D. Kovalenko, SRC RF TRINITI 13th PFMC Workshop / 1st FEMaS Conference 1

Tungsten and carbon based PFCs erosion and eroded material deposition under ITER-like ELM and disruption loads at the plasma gun facility QSPA-T

N. S. Klimova,*, V. L. Podkovyrova, D. V. Kovalenkoa, A. M. Zhitlukhina,V. A. Barsuka, L. B. Begrambekovb, P. A. Shiginb, I. V. Mazulc, R. N. Giniyatulinc,

V. Ye. Kuznetsovc, J. Linked, I. S. Landmane, S. E. Pestchanyie,B. N. Bazyleve, A. Loartef, B. Riccardig, V. S. Koidanh

Troitsk Institute for Innovation and Fusion Research

F4E EfremovInstitute

RRCKurchatovInstitute

aSRC RF TRINITI, Pushkovykh street, 12, 142190, Troitsk, Moscow Region, RussiabNRNU MEPHI, Kashirskoe shosse, 31, 115409, Moscow, Russia

cEfremov Institute, 196641, St. Petersburg, RussiadForschungszentrum Jülich GmbH, EURATOM Association, D-52425 Jülich, Germany

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

gFusion for Energy, Josep Pla, 2, Torres Diagonal Litoral B3, 08019 Barcelona, SpainhRRC «Kurchatov Institute», Moscow, Russia

D. Kovalenko, SRC RF TRINITI 13th PFMC Workshop / 1st FEMaS Conference 2

Outline

This activity is carried out under collaboration between European Union and theRussian Federation and is directed to obtain the data for the empiricalestimation of the PFC lifetime and to validate the available numerical modelsused to predict the erosion under the expected conditions in ITER.

• Experimental conditions• Tungsten erosion (melting, crack formation)• Erosion products investigation• Summary

This work was supported by EFDA (05-994 Task 4), the ROSATOM (Н.4а.52.03.10.1003), the Impuls- und Vernetzungsfond derHemholtz Gemeinschaft e.V. and RFBR grant Nr.11-02-91322

D. Kovalenko, SRC RF TRINITI 13th PFMC Workshop / 1st FEMaS Conference 3

Experimental conditionsQuasistationary 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

D. Kovalenko, SRC RF TRINITI 13th PFMC Workshop / 1st FEMaS Conference 4

Experimental conditionsScheme of PFCs testing under ELM-like heat load

Absorbed energy density profiles

Absorbed energy density distribution,%

• Target was preheated up to 300O C • Plasma pulse duration was t = 0.5 ms• Plasma-surface angle α= 600

• Total number of pulses was up to 1000 for ELMsexperiments• Absorbed energy density was 0.5MJ/m2

D. Kovalenko, SRC RF TRINITI 13th PFMC Workshop / 1st FEMaS Conference 5

Experimental conditionsHigh heat flux test facility TSEFEY-M (Efremov Institute)

• Controlled beam power 1÷200 kW• Maximal beam current 5A• Maximum power density in beam 1000 MW/m2

• Controlled accelerating voltage 0÷40kV• Total deflection angle ±40°• Minimal beam diameter at 40kV accelerating voltage, 5A current, 1m distance to target 15 mm• Maximal density of the absorbed heat flux 30 MW/m2

• Distance from deflecting system to sample 0.6÷1.2 m

TSEFEY-M facility allow to study of damages in various materials caused by abnormal high surface heat loads (including short-pulse loads), thermal strength and thermocyclic life time of multilayer structures at high temperature gradients, the heat exchange intensification processes, when structures with one-sided surface heating are cooled by water or gas.

Technical characteristics of the TSEFEY- M

D. Kovalenko, SRC RF TRINITI 13th PFMC Workshop / 1st FEMaS Conference 6

Experimental conditionsTarget design (cooled mockup)

CFC cooled target

Tungsten cooled target

4 cooled targets: 2 W, and 2 CFC

D. Kovalenko, SRC RF TRINITI 13th PFMC Workshop / 1st FEMaS Conference 7

Experimental conditionsPlasma exposure + high heat flux testing

Step 1: N=500 plasma pulses, Q0=0.5 MJ/m2

Step 5: N=500 plasma pulses, Q0=0.5 MJ/m2

Step 3: N=300 cycles, W=20 MW/m2, ∆t=30 s

tpulse=0.5 ms (W=1 GW//m2), Tsurf=3000C, α=300

αPlasma flow direction

Step 2: N=2000 cycles, W=10 MW/m2, ∆t=30 s

(15 seconds – shot and 15 seconds – pause), Twater=400C, Vwater=10 m/s, Pwater=35 bar. Screening test at 5 MW/m2 before and after

Electron beam action

Water flow

Water flowCu

shield

Plasma flowW

shield

Water flow

Electron beamCu

shield

Step 4: N=300 cycles, W=20 MW/m2, ∆t=30 s

Water flow

Electron beamCu

shield

D. Kovalenko, SRC RF TRINITI 13th PFMC Workshop / 1st FEMaS Conference 8

Experimental results Plasma exposures + High heat flux testing

500

plas

ma

puls

esH

igh

heat

flux

test

ing

(HH

FT):

0

500

plas

ma

puls

es

0%20

00 c

ycle

s of

10M

W/m

2

500+

500=

1000

pla

sma

exp.

500

plas

ma

exp.

COPPERSHIELD

Step 1: 500 plasma pulses Step 2: +2000 cycles of 10MW/m2+300 cycles of 20MW/m2

TUNGSTENSHIELD

Step 3: +500 plasma pulses

300

cycl

es o

f 20M

W/m

230

0 cy

cles

of 2

0MW

/m2

0%20

00 c

ycle

s of

10M

W/m

2

300

cycl

es o

f 20M

W/m

230

0 cy

cles

of 2

0MW

/m2

D. Kovalenko, SRC RF TRINITI 13th PFMC Workshop / 1st FEMaS Conference 9

500 plasma pulses + +2000 cycles of

10MW/m2+300 cycles of 20MW/m2+

500 plasma pulses

500 plasma pulses + +2000 cycles of

10MW/m2+300 cycles of 20MW/m2

After 500 plasma pulses

Tungsten erosionPlasma exposure + High heat flux test

Edge melting and bridges formation

Peeling off of remelted material

Transversal cracks widening

Transversal cracks formation and widening

Longitudinal cracks formation

Edge melting

10 mm

Before exposure

D. Kovalenko, SRC RF TRINITI 13th PFMC Workshop / 1st FEMaS Conference 10

2 mm

Before exposure

2 mm

50 plasma pulses

2 mm

250 plasma pulses

2 mm

500 plasma pulses

2 mm

500 exp.+HHFT

2 mm

500 exp.+HHFT+500 exp.

Tungsten erosionArising and remelted material peeling off

D. Kovalenko, SRC RF TRINITI 13th PFMC Workshop / 1st FEMaS Conference 11

Tungsten erosionTypes of cracks

400 µm

Transversal cracks

400 µm

Transversal crack (width ~100µm)

500 plasma pulses++2000 cycles of 10MW/m2+300

cycles of 20MW/m2

400 µm

The crack bottom (-330 µm)

~25 µm

400 µm

Longitudinal crack top (surface)

~320 µm

D. Kovalenko, SRC RF TRINITI 13th PFMC Workshop / 1st FEMaS Conference 12

400 µm

500 plasma pulses

400 µm

500 plasma pulses+HНFT

400 µm

500 pulses+HHFT+200 pulses

100 µm

500 plasma pulses

100 µm

500 plasma pulses+HНFT

100 µm

500 pulses+HHFT+200 pulses

Tungsten erosionCracks width dynamics

D. Kovalenko, SRC RF TRINITI 13th PFMC Workshop / 1st FEMaS Conference 13

100 µm

Dust investigation PAN-fibers erosion of CFC

«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

• Eroded material is deposited on the vacuum chamber and diagnostics windows in a form of carbon films

Q = 1MJ/m2, ∆t=0.5 ms, N=100 pulses

D. Kovalenko, SRC RF TRINITI 13th PFMC Workshop / 1st FEMaS Conference 14

Dust investigation Dust collectors

14

Collectors of type I:thickness, volume, and mass measurements,

Collectors of type II:thermodesorption spectroscopy

The modernized target vacuum chamber allow to place various dust collectors

Polished silicon and stainless steel substrates

Total number of collectors in the plasma pulse series (200 pulses) were 55 collectors of type I, 10 collectors of type II

D. Kovalenko, SRC RF TRINITI 13th PFMC Workshop / 1st FEMaS Conference 15

Dust investigation Scheme of dust collectors placement

basissubstrate

limiter

mask

h

D. Kovalenko, SRC RF TRINITI 13th PFMC Workshop / 1st FEMaS Conference 16

Dust investigation Typical view of the collector after deposition of CFC erosion products

Collectors of type I Collectors of type II Collectors of type II

D. Kovalenko, SRC RF TRINITI 13th PFMC Workshop / 1st FEMaS Conference 17

Dust investigation Density of the film

X, mmY, mm

h, µm

M=0,34 mg; V=0,31 mm3; ρ=1,1 g/cm3; hmax=2 µm

h, µ

m

X, Y, mm

Thickness profiles along and across the sample

inaccuracy of measurements less than 100 Å

Thickness distribution and film characteristics

Typical film after 200 pulses Technological scratch interference pattern

Typical density varied in the range from 0.5 g/cm3 (flake-like films) to 2 g/cm3 (solid compact films).

D. Kovalenko, SRC RF TRINITI 13th PFMC Workshop / 1st FEMaS Conference 18

solid compact film (film of type 1) Intermediate type

flake-like film (film of type 2)Intermediate type

Dust investigation Various dust films observed on the collectors at the QSPA-T

More detailed information about optical properties of the films were presented in poster presentation of I. Arhipov et al.

D. Kovalenko, SRC RF TRINITI 13th PFMC Workshop / 1st FEMaS Conference 19

100 µm

100 µm

100 µm

100 µm

solid compact film (film of type 1)deposition rate 0.01μm/pulsedensity 1.0-1.5 g/cm3

flake-like film (film of type 2)deposition rate 0.02μm/pulsedensity 0.2-0.5 g/cm3

Intermediate type

Intermediate type

Dust investigation Optical microscopy of the dust film

D. Kovalenko, SRC RF TRINITI 13th PFMC Workshop / 1st FEMaS Conference 20

Dust investigation Electron microscopy of the dust film

solid compact

film (type 1)

flake-like film (type 2)

Intermediatetype

Tem

pera

ture

dec

reas

ing 10 µm 5 µm5 µm

50 µm

100 µm

5 µm 1 µm

2 µm10 µm

D. Kovalenko, SRC RF TRINITI 13th PFMC Workshop / 1st FEMaS Conference 21

Dust investigation Thermodesorption spectroscopy obtained by using MICMA facility (MEPHI)

300 600 900 1200 15000

2

4

6

Скорость вы

хода

, 1015

* cм

-2 *

с-1

Температура, K

D2 #1 D2 #2 D2 #3 D2 #4

300 600 900 1200 15000

2

4

6

Скорость вы

хода

, 1015

* cм

-2 *

с-1

Температура, K

HD #1 HD #2 HD #3 HD #4the typical relative concentration of

hydrogen isotopes (H+D):C equaled 0.2 for the compact films (density ≥ 1.5 g/cm3)

Temperature, K

Temperature, K

Des

orbt

ion

rate

, 101

5 ·cm

-2·c

-1D

esor

btio

nra

te, 1

015 ·c

m-2

·c-1

D. Kovalenko, SRC RF TRINITI 13th PFMC Workshop / 1st FEMaS Conference 22

SummaryTungsten erosion

• Edges melting and cracks formation are the main tungsten erosionprocesses under plasma action at the heat loads up to 0.5MJ/m2.

• The distance between newborn transversal (primary) cracks is 300-500 µm. The width of transversal cracks increases with number of plasma pulses. The maximum width value after 500 pulses is less than 20 µm.

• The width of transversal cracks significantly increases after high heat flux testing (HHFT) up to 50-200 µm.

• As a result of HHFT longitudinal cracks are formed. The width oflongitudinal cracks lie in the range of 100-400 µm.

• As a result of brittle destruction under HHFT remelted material and bridges are peeled off.

D. Kovalenko, SRC RF TRINITI 13th PFMC Workshop / 1st FEMaS Conference 23

SummaryCFC erosion. Dust film study

• Under ELM and disruption heat loads the CFC erosion was mainly due to PAN-fibers damage. The significant part of eroded materials deposited on the vacuum chamber.

• The maximum deposition rate equaled to 2·10-2 µm/pulse (tpulse = 0.5 ms) was observed in the downstream of plasma at the distance 30-60 cm from the target in the disruption simulation experiments (Q = 2.3 MJ/m2).

• The typical deposited film density was varied from 0.5 g/cm3 (flake-like films) to 2 g/cm3 (solid compact films).

• The typical relative concentration of hydrogen isotopes (H+D):C equaled 0.2 for the compact films (density ≥ 1.5 g/cm3).

D. Kovalenko, SRC RF TRINITI 13th PFMC Workshop / 1st FEMaS Conference 24

Thanks for your attention