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Control- oriented SXR simulation on Tore Supra: present status and perspectives

Control- oriented SXR simulation on Tore Supra: present status and perspectives. D. VEZINET, D. MAZON, R. GUIRLET, D. CLAYTON, M. O’MULLANE 7th Workshop on Fusion Data Processing Validation and Analysis March 26‐28, 2012 ENEA Frascati. Didier VEZINET. Tuesday 27th, March 2012.

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Control- oriented SXR simulation on Tore Supra: present status and perspectives

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  1. Control-oriented SXR simulation on Tore Supra: presentstatus and perspectives D. VEZINET, D. MAZON, R. GUIRLET, D. CLAYTON, M. O’MULLANE 7th Workshop onFusion Data Processing Validation and Analysis March 26‐28, 2012 ENEA Frascati Didier VEZINET Tuesday 27th, March 2012

  2. Objective : Give a fast estimation of the total density distribution of each impurity in the plasma Integrated SXR diagnostic Means: SXR diagnostics: (spatial resolution ≈ 5cm) Poloidal tomography : (82 lines of sight, currentlyavailable, absolutelycalibrated) Toroidal pinhole camera: 128 pixels, potentiallyenergy-resolved (prototype underdevelopment, more pixels in near future) Simplified SXR simulation tool (presented here) Didier VEZINET Tuesday 27th, March 2012

  3. State of the art : • Common issues on most Tokamaks regardingimpuritystudies • Somepreliminary observations: • The influence of transport on SXR emissivity and impuritydensity profiles Integrated SXR diagnostic • Atomic data validation / comparison • General framework of a new approach for impuritydensity estimation: • General framework => domain of validity ? • Description of a simplifiedapproach in whichimpurities are known • Example of application : • Ni trace injection on Tore Supra • => testing the domain of validity of the generalframework • Remaining issues and solutions envisaged: • Severalimpurities => identification and density estimation using the GEM ? • Conclusion ans perspectives Didier VEZINET Tuesday 27th, March 2012

  4. State of the art of some issues on most tokamaks: • SXR data isintegratedspectrally(but isusuallyspatiallylocalizedthanks to tomographic reconstructions) Integrated SXR diagnostic • Spectrospic measurements are integrated spatially (but have good spectral resolution) • Transport coefficients for simulations have to be fitted using minimisation algorithms that cannot always guarantee the solution is not a local minimum Didier VEZINET Tuesday 27th, March 2012

  5. Some observations: In some configurations, transport may not play a very important roleas far the total impurity density and the total emissivity profiles are concerned… Integrated SXR diagnostic Courtesy of Daniel Clayton* Simulation run on STRAHL, with CHIANTI atomic data, stationary state after Fe injection and no exchange at the boundary * D. Clayton, Johns Hopkins University, Baltimore, MD, USA Didier VEZINET Tuesday 27th, March 2012

  6. Some observations: In some configurations, transport may not play a very important roleas far the total impurity density and the total emissivity profiles are concerned… Integrated SXR diagnostic Courtesy of Martin O’Mullane* ITER-like Simulation run on SANCO, with ADAS atomic data, stationary state with Ni constant influx and a recycling coefficient, with flat ne profile Slide 13/22 of CDR, ITER, 21st, February 2012 * M. O’Mullane, University of Strathclyde, Glasgow UK Didier VEZINET Tuesday 27th, March 2012

  7. General Framework of a new appraoch: These are preliminary but encouraging results ! Integrated SXR diagnostic Further studies are needed, with experimental data and realistic simulations, to get a more accurate idea of the overall influence of transport on the total density and emissivity profiles. In the yet-to-be-determined domain of validity of this assumption (transport only has limited influence), a simplified approach, without transport (D = 0, V = 0) can be developped to get an estimation of the total density profile. The ideais not to assume thatthereis no transport ! But to assume that transport only has a limited impact on the total density and emissivity (in some cases)! Didier VEZINET Tuesday 27th, March 2012

  8. Data verification : atomic data Fractional abundances vs Te for typical Tokamak ne (D = 0, V = 0) Cumulated absolute differences for Fe Integrated SXR diagnostic Region of best agreement Region of worst agreement Interval of interest for SXR in Tokamaks ADAS = atomic database for plasmas in general (with some work done on W) CHIANTI = atomic database for astrophysics (spectral analysis) Didier VEZINET Tuesday 27th, March 2012

  9. Simplifiedapproach (impurities are known): ADASallows for simple computation of the radiated SXR, all the complexity of atomicphysiciscontained in the coefficients: Integrated SXR diagnostic Te and ne are locallymeasured (ECE and reflectometry for example) D and V are set to zero in oursimplifiedapproach If we assume a pure hydrogenic plasma withonly one knownimpurity: Quasi-neutrality of the plasma => Didier VEZINET Tuesday 27th, March 2012

  10. Simplifiedapproach (impurities are known): ADAS allows for simple computation of the radiated SXR, all the complexity of atomic physic is contained in the coefficients : Integrated SXR diagnostic Requires an absolutely calibrated SXR tomography diagnostic ! (done on TS) (*) Case of trace impurity injection : * the background emissivitycanbesubtracted * the assumptionthatthereisonly one speciesbecomesvalid Didier VEZINET Tuesday 27th, March 2012

  11. Simplifiedapproach (impurities are known): Application: Ni trace injection in Tore Supra (TS # 40801) Integrated SXR diagnostic Impurity transport studied in detail (*) • D and V assumed to be stationary, equal for all ionisation stages • D and V profiles were found iteratively (genetic algorithm) to best fit experimental data (assuming poloidal symetry). • Experimental inputs : Te (ECE) & ne (reflectometry) • Experimental constraints : SXR (line-integrated, relative constraint), Prad (bolometry, absolute constraint), spectroscopy, ... Solution found for (D,V) (*) D. Villegas, R. Guirlet et al., Physical Review Letters, vol. 105, no. 3, Jul. 2010. Didier VEZINET Tuesday 27th, March 2012

  12. Simplifiedapproach (impurities are known): Application: Ni trace injection Normalisedbrightness Integrated SXR diagnostic Sameorder of magnitude (ratio 2,5) Similar total density profile (shape) Normalisederror estimation (nNi) General framework: more relevant some time after the injection (estimatederrordecreaseswith t) Simplifiedapproach Simulation / 2,5 (calibration bolometry ≠ SXR) Measurements Simplifiedapproach (D,V) = (0,0) Simulation / 2,5 Scattering= uncertainty of the tomographic reconstruction (*) D. Villegas, R. Guirlet et al., Physical Review Letters, vol. 105, no. 3, Jul. 2010. Didier VEZINET Tuesday 27th, March 2012

  13. Simplifiedapproach (impurities are known): Application: Ni trace injection (*) Integrated SXR diagnostic (*) With poloidal symetry assumption In thissimplified case, a SXR tomographic reconstruction yieldsa poloidal mapping of the total density of the impurityconsidered (*) D. Villegas et al., Physical Review Letters, vol. 105, no. 3, Jul. 2010. Didier VEZINET Tuesday 27th, March 2012

  14. Remaining issues to beadressed Integrated SXR diagnostic Limits of the simplifiedapproach : • (Domain of validity has bedetermined) • Withn impurities: If severalimpurities have to beconsidered, they have to beidentified (VUV spectroscopy, ...) 1 equation n unknowns Can besolvedwith a means of determiningadditionalconstrains / equations(ratio betweeneachimpurity…) GEM ? Didier VEZINET Tuesday 27th, March 2012

  15. Solution envisaged : The GEM-basedpinhole camera A pinhole SXR camera with 128 pixels viewing the plasma in a toroidal direction. Integrated SXR diagnostic Advantages: Toroidal view => additionalgeometricalconstraint: bettertomographic inversion => Prospective 3D tomographic inversions => Object of significantresearch efforts in Europe: evolutions to come (more pixels, …) • Energy resolution • => electronic discrimination threshold (only 1 on our prototype) • => Impurity identification ? Didier VEZINET Tuesday 27th, March 2012

  16. Solution envisaged : The GEM-basedpinhole camera Use GEM’s energy resolution to identify impurities, by concentrating on expected line emissions, in each pixel of the tomographic inversion Integrated SXR diagnostic On every expected line : I No assumption on transport ! Ifb SXR lines in a plasma with Fe, Ni, Cu and W Ni = 4 % W = 8 % Requires sufficient energy resolution* and absolute calibration * Depends on plasma composition < 10 % would be a good compromise ≈ 15 % for today’s prototype => evolutions to come E (eV) Expected line 2 Expected line 1 Didier VEZINET Tuesday 27th, March 2012

  17. Conclusion and perspectives The domain of validity of the assumptionthattransport has little influence on the total SXR emissivity and on the total impuritydensitystill has to beinvestigated. Preliminary but encouragingresults have been obtained. ADAS waschosen as the referencedatabase for atomic data Additional information isnecessarywhenseveralimpuritiesare present, the GEM’senergyresolutioncouldbe an answer (+ VUV spectroscopy ?). The GEM’senergyresolutionmay have to berefined. The GEM isevolutive: finer spatial and temporal resolutionisachievable. The simultaneous use of GEM + DTOMOX willalloweither for finertomographic reconstructions (withknowledge of the toroidal symetry) or for prospective 3D reconstructions. Integrated SXR diagnostic Didier VEZINET Tuesday 27th, March 2012

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