The diamagnetic flux is the small difference in toroidal flux with plasma and without plasma. This measurement contains valuable information about the fast-ion confinement since energetic particles can significantly contribute to the plasma pressure and modify the diamagnetic flux. The diamagnetic flux diagnostic at ASDEX Upgrade [1] can therefore be used to investigate fast-ion transport in advanced scenario and resonant magnetic perturbation (RMPs) discharges

ASDEX Upgrade Team

Bock, A.

Fischer, R.

Fuchs, J. C.

Geiger, B.

Giannone, L.

Gude, A.

Maraschek, M.

McCarthy, P. J.

MST12 Team

Rittich, D.

Schuhbeck, K. H.

Suttrop, W.

Cork Open Research Archive

UCC Library and UCC researchers have made this item openly available.Please let us know how this has helped you. Thanks!Title Comparing diamagnetic flux measurements and modelling on ASDEXUpgradeAuthor(s) Giannone, L.; Fischer, R.; Geiger, B.; Rittich, D.; Bock, A.; Fuchs, J. C.;Gude, A.; Maraschek, M.; McCarthy, P. J.; Suttrop, W.; Schuhbeck, K.H.; ASDEX Upgrade Team; MST12 TeamPublication date 2017-11-30Original citation Giannone, L., Fischer, R., Geiger, B., Rittich, D., Bock, A., Fuchs, J. C.;Gude, A., Maraschek, M., McCarthy, P. J., Suttrop, W., Schuhbeck, K.H. and the ASDEX Upgrade and MST12 Teams (2017) 'Comparingdiamagnetic flux measurements and modelling on ASDEX Upgrade',44th European Physical Society Conference on Plasma Physics, Belfast,Northern Ireland, 26 - 30 June, P5.133 (4pp). Available at:http://ocs.ciemat.es/EPS2017PAP/pdf/P5.133.pdf (Accessed: 25 August2021)Type of publication Conference itemRights © 2017, the Authors. Published by the European Physical SocietyItem downloadedfromhttp://hdl.handle.net/10468/11785Downloaded on 2021-11-27T15:52:08ZComparing diamagnetic flux measurementsand modelling on ASDEX UpgradeL.Giannone, R.Fischer, B.Geiger, D.Rittich, A.Bock, J.C.Fuchs, A.Gude, M.Maraschek,P.J.McCarthy1, W.Suttrop, K.H.Schuhbeck and the ASDEX Upgrade and MST12 TeamsMax Planck Institute for Plasma Physics, EURATOM Association, 85748 Garching, Germany1Department of Physics, University College Cork, Association EURATOM-DCU, Cork, Ireland2see author list of H. Meyer et al, Nuclear Fusion FEC 2016 Special Issue (2017)AbstractThe diamagnetic flux is the small difference in toroidal flux with plasma and without plasma.This measurement contains valuable information about the fast-ion confinement since energeticparticles can significantly contribute to the plasma pressure and modify the diamagnetic flux.The diamagnetic flux diagnostic at ASDEX Upgrade [1] can therefore be used to investigatefast-ion transport in advanced scenario and resonant magnetic perturbation (RMPs) discharges.IntroductionA detailed understanding of fast ion transport is needed to guarantee the performance andsafety of a future fusion reactor as the generated fast helium ions are responsible for plasmaheating and can damage the first wall. In addition, the positive current carried by fast ionsfrom neutral beam injection (NBI) can be used in future tokamak reactors to ensure steady-stateoperation. A clear modification of the fast ion radial profiles was observed when switching fromon-axis to off-axis sources in neutral beam current drive experiments on ASDEX Upgrade [2].When operating RMP coils on MAST, an increase in fast ion losses was inferred from the sharpdrop in neutron rates and fast ion Dα (FIDA) light emission [3].The demonstration of steady-state advanced scenario plasmas, where the plasma current willbe sustained by electron cyclotron and neutral beam current drive, is the goal of a number ofsupporting experiments on ASDEX Upgrade for ITER [4]. These discharges feature a varietyof MHD modes that could degrade plasma confinement by the redistribution of fast ions.The measured and predicted diamagnetic flux will be compared in discharges with on-axisand off-axis neutral beam heating with an applied n=2 perturbation generated by the RMPcoils and in advanced scenario discharges on ASDEX Upgrade. The transport code, TRANSP[5], and equilibrium reconstruction code, IDE [6], are used to calculate an expected value of thediamagnetic flux using measured plasma pressure profiles and simulations of fast ion populationcontributions without constraints on the measured diamagnetic flux.44th EPS Conference on Plasma Physics P5.133Fast ion redistribution discharges          IBl1 IBl5     RMP coil current  (1kA) Ipa                               PNIPECRH PradPICRHcore edgediaflfitDiat DFLUX0.00.61.2I p( MA )048P( MW )048ne( 1019 m-3 )-0.0080.0000.008F( Wb )#34227  0 2 4 6 8 10Time (s)off offonFigure 1: Comparison of measured and modelled diamagnetic flux in a discharge where off-axis neutral beam heating is replaced by on-axis heating between 4 s and 6 s. The measureddiamagnetic flux, Diat (green) and the predicted values from TRANSP (orange) and IDE (ma-genta) are shown. In the phase without RMP’s up to 2 s, a small difference in the measured andpredicted value of diamagnetic flux is observed. This difference is significantly enhanced duringthe off-axis NBI phase in the time interval from 2 s to 4 s when RMP coil currents are applied.In Fig. 1, the measured diamagnetic flux and the predictions by TRANSP and IDE are plottedfor a discharge where the off-axis NBI is replaced by on-axis NBI between 4 s and 6 s. In thephase of off-axis NBI heating without RMP’s up to 2 s, there is only a small difference betweenthe measured and predicted values of diamagnetic flux. However, with the application of RMPsafter 2 s, this difference is significantly enhanced to a value of 1.5 mWb. This suggests that theradial fast-ion density profile is flattened by RMP induced fast-ion losses and the reduction inplasma pressure leads to an increase in the diamagnetic flux.The observed difference between measured and predicted flux is smaller in the on-axis NBIheating phase. This is expected since the more core-localised on-axis fast-ion populations areless prone to radial transport by the edge-localised error fields from the RMPs. This smalldifference is not present in a similar discharge without RMP coil current and therefore is thoughtto be a perturbation due to the RMP coils.The direct impact of RMPs on the diamagnetic loop measurement has been addressed in44th EPS Conference on Plasma Physics P5.133vacuum discharges with RMP coil excitation in an n=1 and n=2 configuration. The maximumimpact on the diamagnetic flux measurement is only 0.3 mWb. This perturbation is generated bythe toroidal component of the magnetic field produced by the poloidal sections of the RMP coilwindings. However, 0.3 mWb cannot explain the observed difference between the measurementand simulations in the presented experiment with off-axis NBI.Advanced scenariooffon        0.00.81.6I p( MA )        01020P( MW )        048n e( 1019 m-3 )    0 2 4 6 8Time (s)-0.020.000.02F( Wb )#33134Wmhd Wmhd WdiaCurrentPNIPradPECRHcore edgeDiat   dPhi diaflfit   DFLUX  W( MJ )Figure 2: Comparison of measured and modelled diamagnetic flux in an advanced scenariodischarge. The time dependence of applied on-axis and off-axis NBI heating is shown. Themeasured diamagnetic flux, Diat (green) and predicted values from values calculated from thereal-time, dPhi (blue) and IDE (magenta) magnetic equilibrium codes are in good agreement.The diamagnetic flux predicted by TRANSP (orange) differs from the measured value from 4.6 sto 7 s with the addition of a further on-axis beam. The plasma energy calculated from thediamagnetic flux (orange), Wdia, is in good agreement with the values, Wmhd , calculated fromthe real time (blue) and offline (black) equilibrium code.In Fig. 2, the measured diamagnetic flux is compared to that predicted by the TRANSP simu-lation for an advanced scenario discharge. Also plotted are the calculated values of diamagneticflux by IDE and the real-time equilibrium code, JANET. The steady state phase of this dischargehas an estimated value of 1.5 for the central safety factor produced by 2 MW electron cyclotroncurrent drive. The measured and predicted values of diamagnetic flux are in good agreementuntil 4.6 s. The first two NBI sources used have on-axis deposition and the final two sources44th EPS Conference on Plasma Physics P5.133have off-axis deposition, while the final NBI source switched on at 4.6 s has on-axis deposition.The FIDA measurements show a definite redistribution of fast ions in this final phase of thedischarge. Additionally, the IDE equilibrium reconstruction recognises that the plasma pressurecontribution by fast ions needs to be reduced. Relaxing the pressure profile fitting constraintsleads to a better fit of magnetic probe measurements. The predicted diamagnetic flux by IDE andmeasured diamagnetic flux lie closer together than the diamagnetic flux predicted by TRANSP.ConclusionThe measured diamagnetic flux and the predicted values by TRANSP and IDE were found tobe in good agreement for the on-axis NBI heating phase of a discharge with an n=2 perturbationgenerated by RMP coils. Radial transport by the edge-localised error fields from the RMPs havea reduced impact on the core localised fast-ion populations. Total plasma energy reduction dueto fast ion pressure profile modification is suggested as a possible cause of the discrepancy of1.5 mWb between the measured and predicted values of diamagnetic flux when applying theRMP coil perturbations to the off-axis NBI heating phase. In advanced scenario discharges,the measured and IDE modelled diamagnetic flux were found to be in good agreement. TheFIDA measurements suggest that the discrepancy of measured diamagnetic flux and TRANSPsimulations in some advanced scenario experiments can possibly be explained in terms of a fastion profile redistribution.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.References[1] L. Giannone, B. Geiger, R. Bilato, et al., Real-time diamagnetic flux measurements onASDEX Upgrade, Rev. Sci. Instrum. 87 (2016) 0503509.[2] B. Geiger, M. Weiland, A. Jacobsen, et al., Fast-ion transport and neutral beam current drivein ASDEX Upgrade., Nucl. Fusion 55 (2015) 083001.[3] K. McClements, R. Akers, W. Boeglin, et al., The effects of resonant magnetic perturbationson fast ion confinement in the Mega Amp Spherical Tokamak, Plasma Phys. Contr. Fusion57 (2015) 075003.[4] A. Bock, E. Fable, R. Fischer, et al., Non-inductive improved H-Mode operation at ASDEXUpgrade, Nucl. Fusion (2017) "to be published".[5] R. Harwryluk, An empirical approach to tokamak transport, in: B. Coppi, G. Leotta,D. Pfirsch, R. Pozzoli, E. Sindoni (Eds.), Physics of plasmas close to thermonuclear condi-tions, Vol. 1, Pergamon Press, Oxford, UK, 1980, p. 19.[6] R. Fischer, A. Bock, M. Dunne, et al., Coupling of the flux diffusion equation with theequilibrium reconstruction at ASDEX Upgrade, Fusion Sci. Technol. 69 (2016) 526.44th EPS Conference on Plasma Physics P5.133

Comparing diamagnetic flux measurements and modelling on ASDEX Upgrade

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Comparing diamagnetic flux measurements and modelling on ASDEX Upgrade

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