Simulation of experimentally achieved detached plasmas using the UEDGE code Page: 9 of 32
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flux surface which intersects a material wall, typically in the range 1.055 'TN 51.15.
We specify the power across the inner flux surface, Psep, and the density on that
surface, core, as core boundary conditions. The radial power flow is distributed
poloidally to provide approximately constant density and temperature on the
innermost flux surface, as expected because of high parallel conductivity. This
means that the majority of the radial power is transported at the outer mid plane
where the flux surfaces are maximally compressed. The perpendicular particle
diffusion coefficient, and electron and ion thermal diffusivities are determined
empirically by matching the upstream density and temperature radial profiles
measured in DIII-D. We used values of D_ = 0.3 m2/s, Xe = xi=1.5 m2/s for the
simulations reported in this section. We determine the existence of multiple SOL
plasma modes by examining the dependence of the plasma parameters on the
separatrix density and power. The results are summarized in Fig. 4, and the
variation of the plate electron temperature at the separatrix with heating power and
core density is shown in Fig. 5. The parameters for which we have converged
UEDGE solutions are indicated by the circles, squares, and diamonds on Fig. 4.
When the core plasma density is low, and/or the separatrix heating power is high,
we find the separatrix temperature to be high at both the inside and outside divertor
plates-characteristic of attached plasmas. When the heating power is reduced, at
fixed core density, the plate electron temperature decreases. Since the connection
length from the outer mid plane to the inner divertor plate is longer than that to the
outer divertor plate, we find the inner electron temperature decreases more rapidly
than the outer. The temperature drops more rapidly with decreasing power when it
falls below that necessary for efficient ionization of neutrals, about 10 eV. We
somewhat arbitrarily define the transition from attached to detached plasmas as
being the power at which the plate temperature drops below 5 eV. At these low
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Porter, G. D.; Allen, S. & Fenstermacher, M. Simulation of experimentally achieved detached plasmas using the UEDGE code, article, October 30, 1995; California. (https://digital.library.unt.edu/ark:/67531/metadc667586/m1/9/: accessed July 16, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.