1st IAEA Technical Meeting on Fusion Data Processing, Validation and Analysis 1st of June - 3rd of June 2015, Nice, France. Synthetic H-alpha diagnostics for ITER: inverse problems and error estimations for strong nonMaxwellian effects and intense divertor stray light A.B. Kukushkin1,2, V.S. Neverov1, A.G. Alekseev1, S.W. Lisgo3, A.S. Kukushkin1,2 3ITER 1National Research Centre "Kurchatov institute", Moscow, Russia 2National Research Nuclear University "MEPhI", Moscow, Russia Organization, Route de Vinon sur Verdon, St Paul Lez Durance, France The views and opinions expressed herein do not necessarily reflect those of the ITER Organization OUTLINE 1. Introduction 1.1 Motivation 1.2 Goals 1.3 Methods used 2. Inverse problems and their solutions 2.1 Interpretation of direct observation of divertor 2.2 Predictive modeling of the divertor stray light (DSL) spectral line shape 2.3 Interpretation of signals from main chamber with allowance for the DSL 3. Analysis of measurement errors 4. Validation Against Data from JET-ILW 5. Plans, Conclusions 1.1 Motivation – The Role of Diagnostics on ITER Measurement Role Diagnostic Function 1a1 Machine protection (MP) 1a2 Machine control (MC) 1b Advanced scenario plasma control 2 Measurements required for evaluation and physics (PHY) • ITER is unable to operate without a working diagnostic for every group 1a measurement • For advanced operation, there must be a working diagnostic for every group 1b measurement • The machine may operate without group 2 diagnostics in operation Diagnostic assignments: • primary: the diagnostic is well suited to the measurement • back-up: provides similar data to the primary, but with some limitations • supplementary: can validate and/or calibrate the measurement, but cannot make the measurement by itself 1.1 Motivation – The Measurement-Diagnostic Matrix LIST OF RELATED DIAGNOSTICS REQUIRED MEASUREMENTS 1.1 Motivation – The problem of reflections ITER has a metal wall and the divertor will be a strong source of visible light Will the main chamber Ha diagnostic be able to make the required measurements in the presence of divertor stray light (DSL)? NO REFLECTIONS 50% REFLECTIVITY (25% SPECULAR, 25% DIFFUSE) [S. Kajita, 2013 PSI] Plasma from SOLPS+OSM+EIRENE LightTools 1.1 Motivation – The problem of reflections ITER has a metal wall and the divertor will be a strong source of visible light Will the main chamber Ha diagnostic be able to make the required measurements in the presence of divertor stray light (DSL)? LINE-OF-SIGHT INTEGRALS NO REFLECTIONS (red rectangle) [S. Kajita, 2013 PSI] Plasma from SOLPS+OSM+EIRENE LightTools [S. Kajita, PPCF 2013] 1.1 Motivation – Non-Maxwellian atom velocity distributions In addition to the DSL issue, the velocity distribution function (VDF) of neutral hydrogen atoms in the SOL is expected to have a nonMaxwellian distribution, and so advanced modelling of the Balmeralpha spectral line shapes is required ATOM TRAJECTORIES FROM MAIN CHAMBER RECYCLING, AS CALCULATED BY THE EIRENE KINETIC CODE velocity distribution functions along specified linesof-sight are recorded during the code run Can line shape analysis be used to identify the SOL and DSL contributions to the signal for a viewing chord in the main chamber, including the separation of HFS and LFS contributions to SOL emission? (In addition to the D/T ratio.) 1.1 Motivation – Development of solution methods Accuracy of algorithms for processing the data and recovering the parameters needed for ITER operation can only be estimated in the framework of the synthetic diagnostics. Such diagnostics provide so-called “phantom” experimental data by using the results of predictive numerical simulations of the main plasma parameters. The synthetic diagnostics makes it possible to directly compare the “true” values of the desired quantities with their known values in the “phantom” data. 1.2 Goal Estimate the measurement errors of the parameters needed for fusion machine operation with allowance for: strong DSL on the lines-of-sight in the main chamber, substantial deviation of the neutral atom VDF from a Maxwellian in the SOL, data from the direct observation of the divertor. 1.2. Goal At this stage in the model development process, inverse problems are being solved for recovering: • spatial distributions of the isotope ratio and temperature for the neutral hydrogen in the divertor; • spectral line shape of the DSL; • relative contributions of all three sources in the signal for a line-ofsight in the main chamber (namely, from inner and outer sections of the SOL on the line of sight, and from the DSL); • isotope ratios in the SOL. Algorithms for targeting the final goals of the ITER Main Chamber Ha diagnostic are in development 1.3. Methods and Data used a. SOLPS4.3 (B2-EIRENE) predictive modeling of background plasma on the flat-top stage of Q=10 inductive operation of ITER; b. EIRENE stand-alone calculations of neutral deuterium VDF on the SOLPS4.3 background (similarly to [1] but with allowance for poloidally resolved recycling from the first wall [2]); c. model [3] for spectral line shape asymmetry in the SOL, caused by the net inward flux of relatively fast atoms; d. model [4] for recovering main parameters (effective temperatures and their relative content) of non-Maxwellian VDF of neutral hydrogen atoms in the SOL; e. model [5] for the spectral line shape of the DSL. [1] V.S. Lisitsa, M.B. Kadomtsev, V. Kotov, V. S. Neverov, V. A. Shurygin. Atoms 2, 195 (2014) [2] S.W. Lisgo, et al., J. Nucl. Mater. 415, 965 (2011) [3] A.B. Kukushkin, V.S. Neverov, et al., J. Phys.: Conf. Series 548 (2014) 012012 [4] V. S. Neverov, et al., Plasma Phys. Rep., 41, 103 (2015) [5] A.B. Kukushkin, et al. Proc. 24th IAEA FEC, San Diego, USA, 2012, ITR/P5-44 OUTLINE 1. Introduction 1.1 Motivation 1.2 Goals 1.3 Methods used 2. Inverse problems and their solutions 2.1 Interpretation of direct observation of divertor 2.2 Predictive modeling of the divertor stray light (DSL) spectral line shape 2.3 Interpretation of signals from main chamber with allowance for the DSL 3. Analysis of measurement errors 4. Validation Against Data from JET-ILW 5. Plans, Conclusions 2.1. Interpretation of direct observation of divertor total number of spectral channels (pixels) normalized line shape of measured spectrum total number of observation tracks partial contribution of the i–th fraction of atoms partial contribution of a certain hydrogen isotope temperature of the i-th fraction of atoms Unknowns are labeled in red wavelength of the Balmer-alpha line center partial contribution of the Zeeman pi-component to the total spectrum Zeeman splitting Gaussian function isotope mass in eV Calculating the phantom speed of light experimental spectrum: local emissivity (i.e. the power density of the emitted radiation) Possible layout of the 16 observation tracks distribution of the number of the atoms in the projection of the velocity in the distance x along the viewing chord Parameters marked with a tilde “~”, are averaged over the solid angle of of the observation cone associated with x. 2D distribution of the Balmer-alpha emissivity* in the SOL and divertor in ITER, in logarithmic scale. * SOLPS 4.3 (B2-EIRENE) simulation Three-temperature fitting of the phantom experimental signals measured on the 16 lines-of-sight that directly observe the divertor 2.2. Predictive modeling of the DSL spectral line shape for a main chamber view partial contribution major radius of the point of the maximum of the Zeeman emissivity on the track tr -component to the total DSL line shape (free parameter) Parameters marked with the cap, “^”, are the input parameters found by solving the inverse problem for divertor. Comparison of the DSL spectra calculated by a semi-analytic model1 (black) and equation defined above (blue) 1A.B. Kukushkin, et al. Proc. 24th IAEA Fusion Energy Conf., San Diego, USA, 2012, ITR/P5-44. 2.3. Interpretation of signals from main chamber partial contribution of the i-th non-Maxwellian fraction of atoms fraction of the DSL in the total signal normalized line shape, which describes the signal from the non-Maxwellian fractions of atoms partial contribution of the Zeeman -component to the total DSL line shape subscript p indicates that the parameter can have different values for the inner and outer sections of the SOL characteristic wavelength shift, which describes the attenuation of the inward flux Only new parameters are labeled Heaviside function Fitting the phantom experimental signals for the Da line for one main chamber emission region (inner and outer SOL) at a time (no DSL) Inner section of the SOL Outer section of the SOL Spectral resolution is 0.005 nm low density in the far SOL in the L-mode high density in the far SOL in the H-mode Observation track along major radius from equatorial port plug, Z = 0.623 m “Non-Maxw” indicates the non-Maxwellian fraction of the VDF OUTLINE 1. Introduction 1.1 Motivation 1.2 Goals 1.3 Methods used 2. Inverse problems and their solutions 2.1 Interpretation of direct observation of divertor 2.2 Predictive modeling of the divertor stray light (DSL) spectral line shape 2.3 Interpretation of signals from main chamber with allowance for the DSL 3. Analysis of measurement errors 4. Validation Against Data from JET-ILW 5. Plans, Conclusions 3. Analysis of measurement errors Signal contains the light from the both sections of the SOL but not the DSL Different input (i.e. phantom experimental) values of the fraction of inner SOL light in the signal. Phantom inner and outer SOL light spectra are show in dashed lines, while the recovered spectra are shown in solid lines. The accuracy of the recovery of the fraction of inner SOL light in the total signal (without DSL included) Comparison with the “true“, phantom experimental values Six potential ITER operation scenarios examined: density in the far SOL d e f g h i low moderate high mode L H L H L H The recovered value, averaged over six scenarios, is shown in gray curve. Without the DSL, the absolute value of the error in estimating the fraction of the inner SOL light in the total signal does not exceed 0.2. The accuracy of the tritium fraction recovery in the deuterium-tritium mixture (without DSL). The error increases with the increasing fraction of the inner SOL light. However, the error can reach 100% even without any light from the inner SOL. One cannot recover the isotope ratio in D+T mixture by solving the inverse problem in its current formulation. But for D+H mixture everything is OK. The accuracy of recovering the inner SOL light fraction of the total SOL light with the DSL included in the total signal DSL fraction: 20% DSL fraction: 40% DSL fraction: 60% DSL fraction: 80% Fitting the phantom experimental signals for the 80% fraction of the DSL and 2% fraction of inner SOL light in the total signal Legends and titles show the fraction of the inner SOL light in the total SOL light (not in the total signal). The solver of the inverse problem becomes confused when distinguishing the contributions of the DSL and the inner SOL. This is caused by the difference between the phantom DSL spectrum recovered from direct observation of the divertor and the shape from the semi-analytic formula for the DSL (used here) What if we would be able to simulate the DSL with a higher accuracy? Substitution of the semi-analytic spectrum1 at all stages of the (𝐷𝑆𝐿) analysis, including for the phantom data (and keeping the 𝐶𝜋 a free parameter), provides much better accuracy. DSL fraction: 60% DSL fraction: 80% With increasing accuracy of the DSL, it is possible to recover the inner and outer SOL contributions with high accuracy, even for an (𝐷𝑆𝐿) unknown fraction of the Zeeman pi-component, 𝐶𝜋 , and even for the DSL fraction as high as 80%. OUTLINE 1. Introduction 1.1 Motivation 1.2 Goals 1.3 Methods used 2. Inverse problems and their solutions 2.1 Interpretation of direct observation of divertor 2.2 Predictive modeling of the divertor stray light (DSL) spectral line shape 2.3 Interpretation of signals from main chamber with allowance for the DSL 3. Analysis of measurement errors 4. Validation Against Data from JET-ILW 5. Plans, Conclusions 4. Validation Against Data from JET-ILW Theoretical model [1], suggested for the ITER H-alpha (and Visible Light) Diagnostics, was extended and applied [2, 3] for the interpretation of the data from the JET ITER-like wall (ILW) experiments. The results [2, 3] confirmed the importance of non-Maxwellian effects for interpreting the Balmer-alpha emission from the far SOL and suggested the necessity, for the presence of a strong DSL signal, to incorporate data from direct observation of the divertor (the latter is done in Sections 2-3 of the present report). [1] A.B. Kukushkin, et al. Proc. 24th IAEA Fusion Energy Conf., San Diego, USA, 2012, ITR/P5-44. [2] A. B. Kukushkin, et al. AIP Conference Proceedings 1612, 97 (2014). [3] A. B. Kukushkin, et.al. Proc. 25th IAEA Fusion Energy Conf., St. Petersburg, 2014, EX/P5-20. Theoretical Model of ITER High Resolution H-alpha Spectroscopy for a Strong Divertor Stray Light and Validation Against JET-ILW Experiments A multi-parametric inverse problem with allowance for (i) a strong divertor stray light (DSL) on the main-chamber lines-of-sight (LoS), (ii) substantial deviation of neutral atom velocity distribution function from a Maxwellian in the SOL (a model for line shape asymmetry), (iii) data for direct observation of divertor. JPN 85844: Ip=2 MA, Bt=2.8 T, Ne0=5.8 10(19) m(-3), Te0=2.6 keV, Paux(NBI)=7.5 MW, Paux(ICRH)=2 MW • Direct observation of 1.0 aa Counts/(s pixel), DSL/Total=0.25 inner Exp. the divertor from top total 2.0 10(5) SOL OuterSOL/Total=0.40 • Observation of maindivertor 0.8 Fit H/(H+D)=0.038 chamber inner wall Non-Maxw. along tangential and 1.5 Temperatures of fractions within atomic fractions radial LoS (KSRB 0.6 outer warm and hot (their fraction Track 11) from SOL Maxwellians in total intensity) equatorial ports 1.0 1.0 eV (20%) 0.1 eV (3%) 0.4 • Analysis of HRS data 1.5 eV (30%) 6.4 eV (6%) on resolving the power non-Maxw: 6% non-Maxw: 6% 24.9 eV (7%) at D+H Balmer-a 0.5 276.6 eV (9%) 0.2 non-Maxw: 7% spectral lines inner DSL outer SOL SOL DSL The results support the 0 0 expectation of a strong Time, s 5 10 15 20 , nm 655.9 656.1 656.3 656.5 impact of the DSL upon Fitting of measured spectrum, time 10.05 s. Fractions of inner-wall SOL, outer-wall H-alpha (and Visible Asymmetry of Balmer-a spectral line shapes for SOL, and DSL, in total signal vs. time. Light) Spectroscopy inner- and outer-wall SOL is due to Normalized total power of Diagnostic in ITER. H+D Balmer-a emission in divertor. non-Maxwellians (and small admixture of H). A.B.Kukushkin, V.S.Neverov, M.F.Stamp, A.G.Alekseev, S.Brezinsek, A.V.Gorshkov, M.vonHellermann, M.B.Kadomtsev, V.Kotov, A.S.Kukushkin, M.G.Levashova, S.W.Lisgo, V.S.Lisitsa, V.A.Shurygin, E.Veshchev, D.K.Vukolov, K.Yu.Vukolov, and JET Contributors A.B. Kukushkin 1 (1) 25th IAEA-FEC 2014, St. Petersburg, Russia, EX/P5-20 16/10/2014 OUTLINE 1. Introduction 1.1 Motivation 1.2 Goals 1.3 Methods used 2. Inverse problems and their solutions 2.1 Interpretation of direct observation of divertor 2.2 Predictive modeling of the divertor stray light (DSL) spectral line shape 2.3 Interpretation of signals from main chamber with allowance for the DSL 3. Analysis of measurement errors 4. Validation Against Data from JET-ILW 5. Plans, Conclusions 5. Plans, Conclusions The inverse problems are formulated for recovering the parameters of neutral hydrogen in fusion reactors with allowance for high background radiation (“divertor stray light”, DSL) and strong non-Maxwellian effects in the velocity distribution function (VDF) of neutral atoms. Error assessment for the line-of-sight along the major radius from the equatorial port-plug in ITER shows that further extension of the developed approach is needed. The recovery of these parameters requires the solution of additional inverse problems, which should: • incorporate the results of solving the inverse problems formulated in the present paper, • use the data on the background plasma (density, temperature) in the SOL from other diagnostics in ITER, • use available semi-analytic models for kinetics of atomic/molecular flux from the wall (e.g., Ballistic Model [1]), • use the bifurcated-line-of-sight measurements scheme [2], namely, targeting at an optical dump and very close to it. [1] M. B. Kadomtsev, V. Kotov, V. S. Lisitsa, and V. A. Shurygin, in Proc. 39th EPS Conf. Plasma Phys., Stokholm, 2012, ECA 36F, P4.093 (2012) [2] A.B. Kukushkin, et al. Proc. 24th IAEA Fusion Energy Conf., San Diego, USA, 2012, ITR/P5-44 Acknowledgements The authors are grateful to • V.S. Lisitsa, K.Yu. Vukolov, A.V. Gorshkov, M.B. Kadomtsev, M.G. Levashova, V.A. Shurygin, D.K. Vukolov (NRC “Kurchatov Institute”), • V. Kotov (FZ Juelich), • E. Veshchev (ITER Organization), • M.F. Stamp, S. Brezinsek, M. von Hellermann (JET-Eurofusion), for their collaboration in studies on the ITER H-alpha (and Visible Light) Spectroscopy.