The TPL (Toroidal Pump Limiter) has the form of a flat ring of 5m diameter and 0.5m width. In order to extract the particles escaping the plasma, twelve throat-shaped “neutralisers” are located at one of the edges of the ring, under the limiter, each of which is connected to a turbo-molecular pump. The TPL consists of 576 “fingers” (“aiguilles” in French), each clad with carbon fibre tiles bonded to a copper structure that is actively cooled by pressurised water (30 bars) at high temperature (150°C), one centimetre away from the plasma surface. The fabrication by industry of these “fingers” was particularly complex (see exploded view, presented below); especially the bonding of the carbon composite fibre to the water-cooled copper base. It incorporates a proprietary process patented by our supplier, the Austrian company Plansee. The process is based on the engraving of tiny cavities into carbon using a laser, and subsequently impregnating the surface with liquid copper. The solidified 2mm layer of copper is then welded, using an electron beam, to the hardened copperalloy base (copper-chromiumzirconium).

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