Jacek Rzadkiewicz ADAS workshop Warsaw, 29-30.09.2014 Presented by Jacek Rzadkiewicz Spectral characteristics and spectra simulations for high-resolution

Jacek Rzadkiewicz ADAS workshop Warsaw, 29-30.09.2014

Presented by Jacek Rzadkiewicz

Spectral characteristics and spectra simulations for high-resolution X-Ray diagnostic at JET


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.


Spectral measurements

The high-resolution X-ray crystal spectrometer (KX1) is set to measureX-ray spectra in two diagnostic channelsdedicated 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

and toroidal rotation velocity

for central JET plasmas.

The entire spectral range of the KX1 spectrometer for two diagnostic channels


KX1 beam lineHorizontal cross-section of the x-ray crystal spectrometer (KX1) on JET The spectrometer is operated in

Johann geometry with the Rowland circle radius of about 12.5 m giving an extremely high energy resolution.

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.

T-GEM detectors mounted on KX1 diagnostics

‘W’ channel

‘Ni’ channel


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 m (Ni monitor) and 5 m (W monitor) mylar windows

•The detector position resolution has been found to be to not worse than 1 strip width (0.8 mm).

Photon detection efficiencies as a function of photon energy

Structure of the T-GEM X-ray detector for JET diagnostics

Charge position distribution for X-ray source (X-ray tube 2.5 kV,100 mA) with a 0.7mm diameter collimator

Rzadkiewicz et al., NIM A 2013


KX1 crystal bendingCURVED CRYSTAL(S)

Spatial intensity of the fringe pattern for different crystal-detector distances

R=25.134 m

SiO2

Ge

R=24.982 ± 0.144 m

• 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

10.0k 12.0k 14.0k

1 mm

Channel

2R=24.982

4.0k 6.0k 8.0k

1k

2k

3k

2R=24.828

Pho

tons

/ m

s

12.0k 14.0k

2R=25.134

Images of SiO2 bent crystal focus


KX1 instrumental resolving power

7.8 7.9 8.0 8.1 8.2

0.1

0.2

0.3

0.4

0.5

Total

Defocusing

Detector

Crystal

Abberation

Ge (440)

Ni26+

Ba

nd

wid

th (

eV

)

Emission energy (keV)

2.34 2.36 2.38 2.40 2.42 2.44

0.05

0.10

0.15

0.20

0.25

W46+

SiO2 (101)

Aberration

Detector

Defocusing

Crystal

Total

Ba

nd

with

(e

V)

Emission energy [keV]

- FWHM of crystal rocking curve

Det~x/R – detector broadening

defocus~d/R2 – defocusing broadening

Cry

INS = F(Cry, Det , defocus, abber)

abber~W2(H2)/R2

SiO2: E/E~12 380, ins~0.2 eV, i=3 keV) ~0.7-1.0 eV

Ge: E/E~20 040, ins~0.35 eV, i=3 keV) ~4.3 eV,


KX1 crystal reflectivity

49 50 51 52 53

3

6

9

12

Ni26+ at 7.80 keV

Ge (440) @ 7.76-8.28 keV

Rin

t (10

-5 r

ad)

Angle (deg)

Mosaic Perfect bent Perfect flat

49 50 51 52 53

1.5

3.0

4.5

6.0

W46+ @ 2.38 keV

SiO2 (101) @ 2.32-2.48 keV

Rin

t (10

-5 r

ad)

Angle (deg)

Mosaic Perfect bent Perfect flat

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

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.

)( 101

KSk

jj

njtot etrR

Caciuffo et al., RSI1990


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 expectedto 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


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)

Nakano et al., EPS 2014• 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 H-mode JET plasmas.

• The ratio of cMo / cW concentration is ~2.5%-10%. • Mo concentration seems to be proportional to the

W concentration


Comparison with VUV and SXR diagnostic

Nakano et al., EPS 2014

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.


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


Different sets of ionization and recombination rates can be used for the W ionization equilibrium.

Spectra simulations

ADPAK: Post et al 1977 At. Data Nucl. Data TablesCADW Loch et al 2005 Phys. Rev. A



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.

Spectra simulations


*Recombination rates scaled by temperature independent factors

Electron-impact ionization cross section for W45+

has a threshold around 2.5 keV.

Loch PRA 2005


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.

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 high-resolution x-ray spectra registered on JET using KX1 spectrometer.

FAC spectra simulations


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

Summary and outlook

Data acquisition system verification Crystal vertical adjustment and mosaicity verification Ti analysis More precise W and Mo spectra simulations (FA verification)


M. Chernyshova, T. Czarski, T. Nakano, M. Polasik, J. Rzadkiewicz, K. Słabkowska, A Shumack, Ł. Syrocki, E. Szymańska

Thank you for your attention!

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Jacek Rzadkiewicz ADAS workshop Warsaw, 29-30.09.2014 Presented by Jacek Rzadkiewicz Spectral characteristics and spectra simulations for high-resolution