Collector lifetime estimations for the EU-1 MW, 170 GHz CW gyrotron for ITER

Summary form only given. The EU CW gyrotrons for ITER [1] will operate at a frequency of 170 GHz with an output power of 1 MW per tube, at an efficiency of approximately 50 %. With this efficiency, 1 MW of power from the electron beam has to be absorbed in the gyrotron collector. To avoid local overheating of the collector structure, the electron beam is swept across the inner surface at low frequencies (5 Hz - 50 Hz). This leads to local cyclic thermal loads, which induce thermo-mechanical fatigue of the collector material. The mechanical effect on the collector structure is investigated by calculating time-dependent load profiles with the in-house beam optics code ESRAY which are then used in a transient thermo-mechanical FEM-analysis. The obtained strain-stress cycles are used to predict the lifetime of the collector with a Manson-Coffin Basquin equation. The work investigates the influence of different parameters, such as the collector wall thickness and the sweeping frequency on the estimated lifetime of the gyrotron collector. In addition, the impact of the sweeping concept (vertical sweeping at frequencies up to 10 Hz or transverse sweeping [2, 3] at a higher frequency of 50 Hz) is also investigated. While the prediction in the case of vertical sweeping gives an expected lifetime only of the order of hours (using quite conservative assumptions and security factors), the results for transverse sweeping are of the order of 100,000 hours and therefore clearly point out the advantage of the more advanced transverse sweeping concept.