Operation and engineering of the power and particle exhaust in Wendelstein 7-X

The divertor and the pumping system of W7-X are designed for stationary operation at the full range of magnetic and plasma parameters (5/6<ι<5/4; β<5%). The target plates, designed to withstand a stationary heat flux up to 10-12 MW/m2, are shielded with CFC joined to a CuCrZr heat sink cooled by a pressurised water-flow. The final geometry was optimised to reduce the total target area without narrowing the operational range of parameters. Baffles guide the neutrals to the pumping gap into the divertor chamber and keep the neutral pressure in the main chamber low. The baffle plates are designed to withstand a maximum heat flux of 0.5 MW/m2 and consist of graphite tiles clamped on a water-cooled CuCrZr structure. External particle fluxes injected by NBI, localised gas puffing and pellet injection in a range up to 1022 s-1 will be applied for heating and controlling the density profiles. These fluxes have to be pumped out to achieve a stationary regime. The main pumping system of W7-X will consist of turbomolecular pumps (TMPs), connected to the 10 divertor chambers, with their corresponding backing pumps. Cryo-panels will be integrated inside the divertor units. The high pumping speed can be maintained up to two hours. (orig.)