Speaker
Description
UEDGE simulations of a “chimney” divertor, utilizing mid-leg pumping upstream of the divertor target along the outer baffle, predict the formation of a stable radiation front between the pumping plenum and X-point. The mid-leg pumping plenum is proposed as an engineering solution to stabilize the detachment front location downstream of the X-point, maintaining a hot X-point ($\rm T_{e,Xpt}$ ~ $\rm T_{e,sep,OMP}$) simultaneously with a detached divertor target (Te,targ < ~5 eV). UEDGE simulations, including magnetic and $\rm\bf E\times B$ drifts, predict radiation front control between the pumping plenum and X-point using low-field side main-ion gas puffing with the ion $\rm \mathbf{B}\times\nabla B$ directed towards the X-point. In the opposite B-field direction, with ion $\rm \mathbf{B}\times\nabla B$ directed away from the X-point, limited control is predicted due to $\rm\bf E_\theta\times B$ and $\rm\mathbf{E}_r\times \bf B$ divertor drift flows yielding significant current to the pumping surface, resulting in efficient removal of the injected gas.
This work will expand on previous simulations of a proposed mid-leg pumped low-field side “chimney” divertor, planned to be installed in the DIII-D upper divertor [1,2]. The “chimney” design employs a closed divertor structure and an extended outer leg with a 4.5 cm deep volume at the end of the divertor slot, which acts as a neutral reservoir for power exhaust through ion-neutral interaction [3]. The UEDGE-predicted sensitivity of the radiation front location, volume, and power to operational parameters, including main- and impurity particle injection and applied heating power will be presented. Furthermore, UEDGE model fidelity will be increased compared to initial simulations [1] by modeling the transport of individual charge states of the seeded impurities and including fluid molecules as a separate species in the simulations. The UEDGE pumping model applied will be compared to DEGAS2 kinetic Monte-Carlo neutral simulations to assess the fidelity of the UEDGE fluid neutral pumping model and validate previous results [1].
The predictive UEDGE and SOLPS-ITER simulations used to design the divertor will be validated against experimental measurements using the proposed chimney divertor and associated diagnostic systems in DIII-D. If passive radiation front stabilization and location control consistent with edge-plasma code predictions are observed experimentally, mid-leg pumped divertors may present an alternative divertor design for future divertors with reduced requirements on divertor volume and radiating impurity injection.
[1] A. Holm et al., “Modeling a divertor with mid-leg pumping for high-power H-mode scenarios in DIII-D considering E × B drift flows,” Nuclear Materials and Energy, vol. 41, p. 101782, 2024.
[2] J. H. Yu et al., “Simulations of divertor designs that spatially separate power and particle exhaust using mid-leg divertor particle pumping,” Nuclear Materials and Energy, vol. 41, p. 101826, 2024.
[3] R. S. Wilcox, et al., “The “Chimney” divertor: A closed divertor with mid-leg pumping for core-edge integration in DIII-D”, this meeting.
This work was supported in part by the US Department of Energy under contract nos. DE-FC02-04ER54698, DE-AC52-07NA27344, and DE-AC05-00OR22725. LLNL-ABS-2006456.
Disclaimer: This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.
| Speaker's title | Mr |
|---|---|
| Speaker's Affiliation | Lawrence Livermore National Laboratory, Livermore, CA |
| Member State or IGO | United States of America |
