The impact of neutrals on anomalous edge plasma transport and zonal flow (ZF) is considered.As an example, it is assumed that edge plasma turbulence is driven by the resistive drift wave (RDW) instability. It is found that the actual effect of neutrals is not related to a suppression of the instability per se, but due to an impact on the ZF. Particularly, it is shown that, whereas the neutrals make very little impact on the linear growth rate of the RDW instability, they can largely reduce the zonal flow generation in the non-linear stage, which results in an enhancement of the overall anomalous plasma transport. Even though only RDW instability is considered, it seems that such an impact of neutrals on anomalous edge plasma transport, i.e. neutrals enhance the transport via the reduction of ZF, has a very generic feature. It is conceivable that such neutral induced enhancement of anomalous plasma transport is observed experimentally in a detached divertor regime, which is accompanied by a strong increase of neutral density.
Recently, it was shown that strong electron thermionic emission from material walls could result in the formation of an "inverse sheath", which prevents the flow of cold ions to the wall [1][2][3] . Such regimes look very favorably from the point of view of plasma-material interactions at the edge of magnetic fusion devices, where the problem of the erosion of plasma facing components under ion irradiation is one of the key issues for developing of future magnetic fusion reactors. However, it is not clear whether such regimes are compatible with edge plasma parameters and heat removal requirements in fusion reactors.To address the issue of practicality of the "inverse sheath" regime for edge tokamak plasma conditions, we perform a set of numerical simulations with 2D edge plasma transport code UEDGE [4] for a DIII-D-like geometry and magnetic configuration.To describe both "standard" and "inverse sheath" conditions within the framework of the UEDGE code (which does not consider the sheath region per se), at the material surfaces, we apply effective boundary conditions which emulate both "standard" and "inverse sheath" regimes. We demonstrate that for the same input parameters, spatial distributions of edge plasma parameters corresponding to detached divertor and "inverse sheath" regimes are similar, with only a few minor differences. We discuss the compatibility of "inverse sheath" regimes with core plasma parameters.
We assess the toroidal magnetic field Bt asymmetry in DIII-D due to a misalignment of the toroidal field coils with respect to the poloidal magnetic field coils and vacuum vessel. The peak-to-peak variation of the divertor strike point (SP) radius is measured to be 1 cm, with an n=1 toroidal pattern. We use the center of a narrow carbon deposition band on tungsten-coated divertor tiles just inside the outer strike point (OSP) as a proxy for the divertor strike point location. The band occurred in a series of reverse Bt discharges with the OSP positioned on the divertor inserts due to strong E×B drift transport of C from the inner to the outer SP through the private flux region. The variation in band radius (and hence the magnetic SP) is a 5mm shift towards 310° toroidal direction. These measurements agree well with previous measurements of the 3D magnetic field distribution, simulations performed by the MAFOT field line integration code, and recent Langmuir probe measurements in the Small-Angle-Slot (SAS) divertor. Comparison these measurements in the SAS divertor also indicate that there is a tilt (in conjunction with the shift) of the Bt coil field of 0.04° toward the toroidal angle of 215°. Previous measurements suggested a field misalignment of 4.6 mm in the 270° toroidal direction, and a tilt of 0.06° towards the 114° toroidal direction, which is similar to the results reported here, but also suggests that the Bt field misalignment has evolved over time with more than 100,000 coil pulses over the intervening 20 years. These studies will be important for better understanding the radial variation of the toroidal strike line in DIII-D, designing the new generation of the SAS divertor, and developing an understanding of the impact of error fields on tokamaks with tightly baffled slot divertors.
Comprehensive studies of energy and particle balances in the transition to plasma detachment in an alternative divertor configuration with long outer legs are shown. Numerical simulations are performed with the 2D code suite SOLPS 4.3, using a disconnected double null grid with narrow, tightly baffled long poloidal leg divertors at the outer lower target and outer upper target. A density scan is performed using the “closed gas box” model, where the tunable parameter in the simulations is the total number of deuterium particles in the simulation space and all other parameters are held fixed, including a constant input power and trace neon impurity radiation, to assess the physics of the transition to detachment in the system as the density increases. Three main aspects of the physics of divertor detachment are addressed: the criteria for the local onset of divertor detachment in each of the divertors, the distribution of heat flux and other plasma parameters between the four divertors as each divertor transitions to detachment, and the role of perpendicular transport in the transition to the detached regime. A synergistic mechanism by which the cross-field transport is reduced by factors associated with the onset of plasma recombination effects is identified. These results are compared to the existing understanding of the physics of the transition to plasma detachment in standard divertors.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.