Simulation of Double-null Divertor Plasmas with the UEDGE Code PDF Download
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Languages : en
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We describe recent modifications to the UEDGE code that enable us to simulate full double-null magnetic configurations. We present simulation results for magnetically balanced double- nulls, with and without asymmetries due to divertor recycling and cross-field drifts. Up/down electron temperature asymmetries due to recycling are weak for attached plasmas because the magnetic connection length is shorter than for comparable single-null plasmas. Cross-field drifts due to radial electric fields produce strong poloidal ion particle fluxes at the midplane in the SOL that can drive up/down asymmetries.
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Languages : en
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We describe recent modifications to the UEDGE code that enable us to simulate full double-null magnetic configurations. We present simulation results for magnetically balanced double- nulls, with and without asymmetries due to divertor recycling and cross-field drifts. Up/down electron temperature asymmetries due to recycling are weak for attached plasmas because the magnetic connection length is shorter than for comparable single-null plasmas. Cross-field drifts due to radial electric fields produce strong poloidal ion particle fluxes at the midplane in the SOL that can drive up/down asymmetries.
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Languages : en
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We present fluid model simulation results for the edge plasma in the DIII-D tokamak with unbalanced double-null magnetic configurations, including cross field drifts. Input parameters are typical of low-power operation in DIII-D. For high-recycling the plasma tends to be detached from all divertor plates. Midplane plasma and electric field profiles are relatively insensitive to the magnetic imbalance. Divertor heat flux profiles exhibit sharp peaks due to cross-field drifts when the ion grad-B drift direction is away from the x-point toward the magnetic axis.
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Languages : en
Pages : 31
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Languages : en
Pages : 8
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The effect of ExB and diamagnetic drifts on the boundary plasma of a diverted tokamak is examined by comparing simulations obtained from the 2D fluid code UEDGE with data from the DIII-D tokamak. The effect of drifts on a single null L-mode configuration is determined by comparing the measurements with two simulations which are identical except that only one includes drifts. The dominant effect is seen on the high B-field side of the divertor where the plasma density is a factor of two higher when drifts are included. This effect occurs because a radial electric field associated with steep electron temperature radial gradients along the separatrix between the X-point and strike points drives a poloidal flow from the outer to inner divertor in the private region. The higher density yields higher radiation power, moving line radiation zones further off the divertor plate. The simulated profiles of both D{sub {alpha}} and CIII radiation obtained with drift effects included are more consistent with measurements. The drifts also affect the in/out asymmetry of both divertor heating power and divertor ion flux. The effect of drifts on the up/down asymmetry of double null plasma configurations is also considered, although not in as much detail. The up/down asymmetry of the divertor heat flux which is measured in double null plasmas on DIII-D is consistent with that obtained in UEDGE simulations which include the effect of drifts. Drift effects can be important in determining the profile of divertor heating powers, and the distribution of recycling neutrals, and therefore should be included in the design of divertor structures for future fusion devices.
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Languages : en
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We simulate edge plasmas in NSTX double-null divertor configurations with the UEDGE two-dimensional fluid code. The carbon impurity density in the core plasma and total radiated power increase with the core heating power and the magnitude of the physical and chemical sputtering in the divertor. Up/down plasma asymmetries are generated by classical cross-field particle drifts. With the standard toroidal magnetic field direction (ion (nabla)B drift toward the lower x-point) the highest density occurs at the lower inboard divertor plate and the highest heat flux at the upper outboard divertor plate. Simulations of 3-d edge plasma turbulence with the BOUT code show that anomalous radial transport at the outboard midplane should be similar in magnitude for NSTX and DIII-D.
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Languages : en
Pages : 29
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The introduction of a divertor Thomson scattering system in DIII-D has enabled accurate determination of the plasma properties in the divertor region. We identify two plasma regimes; detached and attached. The electron temperature in the detached regime is about 2 eV, much lower than 5 to 10 eV determined earlier. We show that fluid models of the DIII-D scrape-off layer plasma are able to reproduce many of the features of these two plasma regimes, including the boundaries for transition between them. Detailed comparison between the results obtained from the fluid models and experiment suggest the models underestimate the spatial extent of the low temperature region associated the detached plasma mode. We suggest that atomic physics processes at the low electron temperatures reported here may account for this discrepancy.
Author: J. Watkins
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Languages : en
Pages : 17
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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: Quang Thanh Nguyen
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Languages : en
Pages : 238
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Category : Western Australia
Languages : en
Pages : 3
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Photocopy from Premier's Dept file.
Author: A. M. M. Todd
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Category :
Languages : en
Pages : 23
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