- Email: [email protected]
Non-metallic materials for plasma-facing first wall components: Status and further development
Fusion Engineering and Design North-Holland, Amsterdam
NON-METALLIC STATUS AND
9 (1989)
55
55-61
MATERIALS FOR PLASMA-FACING FURTHER DEVELOPMENT
H. BOLT, K. KOIZLIK,
J. LINKE,
H. NICKEL
Institute for Reactor Materials and Institute for Plasma P. 0. Box 19 13. D-51 70 Jiilich, Fed. Rep. Germany
Physics,
FIRST
WALL
COMPONENTS:
and G. WOLF Nuclear
Research
Center
Jiilich,
Association
EURA
TOM-KFA,
During the last few years, systematic investigations of the response of the plasma-facing material to the plasma-wall interaction have been carried out. The goal of this work is to find materials which, on the one hand, withstand the plasma attacks, and, on the other hand, do not contaminate the plasma. The available results allow first systematic conclusions on the status of materials development and on the way that has still to be covered to reach acceptable solutions for this problem area. In this paper, the available test facilities are presented, together with the target values on which the material tests are aiming. The first systematic test results are discussed for non-metallic materials and the conclusions that can be drawn on the status of the already reached position. This is done on the basis of the materials work performed at the Institute for Reactor Materials in cooperation with the Institute for Plasma Physics of the Nuclear Research Center, Jiilich.
1. Introduction
The plasma-facingsurfacesin operating tokamaks consistof stainlesssteelsor high temperatureresistant alloys [1,2] for the low-load areas,and graphites[3] for the higher loaded areasof the fist wall. Obviously, graphiteshave beenselectedon the basisof experience with the HTG fission reactor. Carbon fiber reinforced carbon (CFC), which sometimesis applied to heavily loaded areas like armor against neutral beam shine through [4], seemsto be selectedon the basisof availability. A few experimentshave beenmadewith thin TIC coatingson graphites[S] or TIC layersbondedto refractory metal tiles; however, theseshowedpoor stability of thin coatingsand the fast erosionof titanium during the plasma-wall interaction. During the last few years,a more systematicinvestigation of materialswas started with the aim of finding or developingoptimum materialsfor the plasma-facing components.Two principally different directionsof this work can be seen.One is representedprimarily by the concernedwork in the KFA tokamak, TEXTOR, and aims at the optimization of the in-situ coating of the first wall with thin layers of amorphous,hydrogenated carbon (a-C : H) [6,7] or boronized carbon. The other more conventional work is directed at optimizing or developing bulk ceramics or thick, sacrificial layers bondedto actively cooledmetalliccarriers. In this sense, graphitic materials may also be classifiedas ceramics,
where we use the term “ceramic” to describea “nonmetallic” material. This paper reviews the statusof the developmentof bulk non-metallic materialsfor the plasma-facingareas or componentsof the first wall.
2. Target values
The loadingtypes and load valuesof the plasma-wall interaction which the plasma-facingmaterialsshall endure without being disintegrated and, on the other hand, without an intolerable contamination of the plasma,are primarily given by the NET concept [8]. In the first phaseof operation, the low-loadedareas of the first wall are loaded with a maximumpulsedheat flw of about 0.5 MWmM2 with pulsedurationsof some 10 to few 100 s. When radiation cooled, the plasma-facing material will reachtemperaturesup to 1800a C. The highly loaded components like limiters or divertors, which have to be actively cooled, are loadedwith some 5 MWme2, again for up to a few 100 s, during normal plasma operation. During unstable plasmastates, the power depositioncan reach some50 MWmm2during 20 ms (slow energy deposition) or up to severalthousand MWme2 during 0.1 ms (fast energy deposition). In the secondphase of operation, when a plasma facility operates as a real fusion reactor, the material has to overcomethe irradiation with the 14 MeV fusion
0920-3796/89/$03.50 0 Elsevier Science Publishers B.V.
56 Table 1 Experimental application
H. Bolr et al. / Materials
facilities for material available in the KFA
tests
Electron beam I 150 kV; 100 mA; pulse duration minimum mode; loaded area typically 1 cm2
Electron beam 2 150 kV; 200 mA; or scanned mode;
for
fusion
for plasma-facing
firs1 wall components
reactor
10 ms; steady
state
pulse duration minimum 2 ms; steady loaded area typically 1 cm2
state
HD-SC Laser Ruby-/Eximer-/COz-Laser; CO,-Laser duration 100 ns-1 s (C02-Laser)
Neutral beam injector test facility 50 kV; 88 A; pulse duration minimum loaded area 10 x 30 cm2
TEXTOR Limiter lock chamber;
max.
2.5 kW;
0 065
pulse
power 10 ms, maximum
2.0
10s; 66110 / = 661 9 <666/B &66/l
size typically
12 X 6 X 8 cm-’
=66/b
density
1
length
6.0
0.0
I I
’
t ’
4
1s
/ kW cm-*
4.0
II
sample
0.25
pulse
I 1 pulse
length,=OOSr
)
Diagnostic for on-line data aquisit. during mai. tests Surface temp. 300 o C-3000’ C by two pyrometers; time resolution minimum 2 ms; video image; gas pressure near the sample (outgassing of material) ,‘,‘,,““I 5
Laboratories and equipment for pre- and post-mortem analysis Cold and hot labs from metaIlography/ceramography; optical and electron microscopy (SEM, TEM), chemical analysis, thermal conductivity, dimensional changes; Cpoint bending test; electron beam facility for thermal fatigue/shock/erosion tests - not yet in hot cells
’ 10
15
shot number Fig. 1. Quantitative description of material damage in electron beam tests: (a) material loss by erosion processes; indicated is the load limit (traced line) for sample disintegration; (b) different types of material damage in multiple shot experiments.
Table neutrons (in the case of the D-T tion target values are mentioned:
reaction). 3 dpa
Two irradiaat a first aim,
and 30 dpa for a demo reactor.
3. Experimental
devices
Three groups of experiments are used for systematic materials test, see table 1 [9-111. The first group covers the so-called “out of pile” or laboratory experiments, namely the electron beam tests, the laser tests, and the materials tests in the neutral beam injector test facility, i.e. in hydrogen beams. Here, very systematic experiments to test the thermal fatigue, thermal shock, and erosion behavior of candidate
Neutron irradiation tests materials which are carried forschungszentrum Karlsruhe
with non-metallic out in collaboration and CEA.
spaRation neutrons 400°C (b) Petten, HFR, fission neutrons Petten I 1200°c Petten II 400 o C/600 o C/800 Petten III 400°C Petten IV 1500°C (c) Phenix fast breeder neutrons 450°c (d) Petten, HFR, fission neutrons
plasma-facing with Kem-
(a) Los Alamos,
1 dpa
o
1 10 1 3
dpa dpa dpa dpa
30 dpa
4-6 short time irradiations of graphitic materials at 900 o C to determine low doses
the rapid
decrease
of thermal
conductivity
at
H. Bolt .CI al. / Marerials
for plasma-/acing
materials can be carried out. These experiments result in quantitative descriptions of material damage induced by the simulated plasma-wall interaction processes. Typical results are given in fig. 1 for the thermal shock and thermal fatigue induced material loss, load limit curve for sample disintegration by thermal shock loading, and load limits for different damage types in multiple shot experiments. The second group contains material experiments in the plasma device, TEXTOR, in which the materials, by means of a special limiter lock chamber, are exposed to optional numbers of plasma discharges and then are investigated with respect to the plasma induced material damage. The third group of fusion reactor materials tests contains the neutron irradiation experiments. Since the
jirst
wall components
57
necessary 14 MeV neutrons are not available so far in a sufficient high flux, one has to fall back on fission reactors and spallation neutron sources. The neutron irradiations with non-metallic plasmafacing materials of the KFA - in cooperation with other German (KfK), French (CEA). and other collegues are listed in table 2. They have three particular aims: (1) they allow a first comparison of the influence of the neutron energy: experiments in the spallation neutron source and experiment Petten III; (2) they allow to compare the material damage at different doses: Petten III, Petten II, and Phenix irradiation; and (3) they allow to compare the influence of the irradiation temperature: here, the experiments are not yet really adequate.
Fig. 2. Two typical qualities of graphite after electron beam test, 100 MWm- ‘, 0.1 s: (a) ultra fine grain graphite, without binder; gs Q 4 pm; (b) fine grain graphite, conventionally bonded; gs < 20 pm.
58 Finally, the tions, which information conductivity, influence of
H. Bolt et al. / Materials
for plasma-facing
experimental series with short-time irradiais under preparation, will give a precise on the very fast decrease of the thermal especially of graphitic materials, under the relatively small neutron doses.
4. Test results The systematic tests of plasma-facing materials some important conclusions, which are briefly marized here.
first wall components
of these materials during thermal shock loads is considerably worse than that of conventionally bonded fine grain graphites, as shown in fig. 2. So, the conclusion was to develop a graphite with ultra fine grains and conventional bonds. Such graphite qualities are available from several producers. 4.2. C-C composites
drew sum-
4.1. Graphite
The best neutron irradiation behavior was found for binder-free ultra fine grain graphites, but the behavior
In terms of crack or fracture resistance under thermal shocks, C-C composites proved to be superior to graphites. However, 2-d C-C materials show significant erosion under high heat loads, whereas the erosion of 4-d reinforced materials is greatly reduced (121 (fig. 3). Thus, 2-d composites can be recommended for lowloaded wall parts, whereas for the portions where high
Fig. 3. Two-dimensional C-C composite after electron beam test, 50 MWm-‘, 1 s: (a) Electron beam perpenchcul ar to the fi ber WM ve planes. Heat transfer into the bulk is hampered under heat loads in this direction which results in large erosi on CIrate1‘S. (b) Elec :tron beam parallel to the fiber weave planes. The craters’ sir:e is reduced because of improved heat transport the bIUlk mate]ial.
H. Bolt et a/. / Materials for plasma-facing&r heat fluxes are expected, 4-d materials are better. However, the neutron damage resistance of C-C composites is still highly uncertain.
wafl components
59
4.3. SIC fiber reinforced Sic SIC fiber reinforced SIC material could be an alternative to alloyed SIC compounds, being used to cover the low-loaded area of the first wail. Its erosion behavior is not yet convincing, as shown in fig. 4. But its main disadvantage - at least of the material investigated in IRW - is its very poor thermal stability: already at medium temperatures, and after a relatively short annealing time, the Sic fibers simply “disappear” (fig. 5).
4.4. Coal-mix
material
A completely new class of materials is a graphite/Sic mixtures, produced with a wide spectrum of materials parameters such as porosity, density, SIC content, grain size, etc. It can also be manufactured as a graded quality with a porosity and/or Sic content gradient in the bulk. Fig. 6 shows a ceramographic section of such a material which is now subjected to material testing.
5. Conclusions Materials tests in laboratory experiments and in operating plasma devices such as TEXTOR and the experiences with plasma-facing materials in tokamaks have considerably reduced the number of candidate materials for this application, From the available results, the conclusion may be deduced that, after an additional period of optimization, materials will be at the disposal of the engineers for the low-loaded, during stable plasma operation, also for the highly loaded first wall components. This work, to optimize the materials and may be to develop new ones, has to be done in the near future. More or less open are the problems of the materials behavior under severe plasma disruptions and, at least partly, under 14 MeV neutron irradiation.
References
Fig. 4. Sic fiber reinforced Sic after electron beam experiment, 20 MWmm2, 50 ms; fiber directions vertical to electron beam; SEM micrographs.
[l] Next European Torus, Net Status Report, Euratom Report EU-FU/XII-80/86/51 (1985). [2] P. Deschamps, A Grosman, M. Lipa and A. Samain, Power exhaust and plasma-surface interaction control in Tore Supra, J. Nucl. Mater. 128 & 129 (1984) 38.
60
H. Bolt
et al. / Materials
for plasma-facingfirst
wall
components
Fig. 5. Sic-fiber reinforced Sic (marker = 10 am): (a) as produced; (b) after annealing 1400 o C, 8 h; (c) after annealing 1400 o C, 2 h + 1500 o C, 1 h; (b)+(c) in argon atmosphere; left column: wretched; right column: etched in Murakami.
[3] R.W. Conn, Plasma-materials interaction and high-heatflux component research and development, UCLA-Report UCLA-PPG-1012, Univ. of California, Los Angeles (1986). [4] Jet Joint Undertaking, Progress Report 1986, EuratomReport EUR-11113 EN, EUR-JET-PR 4 (1987). [5] M. Uhickson, Material selection for TFTR limiters, J. Vat. Sci. Technol. 18 (1981) 1037. [6] J. Winter, H.G. Esser, P. Wienhold et al., Properties of
carbonization layers relevant to plasma-surface-interactions, Nucl. Instr. and Meth. B 23 (1987) 538. [7] E. Taglauer and G. Staudenmaier, Surface analysis in fusion devices, J. Vat. Sci. Technol. A S (1987) 1352. [8] G. Vieider, A. Cardella, M. Chazalon, F. Engelmann, H. Gorenflo, B. Libin, B. Pavan, J. Raeder, E. Theisen and Ch. H. Wu, Fusion Engrg. Des. 8-10 (1989), in these Proceedings.
H. Bolt
Fig.
6. Graphite/Sic
mixture
et al. / Materials
for plasma-facing
first
wall
components
produced by liquid Si impregnation of highly porous “coat-mix” manufactured with a wide spectrum of material parameters.
[9] H. Hoven, K. Koizhk, J. Linke, H, Nickel and E. Wallura, Berichte der Kemforschungsanlage Jtihch Jtil-2002 (1985). [lo] H. Bolt, H. Hoven, E. Kny, K. Koixhk, J. Linke, H. Nickel and E. Wallura, Berichte der Kemforschungsanlage J&h Jtil-2086 (1986). [ll] W. Delle, J. Linke, H. Nickel and E. Walhtra, Spezielle
61
material;
this
quality
can be
Berichte der Kemforschungsanlage Jiilich Jtil-Spez-401 (1987). [12] H. Bolt, A. Miyahara, T. Kuroda et al., High heat flux experiments on C-C composite materials, Nagoya Univ. Report IPPJ-AM-51, Nagoya (1987).
NON-METALLIC STATUS AND
9 (1989)
55
55-61
MATERIALS FOR PLASMA-FACING FURTHER DEVELOPMENT
H. BOLT, K. KOIZLIK,
J. LINKE,
H. NICKEL
Institute for Reactor Materials and Institute for Plasma P. 0. Box 19 13. D-51 70 Jiilich, Fed. Rep. Germany
Physics,
FIRST
WALL
COMPONENTS:
and G. WOLF Nuclear
Research
Center
Jiilich,
Association
EURA
TOM-KFA,
During the last few years, systematic investigations of the response of the plasma-facing material to the plasma-wall interaction have been carried out. The goal of this work is to find materials which, on the one hand, withstand the plasma attacks, and, on the other hand, do not contaminate the plasma. The available results allow first systematic conclusions on the status of materials development and on the way that has still to be covered to reach acceptable solutions for this problem area. In this paper, the available test facilities are presented, together with the target values on which the material tests are aiming. The first systematic test results are discussed for non-metallic materials and the conclusions that can be drawn on the status of the already reached position. This is done on the basis of the materials work performed at the Institute for Reactor Materials in cooperation with the Institute for Plasma Physics of the Nuclear Research Center, Jiilich.
1. Introduction
The plasma-facingsurfacesin operating tokamaks consistof stainlesssteelsor high temperatureresistant alloys [1,2] for the low-load areas,and graphites[3] for the higher loaded areasof the fist wall. Obviously, graphiteshave beenselectedon the basisof experience with the HTG fission reactor. Carbon fiber reinforced carbon (CFC), which sometimesis applied to heavily loaded areas like armor against neutral beam shine through [4], seemsto be selectedon the basisof availability. A few experimentshave beenmadewith thin TIC coatingson graphites[S] or TIC layersbondedto refractory metal tiles; however, theseshowedpoor stability of thin coatingsand the fast erosionof titanium during the plasma-wall interaction. During the last few years,a more systematicinvestigation of materialswas started with the aim of finding or developingoptimum materialsfor the plasma-facing components.Two principally different directionsof this work can be seen.One is representedprimarily by the concernedwork in the KFA tokamak, TEXTOR, and aims at the optimization of the in-situ coating of the first wall with thin layers of amorphous,hydrogenated carbon (a-C : H) [6,7] or boronized carbon. The other more conventional work is directed at optimizing or developing bulk ceramics or thick, sacrificial layers bondedto actively cooledmetalliccarriers. In this sense, graphitic materials may also be classifiedas ceramics,
where we use the term “ceramic” to describea “nonmetallic” material. This paper reviews the statusof the developmentof bulk non-metallic materialsfor the plasma-facingareas or componentsof the first wall.
2. Target values
The loadingtypes and load valuesof the plasma-wall interaction which the plasma-facingmaterialsshall endure without being disintegrated and, on the other hand, without an intolerable contamination of the plasma,are primarily given by the NET concept [8]. In the first phaseof operation, the low-loadedareas of the first wall are loaded with a maximumpulsedheat flw of about 0.5 MWmM2 with pulsedurationsof some 10 to few 100 s. When radiation cooled, the plasma-facing material will reachtemperaturesup to 1800a C. The highly loaded components like limiters or divertors, which have to be actively cooled, are loadedwith some 5 MWme2, again for up to a few 100 s, during normal plasma operation. During unstable plasmastates, the power depositioncan reach some50 MWmm2during 20 ms (slow energy deposition) or up to severalthousand MWme2 during 0.1 ms (fast energy deposition). In the secondphase of operation, when a plasma facility operates as a real fusion reactor, the material has to overcomethe irradiation with the 14 MeV fusion
0920-3796/89/$03.50 0 Elsevier Science Publishers B.V.
56 Table 1 Experimental application
H. Bolr et al. / Materials
facilities for material available in the KFA
tests
Electron beam I 150 kV; 100 mA; pulse duration minimum mode; loaded area typically 1 cm2
Electron beam 2 150 kV; 200 mA; or scanned mode;
for
fusion
for plasma-facing
firs1 wall components
reactor
10 ms; steady
state
pulse duration minimum 2 ms; steady loaded area typically 1 cm2
state
HD-SC Laser Ruby-/Eximer-/COz-Laser; CO,-Laser duration 100 ns-1 s (C02-Laser)
Neutral beam injector test facility 50 kV; 88 A; pulse duration minimum loaded area 10 x 30 cm2
TEXTOR Limiter lock chamber;
max.
2.5 kW;
0 065
pulse
power 10 ms, maximum
2.0
10s; 66110 / = 661 9 <666/B &66/l
size typically
12 X 6 X 8 cm-’
=66/b
density
1
length
6.0
0.0
I I
’
t ’
4
1s
/ kW cm-*
4.0
II
sample
0.25
pulse
I 1 pulse
length,=OOSr
)
Diagnostic for on-line data aquisit. during mai. tests Surface temp. 300 o C-3000’ C by two pyrometers; time resolution minimum 2 ms; video image; gas pressure near the sample (outgassing of material) ,‘,‘,,““I 5
Laboratories and equipment for pre- and post-mortem analysis Cold and hot labs from metaIlography/ceramography; optical and electron microscopy (SEM, TEM), chemical analysis, thermal conductivity, dimensional changes; Cpoint bending test; electron beam facility for thermal fatigue/shock/erosion tests - not yet in hot cells
’ 10
15
shot number Fig. 1. Quantitative description of material damage in electron beam tests: (a) material loss by erosion processes; indicated is the load limit (traced line) for sample disintegration; (b) different types of material damage in multiple shot experiments.
Table neutrons (in the case of the D-T tion target values are mentioned:
reaction). 3 dpa
Two irradiaat a first aim,
and 30 dpa for a demo reactor.
3. Experimental
devices
Three groups of experiments are used for systematic materials test, see table 1 [9-111. The first group covers the so-called “out of pile” or laboratory experiments, namely the electron beam tests, the laser tests, and the materials tests in the neutral beam injector test facility, i.e. in hydrogen beams. Here, very systematic experiments to test the thermal fatigue, thermal shock, and erosion behavior of candidate
Neutron irradiation tests materials which are carried forschungszentrum Karlsruhe
with non-metallic out in collaboration and CEA.
spaRation neutrons 400°C (b) Petten, HFR, fission neutrons Petten I 1200°c Petten II 400 o C/600 o C/800 Petten III 400°C Petten IV 1500°C (c) Phenix fast breeder neutrons 450°c (d) Petten, HFR, fission neutrons
plasma-facing with Kem-
(a) Los Alamos,
1 dpa
o
1 10 1 3
dpa dpa dpa dpa
30 dpa
4-6 short time irradiations of graphitic materials at 900 o C to determine low doses
the rapid
decrease
of thermal
conductivity
at
H. Bolt .CI al. / Marerials
for plasma-/acing
materials can be carried out. These experiments result in quantitative descriptions of material damage induced by the simulated plasma-wall interaction processes. Typical results are given in fig. 1 for the thermal shock and thermal fatigue induced material loss, load limit curve for sample disintegration by thermal shock loading, and load limits for different damage types in multiple shot experiments. The second group contains material experiments in the plasma device, TEXTOR, in which the materials, by means of a special limiter lock chamber, are exposed to optional numbers of plasma discharges and then are investigated with respect to the plasma induced material damage. The third group of fusion reactor materials tests contains the neutron irradiation experiments. Since the
jirst
wall components
57
necessary 14 MeV neutrons are not available so far in a sufficient high flux, one has to fall back on fission reactors and spallation neutron sources. The neutron irradiations with non-metallic plasmafacing materials of the KFA - in cooperation with other German (KfK), French (CEA). and other collegues are listed in table 2. They have three particular aims: (1) they allow a first comparison of the influence of the neutron energy: experiments in the spallation neutron source and experiment Petten III; (2) they allow to compare the material damage at different doses: Petten III, Petten II, and Phenix irradiation; and (3) they allow to compare the influence of the irradiation temperature: here, the experiments are not yet really adequate.
Fig. 2. Two typical qualities of graphite after electron beam test, 100 MWm- ‘, 0.1 s: (a) ultra fine grain graphite, without binder; gs Q 4 pm; (b) fine grain graphite, conventionally bonded; gs < 20 pm.
58 Finally, the tions, which information conductivity, influence of
H. Bolt et al. / Materials
for plasma-facing
experimental series with short-time irradiais under preparation, will give a precise on the very fast decrease of the thermal especially of graphitic materials, under the relatively small neutron doses.
4. Test results The systematic tests of plasma-facing materials some important conclusions, which are briefly marized here.
first wall components
of these materials during thermal shock loads is considerably worse than that of conventionally bonded fine grain graphites, as shown in fig. 2. So, the conclusion was to develop a graphite with ultra fine grains and conventional bonds. Such graphite qualities are available from several producers. 4.2. C-C composites
drew sum-
4.1. Graphite
The best neutron irradiation behavior was found for binder-free ultra fine grain graphites, but the behavior
In terms of crack or fracture resistance under thermal shocks, C-C composites proved to be superior to graphites. However, 2-d C-C materials show significant erosion under high heat loads, whereas the erosion of 4-d reinforced materials is greatly reduced (121 (fig. 3). Thus, 2-d composites can be recommended for lowloaded wall parts, whereas for the portions where high
Fig. 3. Two-dimensional C-C composite after electron beam test, 50 MWm-‘, 1 s: (a) Electron beam perpenchcul ar to the fi ber WM ve planes. Heat transfer into the bulk is hampered under heat loads in this direction which results in large erosi on CIrate1‘S. (b) Elec :tron beam parallel to the fiber weave planes. The craters’ sir:e is reduced because of improved heat transport the bIUlk mate]ial.
H. Bolt et a/. / Materials for plasma-facing&r heat fluxes are expected, 4-d materials are better. However, the neutron damage resistance of C-C composites is still highly uncertain.
wafl components
59
4.3. SIC fiber reinforced Sic SIC fiber reinforced SIC material could be an alternative to alloyed SIC compounds, being used to cover the low-loaded area of the first wail. Its erosion behavior is not yet convincing, as shown in fig. 4. But its main disadvantage - at least of the material investigated in IRW - is its very poor thermal stability: already at medium temperatures, and after a relatively short annealing time, the Sic fibers simply “disappear” (fig. 5).
4.4. Coal-mix
material
A completely new class of materials is a graphite/Sic mixtures, produced with a wide spectrum of materials parameters such as porosity, density, SIC content, grain size, etc. It can also be manufactured as a graded quality with a porosity and/or Sic content gradient in the bulk. Fig. 6 shows a ceramographic section of such a material which is now subjected to material testing.
5. Conclusions Materials tests in laboratory experiments and in operating plasma devices such as TEXTOR and the experiences with plasma-facing materials in tokamaks have considerably reduced the number of candidate materials for this application, From the available results, the conclusion may be deduced that, after an additional period of optimization, materials will be at the disposal of the engineers for the low-loaded, during stable plasma operation, also for the highly loaded first wall components. This work, to optimize the materials and may be to develop new ones, has to be done in the near future. More or less open are the problems of the materials behavior under severe plasma disruptions and, at least partly, under 14 MeV neutron irradiation.
References
Fig. 4. Sic fiber reinforced Sic after electron beam experiment, 20 MWmm2, 50 ms; fiber directions vertical to electron beam; SEM micrographs.
[l] Next European Torus, Net Status Report, Euratom Report EU-FU/XII-80/86/51 (1985). [2] P. Deschamps, A Grosman, M. Lipa and A. Samain, Power exhaust and plasma-surface interaction control in Tore Supra, J. Nucl. Mater. 128 & 129 (1984) 38.
60
H. Bolt
et al. / Materials
for plasma-facingfirst
wall
components
Fig. 5. Sic-fiber reinforced Sic (marker = 10 am): (a) as produced; (b) after annealing 1400 o C, 8 h; (c) after annealing 1400 o C, 2 h + 1500 o C, 1 h; (b)+(c) in argon atmosphere; left column: wretched; right column: etched in Murakami.
[3] R.W. Conn, Plasma-materials interaction and high-heatflux component research and development, UCLA-Report UCLA-PPG-1012, Univ. of California, Los Angeles (1986). [4] Jet Joint Undertaking, Progress Report 1986, EuratomReport EUR-11113 EN, EUR-JET-PR 4 (1987). [5] M. Uhickson, Material selection for TFTR limiters, J. Vat. Sci. Technol. 18 (1981) 1037. [6] J. Winter, H.G. Esser, P. Wienhold et al., Properties of
carbonization layers relevant to plasma-surface-interactions, Nucl. Instr. and Meth. B 23 (1987) 538. [7] E. Taglauer and G. Staudenmaier, Surface analysis in fusion devices, J. Vat. Sci. Technol. A S (1987) 1352. [8] G. Vieider, A. Cardella, M. Chazalon, F. Engelmann, H. Gorenflo, B. Libin, B. Pavan, J. Raeder, E. Theisen and Ch. H. Wu, Fusion Engrg. Des. 8-10 (1989), in these Proceedings.
H. Bolt
Fig.
6. Graphite/Sic
mixture
et al. / Materials
for plasma-facing
first
wall
components
produced by liquid Si impregnation of highly porous “coat-mix” manufactured with a wide spectrum of material parameters.
[9] H. Hoven, K. Koizhk, J. Linke, H, Nickel and E. Wallura, Berichte der Kemforschungsanlage Jtihch Jtil-2002 (1985). [lo] H. Bolt, H. Hoven, E. Kny, K. Koixhk, J. Linke, H. Nickel and E. Wallura, Berichte der Kemforschungsanlage J&h Jtil-2086 (1986). [ll] W. Delle, J. Linke, H. Nickel and E. Walhtra, Spezielle
61
material;
this
quality
can be
Berichte der Kemforschungsanlage Jiilich Jtil-Spez-401 (1987). [12] H. Bolt, A. Miyahara, T. Kuroda et al., High heat flux experiments on C-C composite materials, Nagoya Univ. Report IPPJ-AM-51, Nagoya (1987).