exhausted by the DIII-D cryopumping system. Deuterium was puffed at rates of 80 Torr L/s and 150 Torr L/s from the midplane and the divertor private region in these experiments. Results of the simulations are given.
Download or read book Impurity Enrichment and Radiative Enhancement Using Induced SOL Flow in DIII D written by and published by . This book was released on 2001 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Experiments on DIII-D have demonstrated the efficacy of using induced scrap-off-layer (SOL) flow to preferentially enrich impurities in the divertor plasma. This SOL floe is produced through simultaneous deuterium gas injection at the midplane and divertor exhaust. Using this SOL flow, an improvement in enrichment (defined as the ratio of impurity fraction in the divertor to that in the plasma core) has been observed for all impurities in trace-level experiments (i.e., impurity level is non-perturbative), with the degree of improvement increasing with impurity atomic number. In the case of argon, exhaust gas enrichment using modest SOL flow is as high as 17. Using this induced SOL flow technique and argon injection, radiative plasmas have been produced that combine high radiation losses (P[sub rad]/P[sub input]> 70%), low core fuel dilution (Z[sub eff]1.9), and good core confinement ([tau][sub E] 1.0[tau][sub E, ITER93H]).
Download or read book Reconstruction of Detached Divertor Plasma Conditions in DIII D Using Spectroscopic and Probe Data written by P. Stangeby and published by . This book was released on 2004 with total page 8 pages. Available in PDF, EPUB and Kindle. Book excerpt: For some divertor aspects, such as detached plasmas or the private flux zone, it is not clear that the controlling physics has been fully identified. This is a particular concern when the details of the plasma are likely to be important in modeling the problem--for example, modeling co-deposition in detached inner divertors. An empirical method of ''reconstructing'' the plasma based on direct experimental measurements may be useful in such situations. It is shown that a detached plasma in the outer divertor leg of DIII-D can be reconstructed reasonably well using spectroscopic and probe data as input to a simple onion-skin model and the Monte Carlo hydrogenic code, EIRENE. The calculated 2D distributions of n{sub e} and T{sub e} in the detached divertor were compared with direct measurements from the divertor Thomson scattering system, a diagnostic capability unique to DIII-D.
Download or read book Measurements of Divertor Impurity Concentrations on DIII D written by and published by . This book was released on 1996 with total page 4 pages. Available in PDF, EPUB and Kindle. Book excerpt: Carbon emissions in the DIII-D divertor during partial detachment have been measured, and the deduced radiated power and the temporal behavior of the impurity emissions from spectroscopy are in good agreement with bolometer measurements. Effective electron temperatures from line ratios for CIV (9-11 eV) and CIII (6-8 eV) are correlated with DTS measured electron temperatures to determine the spatial location of the carbon radiation zone. During PDD operation, the bulk of the divertor radiation is emitted from CIV near the X- point while deuterium radiation is strongest near the outer strikepoint. The carbon ion concentrations are in the range of 1% - 4% of the electron density.
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 Particle Exhaust Modeling for the Collaborative DIII D Advanced Divertor Program written by and published by . This book was released on 1990 with total page 17 pages. Available in PDF, EPUB and Kindle. Book excerpt: A principal objective of the collaborative DIII-D Divertor Program (ADP) is to achieve density control in H-mode discharges with edge biasing and with continuous particle exhaust at a rate determined by the external fueling sources (typically 20 Torr{center dot}L/s). The divertor baffle-bias ring system has been optimized for pumping speeds (almost equal to)50,000 L/s with the neutral transport code DEGAS. With an entrance slot conductance of 50,000 L/s, a pumping speed of the same order is required to remove half of the (almost equal to)40 Torr{center dot}L/s that enters the baffle chamber for typical H-mode discharges. Increasing the exhaust fraction with higher pumping speed is self-limiting, owing to the attendant reduction of the recycling flux. The effects of pumping on the plasma core, scrape-off layer (SOL), and divertor have been estimated with a model that self-consistently couples the transport in these regions. The required (almost equal to)50,000 L/s pumping speed can be achieved with either titanium getter pumps or cryopumps. Evaluation of both systems has led to the conclusion that cryopumps will be more compatible with the environment of the DIII-D divertor. 8 refs., 7 figs.
Download or read book Noble Gas Impurity Balance and Exhaust Model for DIII D and JET written by and published by . This book was released on 1998 with total page 17 pages. Available in PDF, EPUB and Kindle. Book excerpt: Experiments to study the exhaust of noble gases (helium, neon) with cryopumping in DIII-D Advanced Divertor Program (ADP) configuration and in JET (Mk1 configuration) found significant differences in the global exhaust rate of helium, while efficient neon exhaust was observed in both machines. An attempt to better understand the basic processes governing the exhaust of noble gases in ELMy H-mode with cryopumping has been undertaken. Since divertor geometries investigated in the DIII-D and in the JET cases have significant differences, a comparative modeling study has been undertaken using the MIST core impurity transport code and the b2.5 time-independent divertor transport code. Photodiode measurements are used to determine ELM frequency, and charge-exchange recombination (CER) measurements are compared with the MIST ELM model to evaluate transport coefficients in the core plasma. A significant reduction in the anomalous diffusivities is found for the non-ELM component of radial transport without the need for a pinch velocity, and the model provides a more coherent description than the conventional ELM-averaged approach. Sensitivity to boundary conditions has been studied through establishment of a database of divertor enrichment cases using b2.5.
Download or read book Valojuova written by and published by . This book was released on 1945 with total page 64 pages. Available in PDF, EPUB and Kindle. Book excerpt:
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.
Download or read book The DIII D Summary Contribution to the Final INTOR Workshop written by and published by . This book was released on 1988 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: In SIII-D, good H-mode confinement has been obtained with up to 6 MW of neutral-beam injection (NBI). In this report we summarize the essential features of divertor operation for DIII-D H-mode plasma. Briefly, our measurements show that: Large edge density and temperarture gradients are obtained with scale lengths of a few cm at the midplane; In the steady state, approximately 10-20% of the input power is deposited on the divertor plates in a region that is peaked on the separatrix and extends radially over)approx equal) 2-4 cm at the outboard intercept. More power (2:1) reaches the outboard intercept than the inboard; Low electron temperature (less than or equal to20eV) and high density (n/sub e//sup div/)approx equal) n/sub e//sup main/ greater than or equal to 3-10)times)1019 m−3 at the divertor plates indicate that DIII-D obtains a high-recycling divertor during H-mode. DEGAS neutral transport modeling is consistent with these results; The duration of good H-mode confinement is limited by Edge Localized Modes (ELMs) rather than increasing impurity radiation; The dominant impurities, C and Ni are concentrated in the edge plasma (ra greater than or equal to 0.5) for I/sub p/ greater than or equal to 1 MA; and Global impurity concentrations fall markedly with increasing plasma current. The remainder of this report contains a brief description of the DIII-D tokamak and the relavant diagnostics, a summary of the divertor plasma parameters obtained during the H-mode and the heat loads on the diverotr target plates. The results of measurements of the central radiation and impurity content using data from an EUV spectrometer and a 21 channel bolometer array are discussed, and finally a discussion of the implication of these results for the CIT and ITER tokamak designs is given. 8 refs., 8 figs.
Download or read book COMPARISON OF ELM PULSE PROPAGATION IN THE DIII D SOL AND DIVERTORS WITH AN ION CONVECTION MODEL written by and published by . This book was released on 2003 with total page 7 pages. Available in PDF, EPUB and Kindle. Book excerpt: OAK-B135 Results from dedicated ELM experiments, performed in DIII-D with fast diagnostics to measure the evolution of Type-I ELM effects in the SOL and divertor, are compared with a simple ion convection model and with initial time-dependent UEDGE simulations. Delays between ELM effects observed in the inner versus the outer divertor regions in the experiments scale, as a function of density, with the difference in ion convection time along field lines from the outer midplane to the divertor targets. The ELM perturbation was modeled as an instantaneous radially uniform increase of diffusion coefficients from the top of the pedestal to the outer SOL. The perturbation was confined to a low field side poloidal zone " 40{sup o} from the outer midplane. The delays in the simulations are similar to those observed in the experiments.
