Which superconducting material for the toroidal field system of the fusion DEMO reactor?

The reflexion about DEMO, a fusion demonstration reactor, has already been initiated in the framework of European tasks and the decision to build ITER at CEA Cadarache has even reinforced the interest for such studies. A key component of this fusion demonstration reactor is the superconducting magnetic system, which represents in ITER 30% of the investment cost. Which superconducting materials are adequate for DEMO and are the emerging HTc superconducting material a necessary technology which cannot be avoided? This crucial question will be examined and discussed, taking into account key parameters of the project such as: - the toroidal magnetic field Bt which plays a determining role in the fusion power and the amplification factor, in association with the major radius R of the machine which is a characteristics of the reactor size. - the operating temperature of the magnet system which can affect the global efficiency of the reactor. As a matter of fact the electrical power associated with the cryogenic refrigeration of the magnet will be estimated and discussed. Two temperatures will be considered: 5 K and 20K. The dimensions of the TF magnet system can be estimated, thanks to a simplified approach. These dimensions have an impact on the machine and enable to obtain a realistic integration of the superconducting magnet system with all aspects of the machine within a system approach