Availability of Present Fusion Devices

Operation of tokamaks has now reached few hundred device-years. Availability is a top level parameter vital for the efficient management of complex plants, like fusion devices, for decision making and to judge the quality of design, manufacturing and operation. There is no standard way to analyze the operating experience: different techniques are adopted, various levels of detail are reached and also the kind of analysis and corrective actions are different. Nevertheless most of the results for the various tokamaks are expressed in similar terms like number of plasma pulses, operating time and delays, experimental sessions lost. An overall analysis of JET, JT-60, DIII-D, ASDEX-U, Tore Supra, FTU and RFX operating experiences has been performed to find out main results, lessons learned and possible suggestions to improve availability of the devices themselves and of those under design or construction, like ITER. The main results are here presented and discussed