Development and achievements on the high power ECRF system in JT-60U

Abstract

An output power of 1.5 MW for 1 s was achieved at 110 GHz in a recent gyrotron development using the JT-60U ECRF system. It is the world's highest power oscillation for a pulse duration of at least 1 s. The achievement was enabled by, in addition to the carefully designed cavity and collector, necessary because of thermal stress, an RF shield for the adjustment bellows and a low-dielectric-loss dc break. The way the power was modulated was improved upon by controlling the anode voltage, with high modulation frequency of 5 kHz being achieved in NTM stabilization experiments. Moreover, as a developmental step to realizing a reliable ECRF system for use in future fusion experiments, a long pulse demonstration of 0.4 MW and a 30 s injection into the plasma was achieved with real time control of the anode/cathode-heater. Confirmation was made that the temperature of the cooled components had been saturated with no evidence of any damage being discovered in the waveguides and antenna without forced cooling. An innovative antenna with a relatively wide range of beam steering capabilities utilizing a linearly moving-mirror concept was also designed for use as an active cooling antenna with longer pulses in the future, e.g. for JT-60SA. The beam profile and mechanical strength analyses proved the feasibility of the antenna.

Development of a dual frequency (110/138 GHz) gyrotron for JT-60SA and its extension to an oscillation at 82 GHz

“…Figure 5 (top) shows calculated beam patterns at the output window for each frequency. It is noted that the calculated diffraction loss is comparable with that of the original 110 GHz gyrotron used in JT-60, which successfully generated 1 MW for 5 s [2].…”

“…Pre-programmed control systems for AVD and heater power supply (P/S) developed in JT-60 [2] were used. The control system for the AVD (originally available up to 60 s) was modified for maximum duration of 240 s while the control system for the heater P/S (available up to 60 s) was used as it was.…”

“…In the early 2000s from the late 1990s, high-power (~ 1 MW) oscillations at the millimetre wave frequencies above 100 GHz were realized by some individually developed gyrotrons in Japan, EU, Russia and US [1]. These gyrotrons were used in some tokamak devices such as JT-60U [2], DIII-D [3] and ASDEX-U [4]. Recently, long-pulse oscillations of several hundreds of seconds at an output power of 1 MW have been demonstrated at the frequencies of 140 GHz for W7-X [5] and 170 GHz for ITER [6,7].…”

“…In JT-60SA, an ECH/ECCD system [12] will be used by upgrading the existing ECH/ECCD system used for JT-60U [2]. Main parameters of the ECH/ECCD system in both JT-60U and JT-60SA are shown in Table 1.…”

Commissioning of 170 GHz, 1 MW EC H&CD in KSTAR

“…As a result, decrease of the beam current can be suppressed just a little. However, the test result was not effective during the 20 sec and the oputput power dose not change because the cathode heater has a large heat capacity and the temperature response on the electron emmitter is delayed a few minutes [3]. …”