Synthetic H-alpha diagnostics for ITER: inverse problems and error estimations for strong non-Maxwellian effects and intense divertor stray light

1
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
non-Maxwellian effects and intense divertor stray
light
A.B. Kukushkin1,2, V.S. Neverov1, A.G. Alekseev1,
S.W. Lisgo3, A.S. Kukushkin1,2
1National Research Centre "Kurchatov institute",
Moscow, Russia 2National Research Nuclear
University "MEPhI", Moscow, Russia 3ITER
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
2
OUTLINE

• 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
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

4
1.1 Motivation The Measurement-Diagnostic Matrix
5
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)?

• ITER has a metal wall and the divertor will be a
  strong source of visible light

• Plasma from SOLPSOSMEIRENE ? LightTools

6
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(?red rectangle)
S. Kajita, PPCF 2013

• Plasma from SOLPSOSMEIRENE ? LightTools

7
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
  non-Maxwellian distribution, and so advanced
  modelling of the Balmer-alpha spectral line
  shapes is required

• 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.)

8
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.

9
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-of-sight 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

10
1.3. Methods and Data used

1. SOLPS4.3 (B2-EIRENE) predictive modeling of
   background plasma on the flat-top stage of Q10
   inductive operation of ITER
2. 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)
3. model 3 for spectral line shape asymmetry in
   the SOL, caused by the net inward flux of
   relatively fast atoms
4. model 4 for recovering main parameters
   (effective temperatures and their relative
   content) of non-Maxwellian VDF of neutral
   hydrogen atoms in the SOL
5. 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
11
OUTLINE

• 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

12
2.1. Interpretation of direct observation of
divertor
13
Calculating the phantomexperimental spectrum
speed of light
local emissivity (i.e. the power density of the
emitted radiation)
distribution of the number of the atoms in the
projection of the velocity in the distance x
along the viewing chord
Possible layout of the 16 observation tracks
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
14
Three-temperature fitting of the phantom
experimental signals measured on the 16
lines-of-sight that directly observe the divertor
15
2.2. Predictive modeling of the DSL spectral line
shape for a main chamber view
partial contribution of the Zeeman ?-component
to the total DSL line shape (free parameter)
major radius of the point of the maximum
emissivity on the track tr
Parameters marked with the cap, , are the
input parameters found by solving the inverse
problem for divertor.
16
2.3. Interpretation of signals from main chamber
fraction of the DSL in the total signal
partial contribution of the Zeeman ?-component
to the total DSL line shape
partial contribution of the i-th non-Maxwellian
fraction of atoms
subscript p indicates that the parameter can have
different values for the inner and outer sections
of the SOL
17
Fitting the phantom experimental signals for the
Da line for one main chamber emission region
(inner and outer SOL) at a time (no DSL)
18
OUTLINE

• 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

19
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.
20
The accuracy of the recovery of the fraction of
inner SOL light in the total signal (without DSL
included)
Six potential ITER operation scenarios examined
density in the far SOL mode
d low L
e low H
f moderate L
g moderate H
h high L
i high 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.
21
The accuracy of the tritium fraction recovery in
the deuterium-tritium mixture (without DSL).
22
The accuracy of recovering the inner SOL light
fraction of the total SOL light with the DSL
included in the total signal
23
Fitting the phantom experimental signals for the
80 fraction of the DSL and 2 fraction of inner
SOL light in the total signal
24
What if we would be able to simulate the DSL with
a higher accuracy?
 
 
25
OUTLINE

• 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

26
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.
27
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 Ip2 MA, Bt2.8 T, Ne05.8 10(19)
m(-3), Te02.6 keV, Paux(NBI)7.5 MW,
Paux(ICRH)2 MW

• Direct observation of the divertor from top
• Observation of main-chamber inner wall along
  tangential and radial LoS (KSRB Track 11) from
  equatorial ports
• Analysis of HRS data on resolving the power at
  DH Balmer-? spectral lines

1.0 0.8 0.6 0.4 0.2 0
2.0 1.5 1.0 0.5 0

aa

inner SOL
Counts/(s pixel), 10(5)

DSL/Total0.25 OuterSOL/Total0.40 H/(HD)0.038
total divertor
Exp.
Fit
Non-Maxw. fractions within warm and hot
Maxwellians
Temperatures of atomic fractions (their
fraction in total intensity)
outer SOL


0.1 eV (3) 1.5 eV (30) non-Maxw 6 24.9 eV
(7) non-Maxw 7
1.0 eV (20) 6.4 eV (6) non-Maxw 6 276.6 eV
(9)
inner SOL
DSL
outer SOL
DSL
The results support the expectation of a strong
impact of the DSL upon H-alpha (and Visible
Light) Spectroscopy Diagnostic in ITER.
Time, s 5 10 15
20
?, nm 655.9 656.1
656.3 656.5
Fitting of measured spectrum, time 10.05 s.
Asymmetry of Balmer-? spectral line shapes for
inner- and outer-wall SOL is due to
non-Maxwellians (and small admixture of H).
Fractions of inner-wall SOL, outer-wall SOL, and
DSL, in total signal vs. time. Normalized total
power of HD Balmer-? emission in divertor.
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.Lisit
sa, 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
28
OUTLINE

• 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

29
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.

30

• 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
31

• 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.