The Divertor Cassette Project (L- 5)

Figure 1:Vertical Target medium-scale
divertor prototype tested in FE200
electron beam facility by CEA and
Framatome at Le Creusot (F)

The main aims of the L-5 project were to develop the technologies required in the ITER divertor and to integrate key plasma facing components together onto a realistic prototype of the cassette body. This was done with a mixture of real and dummy armour components. Major issues include the bonding of different plasma facing materials on the same component, the mastering of different bonding technologies for the supporting structure, the development of suitable non-destructive testing, the selection of the heat sink material (CuCrZr preferred), and the demonstration that it maintains its properties after manufacturing.

The L-5 project has helped developing the technology needed to construct components capable of providing adequate armour lifetime, armour-heat sink joint lifetime (CfC-Cu and W-Cu) and heat sink lifetime, sustaining thermo-hydraulic and electro-mechanical loads, whilst seeking the most cost effective and reliable manufacturing options. All four original ITER Parties have contributed to the development of the armoured plasma facing components which are to be assembled on a stainless steel cassette body. The test results show that the monoblock, flat tile and saddleblock geometries all have the capability to meet the ITER requirements. However, the monoblock proved to be the most reliable with no reported complete detachment of tiles.

The main distiguishing features of the EU contribution to the L-5 project are the following:

• development of relevant bonding technologies for both CFC and tungsten armours, all exceeding the ITER design requirements
• manufacturing of components with both CFC and tungsten armours on them
• manufacturing of full-scale prototypes for each divertor component, namely the vertical target, the dome and the cassette body
• development of three-dimensional high thermal conductivity CFC material
• Expertise in large series production (several hundreds) for high heat flux components based on the CIEL project for the tokamak Tore Supra (CEA Cadarache, F) and on the stellarator W7-X divertor (IPP Greifswald, D)

Following the decision of the US to pull out of ITER, the EU has constructed an outer cassette body in addition to the already planned vertical target and wing full-scale integration prototypes. The assembly of these prototypes with the RF liner mockup was completed in May 2000, and thermal cycling and flow tests followed. The main feature of these integration prototypes is the replacement of the armour with an equivalent thickness of CuCrZr copper alloy to reduce the manufacturing cost.

Figure 2:Vertical target full-scale
divertor prototype

Figure 3:Dome full-scale prototype

EU Divertor prototypes

An extensive technology development program has been carried out in the EU on high heat flux components. This effort culminated with the manufacturing and testing of a vertical target medium-scale prototype. The manufacturing was carried out by Plansee (A) together with Ansaldo Ricerche (I). This component was 600 mm long and contained all the main features of the corresponding ITER design. The upper part of the prototype had tungsten macro-brush armour whereas the lower part was covered by CFC monoblocks. The component endured 1000 cycles at 15 MW/m2 and 2000 cycles at 20 MW/m2 plus a few cycles at 30 MW/m2, on the tungsten and CFC armoured region, respectively.
Based on this experience a full-scale vertical target prototype and a dome prototype were also successfully manufactured. They will be high heat flux tested in FE200 electron beam facility.

Full-scale integration prototypes

Figure 4:Full-scale integration prototypes
assembled at ENEA at Brasimone (I)

An integration exercise and thermohydraulic testing was completed in collaboration with the Russian Federation (RF) Home Team. This activity demonstrated that full-scale components manufactured by different EU companies as well as by the RF Home Team could achieve the tolerances required to be assembled together. Furthermore the thermohydraulic testing gave essential information on the water flow distribution along the different cooling tubes and on the resulting pressure drop.