Statistical analysis of disruptions in ASDEX

A database of disruptive discharges in ASDEX has been set up. It contains data for all 33509 ASDEX shots. The statistics of disruptions on ASDEX are evaluated for all these shots; in a more detailed analysis, different operation regimes are regarded separately. It is found that after eliminating the most dangerous operation regimes, 17% of all shots end with a disruption. There is an indication that a well established discharge may be repeated several times at a lower disruption rate (less than 5% for ELMy H modes). The statistics of the flux expulsion at a disruption indicate that a major disruption is characterized by a typical current profile change of Δli ≈ 0.37. It is found that about 50% of all disruptions have clear precursors lasting for more than 50 ms, namely locked modes or minor disruptions which in a future machine, might be used to trigger the application of stabilization or shutdown schemes. From the statistics of the radial and vertical displacements during a disruption the average forces on the vacuum vessel are calculated which, in the case of ASDEX, are not critical, but may be of concern for future large devices