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Report No.

Operational experiences of the super conducting magnet for a gyrotron of the JT-60U ECH system

Igarashi, Koichi*; Seki, Masami; Shimono, Mitsugu; Terakado, Masayuki; Ishii, Kazuhiro*; Takahashi, Masami*

The JT-60U electron cyclotron heating (ECH) system can heat plasmas locally and drive a plasma current with four 1 MW-5 sec gyrotrons. The super conducting magnets (SCM) are required for oscillation of the gyrotron at a working frequency of 110 GHz. The SCM provides a high magnetic field of 4.5T at the cavity inside the gyrotron. This SCM system is characterized by (1) operation without liquid Helium owing to a 4 K-refrigerator applied to the magnetic coils, (2) easy maintenance. Operational experiences about the SCM system through a long term experiment for a high power gyrotron are very valuable. According to those operational experiences, it is clarified the 4 K-refrigerator should be renewed in oder to keep low temperature of the SCM. It is also found that 200 hours or less are required for the super conducting condition ($$<$$5K) after long stopping time of the refrigerator up to 150 hours. This is useful information for making a plan about ECH experiments.



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