i-7, g. pintsuk, forschungszentrum julich 19 psi, 20101 experimental study of pfcs erosion and...

I-7, G. Pintsuk, Forschungszentrum Julich 19 PSI, 2010 1

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, 142190, Troitsk, Moscow Region, Russia2Forschungszentrum Jülich GmbH, EURATOM Association, D-52425 Jülich, Germany

3Karlsruhe Institute of Technology, P.O. Box 3640, 76021 Karlsruhe, Germany (KIT)4ITER Organization, St. Paul-lez-Durance, F-13108 Cadarache, France

5Fusion for Energy, ITER Department, Josep Pla, 2, Torres Diagonal Litoral B3, 08019 Barcelona, Spain6Efremov Institute, 196641, St. Petersburg, Russia

7RRC «Kurchatov Institute», Moscow, Russia

Troitsk Institute for Innovation and Fusion Research

F4E EfremovInstitute

RRCKurchatovInstitute


Outline

• Experimental facilities, targets, diagnostics

• ELMs simulation experiments at low heat loads

• Mixed materials and erosion products investigation

• Conclusion


Experimental facilitiesQuasistationary plasma accelerator

QSPA plasma parameters (ELMs):

• Heat load 0.5 ÷ 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 1022 ÷ 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

QSPA-T facility QSPA-Be facility


Experimental conditionsTarget design

CFCSNECMA NB31

pure W orW-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

3(7)2

5

2020

W – grain orientation orCFC - pitch fibre orientation

Cu

SS

CFCSNECMA NB31

15019.5

19.5

60

9.5

9.5

W (>99,96%) и

W-1% La2О3

Be-clad and Be-coated


Experimental conditionsScheme of PFCs testing

• 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 experiments2.3 MJ/m2 in disruption experiments

View of the target on a heater

Plasma flow

Castellated tungsten (or CFC) target

60O

Absorbed energy density profile

Target orientation


DiagnosticsMeasurements of absorbed energy density distribution

25

180

90

15

X

Y

110

195

Cells with thermocouplesShield frame

Plasma facingsurface (CFC)10x10 mm2

Surface connected to thermocouple

Copper layer

Absorbed energy density distribution was measured by means of special CFC and tungsten target-like calorimeters

Schemes and views of the calorimeters


Experimental conditionsAbsorbed energy density distribution

Typical energy density profile on W surface The energy density distribution on W surface,%

The energy density distribution on CFC surface,%Typical energy density profile on CFC surface


DiagnosticsPlasma parameters

measurementsPFCs erosion measurement

Products erosion study

1. Pressure probe

2. System of plasma stream velocity measurements

3. Calorimeters

1. Microbalance

2. Mechanical profilometer

3. Laser profilometer

4. SEM with X-ray analysis

5. IR-cameras

6. Optical microscopes

1. Online diagnostics for dust particle ejection study

2. Dust collectors

3. Quartz crystal microbalance

4. Optical microscopes

5. SEM with X-ray analysis

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


Experimental resultsCFC NB31, PAN-fibers erosion

«PAN» fibers (6%)

«Needled PAN» fibers (2%)

Z

Y

X

Plasma flow

«pitch»fibers

(25-30%)10 mm

PAN fiber damage is a main mechanism of CFC erosion under ELM-like and disruption-like plasma load

100 мкм

Q = 1MJ/m2, Δt=0.5 ms, N=100 pulses

Pitch fibers PAN fibers

Forschungszentrum Jülich

J.Linke, T.Hirai


After 500 pulses

Q0=0.5 MJ/m2

Plasma flow direction

CFC erosionPAN-fibers erosion measurement

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.

After 5 pulses

Q0=2.3 MJ/m2

Measurement points


CFC erosion Comparison of experimental and modeling results

PAN-fiber erosion increase from 0.01 μm/pulse to 10 μm/pulse in the heat load range of 0.2-2.4MJ/m2

Numerical modeling(code PEGASUS-3D)

Forschungszentrum Karlsruhe (I.S. Landman, B.N. Bazylev, and S.E. Pestchanyi)


Tungsten erosion Pure W. Crack formation. Primary and secondary cracks

W, 1MJ/m2, 20 pulses

1mm

100 pulses

1mm

Secondary cracks: depth 50 µm

Primary crack: depth 500 µm

Forschungszentrum Jülich

J.Linke, T.Hirai

W, Q=1MJ/m2, 100 pulses


Numerical simulation PEGASUS-3D. Cracks formation.

Forschungszentrum Karlsruhe (I.S. Landman, B.N. Bazylev, and S.E. Pestchanyi)

Primary cracks (at a depth of 200 μm)

Secondary cracks (on the surface)

Secondary cracks

500 µm 100 µm

200 µm

GrainPrimary cracks

Numerical simulation(cod PEGASUS-3D)


Tungsten erosion Another type of cracks: cracks of the remelted W-1%La2O3


Tungsten erosion Dust generation as a result of cracking

crack width 10µm

Small tungsten dust particles

Melt layer delamination

100 µm

W-1%La2O3

W, Q=1MJ/m2, 100 pulses


Q, MJ/m2

X, cm

Y,

cm

Plasma flow direction

Experimental resultsCombined target (W+CFC), disruptions, Q0 = 2.3MJ/m2

-6 g/m2/pulse(mass loss)



+25 g/m2/pulse(mass growth)

W-1%La2O3

CFC NB31 CFC NB31Pure W


a b

c d

100 µm

200 µm

50 µm

PAN-fibers area

pitch-fibers area

Experimental resultsCombined target, Q = 2.3MJ/m2

20 µm


Dust investigation Dust collectors

18

Polished silicon substrates


Polished tungsten substrates

Traps of solid particles

Fitting elements

Copperplates

Particle flow

а б

The modernized target vacuum chamber allow to place various dust collectors and dust traps


Chamber 2Chamber 1

Plasma flow

Target

Collectors circles Collectors lines

Dust investigation Scheme of dust collectors placement


Polished tungsten

substrates

• 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

After 5 pulses

Combined target

W+CFC


Dust investigation Various dust structures, W+CFC, disruption experiments, Q=2.3MJ/m2

5 µм

1 µм

5 µм

2 µм

Cauliflower-like structure

100 µм

20 µм

Crystallite structureAmorphous films


Dust investigation Combined target (W+CFC). Size distributions of deposited particles,

10 µм

100 µm

Tungsten droplets on the CFC PAN-

fibers area

Cauliflower-like structure on the dust collectors


Y

XPlasma flow direction

DiagnosticsOnline diagnostics for droplets and particles ejection study

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.

The scheme of diagnostics

.2)()(

)(

,)()(

)(

0

2

0

0

0

tvz

gttvy

ftytz

ftyktY

tvz

tvxftx

tz

ftxktX

z

y

z

x

x(t), y(t), z(t) – droplets coordinates


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


SummaryCFC 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 0.2-2.4 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.


SummaryW 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 100-300 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.


SummaryW 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 19 psi, 20101 experimental study of pfcs erosion and...

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