Adamek, J.

Dimitrova, M.

Hecko, J.

Hromasova, K.

Komm, M.

Lindl, H.

Sos, M.

Svorc, D.

Vondracek, P.

English

MPG.PuRe

Validation of tokamak magnetic equilibrium reconstructions using theSOLPS-ITER edge plasma transport code simulationsD. Svorc1, K. Hromasova2, J. Hecko2, J. Adamek2, M. Dimitrova2,M. Komm2, H. Lindl3, M. Sos2, P. Vondracek2, and the COMPASS team2,∗1 Faculty of Nuclear Sciences and Physical Engineering, CTU, Prague, Czech Republic2 Institute of Plasma Physics of the CAS, Prague, Czech Republic3 Max–Planck-Institut für Plasmaphysik, Garching, Germany ∗ See the author list of [4]IntroductionFigure 1: Separatrix position of equilib-rium reconstructions on the COMPASStokamak cross section.Precise knowledge of the magnetic equilibriumof a tokamak discharge is vital for experiment con-trol, data analysis, and simulations. [5] Reconstruc-tions of the magnetic equilibrium of the COMPASStokamak are, however, often inaccurate. [1][2] Sev-eral refinements to the reconstruction have beenproposed during the operation of the COMPASStokamak at the Institute of Plasma Physics, CzechAcademy of Sciences. [3][4] SOLPS-ITER edgeplasma transport code uses a magnetic equilibriumreconstruction to construct its computational mesh.In interpretative modeling, an inaccurate equilib-rium reconstruction can affect the final model-experiment match. In this paper, we create severalSOLPS-ITER simulations based on different equi-librium reconstruction variants of COMPASS L-mode discharge #17692 at 1120 ms. This allows usto investigate the effect of inaccurate equilibriumreconstructions on SOLPS-ITER modeling and toevaluate the equilibrium reconstruction variants.Several edge plasma diagnostics were used in the evaluation. Upstream measurements wereprovided by the Thomson scattering (plasma top) and a reciprocating probe (outer midplane).Divertor measurements were carried out by an infrared camera, a swept probe array, and acombined probe array, which uses a combination of ball-pen probes and Langmuir probes. [6]50th EPS Conference on Contr. Fusion and Plasma Phys, 8-12 July 2024 D. Svorc et al. : P2.084 (2024)Figure 2: Comparison of the separatrix positions (vertical lines) with diagnostic measurements.Left column: plasma top, middle column: outer midplane, right column: divertor.Magnetic equilibrium reconstructionsFigure 1 shows the five equilibrium reconstruction variants considered. The equilibrium re-constructions are created by the EFIT++ code based on different input constraints. (i) The’standard’ reconstruction uses data from various diagnostics, notably including 16 Inner Par-tial Rogowski (IPR) coils to constrain the solution. (ii) Reconstruction with corrected IPR coilpositions and angles. [3] (iii) Reconstruction with IPR corrections and also using measurementsfrom Mirnov coils and flux loops. [3] (iv) Reconstruction using realistic pressure profile mea-sured by the Thomson scattering diagnostic, while assuming p = 2pe. (v) The final variant usesdivertor probe measurements and the two-point model to constrain upstream separatrix positionto improve the standard reconstruction.Figure 2 shows the position of the separatrix for each equilibrium reconstruction compared todiagnostic measurements. For each equilibrium, there are significant differences in the measuredelectron temperature and density at the separatrix at both upstream locations. This presents aproblem when trying to match the SOLPS-ITER simulation to the experiment. This was cor-rected by shifting the separatrix at the plasma top and at the outer midplane.50th EPS Conference on Contr. Fusion and Plasma Phys, 8-12 July 2024 D. Svorc et al. : P2.084 (2024)Figure 3: Comparison of the SOLPS-ITER simulation data based on different equilibrium re-constructions with diagnostic measurements. Left column: plasma top, middle column: outermidplane, right column: divertor.Interpretative SOLPS-ITER simulationsThe COMPASS discharge #17692 used was in L-mode with BT = −1.38 T, Ip = 200 kAand line-averaged density n̄e = 2 ·1019 m−3. The SOLPS-ITER simulations were run with B2.5coupled with EIRENE, deuterium only, and no drifts. The ’p = 2pe’ equilibrium reconstructionwas chosen to build a mesh for initial SOLPS-ITER simulations. These initial runs were used tofind the anomalous diffusion coefficients Dn = 0.3 m2s−1, χe = χi = 1.2 m2s−1 and the bound-ary conditions ne,core = 1.4 ·1019 m−3, PSOL = 150 kW. The separatrix shifts at the plasma topand at the OMP are two additional free parameters. The match was found by running parameterscans and selecting values that provide the best match with diagnostic measurements.The same boundary conditions and transport coefficients were then used as inputs for sim-ulations using different equilibrium reconstructions. The separatrix shifts were found indepen-dently for each simulation. Figure 3 shows the comparison of these simulations with diagnosticmeasurements. The figure shows only small differences between simulation profiles, and theyfall within the fluctuations of the diagnostic measurements. This shows that using different and50th EPS Conference on Contr. Fusion and Plasma Phys, 8-12 July 2024 D. Svorc et al. : P2.084 (2024)Reconstruction ∆R [mm] ∆Z [mm] R [mm] Z [mm]p = 2pe -3 4 738 2822PM 18 8 739 284IPR corrected 10 -22 738 281Table 1: Separatrix shifts and separatrix position found for each SOLPS-ITER simulation.inaccurate equilibrium reconstructions does not significantly alter the SOLPS-ITER simulationresults as long as they are corrected. The method of these corrections by shifting the position ofthe separatrix also seems to be valid, as it does not lead to significant differences in simulationresults. The ’p = 2pe’ equilibrium reconstruction using pressure profile from Thomson scatter-ing required the smallest separatrix shifts, so we deem it the most accurate. The ideal separatrixpositions for each simulation, shown in table 1, were found to fall within a few millimeters ofeach other. This suggests that a better position of the separatrix was found using SOLPS-ITER.ConclusionsThe SOLPS-ITER code has been used to compare the different equilibrium reconstructionson the tokamak COMPASS discharge #17692 and to study their effect on the model-experimentmatch. Using inaccurate equilibrium reconstructions was found to minimally affect the SOLPS-ITER simulation results as long as they are corrected. The method of these corrections by shift-ing the separatrix position was found to be valid. A more precise position of the separatrix wasfound, which can be used as a further constraint to improve the equilibrium reconstructions.AcknowledgmentsThis work was supported by the Grant Agency of the Czech Technical University in Prague,grant No. SGS22/175/OHK4/3T/14. The results are obtained with the help of the EIRENEpackage (see www.eirene.de) including the related code, data and tools. [7]References[1] K. Hromasova, et al, 47th EPS Conference, P5.1028 (2021)[2] K. Jirakova et al, Journal of Instrumentation 14, C11020 (2019)[3] O. Kovanda et al, 46th EPS Conference, P4.1032 (2019)[4] M. Hron et al, Nuclear Fusion 62, 042021 (2022)[5] S. Wiesen et al, Journal of Nuclear Materials 463, 480-484 (2015)[6] J. Adamek et al, Nuclear Fusion 57, 116017 (2017)[7] D.Reiter et al, Fusion Science and Technology 47, 172 (2005)50th EPS Conference on Contr. Fusion and Plasma Phys, 8-12 July 2024 D. Svorc et al. : P2.084 (2024)

Validation of tokamak magnetic equilibrium reconstructions using the SOLPS-ITER edge plasma transport code simulations

http://hdl.handle.net/21.11116/0000-0010-3224-D

Validation of tokamak magnetic equilibrium reconstructions using the SOLPS-ITER edge plasma transport code simulations

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