1. Preliminary study for Soft X-ray Spectroscopy in VEST
Jungmin Jo, Jeong-Jeung Dang, Young-Gi Kim, and Y.S. Hwang
Center for Advance Research
in Fusion Reactor Engineering
Department of Nuclear Engineering Seoul National University

2. Impurity characteristic radiation Future Experimental plan Summary
Contents
Introduction
Background theory
Experimental setup
Result
Continuum radiation
Impurity characteristic radiation
Future Experimental plan
Summary

3. Passive Spectroscopy Introduction Near Infrared Visible
[1]
Spectral region
Wavelength (nm)
Energy (eV)
Near infrared
700 to 1200
1 to 2
Visible
400 to 700
2 to 3
Ultraviolet
200 to 400
3 to 6
Vacuum ultraviolet
30 to 200
6 to 40
Extreme ultraviolet
10 to 30
40 to 120
Soft X-ray
0.1 to 10
120 to 12,000
Near Infrared
Visible
Vacuum UltraViolet
Extreme UltraViolet
Soft X-ray
Target
Measuring value
Purpose
Note
Continuum radiation (bremsstrahlung, recombination)
Density, temperature, impurity convolution value
(with tomography technique) Plasma imaging
MHD phenomena
EC wave or EBW heating effect
Radiation from electrons heated by EC wave
Line radiation
Impurity
Certain impurity lines
Impurity content inform.
Impurity transport
Inform. of Te
Appropriate for diagnose core region plasma

4. Background Theory – mechanism of Soft X-ray
Continuum radiation
Coulomb interaction between free electrons and ions
Bremsstrahlung radiation (free – free transition)
Spectral power density
[2] + -
Recombination radiation (free – bound transition)
Spectral power density
[2] + -
Line radiation
characteristic line radiation from ionized impurity + -

5. Signal processing circuit
Experimental Setup
VEST Plasma
Detector position
128 mm
R = 1900 mm
Detector
AXUV 16ELG
Filter foil holder &
Foil filter
In-vacuum component
Limit the line of sight
Collimator (SUS pipe)
Signal processing circuit
Vacuum feedthrough

6. Result VUV, EUV and SXR range radiation from VEST
Signal level examination
Aluminum 1.5 μm
Aluminum 1.5 μm thickness foil can be used as VUV, EUV and SXR region filter.
Shot #9620
Lots of radiation signal is detected.
Because the spectroscopic applications are depends on radiation source
so firstly we have to identify the radiation mechanism.
Possible sources for this radiation
Continuum radiation
Impurity characteristic radiation.
High energy radiations caused by non-thermal energetic electrons

7. Result Identifying radiation source_Continuum radiation
Theoretical calculation of expected continuum radiation signal
(At the current peak time)
Plasma volume at the line of sight
0.04 m^3
Plasma density, temperature
Ne= 5 E18
Te=100eV
Generated bremsstrahlung radiation power
0.15 W
Solid angle
5.47 E-8
Filter
Carbon, 4.5 um
Generated Photocurrent
9.5395e-12 (A)
Dark current
~0.1 nA
Circuit gain : 𝟏𝟎 𝟔 V / A
Expected Voltage signal
9.5395e-6 (V)
In our case Continuum radiation effect will be negligible

8. Result Identifying radiation source_Continuum radiation
To check the continuum radiation level experimentally, choose impurity line free region
Expected major impurity(oxygen, carbon) characteristic line radiation (vertical lines) and Transmission curve of appropriate filters
Experimental result (shot #9464)
By using carbon 4.5 μm thickness filter we can filter out
most of expected major impurity characteristic radiation
Negligible continuum radiation in VEST
Negligible high energy radiation
VUV, EUV and SXR range radiation in VEST is mostly caused by impurity characteristic lines

9. Result Identifying radiation source_Impurity characteristic radiation
C III
C VI
C V
O V
O VI
O VII
O VIII
Fe XV
Fe XVI
Fe XXIII
Fe XXIV
W (quasi-continuum)
97.7
154.82
4.03
3.37
15.61
15.01
12.03
10.24
28.42
33.54
13.28
19.2
4.5~6.5
38.62
155.08
22.72
2.84
19.28
17.3
12.85
7.59
36.08
25.51
41.96
24.87
2.7
21.5
18.4
2.16
1.9
38.41
13.49
62.97
103.19
31.24
18.22
76.03
103.76
24.49
Expected minor impurities in VEST : Iron, Tungsten(limiter material)
Goal : Identifying impurity species and lines
Result Identifying radiation source_Impurity characteristic radiation
By using list of intense spectral lines we can reduce the expected impurity lines.
(This data mostly based on spectra which were measured at TEXTOR and JET and to some extent on data from literature.)
Expected major impurities in VEST : Oxygen, Carbon
[3]
Ion species
C III
C VI
C V
O V
O VI
O VII
O VIII
wavelength
97.7
154.82
4.03
3.37
15.61
15.01
12.03
10.24
38.62
155.08
22.72
2.84
19.28
17.3
12.85
7.59
41.96
24.87
2.7
21.5
18.4
2.16
1.9
38.41
13.49
62.97
103.19
31.24
18.22
76.03
103.76
24.49
Oxygen
Carbon
Firstly, assume this list also intense lines in VEST and check the existence

10. Result Identifying radiation source_Impurity characteristic radiation
Spectrum scanning and line radiation existence check
Carbon 3 μm Transmission
Shot #9613
Line
Transmission (%)
Al 3 μm
C 3 μm
(O VIII)
4.70 1
If the aluminum filter signal is mainly from the highest energy line radiation (upper yellow circle), the carbon filter signal level should be one fourth of aluminum signal (~ 5 mV) due to the transmission rate difference.
Aluminum 3 μm Transmission
However there is no signal in carbon filter, so the highest energy line is negligible and aluminum filter signal is more likely from low energy region
line negligible

11. Result Identifying radiation source_Impurity characteristic radiation
Spectrum scanning and line radiation existence check
Carbon 1.5 μm Transmission
Large signal difference between two filters, about hundreds times
Most of EUV~SXR radiation is from the low energy region
Aluminum 1.5 μm Transmission
To check low and high energy region each, other material filters are necessary.

12. Necessary filters for identification of the other impurity lines
Future Experimental plan Identifying radiation source_Impurity characteristic radiation
Necessary filters for identification of the other impurity lines
Ni (250 nm) + Cr (500 nm)
+ Parylene (200 nm) 1
Al (400 nm) + V (600 nm) 2
Ti (400 nm) + CaF2 (600 nm) 3 1 2
Identify O VII line effect 2
Identify C VI line effect 3
Identify C V line effect
Necessary for Verification Method
Because of possibility of existence of other lines verification method are needed
Multi-Layer Mirror monochromator
Spectrometer (e.g. grazing incidence spectrometer)

13. Summary Conclusion Summary
Preliminary study for SXR spectroscopy was progressed
For the identification of impurity lines necessary filter foil is selected
Because of possibility of existence of other lines verification method are needed and MLM method
or spectrometer can be used.
Summary
Summary
Preliminary study for SXR spectroscopy was progressed
Radiation source identifying experiments are performed using filtered diode method
For the identification of impurity lines more precisely necessary filter foil is selected
Because of possibility of existence of other impurity lines verification method are needed. MLM monochromator or spectrometer can be used.

14. Reference
[1] Fusion Science and Technology, Vol. 53, 2008, Special issue on plasma diagnostics for magnetic fusion research
[2] I. H. Hutchinson, Cambridge univ. press, Principles of plasma diagnostics
[3] W. Biel, FZJ, Design of the ITER VUV spectrometer system, Draft report 15 October 2007