Shell, vessel and first wall
The first wall
The RFX first wall is composed of 2016 trapezoidal graphite tiles (72 in the toroidal direction, 28 in the poloidal direction); it is only 18 mm thick, to keep the plasma edge as near as possible to the stabilizing shell.
The choice was based on the following considerations:
- a metallic wall (with or without metallic limiters) would produce high- Z contamination and could be seriously damaged by thermal flux concentration;
- a metallic wall with low-Z limiters would produce both high-Z and low-Z contamination; the metallic wall could be damaged during badly controlled pulses or fast current terminations;
- low-Z limiters on a low-Z armor would increase plasma-shell separation and would concentrate transport losses on small surfaces with enhanced erosion.
|Inner minor radius excluding armour (ambient temperature)||475 mm|
|Overall thickness||30 mm|
|Evacuated volume||9 m3|
|Toroidal resistance||1,1 mOhm|
|Transverse field diffusion time constant||2.1 ms|
|Number of ports||96|
The vacuum vessel
The RFX vacuum vessel is comprised of 72 wedge-shaped elements, each of which consists of a sandwich structure, with a 2 mm thick inner wall and a 1 mm thick outer wall connected together by a 0.5 mm corrugated sheet and two poloidal stiffening end rings, welded to the inner and the outer walls.
The thicker end ring bears the 28 equispaced holes housing the supports for the first wall tiles, and provides the required stiffness, whereas the thinner one is only required to close the structure and for joining.