Four two-frequency gyrotrons were in operation dur-ing the latest experimental campaign at ASDEX Upgrade(AUG), operating at 105 and 140 GHz with a pulse lengthof 10 s, corresponding to the maximum flat top time ofAUG plasma discharges, and output powers close to1 MW. The gyrotrons have single-stage depressed collec-tors and their efficiencies are around or above 50%. Re-cently, an old 140 GHz single-frequency ECRH systemwhich was built in 1996 (4 gyrotrons with 500 kW outputpower and 2 s pulse length) has been dismantled. It isbeing replaced by four new 1 MW two-frequency gyro-trons using the same launching positions with slightlymodified launchers [1]. The new gyrotrons will be oper-ated in cryogen-free superconducting magnets.
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