1. Troitsk Institute for Innovation and Fusion Research
Experimental study of PFCs erosion and eroded material deposition under ITER-like transient loads at plasma gun facility QSPA
N. Klimov1, V. Podkovyrov1, A. Zhitlukhin1, D. Kovalenko1, J. Linke2, G.Pintsuk2, I. Landman3, S. Pestchanyi3, B. Bazylev3, G. Janeschitz3, A. Loarte4, M. Merola4, T. Hirai4, G. Federici5, B. Riccardi5, I. Mazul6, R. Giniyatulin6, L. Khimchenko7, V.Koidan7
1SRC RF TRINITI, ul. Pushkovykh, vladenie 12, , Troitsk, Moscow Region, Russia
2Forschungszentrum Jülich GmbH, EURATOM Association, D Jülich, Germany
3Karlsruhe Institute of Technology, P.O. Box 3640, Karlsruhe, Germany (KIT)
4ITER Organization, St. Paul-lez-Durance, F Cadarache, France
5Fusion for Energy, ITER Department, Josep Pla, 2, Torres Diagonal Litoral B3, Barcelona, Spain
6Efremov Institute, , St. Petersburg, Russia
7RRC «Kurchatov Institute», Moscow, Russia
Troitsk Institute for Innovation and Fusion Research
F4E
RRC
Kurchatov Institute
Efremov
Institute
I-7, G. Pintsuk, Forschungszentrum Julich PSI, 2010

2. Outline Experimental facilities, targets, diagnostics
ELMs simulation experiments at low heat loads
Mixed materials and erosion products investigation
Conclusion
I-7, G. Pintsuk, Forschungszentrum Julich PSI, 2010

3. Experimental facilities Quasistationary plasma accelerator
QSPA-T facility
QSPA-Be facility
QSPA plasma parameters (ELMs):
Heat load ÷ 5 MJ/m2
Pulse duration 0.1 ÷ 0.6 ms
Plasma stream diameter 6 cm
Ion impact energy 0.1 ÷ 1.0 keV
Electron temperature < 10 eV
Plasma density ÷ 1023 m-3
QSPA plasma gun
1 – coil of pulse electromagnetic gas valve;
2 – valve disk; 3 – volume of pulse valve;
4 – isolator; 5 – gas supply tube;
6 – cathode; 7 – anode.
QSPA facility provides adequate pulse durations and energy densities. It is applied for erosion measurement in conditions relevant to ITER ELMs and disruptions
I-7, G. Pintsuk, Forschungszentrum Julich PSI, 2010

4. Experimental conditions Target design
3(7) 2 5 20
W –  grain orientation or
CFC -  pitch fibre orientation Cu SS
CFC
SNECMA NB31
150
19.5 60
9.5
W (>99,96%)
и W-1% La2О3
Be-clad and
Be-coated
CFC
SNECMA NB31
pure W or W-1% La2O3
Special 31 ITER-like targets (6 CFC, 3 pure W, 6 W-1%La2O3, and 16 Ве)
were designed and manufactured by EU
were pre-characterized by Forschungszentrum Jülich (Germany) by optical / electron microscopy and laser-profilometry
I-7, G. Pintsuk, Forschungszentrum Julich PSI, 2010

5. Experimental conditions Scheme of PFCs testing
View of the target on a heater
Plasma flow
Castellated tungsten (or CFC) target
60O
Absorbed energy density profile
Target orientation
Target was preheated up to 500O C
Plasma pulse duration was t = 0.5 ms
Plasma-surface angle α = 300
Total number of pulses was up to 1000 for ELMs experiments and up to 10 for disruptions experiments
Absorbed energy density at plasma axis was
0.5÷1.5 MJ/m2 in ELMs experiments
2.3 MJ/m2 in disruption experiments
I-7, G. Pintsuk, Forschungszentrum Julich PSI, 2010

6. Diagnostics Measurements of absorbed energy density distribution
Shield frame
110
195
Cells with thermocouples 25
180 90 15 X Y
Plasma facing
surface (CFC)
10x10 mm2
Surface connected to thermocouple
Copper layer
Schemes and views of the calorimeters
Absorbed energy density distribution was measured by means of special CFC and tungsten target-like calorimeters
I-7, G. Pintsuk, Forschungszentrum Julich PSI, 2010

7. Experimental conditions Absorbed energy density distribution
Typical energy density profile on CFC surface
The energy density distribution on CFC surface,%
Typical energy density profile on W surface
The energy density distribution on W surface,%
I-7, G. Pintsuk, Forschungszentrum Julich PSI, 2010

8. Diagnostics Plasma parameters measurements PFCs erosion measurement
Products erosion study
Pressure probe
System of plasma stream velocity measurements
Calorimeters
Microbalance
Mechanical profilometer
Laser profilometer
SEM with X-ray analysis
IR-cameras
Optical microscopes
Online diagnostics for dust particle ejection study
Dust collectors
Quartz crystal microbalance
Plasma pressure, plasma flow duration, plasma stream velocity, ion impact energy, plasma flow energy density, absorbed energy density
Mass losses, erosion value, surface modification, surface profile, local erosion value
Velocities and sizes of dust
particles, onset conditions;
parameters of films,
porosity and fractal structure, films thickness and density, chemical composition
I-7, G. Pintsuk, Forschungszentrum Julich PSI, 2010

9. Experimental results CFC NB31, PAN-fibers erosion
100 мкм
Q = 1MJ/m2, Δt=0.5 ms, N=100 pulses
Pitch fibers
PAN fibers
«PAN» fibers (6%)
«Needled PAN» fibers (2%) Z Y X
Plasma flow
«pitch»
fibers (25-30%)
10 mm F o r s c h u n g z e t m J ü l i
J.Linke, T.Hirai
PAN fiber damage is a main mechanism of CFC erosion under ELM-like and disruption-like plasma load
I-7, G. Pintsuk, Forschungszentrum Julich PSI, 2010

10. CFC erosion PAN-fibers erosion measurement
After 5 pulses
Q0=2.3 MJ/m2
Measurement points
After 500 pulses
Q0=0.5 MJ/m2
Plasma flow direction
PAN-fiber erosion value measured along the target surface is correlated to the measured value of absorbed energy density. This correlation allow to define PAN-fiber erosion rate as a function of heat load.
I-7, G. Pintsuk, Forschungszentrum Julich PSI, 2010

11. CFC erosion Comparison of experimental and modeling results
Numerical modeling
(code PEGASUS-3D)
Forschungszentrum Karlsruhe (I.S. Landman, B.N. Bazylev, and S.E. Pestchanyi)
PAN-fiber erosion increase from 0.01 μm/pulse to 10 μm/pulse in the heat load range of MJ/m2
I-7, G. Pintsuk, Forschungszentrum Julich PSI, 2010

12. Tungsten erosion Pure W. Crack formation. Primary and secondary cracks
W, 1MJ/m2, 20 pulses
1mm
Primary crack: depth  500 µm
W, Q=1MJ/m2, 100 pulses
100 pulses
1mm F o r s c h u n g z e t m J ü l i
J.Linke, T.Hirai
Secondary cracks: depth  50 µm
I-7, G. Pintsuk, Forschungszentrum Julich PSI, 2010

13. Numerical simulation PEGASUS-3D. Cracks formation.
Forschungszentrum Karlsruhe (I.S. Landman, B.N. Bazylev, and S.E. Pestchanyi)
500 µm
100 µm
Primary cracks (at a depth of 200 μm)
Primary cracks
Grain
Secondary cracks
200 µm
Numerical simulation
(cod PEGASUS-3D)
Secondary cracks (on the surface)
I-7, G. Pintsuk, Forschungszentrum Julich PSI, 2010

14. Tungsten erosion Another type of cracks: cracks of the remelted W-1%La2O3
I-7, G. Pintsuk, Forschungszentrum Julich PSI, 2010

15. Tungsten erosion Dust generation as a result of cracking
100 µm
W-1%La2O3
W, Q=1MJ/m2, 100 pulses
crack width  10µm
Melt layer delamination
Small tungsten dust particles
I-7, G. Pintsuk, Forschungszentrum Julich PSI, 2010

16. Experimental results Combined target (W+CFC), disruptions, Q0 = 2
Experimental results Combined target (W+CFC), disruptions, Q0 = 2.3MJ/m2
Q, MJ/m2
X, cm
Y, cm
Plasma flow direction
W-1%La2O3
-60 g/m2/pulse
(mass loss)
Pure W
CFC NB31
CFC NB31
-80 g/m2/pulse
(mass loss)
+25 g/m2/pulse
(mass growth)
-6 g/m2/pulse
(mass loss)
I-7, G. Pintsuk, Forschungszentrum Julich PSI, 2010

17. Experimental results Combined target, Q = 2.3MJ/m2
PAN-fibers area a b
200 µm
50 µm
pitch-fibers area c d
I-7, G. Pintsuk, Forschungszentrum Julich PSI, 2010

18. Dust investigation Dust collectors
The modernized target vacuum chamber allow to place various dust collectors and dust traps
Polished tungsten substrates
Polished silicon substrates
Polished silicon substrates
Traps of solid particles
Fitting elements
Copperplates
Particle flow а б
I-7, G. Pintsuk, Forschungszentrum Julich PSI, 2010 18

19. Polished silicon substrates Polished tungsten substrates
Dust investigation Scheme of dust collectors placement
Chamber 2
Chamber 1
Plasma flow
Target
Collectors circles
Collectors lines
Polished silicon substrates
Polished tungsten substrates
After 5 pulses
The dust films deposit mainly after the target in plasma flow direction on the cooled part of vacuum chamber
The maximum rate of film growth observed on disruption simulation experiment is equal to 0.4 μm/pulse
Combined target
W+CFC
I-7, G. Pintsuk, Forschungszentrum Julich PSI, 2010

20. Dust investigation Various dust structures, W+CFC, disruption experiments, Q=2.3MJ/m2
100 µм
5 µм
5 µм
20 µм
2 µм
1 µм
Cauliflower-like structure
Crystallite structure
Amorphous films
I-7, G. Pintsuk, Forschungszentrum Julich PSI, 2010

21. Dust investigation Combined target (W+CFC)
Dust investigation Combined target (W+CFC). Size distributions of deposited particles,
100 µm
Tungsten droplets on the CFC PAN-fibers area
10 µм
Cauliflower-like structure on the dust collectors
I-7, G. Pintsuk, Forschungszentrum Julich PSI, 2010

22. Diagnostics Online diagnostics for droplets and particles ejection study
The scheme of diagnostics Y X
Plasma flow direction
Pure tungsten, Qabs = 1.2 MJ/m2 , p = 1.8 atm
The scheme allows to define:
threshold plasma loads for dust particles ejection starting;
components of the dust particle velocity vector;
absolute velocity value and flight angle of the particle;
point of time formation and size of the dust particle.
x(t), y(t), z(t) – droplets coordinates
I-7, G. Pintsuk, Forschungszentrum Julich PSI, 2010

23. Plasma stream direction
Droplets ejection study Droplet ejection, pure tungsten, energy density Q = 1.6 MJ/m2
Surface of the sample
Plasma stream direction γ x y v z
I-7, G. Pintsuk, Forschungszentrum Julich PSI, 2010

24. Summary CFC erosion
PAN-fiber erosion is the main CFC erosion process under ITER-like transient plasma heat loads.
The distribution of PAN-fiber erosion is determined on the CFC surface and related to the absorbed energy density distribution.
The value of PAN-fiber erosion increases from 0.01 to 10 μm/pulse with a heat load in the range of MJ/m2 according to the following law ΔhPAN = 0.9Q2.7.
The amount of PAN-fiber erosion under plasma action correlates with results from numerical calculations taking vapor shielding and thermal conductivity degradation into account.
I-7, G. Pintsuk, Forschungszentrum Julich PSI, 2010

25. Summary W erosion
Crack formation is the main W erosion process under ITER-like transient plasma heat loads below the tungsten melting threshold.
Primary cracks with a significant depth of up to 500 µm (after 100 pulses) form a grid on the surface with 1-3 mm characteristic cell size.
Secondary cracks reach a depth of up to 50 µm (after 100 pulses) and form a surface grid with  µm characteristic cell size.
The width of primary and secondary cracks increases with number of pulses.
The cracks observed on the lanthanum tungsten remelted surface form a grid with cell sizes in the range from 1-100 µm and a melt layer thickness dependent depth.
I-7, G. Pintsuk, Forschungszentrum Julich PSI, 2010

26. Summary W erosion
Melt layer movement and droplets ejection are the main W erosion processes under ITER-like transient plasma heat loads higher than the tungsten melting threshold.
The main part of the droplets (>80%) follow the plasma flow direction at an angle between target surface and velocity vector in the range from 0 to 600.
The absolute droplets velocity was determined to be in the range from 0 to 25 m/s.
As a result of the exposure of combined W and CFC targets the mass of CFC target increased due to tungsten deposition and accumulation.
I-7, G. Pintsuk, Forschungszentrum Julich PSI, 2010