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Optimization of armour geometry and bonding techniques for tungsten-armoured high heat flux components
Fusion Engineering and Design 61 /62 (2002) 185 /190 www.elsevier.com/locate/fusengdes
Review article
Optimization of armour geometry and bonding techniques for tungsten-armoured high heat flux components R.N. Giniyatulin , V.L. Komarov, E.G. Kuzmin, A.N. Makhankov, I.V. Mazul, N.A. Yablokov, A.N. Zhuk Efremov Institute, Sovetsky pr. 1, 196641 St. Petersburg, Russia
Abstract Joining of tungsten with copper-based cooling structure and armour geometry optimization are the major aspects in development of the tungsten-armoured plasma facing components (PFC). Fabrication techniques and high heat flux (HHF) tests of tungsten-armoured components have to reflect different PFC designs and acceptable manufacturing cost. The authors present the recent results of tungsten-armoured mock-ups development based on manufacturing and HHF tests. Two aspects were investigated */selection of armour geometry and examination of tungsten /copper bonding techniques. Brazing and casting tungsten /copper bonding techniques were used in small mock-ups. The mockups with armour tiles (20/5 /10, 10 /10 /10, 20 /20 /10, 27 /27/10) mm3 in dimensions were tested by cyclic heat fluxes in the range of (5 /20) MW/m2, the number of thermal cycles varied from hundreds to several thousands for each mock-up. The results of the tests show the applicability of different geometry and different bonding technique to corresponding heat loading. A medium-scale mock-up 0.6-m in length was manufactured and tested. HHF tests of the medium-scale mock-up have demonstrated the applicability of the applied bonding techniques and armour geometry for full-scale PFC’s manufacturing. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Tungsten-armour; Plasma facing components; Heat flux
1. Introduction Tungsten-armoured structures are used in various high heat flux (HHF) components. The design of plasma facing components (PFCs) such as the vertical target (VT) and Dome for the International Thermonuclear Experimental Reactor
Corresponding author. Tel.: /7-812-462-7834; fax: 7-812464-4623 E-mail address: [email protected] (R.N. Giniyatulin).
(ITER) Divertor requires the joints between armour tiles and actively-cooled copper-based heat sink (HS) [1]. These joints must provide a thermal contact and strong attachment of armour material with the HS structure. For tungsten-armoured divertor components cyclic heat loading varies from 3 MW/m2 for the Dome up to 20 MW/m2 for the lower part of the VT [2]. The wide range of operational conditions for different components results in their corresponding designs. Different approaches to joining techniques together with various geometry concepts are used.
0920-3796/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 0 - 3 7 9 6 ( 0 2 ) 0 0 2 9 7 - 1
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R.N. Giniyatulin et al. / Fusion Engineering and Design 61 /62 (2002) 185 /190
This paper summarizes the most acceptable recent results obtained in tungsten-armoured PFC development. Two bonding techniques, such as casting and brazing, together with the armour tile geometry optimization were considered. The flat-tile and monoblock concepts were tested. Smooth cylindrical and hypervapotron cooling channels were used for the components. The results of HHF tests of small- and medium-scale mock-ups confirming the selected bonding techniques and geometries are presented.
2. Development of small-scale mock-ups The mock-ups were developed using the following types of armour tiles: lamella-type armour; monoblock armour; flat tile armour. The general approach was considered for development of small-scale mock-ups */manufacturing of the mock-ups and their HHF testing under reference conditions. 2.1. Components geometry The components consist of tungsten tiles attached to the copper-based HS. The problem of a considerable mismatch of their thermal expansion coefficients has been solved by castellation of armour tiles (or using separate tiles) and by using a soft intermediate copper layer between tungsten and HS. 2.2. Applied materials Precipitation hardened CuCrZr-alloy was used as a HS material. The optimum properties of the HS were to be retained after subsequent thermal heat treatment. Tungsten of several grades in various half-finished products was used as an armour material: single crystal (rods), sintered pure and cast alloy (rods and rolled sheets). Thick rolled sheets (up to 30 mm) were produced for this stage of work to minimize the manufacturing cost. The brazing CuInSnNiMn alloy (STEMET 1108, MEPHI AMETO) with a brazing temperature of 800 8C was used as a filler metal for both W/Cu and Cu/CuCrZr joints [3]. Pure copper was
used for casting technique to produce W/Cu cast structures and for soft intermediate layer in a W/ Cu brazed jointS. 2.3. Bonding techniques Two bonding techniques for W/Cu joining were used for fabrication of mock-ups: fast brazing by electron-beam heating; casting of pure copper to tungsten tile [3]. Brazing technique for W/Cu joint was used as an alternative to casting. It was necessary to compare brazed and cast joints under relevant testing conditions and find the HHF limit for brazing. One-step brazing for W /Cu /CuCrZr joint and two-step brazing for W /Cu and W/ Cu /CuCrZr joint were applied. W/Cu cast bimetallic tiles of the mock-ups were prepared from long (L/200 mm) half-finished bimetallic blocks. 2.4. Geometry of tiles The thickness of armour material was taken as 10 mm for all flat-tile mock-ups. This thickness is limited by maximum level of expected heat flux with corresponding surface temperature, on the one hand, and maximum allowable thickness to be retained during plasma disruption, on the other hand. Several planar dimensions of flat armour tiles were used (A /B /C mm3, where A, width; B, length; C, thickness): lamella */(20 /5) mm2; macrobrush*/(27 /27) mm2; macrobrush */ (20 /20) mm2; macrobrush */(10 /10) mm2. Two options of flat tiles were compared */rectangular-shape and trapezoid-shape. Monoblock-type mock-up has tiles (25 /20 /3) mm3 in dimension. 2.5. Fabrication of mock-ups Rectangular HS blocks from CuCrZr alloy which have cooling channel 12 mm in diameter were used for flat-tile components. CuCrZr-tube 12 mm in diameter was used for a monoblock mock-up. Electric discharge machining (EDM) is the final step of armour tiles preparation that provides the required castellation. The depth of EDM cut is equal to or more than the tungsten thickness.
R.N. Giniyatulin et al. / Fusion Engineering and Design 61 /62 (2002) 185 /190
The machined tungsten and W/Cu tiles were brazed with HS blocks. Two types of bimetallic tiles were used in the mock-ups for both bonding techniques: separate bimetallic tiles (10 /10, 20 /20, 27/27 mm2) with all sides ground; bimetallic macrotiles (20 / 20 mm2 with a castellation step of 10 mm and 27 /27 mm2 with a castellation step of 9 mm) with only outer sides ground and without grinding in EDM gaps. The grinding of all tile sides after EDM is very important to remove the cracked layers, but macrotile option is attractive in view of manufacturing cost reduction. Thus, the use of unground armour tiles has to be examined under relevant testing conditions. The use of trapezoid-shape separate tiles is one of the cost-effective approaches for armouring by separate flat tiles. The assembly process with such tiles during brazing does not require setting of the gaps between them. The monoblock mock-up was produced by the cast technology. The pack of six (25 /20 /3) mm3-tiles with holes was cast by pure copper. The subsequent machining removed extra copper inside the channel and outside the block. Brazing of W/Cu block with CuCrZr tube and a stainless steel (SS) block was the final step. Twenty small-scale mock-ups (few mock-ups of each type) were manufactured and tested. The most acceptable results and mock-up photos are presented in Table 1. 2.6. Testing conditions The expected heat fluxes onto W-armoured divertor components vary, i.e. up to 20 MW/m2 for the VT and up to 5 MW/m2 for the Dome. Therefore, the Tsefey electron-beam facility (Efremov Institute, Russia) [4] was used. The mock-ups were tested at the following conditions: heat flux density range */(5 /20) MW/m2; time of load/ pause*/(10 /15)/10 s, inlet water pressure */(1.0 / 1.5) MPa; water flow rate */(10 /15) m/s; background pressure in the chamber */104 Pa. For all mock-ups tested at heat fluxes higher than 10 MW/m2 a twisted tape was used to facilitate the heat transfer capability.
187
Typical diagnostic methods were used during HHF testing: bulk thermocouples measuring, TVrecording, IR-recording, Spot pyrometers, water calorimeter. The criterion for mock-up reliability was to maintain the thermal contact in W/Cu and Cu/ CuCrZr joints. Failure event during the tests means cracking in any joints or in armour material that affect in overheating of the surface.
2.7. Results of testing of small-scale mock-ups Fig. 1 presents the results of testing of smallscale mock-ups of different armour geometry and with different W/Cu joining techniques (Table 1), as well as previously obtained results of testing of cast mock-ups with tiles (10 /10 /10) mm3 [5] and (44 /44/3) mm3 [6] in dimension. It is shown (Fig. 1) that the acceptable level of heat flux loading during fatigue testing strongly depends on the armour tile dimensions. It is obvious that the minimum planar dimensions are preferable for high loading conditions (15 /20 MW/m2) and the maximum dimensions are suitable for moderate conditions (3 /5 MW/m2), but the cost issues require the optimal dimensions to be chosen. The results allow the following conclusion: 1) All tungsten grades demonstrate similar thermal fatigue performance in case of proper orientation (texture in the heat flux flow direction). 2) Armour with tiles (20 /20 /10) mm3 and (27 /27/10) mm3 in dimensions has an HHF limitation of /10 MW/m2 for both casting and brazing technology. 3) Brazing CuSnInNiMn filler metal for W/Cu joint demonstrates the acceptable reliability up to heat fluxes of (15 /17) MW/m2 for tiles (10 /10/10) mm3 in dimension, and the brazing technique is recommended, as being a cheaper alternative, for the components that work at heat fluxes below /15 MW/m2. 4) Experiments show that the gap width and shape between tiles do not affect the armour performance, if the tiles do not touch each other during loading. A gap of 0.2 mm at the
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Table 1 Summary of the most representative HHF tests of W armoured mock-ups Geometry of tiles
W/Cu joining Testing conditions technique
Picture
Heat flux MW/m2
Number of cycles
15
1000
17 15
100(FJ) 1000
17.5 20 10 15
1000 130(FA) 1000 300(FA)
10
1000
15 17
500(FJ) 260(FH)
9/9/10 (Hypervapotron mock-up)
7 10 12.5 20
1000 1000 1000 2000(WF)
27/27/10 (Hypervapotron mock-up)
7 10 12.5
1000 1000 1000(WF)
20/5/10
Brazing
10/10/10
20/20/10
20/20/10
20/25/3 (Monoblock)
Casting
Designations: FJ */failure in joint; FA */failure in armour; FH */failure in heal sink; WF */without failure.
top of the tiles is sufficient for all ITER HHF components. 5) Armour tiles without grinding in EDM gaps survive the cyclic heat flux loading up to 20 MW/m2, rectangular and trapezoidal armour tiles demonstrate similar performance. 6) The cost-saving manufacturing process like casting of large W/Cu bimetallic plates fol-
lowed by EDM sizing and castellation of the tiles is recommended for full-scale manufacturing sequence. 7) The monoblock concept tested up to 17 MW/ m2 seems to be one of the most reliable attachment schemes. However, it requires tungsten nearly three times more than for other approaches because of substantial ma-
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3.1. Design and fabrication of hypervapotron mockups
Fig. 1. Testing results of small-scale mock-ups with different armour geometry and W/Cu joining techniques (N E/1000).
chining. The production cost for this approach is the highest and it should be applied, if other approaches fail.
3. Development of medium-scale mock-up The results of development of small-scale mockups were applied for manufacturing and testing of the VT medium-scale mock-up armoured with flat tungsten tiles. The main purpose of medium-scale development was to demonstrate the PFC manufacturability.
The hypervapotron VT design [7] was considered for full-scale demonstration of PFC manufacture. VT itself is the assembly of HHF armoured elements fastened to the SS support plate. The medium-scale VT mock-up (Fig. 2) has two tungsten-armoured HHF elements 27 mm in width and 600 mm in length and welded to the SS watercooled support structure. The highly loaded ( /20 MW/m2) lower part of HHF elements has a hypervapotron HS beam armoured by (9 /9 /9) mm3 tungsten tiles. The moderately loaded ( /3 MW/m2) upper part of HHF elements has a HS with smooth rectangular cooling channel armoured by (27 /27/10) mm3 tungsten tiles. Tungsten tiles are joined to the CuCrZr HS through the 2-mm-thick cast copper interlayer. The HS beams are a bimetallic CuCrZr/SS structure with direct and reverse cooling channels. The HHF elements are joined to the support structure by laser welding. Tungsten /copper bimetallic armour tiles were produced by the cast technique. Pure copper was cast to rolled tungsten plates 120 mm in length to produce (54 /27) mm2 tiles for the moderately loaded part of the mock up. For the highly loaded part of the mock-up 30-mm-diameter tungsten rods were used and (27 /27) mm2 tiles with a castellation of (9 /9) mm2 were produced. The EDM machining followed by grinding was used for bimetallic tiles sizing and castellation. Fast
Fig. 2. Tungsten-armoured medium-scale VT mock-up.
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brazing technique with a brazing temperature of 800 8C was used for brazing of bimetallic tiles with CuCrZr/SS HSs. To verify the manufacturing sequence of the medium-scale mock-up a small-scale hypervapotron mock-up (Table 1) was manufactured. Its design reflects the main features of the mediumscale mock-up. The small mock-up was subjected to HHF tests. It was shown that the design reflected in the small-scale mock-up is suitable for heat fluxes up to 20 MW/m2 during several thousands of thermal cycles. 3.2. HHF tests of medium-scale mock-up Thermal fatigue testing of the VT medium-scale mock-up was performed to demonstrate the reliability of the large-scale bonding technologies and mock-up design under the cyclic heat loading. The mock-up was tested at the Tsefey electronbeam facility. The tests were performed at reduced areas because of the power limit of the testing facility. The highly loaded areas of (27 /42) and (18 /42) mm2 were tested by fluxes of 18.5 and 20 MW/m2 during 1000 and 150 cycles, respectively. The moderately loaded area of (54 /42) mm2 was tested by a flux of 5 MW/m2 during 1000 cycles. No leaks were detected in the mock-up during testing and no damages in the joints were observed. Erosion and melting of the tungsten surface were observed after the tests, but these effects did not affect in the mock-up workability.
4. Conclusions The development of W/Cu joining technologies has demonstrated the applicability of casting and brazing techniques for a wide range of PFC geometry. Manufacturing and testing of smalland medium-scale HHF components verified the
selected armour geometry and joining techniques for tungsten-armoured divertor components operating under different loading conditions. It was shown that for the Dome (or the upper part of the VT) the brazing and casting techniques are reliable and armour tiles (20 /20 /10) or (27 /27 /10) mm3 in dimensions can be used. These dimensions were checked at a moderate heat flux level of (5 /10) MW/m2. The casting technique in combination with the use of (10 /10/10) mm3 tiles is reliable for the lower part of the VT. Such approaches were checked at a HHF of 20 MW/m2. Used joining techniques together with the costeffective manufacturing technique and the selected armour geometry can be recommended for the full-scale manufacturing processes of the ITER divertor components or other tungsten-armoured PFCs for fusion application.
References [1] ITER Final Design Report 1998, G 17 FDR 5 98 /05 /29 W 0.2, Design Description Document WBS 1.7, Divertor. [2] C. Ibbot, et al., Overview of the engineering design of the ITER divertor, Proceeding of 21st SOFT, Madrid, Spain, 2000. [3] A. Makhankov, et al., Development and optimization of tungsten armour geometry for ITER, Proceeding of 20th SOFT, Marseille, France, 1998. [4] V. Gagen-Torn, et al., Experimental complex for high heat flux materials interaction research, 18th SOFT, Germany, Karlsruhe, 1994, vol. 1, pp. 363 /366. [5] A. Makhankov, et al., Investigation of cascade effect failure for tungsten armour, Fusion Engineering and Design 56 /57 (2001) 337 /342. [6] R. Giniatulin, et al., High heat flux tests of mockups for ITER divertor application, Fusion Engineering and Design 38 /40 (1998) 385 /391. [7] G. Janescitz, et al., Divertor design and its integration into ITER Machine, 18th IAEA Fusion Energy Conference, Sorrento, Italy, 2000.
Review article
Optimization of armour geometry and bonding techniques for tungsten-armoured high heat flux components R.N. Giniyatulin , V.L. Komarov, E.G. Kuzmin, A.N. Makhankov, I.V. Mazul, N.A. Yablokov, A.N. Zhuk Efremov Institute, Sovetsky pr. 1, 196641 St. Petersburg, Russia
Abstract Joining of tungsten with copper-based cooling structure and armour geometry optimization are the major aspects in development of the tungsten-armoured plasma facing components (PFC). Fabrication techniques and high heat flux (HHF) tests of tungsten-armoured components have to reflect different PFC designs and acceptable manufacturing cost. The authors present the recent results of tungsten-armoured mock-ups development based on manufacturing and HHF tests. Two aspects were investigated */selection of armour geometry and examination of tungsten /copper bonding techniques. Brazing and casting tungsten /copper bonding techniques were used in small mock-ups. The mockups with armour tiles (20/5 /10, 10 /10 /10, 20 /20 /10, 27 /27/10) mm3 in dimensions were tested by cyclic heat fluxes in the range of (5 /20) MW/m2, the number of thermal cycles varied from hundreds to several thousands for each mock-up. The results of the tests show the applicability of different geometry and different bonding technique to corresponding heat loading. A medium-scale mock-up 0.6-m in length was manufactured and tested. HHF tests of the medium-scale mock-up have demonstrated the applicability of the applied bonding techniques and armour geometry for full-scale PFC’s manufacturing. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Tungsten-armour; Plasma facing components; Heat flux
1. Introduction Tungsten-armoured structures are used in various high heat flux (HHF) components. The design of plasma facing components (PFCs) such as the vertical target (VT) and Dome for the International Thermonuclear Experimental Reactor
Corresponding author. Tel.: /7-812-462-7834; fax: 7-812464-4623 E-mail address: [email protected] (R.N. Giniyatulin).
(ITER) Divertor requires the joints between armour tiles and actively-cooled copper-based heat sink (HS) [1]. These joints must provide a thermal contact and strong attachment of armour material with the HS structure. For tungsten-armoured divertor components cyclic heat loading varies from 3 MW/m2 for the Dome up to 20 MW/m2 for the lower part of the VT [2]. The wide range of operational conditions for different components results in their corresponding designs. Different approaches to joining techniques together with various geometry concepts are used.
0920-3796/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 0 - 3 7 9 6 ( 0 2 ) 0 0 2 9 7 - 1
186
R.N. Giniyatulin et al. / Fusion Engineering and Design 61 /62 (2002) 185 /190
This paper summarizes the most acceptable recent results obtained in tungsten-armoured PFC development. Two bonding techniques, such as casting and brazing, together with the armour tile geometry optimization were considered. The flat-tile and monoblock concepts were tested. Smooth cylindrical and hypervapotron cooling channels were used for the components. The results of HHF tests of small- and medium-scale mock-ups confirming the selected bonding techniques and geometries are presented.
2. Development of small-scale mock-ups The mock-ups were developed using the following types of armour tiles: lamella-type armour; monoblock armour; flat tile armour. The general approach was considered for development of small-scale mock-ups */manufacturing of the mock-ups and their HHF testing under reference conditions. 2.1. Components geometry The components consist of tungsten tiles attached to the copper-based HS. The problem of a considerable mismatch of their thermal expansion coefficients has been solved by castellation of armour tiles (or using separate tiles) and by using a soft intermediate copper layer between tungsten and HS. 2.2. Applied materials Precipitation hardened CuCrZr-alloy was used as a HS material. The optimum properties of the HS were to be retained after subsequent thermal heat treatment. Tungsten of several grades in various half-finished products was used as an armour material: single crystal (rods), sintered pure and cast alloy (rods and rolled sheets). Thick rolled sheets (up to 30 mm) were produced for this stage of work to minimize the manufacturing cost. The brazing CuInSnNiMn alloy (STEMET 1108, MEPHI AMETO) with a brazing temperature of 800 8C was used as a filler metal for both W/Cu and Cu/CuCrZr joints [3]. Pure copper was
used for casting technique to produce W/Cu cast structures and for soft intermediate layer in a W/ Cu brazed jointS. 2.3. Bonding techniques Two bonding techniques for W/Cu joining were used for fabrication of mock-ups: fast brazing by electron-beam heating; casting of pure copper to tungsten tile [3]. Brazing technique for W/Cu joint was used as an alternative to casting. It was necessary to compare brazed and cast joints under relevant testing conditions and find the HHF limit for brazing. One-step brazing for W /Cu /CuCrZr joint and two-step brazing for W /Cu and W/ Cu /CuCrZr joint were applied. W/Cu cast bimetallic tiles of the mock-ups were prepared from long (L/200 mm) half-finished bimetallic blocks. 2.4. Geometry of tiles The thickness of armour material was taken as 10 mm for all flat-tile mock-ups. This thickness is limited by maximum level of expected heat flux with corresponding surface temperature, on the one hand, and maximum allowable thickness to be retained during plasma disruption, on the other hand. Several planar dimensions of flat armour tiles were used (A /B /C mm3, where A, width; B, length; C, thickness): lamella */(20 /5) mm2; macrobrush*/(27 /27) mm2; macrobrush */ (20 /20) mm2; macrobrush */(10 /10) mm2. Two options of flat tiles were compared */rectangular-shape and trapezoid-shape. Monoblock-type mock-up has tiles (25 /20 /3) mm3 in dimension. 2.5. Fabrication of mock-ups Rectangular HS blocks from CuCrZr alloy which have cooling channel 12 mm in diameter were used for flat-tile components. CuCrZr-tube 12 mm in diameter was used for a monoblock mock-up. Electric discharge machining (EDM) is the final step of armour tiles preparation that provides the required castellation. The depth of EDM cut is equal to or more than the tungsten thickness.
R.N. Giniyatulin et al. / Fusion Engineering and Design 61 /62 (2002) 185 /190
The machined tungsten and W/Cu tiles were brazed with HS blocks. Two types of bimetallic tiles were used in the mock-ups for both bonding techniques: separate bimetallic tiles (10 /10, 20 /20, 27/27 mm2) with all sides ground; bimetallic macrotiles (20 / 20 mm2 with a castellation step of 10 mm and 27 /27 mm2 with a castellation step of 9 mm) with only outer sides ground and without grinding in EDM gaps. The grinding of all tile sides after EDM is very important to remove the cracked layers, but macrotile option is attractive in view of manufacturing cost reduction. Thus, the use of unground armour tiles has to be examined under relevant testing conditions. The use of trapezoid-shape separate tiles is one of the cost-effective approaches for armouring by separate flat tiles. The assembly process with such tiles during brazing does not require setting of the gaps between them. The monoblock mock-up was produced by the cast technology. The pack of six (25 /20 /3) mm3-tiles with holes was cast by pure copper. The subsequent machining removed extra copper inside the channel and outside the block. Brazing of W/Cu block with CuCrZr tube and a stainless steel (SS) block was the final step. Twenty small-scale mock-ups (few mock-ups of each type) were manufactured and tested. The most acceptable results and mock-up photos are presented in Table 1. 2.6. Testing conditions The expected heat fluxes onto W-armoured divertor components vary, i.e. up to 20 MW/m2 for the VT and up to 5 MW/m2 for the Dome. Therefore, the Tsefey electron-beam facility (Efremov Institute, Russia) [4] was used. The mock-ups were tested at the following conditions: heat flux density range */(5 /20) MW/m2; time of load/ pause*/(10 /15)/10 s, inlet water pressure */(1.0 / 1.5) MPa; water flow rate */(10 /15) m/s; background pressure in the chamber */104 Pa. For all mock-ups tested at heat fluxes higher than 10 MW/m2 a twisted tape was used to facilitate the heat transfer capability.
187
Typical diagnostic methods were used during HHF testing: bulk thermocouples measuring, TVrecording, IR-recording, Spot pyrometers, water calorimeter. The criterion for mock-up reliability was to maintain the thermal contact in W/Cu and Cu/ CuCrZr joints. Failure event during the tests means cracking in any joints or in armour material that affect in overheating of the surface.
2.7. Results of testing of small-scale mock-ups Fig. 1 presents the results of testing of smallscale mock-ups of different armour geometry and with different W/Cu joining techniques (Table 1), as well as previously obtained results of testing of cast mock-ups with tiles (10 /10 /10) mm3 [5] and (44 /44/3) mm3 [6] in dimension. It is shown (Fig. 1) that the acceptable level of heat flux loading during fatigue testing strongly depends on the armour tile dimensions. It is obvious that the minimum planar dimensions are preferable for high loading conditions (15 /20 MW/m2) and the maximum dimensions are suitable for moderate conditions (3 /5 MW/m2), but the cost issues require the optimal dimensions to be chosen. The results allow the following conclusion: 1) All tungsten grades demonstrate similar thermal fatigue performance in case of proper orientation (texture in the heat flux flow direction). 2) Armour with tiles (20 /20 /10) mm3 and (27 /27/10) mm3 in dimensions has an HHF limitation of /10 MW/m2 for both casting and brazing technology. 3) Brazing CuSnInNiMn filler metal for W/Cu joint demonstrates the acceptable reliability up to heat fluxes of (15 /17) MW/m2 for tiles (10 /10/10) mm3 in dimension, and the brazing technique is recommended, as being a cheaper alternative, for the components that work at heat fluxes below /15 MW/m2. 4) Experiments show that the gap width and shape between tiles do not affect the armour performance, if the tiles do not touch each other during loading. A gap of 0.2 mm at the
188
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Table 1 Summary of the most representative HHF tests of W armoured mock-ups Geometry of tiles
W/Cu joining Testing conditions technique
Picture
Heat flux MW/m2
Number of cycles
15
1000
17 15
100(FJ) 1000
17.5 20 10 15
1000 130(FA) 1000 300(FA)
10
1000
15 17
500(FJ) 260(FH)
9/9/10 (Hypervapotron mock-up)
7 10 12.5 20
1000 1000 1000 2000(WF)
27/27/10 (Hypervapotron mock-up)
7 10 12.5
1000 1000 1000(WF)
20/5/10
Brazing
10/10/10
20/20/10
20/20/10
20/25/3 (Monoblock)
Casting
Designations: FJ */failure in joint; FA */failure in armour; FH */failure in heal sink; WF */without failure.
top of the tiles is sufficient for all ITER HHF components. 5) Armour tiles without grinding in EDM gaps survive the cyclic heat flux loading up to 20 MW/m2, rectangular and trapezoidal armour tiles demonstrate similar performance. 6) The cost-saving manufacturing process like casting of large W/Cu bimetallic plates fol-
lowed by EDM sizing and castellation of the tiles is recommended for full-scale manufacturing sequence. 7) The monoblock concept tested up to 17 MW/ m2 seems to be one of the most reliable attachment schemes. However, it requires tungsten nearly three times more than for other approaches because of substantial ma-
R.N. Giniyatulin et al. / Fusion Engineering and Design 61 /62 (2002) 185 /190
189
3.1. Design and fabrication of hypervapotron mockups
Fig. 1. Testing results of small-scale mock-ups with different armour geometry and W/Cu joining techniques (N E/1000).
chining. The production cost for this approach is the highest and it should be applied, if other approaches fail.
3. Development of medium-scale mock-up The results of development of small-scale mockups were applied for manufacturing and testing of the VT medium-scale mock-up armoured with flat tungsten tiles. The main purpose of medium-scale development was to demonstrate the PFC manufacturability.
The hypervapotron VT design [7] was considered for full-scale demonstration of PFC manufacture. VT itself is the assembly of HHF armoured elements fastened to the SS support plate. The medium-scale VT mock-up (Fig. 2) has two tungsten-armoured HHF elements 27 mm in width and 600 mm in length and welded to the SS watercooled support structure. The highly loaded ( /20 MW/m2) lower part of HHF elements has a hypervapotron HS beam armoured by (9 /9 /9) mm3 tungsten tiles. The moderately loaded ( /3 MW/m2) upper part of HHF elements has a HS with smooth rectangular cooling channel armoured by (27 /27/10) mm3 tungsten tiles. Tungsten tiles are joined to the CuCrZr HS through the 2-mm-thick cast copper interlayer. The HS beams are a bimetallic CuCrZr/SS structure with direct and reverse cooling channels. The HHF elements are joined to the support structure by laser welding. Tungsten /copper bimetallic armour tiles were produced by the cast technique. Pure copper was cast to rolled tungsten plates 120 mm in length to produce (54 /27) mm2 tiles for the moderately loaded part of the mock up. For the highly loaded part of the mock-up 30-mm-diameter tungsten rods were used and (27 /27) mm2 tiles with a castellation of (9 /9) mm2 were produced. The EDM machining followed by grinding was used for bimetallic tiles sizing and castellation. Fast
Fig. 2. Tungsten-armoured medium-scale VT mock-up.
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brazing technique with a brazing temperature of 800 8C was used for brazing of bimetallic tiles with CuCrZr/SS HSs. To verify the manufacturing sequence of the medium-scale mock-up a small-scale hypervapotron mock-up (Table 1) was manufactured. Its design reflects the main features of the mediumscale mock-up. The small mock-up was subjected to HHF tests. It was shown that the design reflected in the small-scale mock-up is suitable for heat fluxes up to 20 MW/m2 during several thousands of thermal cycles. 3.2. HHF tests of medium-scale mock-up Thermal fatigue testing of the VT medium-scale mock-up was performed to demonstrate the reliability of the large-scale bonding technologies and mock-up design under the cyclic heat loading. The mock-up was tested at the Tsefey electronbeam facility. The tests were performed at reduced areas because of the power limit of the testing facility. The highly loaded areas of (27 /42) and (18 /42) mm2 were tested by fluxes of 18.5 and 20 MW/m2 during 1000 and 150 cycles, respectively. The moderately loaded area of (54 /42) mm2 was tested by a flux of 5 MW/m2 during 1000 cycles. No leaks were detected in the mock-up during testing and no damages in the joints were observed. Erosion and melting of the tungsten surface were observed after the tests, but these effects did not affect in the mock-up workability.
4. Conclusions The development of W/Cu joining technologies has demonstrated the applicability of casting and brazing techniques for a wide range of PFC geometry. Manufacturing and testing of smalland medium-scale HHF components verified the
selected armour geometry and joining techniques for tungsten-armoured divertor components operating under different loading conditions. It was shown that for the Dome (or the upper part of the VT) the brazing and casting techniques are reliable and armour tiles (20 /20 /10) or (27 /27 /10) mm3 in dimensions can be used. These dimensions were checked at a moderate heat flux level of (5 /10) MW/m2. The casting technique in combination with the use of (10 /10/10) mm3 tiles is reliable for the lower part of the VT. Such approaches were checked at a HHF of 20 MW/m2. Used joining techniques together with the costeffective manufacturing technique and the selected armour geometry can be recommended for the full-scale manufacturing processes of the ITER divertor components or other tungsten-armoured PFCs for fusion application.
References [1] ITER Final Design Report 1998, G 17 FDR 5 98 /05 /29 W 0.2, Design Description Document WBS 1.7, Divertor. [2] C. Ibbot, et al., Overview of the engineering design of the ITER divertor, Proceeding of 21st SOFT, Madrid, Spain, 2000. [3] A. Makhankov, et al., Development and optimization of tungsten armour geometry for ITER, Proceeding of 20th SOFT, Marseille, France, 1998. [4] V. Gagen-Torn, et al., Experimental complex for high heat flux materials interaction research, 18th SOFT, Germany, Karlsruhe, 1994, vol. 1, pp. 363 /366. [5] A. Makhankov, et al., Investigation of cascade effect failure for tungsten armour, Fusion Engineering and Design 56 /57 (2001) 337 /342. [6] R. Giniatulin, et al., High heat flux tests of mockups for ITER divertor application, Fusion Engineering and Design 38 /40 (1998) 385 /391. [7] G. Janescitz, et al., Divertor design and its integration into ITER Machine, 18th IAEA Fusion Energy Conference, Sorrento, Italy, 2000.