Development of Gyrotrons and the High Power Operation for the LHD Experiments

Abstract The electron cyclotron heating (ECH) system has played a key role in plasma heating and control since the earliest stages of the Large Helical System (LHD) project. In this paper, we will show the history of the strategic installation of gyrotrons, which are the core components of the ECH system, into the LHD and the progress of increasing ECH power. In the LHD, total injection power has been increased by repeatedly installing and replacing gyrotrons, and in particular, 1 MW-class gyrotrons, which began operation in 2007 and have led to a significant increase in the ECH power of the LHD. For these gyrotrons, the frequencies of 77–154 GHz were selected to initiate and heat the plasma under a magnetic field strength of 2.75 T for the standard magnetic configuration in the LHD. With the installation of the gyrotrons and a significant increase in millimeter wave power per tube, due to the stepped anode voltage rising, simultaneous ECH injection power into the LHD reached 5.6 MW.