Production and tests of the discharge resistors for Wendelstein 7-X

One of the goals of Wendelstein 7-X is to demonstrate steady state operation which is an inherent property of stellarators and essential for a future power plant. Magnetic confinement in Wendelstein 7-X will be archived by 50 non-planar and 20 planar coils with diameters of up to 5 in and masses of typically 6 t. To achieve steady state operation, all coils are superconducting. The large amount of stored energy in the coils of up to 900 MJ requires a fast and reliable protection system. In case of a quench or the need for rapid shut-down the current in the coils has to be commutated to external discharge resistors and ramped down within 10 s. In order to limit the voltage for the breakers, a resistor made of pure Nickel with low starting resistance and high thermal coefficient of the specific electric resistance was chosen. The paper describes briefly the results of simulations prior to the production as well as results of simulation during production, based on material tests during production. After the production all resistors were tested under real W7-X conditions regarding amount of stored energy, heat impact and current rise time. It was confirmed that the resistor are usable for the operation in W7-X.