ITER hybrid equilibrium solved by JOREK from the TORAX EQDSK
A JOREK stability run starts from an equilibrium that JOREK solves itself, from a boundary, a pressure profile and the poloidal current function FF′. A growth rate is only meaningful if that equilibrium matches the one it is meant to represent. We therefore solved the ITER hybrid equilibrium in JOREK from the EQDSK file that TORAX ships, and compared the safety factor q.
The route needed three changes: - JOREK’s EQDSK converter needs a spline library, which we built from source. - The converter’s spline smoothing had to be raised slightly for the fit to succeed. - The converter’s outside-separatrix pressure went negative, because this EQDSK has zero pressure at the separatrix. JOREK rejects a non-positive temperature, so the temperature file was written by the toolkit adapter instead. Inside the plasma it uses the EQDSK pressure, with a small floor outside it.
JOREK read that file back exactly. The sign conventions agree: q, the toroidal field function and the axis flux all come out with the expected signs.
The core agrees, and the edge does not yet (JOREK solving the ITER hybrid equilibrium from the TORAX EQDSK matches its safety factor q to 0.4% (median) for normalised flux 0.1-0.5, but is 3.6% high for 0.5-0.9 and 5.8% high for 0.9-0.95 (q 5.12 vs 4.67 at 0.95); plasma current 12.06 vs 11.77 MAC-216). JOREK’s plasma current and q are a few percent high towards the edge. That is too large for edge-stability work, where the result depends on edge q and current. The likely causes are not yet separated: the converter’s default boundary contour lies outside the separatrix, and the FF′ spline and taper act near the edge. The proposed next step is to use the separatrix itself as the boundary and refine the grid. Stability runs would then start only once q and current match the EQDSK within an agreed tolerance.
Where this stands: the equilibrium route works end to end. The acceptance tolerance, model, dissipation, mode numbers, instability criterion and compute envelope for the first stability scans await the owner (OQ-39).
Technical details → JOREK. Decision → OQ-39.
JOREK acknowledgement. JOREK is developed by the JOREK team and is open source under the GNU LGPL v3. Results here use JOREK at commit 01a52be3. Citations: M. Hoelzl et al., Nuclear Fusion 61, 065001 (2021); M. Hoelzl et al., Nuclear Fusion 66, 116006 (2026). For a list of JOREK team members, refer to the author list of M. Hoelzl, G.T.A. Huijsmans, F.J. Artola, E. Nardon, M. Becoulet, N. Schwarz, A. Cathey, S.J.P. Pamela et al., Nuclear Fusion 64, 112016 (2024).
Technical details → JOREK › iter equilibrium
Decisions → OQ-37 · OQ-39