The real-time equilibrium reconstruction code for the ASDEX Upgrade tokamak, JANET [1], is in the process of migration to a Linux based C11++ code. This is motivated by the need for closer integration into the ASDEX Upgrade control system and the long term goal of replacing the currently used function parameterisation based control when upper divertor coils for studying advanced magnetic configurations are installed [2

ASDEX Upgrade Team

Fischer, R.

Fuchs, J. C.

Giannone, L.

McCarthy, Patrick J.

Schuhbeck, K. H.

Sieglin, B.

Treutterer, W.

Irish Universities

Real-time equilibrium reconstruction integration into the ASDEX Upgrade control system

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UCC Library and UCC researchers have made this item openly available.Please let us know how this has helped you. Thanks!Title Real-time equilibrium reconstruction integration into the ASDEXUpgrade control systemAuthor(s) Giannone, L.; Sieglin, B.; Fischer, R.; Fuchs, J. C.; McCarthy, Patrick J.;Schuhbeck, K. H.; Treutterer, W.; ASDEX Upgrade TeamPublication date 2018-07Original citation Giannone, L., Sieglin, B., Fischer, R., Fuchs, J. C., McCarthy, P. J.,Schuhbeck, K. H., Treutterer, W. and the ASDEX Upgrade Team (2018)'Real-time equilibrium reconstruction integration into the ASDEXUpgrade control system', 45th European Physical Society Conference onPlasma Physics Prague, Czech Republic, 2-6 July, P2.1041 (4pp).Type of publication Conference itemLink to publisher'sversionhttp://ocs.ciemat.es/EPS2018PAP/pdf/P2.1041.pdfAccess to the full text of the published version may require asubscription.Rights © 2018, the Authors. This paper is made available under the termsof the Creative Commons Attribution (CC BY) licence, which allowsothers to freely access, use, and share the work, with anacknowledgement of the work's authorship and its initialpresentation at 45th European Physical Society Conference onPlasma Physics (2018).https://creativecommons.org/licenses/by/3.0/Item downloadedfromhttp://hdl.handle.net/10468/7286Downloaded on 2021-11-27T07:10:20ZReal-time equilibrium reconstruction integrationinto the ASDEX Upgrade control systemL.Giannone, B.Sieglin, R.Fischer, J.C.Fuchs, P.J.McCarthy1,K.H.Schuhbeck, W.Treutterer and the ASDEX Upgrade TeamMax Planck Institute for Plasma Physics, EURATOM Association, 85748 Garching, Germany1Department of Physics, University College Cork, Association EURATOM-DCU, Cork, IrelandAbstractThe real-time equilibrium reconstruction code for the ASDEX Upgrade tokamak, JANET[1], is in the process of migration to a Linux based C11++ code. This is motivated by theneed for closer integration into the ASDEX Upgrade control system and the long term goal ofreplacing the currently used function parameterisation based control when upper divertor coilsfor studying advanced magnetic configurations are installed [2].IntroductionReal-time control of a tokamak discharge using cyclic reduction to solve the Grad-Shafranovequation was originally demonstrated on Doublet III-D [3]. A Grad-Shafranov solver for amulticore CPU with improved performance has been reported [4]. This algorithm has beenmodified so that only a single discrete sine transform and inverse discrete sine transform isnecessary [1]. A parallel Grad-Shafranov solver using a graphic processing unit (GPU) for thecontrol system of EAST has also been developed. The P-EFIT code is built with the CUDAarchitecture to take advantage of the large number of parallel GPU cores [5].Data acquisition and control systemThe position and orientation of the magnetic probes and flux loops, the position of thepoloidal field coils and limiters and the surface locations of the 7 rows of ferromagnetic tilesinstalled in 2017 are input from an XML based machine description file. Recently developedanalog integration electronics with 16 bit analog-to-digital converters, record data at a samplefrequency of 20 kHz. The integrator output has a 10 kHz low pass filter. The integration timeconstant is measured before every discharge. A chassis with 16 channels is connected to oneof four ports of a PXIe 7821 digital input/output module. On board memory of 512 megabytesallows the data acquired for 64 channels for a time interval up to 200 s to be stored locally whileproviding real-time data at a reduced sampling frequency to the control system. The recordeddata is transmitted in real-time by an optical bus extender (MXI Express x4) to the comput-ing node with an 8 core Intel Xeon E5-2667 v3 running at 3.2 GHz. Presently 96 magnetic45th EPS Conference on Plasma Physics P2.1041probes and flux loops are connected. This extends the measurement capability to five toroidallyseparated poloidal arrays and two toroidally separated diamagnetic flux loops.The control system runs C++ code on a Linux multicore computer. The cycle time for feed-back control is currently 1 ms. There exists also physical limits to discharge control as the powersupplies for feedback control of vertical plasma position are limited to a 1 kHz bandwidth. Ad-ditionally, the vacuum vessel acts as a low pass filter. Consequently, above 100 Hz the higherfrequency components are attenuated and vertical position control on a fast time scale is limited.A real-time equilibrium reconstruction code that completes the required calculations in a timeless than 0.5 ms will be therefore adequate for discharge control on ASDEX Upgrade.BenchmarksShown in Fig. 1 are the benchmarks of the individual elements of the real-time Grad-Shafranovsolver. The execution time in microseconds for every step of the algorithm is shown in brackets.The matrix-matrix and matrix-vector operations use single threaded Intel Math Kernel Library,MKL, functions.DST2πR µoj(r,z)Tridiag BC1XXAUXBC2+iDSTBC2boundary(12)(18)(20) (15) (19)(13) (1) (92)(108)64x13 proberesponses (156)Probe corrections(PF+Ferromagnetic)LAPACKE_dgelscblas_dgemvcblas_dgemmcblas_dgemv cblas_dgemv cblas_dgemvcblas_dgemm cblas_daxpycblas_dgemv(19)Fit 64 corrected probemeasurements(35)cblas_dgemmPsi(r,z)Tridiag Xcontour13 Basis functionsj[i](r,z)j(r,z)(7)cblas_dgemvFigure 1: Benchmarks of the individual elements of the real-time Grad-Shafranov solver. Shownin brackets is the execution time in microseconds for every step of the algorithm.The matrix-matrix and matrix-vector operations use the single threaded MKL library.On a 65x129 grid, the Grad-Shafranov solver then calculates a flux matrix, ψ(R,Z), that is abest fit to the magnetic probe measurements in 117 µs. The setting up of the 13 basis currentfunctions on the flux matrix from the previous time step requires 108 µs. The calculation of themagnetic probe responses for these basis current functions requires 156 µs. This slowest stepcalculates the 64 magnetic probe responses by using precalculated Green’s functions for everycurrent element on the grid. Therefore a 64×8001 matrix and 8001×13 matrix multiplicationis needed. If necessary, this execution time can be reduced by using a parallel version of thematrix-matrix multiplication. The total time for completion of a single cycle is 388 µs. In theoriginal [3] and this real-time version of the equilibrium reconstruction algorithm, only a singleiteration for a given time step of magnetic probe data is performed. An interpolation routine45th EPS Conference on Plasma Physics P2.1041on 16 grid points is used to find the magnetic axis and the X-points of the divertor magneticconfigurations. The measured currents in each of the poloidal field coils is used rather thanbeing fitted. It is necessary to subtract the poloidal field coil and ferromagnetic tile contributionsto the magnetic probe measurements before they are used to determine the best fit coefficientsof the current basis functions.The benchmark for the GPU based system on EAST is 375 µs on a 129 × 129 grid [5]. Inthis real time version of the equilibrium reconstruction algorithm, a number of iterations for agiven time step of magnetic probe data is performed.ContouringThe contouring algorithm finds the co-ordinates on the lines joining the grid points with thesame value of the flux matrix solution of the Grad-Shafranov equation. Vector sums, vectormultiplications and dot products are performed with MKL functions. Contour integrals at 10normalised radii required for input to the RAPTOR code [6] and at the separatrix to calculatebeta poloidal and plasma inductance from the Shafranov integrals are carried out in 92 µs. Ifnecessary, this execution time can be improved by starting parallel processes for each of the 10contour integrals.Internal diamagnetic fluxThe operation of the external diamagnetic loop in ASDEX Upgrade has a limited bandwidthof operation owing to the low pass filtering effect of the vacuum vessel [7]. The improvementin bandwidth when using internal measurement and compensation loops is the motivation forbringing the internal diamagnetic flux measurement into operation. The internal measurementloop is a single winding in the poloidal direction around the inside of the vacuum vessel. Thecompensation loop is one of two magnetic probes with orientation in the toroidal field direction.There are two sets of measurement and compensation loops separated by 180 degrees in thetoroidal direction. In Fig. 2, the measured diamagnetic flux is compared to that predicted by theTRANSP simulation. The diamagnetic flux measurements are mostly in good agreement withthe values calculated from the real-time and offline magnetic equilibrium reconstruction codes.This measurement will be used as a constraint for real-time equilibrium reconstruction.ConclusionThe first steps towards migrating the equilibrium reconstruction software to Linux C11++code indicate that satisfactory performance with a single CPU core can be achieved.This work has been carried out within the framework of the EUROfusion Consortium and has received fundingfrom the Euratom research and training programme 2014-2018 under grant agreement No 633053. The views andopinions expressed herein do not necessarily reflect those of the European Commission.45th EPS Conference on Plasma Physics P2.1041    0 2 4 6 8 10Time (s)-10-50510F [mWb]              dPhiDiaFluxDIAtDIAf89DIAf87DIAf38DIAf39#34814DFLUXFigure 2: Comparison of diamagnetic flux calculations and measurements. The predicted valuefrom TRANSP (DFLUX), the calculated values from the real-time equilibrium reconstruction(dPhi) and offline equilibrium reconstruction (DiaFlux) and the external (DIAt) and 4 internal(DIAf89,DIAf87,DIAf38,DIAf39) diamagnetic flux measurements are in good agreement.References[1] L. Giannone, M. Reich, M. Maraschek, et al., A data acquisition system for real-time mag-netic equilibrium reconstruction on ASDEX Upgrade and its application to NTM stabiliza-tion experiments, Fusion Eng. Des. 88 (2013) 3299.[2] T. Lunt, H. Zohm, A. Herrmann, et al., Proposal of an alternative upper divertor in ASDEXUpgrade supported by EMC3-EIRENE simulations, Nucl. Mat. and Energy 12 (2017) 1037.[3] J. Ferron, M. Walker, L. Lao, H. E. St. John, D. Humphreys, J. Leuer, Real time equilibriumreconstruction for tokamak discharge control, Nucl. Fusion 38 (1998) 1055.[4] M. Rampp, R. Preuss, R. Fischer, ASDEX Upgrade Team, GPEC, a real-time capable toka-mak equilibrium code., Fusion Sci. Technol. 70 (2016) 1.[5] Y. Huang, B.-J. Xiao, Z.-P. Luo, Q. Yuan, Improvement of GPU parallel real-time equilib-rium reconstruction for plasma control, Fusion Eng. Des. 128 (2018) 82.[6] F. Felici, O. Sauter, S. Coda, et al., Real-time physics-model-based simulation of the currentdensity profile in tokamak plasmas, Nucl. Fusion 51 (2010) 083052.[7] L. Giannone, B. Geiger, R. Bilato, et al., Real-time diamagnetic flux measurements onASDEX Upgrade, Rev. Sci. Instrum. 87 (2016) 0503509.45th EPS Conference on Plasma Physics P2.1041

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Real-time equilibrium reconstruction integration into the ASDEX Upgrade control system

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