Spectral characteristics and spectra simulations
for high-resolution X-Ray diagnostic at JET
Presented by Jacek Rzadkiewicz
Jacek Rzadkiewicz
ADAS workshop
Warsaw, 29-30.09.2014
Outline
 Introduction
 Spectral characteristics of KX1 diagnostic at JET
- Crystal bending
- X-ray energy (wavelength) bandwidth
- Integrated reflectivities
 Spectra simulations at the x-ray energy range of KX1 diagnostic at JET.
Jacek Rzadkiewicz
ADAS workshop
Warsaw, 29-30.09.2014
Spectral measurements
The high-resolution X-ray crystal
spectrometer (KX1) is set to measure
X-ray spectra in two diagnostic channels
dedicated for Ni and W emission.
The KX1 measurements are based on the
 Ni+26 resonance line at 7.806 keV
 W46+ line at 2.387 keV
 and continuum radiation.
From the KX1 measurements one can obtain:
 impurity concentrations (Ni and W)
 ion temperature
The entire spectral range of the KX1
spectrometer for two diagnostic channels
 and toroidal rotation velocity
for central JET plasmas.
Jacek Rzadkiewicz
ADAS workshop
Warsaw, 29-30.09.2014
KX1 beam line
 The spectrometer is operated in
Johann geometry with the Rowland
circle radius of about 12.5 m giving an
extremely high energy resolution.
Horizontal cross-section of the x-ray crystal
spectrometer (KX1) on JET
 The X-ray photons emitted by plasma
are reflected by crystals and register in
two diagnostic channels (divided in the
vertical direction by a septum) by T-GEM
detectors with energy and spatial
resolution.
‘W’ channel
‘Ni’ channel
T-GEM detectors mounted on KX1 diagnostics
Jacek Rzadkiewicz
ADAS workshop
Warsaw, 29-30.09.2014
T-GEM detectors
• The T-GEM detectors with a detection area of
206x92 mm2 are energy and position sensitive
• The detector readout plane consists of 256 strips of
96mm length with 0.8 mm pitch
• Detection efficiencies above 40% and around 20%
for Ni and W monitor X-ray detectors have been
achieved by use of 12 mm (Ni monitor) and 5 mm (W
monitor) mylar windows
Structure of the T-GEM X-ray detector for JET diagnostics
•The detector position resolution has been found to
be to not worse than 1 strip width (0.8 mm).
Charge position distribution for X-ray source (X-ray tube 2.5 kV,
100 mA) with a 0.7mm diameter collimator
Photon detection efficiencies as a function of photon energy
Rzadkiewicz et al., NIM A 2013
Jacek Rzadkiewicz
ADAS workshop
Warsaw, 29-30.09.2014
KX1 crystal bending
CURVED
CRYSTAL(S)
• In order to bent both crystals cylindrically to a curvature of 24.98 m,
a reflecting metrology were applied
• The use of the laser and 200 mm pinhole, mirrors, the crystal bending jig
with four back micrometers and 1D CCD camera (DxCCD=7mm) enabled to
obtain the reflected image in a distance corresponding to the crystal radius
of curvature. The best sharpness of the reflection image was obtained at
distance 2R=24.98±0.10 m
• The analogical measurements performed for Ge crystal confirmed this
value
3k
2R=24.828
2R=25.134
2R=24.982
Spatial intensity of the fringe pattern for different crystal-detector distances
Photons / ms
R=25.134 m
2k
R=24.982 ± 0.144 m
1 mm
SiO2
1k
4.0k
6.0k
8.0k
10.0k 12.0k 14.0k
12.0k
14.0k
Ge
Channel
Images of SiO2 bent crystal focus
Jacek Rzadkiewicz
ADAS workshop
Warsaw, 29-30.09.2014
KX1 instrumental resolving power
DqINS = F(DqCry, DqDet , Dqdefocus, Dqabber)
DqDet~Dx/R – detector broadening
SiO2 (101)
Total
0.20
Bandwith (eV)
DqCry - FWHM of crystal rocking curve
0.25
Crystal
0.15
W
0.10
Dqdefocus~Dd/R2 – defocusing broadening
46+
Defocusing
Detector
0.05
Aberration
Dqabber~W2(H2)/R2
2.34
2.36
2.38
2.40
2.42
2.44
Emission energy [keV]
0.5
Ge: E/DE~20 040,
Gins~0.35 eV, G(Ti=3 keV) ~4.3 eV,
Ge (440)
Bandwidth (eV)
SiO2: E/DE~12 380,
Gins~0.2 eV, G(Ti=3 keV) ~0.7-1.0 eV
0.4
0.3
Total
Defocusing
26+
Ni
Detector
0.2
Crystal
0.1
Abberation
7.8
Jacek Rzadkiewicz
ADAS workshop
7.9
8.0
8.1
8.2
Emission energy (keV)
Warsaw, 29-30.09.2014
KX1 crystal reflectivity
12
Ge (440) @ 7.76-8.28 keV
9
-5
Rint (10 rad)
Calculations of integrated reflectivities for KX1 were
performed by means of the multi-lamellar method
(XOP code)
The calculations require the decomposition of a
crystal into a series of perfect crystal layers, each
oriented slightly differently, following the cylindrical
surface of the crystal
j 1
r j ( 0 t k e
 mS K
ri and ti are the reflectivity and transmission ratios,
μ is the X-ray absorption coefficient,
and SK is the X-ray path inside the K-th layer.
Mosaic
Perfect bent
Perfect flat
49
)
6.0
-5
n
j 1
3
Rint (10 rad)
R tot  
6
Ni
50
51
Angle (deg)
26+
at 7.80 keV
52
53
SiO2 (101) @ 2.32-2.48 keV
4.5
3.0
W
46+
@ 2.38 keV
Mosaic
Perfect bent
Perfect flat
1.5
49
50
51
Angle (deg)
52
53
Caciuffo et al., RSI1990
Jacek Rzadkiewicz
ADAS workshop
Warsaw, 29-30.09.2014
KX1 crystal reflectivity and KX1 sensitivity
 The theoretical reflectivities have been used
in calculations of sensitivity for W and Ni
measurement channels are 1.6x10-11 and
6.5x10-11 cnts.ph-1m2sr.
 This gives W and Ni concentrations in the
range: 10-6-10-4.
 These values use the multi-lamellar
reflectivity calculations, that are expected
to give the most accurate results.
 Inclusion of experimentally determined line
broadening for the mosaic calculations in the
future will verify the sensitivities.
Shumack et al., RSI 2014
Jacek Rzadkiewicz
ADAS workshop
Warsaw, 29-30.09.2014
KX1 line identification
and impurity concentration
• Two 3p-4d lines have been identified for
W46+ and W45+
• Laser-blow-off experiments confirmed that
the central two spectral lines originate from
Mo32+ (3p-2s)
• It was found that the W and Mo concentrations are
in the range of 10-5 and 10-7, respectively, both in
non-seeded and in N2 or Ne seeded ELMy Hmode JET plasmas.
• The ratio of cMo / cW concentration is ~2.5%-10%.
• Mo concentration seems to be proportional to the
W concentration
Jacek Rzadkiewicz
ADAS workshop
Nakano et al., EPS 2014
Warsaw, 29-30.09.2014
Comparison with VUV and SXR diagnostic
Comparison of the W concentration from the
X-ray spectrometer with that from the VUV
spectrometer in plasmas with low toroidal
rotation velocity showed good agreement.
The W concentration from the SX measurement
is about a factor of seven higher than that from
the KX1 spectrometer, and this discrepancy is
larger than the uncertainty of the sensitivity of
the KX1 spectrometer.
Nakano et al., EPS 2014
Jacek Rzadkiewicz
ADAS workshop
Warsaw, 29-30.09.2014
Spectra simulations
Proper spectra simulations require
information on the fractional abundance
of tungsten ions along the LOS of the
diagnostic.
For central plasma transport
processes weakly affect the ionization
equilibrium of W.
Assumed impurity diffusion coefficient
D(r)=0.1 m2s-1 allows to reproduce the
experimental values within factor of 2.
Larger transport coefficients do not
change sihnificantly the abundant
ionization stages of W for Te=4.1 keV
Putterich et al., 2008
Jacek Rzadkiewicz
ADAS workshop
Warsaw, 29-30.09.2014
Spectra simulations
Different sets of ionization and recombination rates can be used for the W
ionization equilibrium.
Putterich et al., 2008
ADPAK: Post et al 1977 At. Data Nucl. Data Tables
CADW Loch et al 2005 Phys. Rev. A
Jacek Rzadkiewicz
ADAS workshop
Warsaw, 29-30.09.2014
Spectra simulations
Putterich et al., 2008
For the W45+ and W46+ ionization
states the CADW+ADPAK model
underestimates the line intensities
for the unmodified case by up to a
factor of 50 and the modifications*
reduce this discrepancy to a factor
of 10.
Electron-impact ionization cross section for
W45+ has a threshold around 2.5 keV.
*Recombination rates scaled by temperature
independent factors
Jacek Rzadkiewicz
ADAS workshop
Loch PRA 2005
Warsaw, 29-30.09.2014
FAC spectra
simulations
Motivation
 The FAC code not only allows to
compute atomic data, such as energy
levels and transition probabilities for
radiative transitions and auto-ionization,
but also cross sections for excitation and
ionization by electron impact and the
inverse
processes
(e.g.,
radiative
recombination and dielectronic capture).
 The FAC package contain three main
components
which
determine
the
radiation from a unit plasma volume: (1)
the energy and emission probability of a
photon by a radiative transition from some
excited state; (2) how many ions exist in
the various excited states in the plasma;
and (3) what is the rate of the emitted
photons.
Jacek Rzadkiewicz
ADAS workshop
Warsaw, 29-30.09.2014
FAC spectra
simulations
Motivation
 L x-ray spectra for molybdenum can
have significant contribution in the same
region as the M x-ray spectra for tungsten
and therefore both elements should be
included in the interpretation of the highresolution x-ray spectra registered on JET
using KX1 spectrometer.
Jacek Rzadkiewicz
ADAS workshop
Warsaw, 29-30.09.2014
Summary
and outlook
Motivation
 Updated T-GEM detectors register X-ray spectra from specific
reflection order
 KX1 diagnostic achieved an excellent instrumental resolving power
 Sensitivity function determine with high precision
 Preliminary analysis of W impurity level and comparison with other
diagnostics (VUV and SXR) have been performed
 Preliminary FAC spectra simulations have been performed
 Data acquisition system verification
 Crystal vertical adjustment and mosaicity verification
 Ti analysis
 More precise W and Mo spectra simulations (FA verification)
Jacek Rzadkiewicz
ADAS workshop
Warsaw, 29-30.09.2014
Thank you for your attention!
M. Chernyshova, T. Czarski, T. Nakano, M. Polasik, J. Rzadkiewicz,
K. Słabkowska, A Shumack, Ł. Syrocki, E. Szymańska
Jacek Rzadkiewicz
ADAS workshop
Warsaw, 29-30.09.2014