Abstract
The National Spherical Tokamak Experiment (NSTX) upgrade (NSTX-U) requirements lead to enhanced heat loads on plasma-facing components (PFCs) especially in the divertor regions, where normal heat flux density can reach up to 8 MW/m2. For these high heat flux (HHF) regions, the PFCs were redesigned, to use castellations which relieved the thermal stresses associated with high incident heat flux. Another design feature of HHF PFCs is the absence of front face mounting holes which create localized areas of high temperature and thermal stress concentrations. Optimized shaping of the front face of the HHF PFCs eliminates regions where the front face is perpendicular to the heat flux direction during normal helicity operation and spreads the heat load. A unique mechanism was designed to connect PFC tiles to the NSTX-U center stack casing using locking features accessible from the low heat flux regions. Isotropic graphite was selected as the HHF PFC tile material. Initial tile design parameters were accessed using analytical expressions for pulsed heat flux loading. A working prototype of the locking mechanism was created during the initial stages of the design to prove the concept performance. This article presents an overview of the divertor HHF PFC design and the results of the thermal and structural analyses performed using ANSYS software. The results of the analyses cover normal operating conditions and disruptions which impose electromagnetic (EM) loads from eddy and halo currents. The 3-D, transient, nonlinear analyses took into account the temperature-dependent properties of the materials, friction interfaces between the parts, and variable electric properties of the parts and interfaces. The results confirm that the HHF PFC tiles remain within the allowable limits for the loads defined by the NSTX-U Recovery Project. In addition, tolerance stack up analyses were performed to ensure tile performance in the worst possible assembly configuration. The design process was completed successfully, and the NSTX HHF PFC tiles are currently in the production phase.
| Original language | English |
|---|---|
| Article number | 9321342 |
| Pages (from-to) | 886-892 |
| Number of pages | 7 |
| Journal | IEEE Transactions on Plasma Science |
| Volume | 49 |
| Issue number | 2 |
| DOIs | |
| State | Published - Feb 2021 |
Funding
Manuscript received September 3, 2019; revised July 22, 2020 and October 2, 2020; accepted November 21, 2020. Date of publication January 13, 2021; date of current version March 10, 2021. This work was supported in part by the U.S. Department of Energy, Office of Science, Office of Fusion Energy Sciences, and in part by Princeton University with the U.S. Department of Energy under Contract DE-AC02-09CH11466. The review of this article was arranged by Senior Editor G. H. Neilson. (Corresponding author: Andrei Khodak.) Andrei Khodak, Douglas Loesser, Michael Messineo, and Arthur Brooks are with the Princeton Plasma Physics Laboratory, Princeton, NJ 08543 USA (e-mail: [email protected]).
| Funders | Funder number |
|---|---|
| U.S. Department of Energy | |
| Fusion Energy Sciences | |
| Princeton University | DE-AC02-09CH11466 |
| Office of Science |
Keywords
- High heat flux (HHF)
- numerical analysis
- plasma-facing components (PFCs)
