TH/3-3: Assessment of Scrape-off Layer Simulations with Drifts against L-mode Experiments in ASDEX Upgrade and JET L. Aho-Mantila 1 , S. Potzel 2 , M. Wischmeier 2 , D. Coster 2 , H.W. Müller 2 , S. Marsen 3 , S. Müller 2 , A. Meigs 4 , M. Stamp 4 , S. Brezinsek 5 , the ASDEX Upgrade Team and the JET Contributors JET-EFDA, Culham Science Centre, Abingdon, OX14 3DB, UK 1 VTT Technical Research Centre of Finland, Espoo, Finland 2 Max-Planck-Institut für Plasmaphysik, Garching, Germany 3 Max-Planck-Institut für Plasmaphysik, Greifswald, Germany 4 CCFE, Culham Science Centre, Abingdon, UK 5 Institut für Energie- und Klimaforschung - Plasmaphysik, FZ Jülich, Germany
Outline • Introduction • Influence of drifts on a density scan in ASDEX Upgrade • Influence of drifts on a N-seeding scan in JET • Underlying physics • Conclusions L. Aho-Mantila 25th IAEA Fusion Energy Conference TH/3-3 2
Outline • Introduction • Influence of drifts on a density scan in ASDEX Upgrade • Influence of drifts on a N-seeding scan in JET • Underlying physics • Conclusions L. Aho-Mantila 25th IAEA Fusion Energy Conference TH/3-3 3
Understanding and predicting divertor exhaust In ITER and DEMO, divertor exhaust involves power dissipation by impurities and detachment SOL � A possible bottleneck for reactors Coupled plasma-neutral simulations required core for predicting power and particle exhaust � plasma fluid / Monte Carlo neutral code packages The codes do not reproduce all present-day X-point experimental observations, predictions uncertain � detachment � divertor asymmetries inner outer divertor divertor L. Aho-Mantila 25th IAEA Fusion Energy Conference TH/3-3 4
The role of drifts in divertor asymmetries Experimental studies suggest that ion divertor asymmetries are sensitive to cross-field drifts e.g. R. Pitts et al, J. Nucl. Mat. 2005 Analytic assessments are not sufficient to verify this, because the ExB drifts are sensitive to temperature and pressure gradients A. Chankin, J. Nucl. Mat. 1997 ion Activation of drift terms in SOL simulations is computationally challenging and not routinely done L. Aho-Mantila 25th IAEA Fusion Energy Conference TH/3-3 5
Drift effects modelled using SOLPS5.0 Example grid for B2.5 : 2D plasma fluid code ASDEX Upgrade Eirene : Monte Carlo neutrals code + multiple impurities ExB and diamagnetic drifts , currents L. Aho-Mantila 25th IAEA Fusion Energy Conference TH/3-3 6
Modelling is validated against L-mode discharges in ASDEX Upgrade and JET Different divertor ASDEX Upgrade JET configurations W • Vertical targets (AUG) Be Be • Horizontal outer target (JET) Different divertor regimes • D fuelling and N seeding Validation of modelled power exhaust and drift effects: • target measurements • volume W W W measurements W R~3m, R~1.7m, a~1.3m a~0.5m B t =2.5T, I p =2.5MA B t =2.5T, I p =1.0MA L. Aho-Mantila 25th IAEA Fusion Energy Conference TH/3-3 7
Outline • Introduction • Influence of drifts on a density scan in ASDEX Upgrade • Influence of drifts on a N-seeding scan in JET • Underlying physics • Conclusions L. Aho-Mantila 25th IAEA Fusion Energy Conference TH/3-3 8
Activation of drifts leads to an asymmetric roll- over of the simulated ion fluxes modelled total ion fluxes high-recycling detached n sep varied high-recycling detached low- recycling � Drift effects most significant in the high-recycling regime (hot SOL – cool divertor) L. Aho-Mantila 25th IAEA Fusion Energy Conference TH/3-3 9
Two regimes considered in detail modelled total ion fluxes high-recycling detached 1. Low density • Strong drift effects in the inner divertor 2. High density high-recycling detached • Atomic physics low- recycling important, weak drift effects at the target 1. 2. L. Aho-Mantila 25th IAEA Fusion Energy Conference TH/3-3 10
Low density: drifts provide a significantly cooler and denser inner divertor Target measurements inner target outer target T T eV e eV SOLPS5.0 e Inner target with drifts measurements SOLPS5.0 indicate without drifts detachment and x Langmuir probes do not confirm the high � || � Either drifts � || � || or particle exhaust 10 24 10 24 high-recycling incorrectly m -2 s- 1 m -2 s- 1 modelled detached L. Aho-Mantila 25th IAEA Fusion Energy Conference TH/3-3 11
Low density: volume measurements confirm the modelled drift effects Volume measurements n e [1e20 1/m 3 ] SOLPS5.0 with drifts X-point probe SOLPS5.0 measurements without drifts confirm higher � || in x Spectroscopy the inner divertor saturates OK Stark broadening confirms the modelled high 6 densities in the 7 . inner divertor . . . . . 1 1 1...5 1,2 L. Aho-Mantila 25th IAEA Fusion Energy Conference TH/3-3 12
High density: small discrepancies in the inner divertor Target measurements Volume measurements n e [1e20m -3 ] inner target SOLPS5.0 � || with drifts SOLPS5.0 10 24 without drifts m -2 s- 1 x Spectroscopy 6 . SOLPS5.0 . . with drifts 1 SOLPS5.0 without drifts x Langmuir probes 1...5 1,2 L. Aho-Mantila 25th IAEA Fusion Energy Conference TH/3-3 13
High density: strong discrepancies in outer divertor conditions with and without drifts Target measurements Volume measurements outer target SOLPS5.0 D � � || with drifts SOLPS5.0 10 24 without drifts m -2 s- 1 x Spectroscopy LOS index SOLPS5.0 7 with drifts . . 7 . SOLPS5.0 1 . without drifts . . x Measured neutral pressure 6 Langmuir probes 1 times higher than modelled L. Aho-Mantila 25th IAEA Fusion Energy Conference TH/3-3 14
Observed discrepancies modelled total ion fluxes The modelling overestimates the inner target peak ion flux by factors 2-3 The modelling underestimates the outer target peak ion flux by a factor of 6 L. Aho-Mantila 25th IAEA Fusion Energy Conference TH/3-3 15
Problematic regimes encountered when the measurements deviate from the simple 2-pt model Measured � tot inner / outer Points towards an important role � � � � vs. 2-pt model of plasma-neutral interaction and atomic processes � Radiation losses � Momentum losses � Volume recombination � (or convection) exp 2-pt � Reasons for the model discrepancies are unclear* � Not likely to be due to drifts S. Potzel et al, Nucl. Fus. 2014 *M. Wischmeier et al, J. Nucl. Mat. 2011 L. Aho-Mantila 25th IAEA Fusion Energy Conference TH/3-3 16
Outline • Introduction • Influence of drifts on a density scan in ASDEX Upgrade • Influence of drifts on a N-seeding scan in JET • Underlying physics • Conclusions L. Aho-Mantila 25th IAEA Fusion Energy Conference TH/3-3 17
Drift effects are large throughout a N-seeding scan at low density modelled total ion fluxes high-recycling n sep fixed detached low- recycling high-recycling detached � N varied L. Aho-Mantila 25th IAEA Fusion Energy Conference TH/3-3 18
2 regimes considered in detail modelled total ion fluxes 1. No seeding high-recycling • Strong drift effects in the detached inner divertor, similar to AUG low- recycling high-recycling detached 2. N-seeding • High-recycling conditions at low density 1. 2. L. Aho-Mantila 25th IAEA Fusion Energy Conference TH/3-3 19
No impurities: drifts yield a cooler and denser inner divertor Target measurements inner target outer target with T T eV e eV drifts e without drifts � || � || Attached inner 10 24 10 24 divertor conditions m -2 s- 1 m -2 s- 1 confirmed by the measurements L. Aho-Mantila 25th IAEA Fusion Energy Conference TH/3-3 20
No impurities: drift effects confirmed by volume measurements Volume measurements with drifts [Ph/sr/m 2 /s] inner divertor outer divertor without drifts D � D � 1e18 1e18 D � D � 1e17 1e20 L. Aho-Mantila 25th IAEA Fusion Energy Conference TH/3-3 21
N seeding: drifts yield higher ion fluxes when 60% of the heating power is radiated Target measurements inner target outer target T T eV Drifts increase � tot at both targets e eV e The peak � || is still underestimated by a factor of 2 with � || � || drifts without 10 24 10 24 drifts m -2 s- 1 m -2 s- 1 L. Aho-Mantila 25th IAEA Fusion Energy Conference TH/3-3 22
Outline • Introduction • Influence of drifts on a density scan in ASDEX Upgrade • Influence of drifts on a N-seeding scan in JET • Underlying physics • Conclusions L. Aho-Mantila 25th IAEA Fusion Energy Conference TH/3-3 23
Low density: asymmetries are caused by E r and currents Heat flux to inner Heat flux to outer 1. Poloidal ExB divertor (15%) divertor (85%) drifts and currents conducted in the SOL transport cond. current E r xB convected power from the inner conv. E r xB conv. divertor to the outer (current) divertor Heat flux through the 2. The ExB drift in the PFR PFR to outer divertor transports particles from the outer cond. current divertor to the inner divertor conv. E r xB Diamagnetic drifts affect the level of divertor heat flux, but not the in-out asymmetry See also: T. Rognlien et al, J. Nucl. Mat. 1997 V. Rozhansky et al, Nucl. Fus. 2012 L. Aho-Mantila 25th IAEA Fusion Energy Conference TH/3-3 24
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