M. Terakado

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

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 worlds 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.

High power long pulse tests of the IFP-CNR dummy load for the European ITER gyrotron

The development of high power gyrotrons needs matched loads with good performance capable of absorbing and measuring powers as high as 1 MW in ITER and higher (up to two times) in future devices like DEMO. At IFP-CNR (Milano), several spherical loads were developed with identical absorbing geometry but different heat removal systems for operation with pulse lengths from a few ms to CW. A dummy load designed for 170 GHz/2 MW has been constructed in the frame of the development programme of European gyrotron for ITER. The first prototype hemisphere of this load, joined with an uncoated one, has been successfully tested with long pulses and under vacuum using the JAEA gyrotron for ITER in Naka. The symmetry of the system is such that the equivalent power load of the absorbing (coated) hemisphere is doubled when the second one is reflective (uncoated), with almost unchanged distribution with respect to a fully coated load. The tests demonstrate the capability of the IFP-CNR load to withstand and measure radiation at an equivalent power in excess of 1.5 MW. Gyrotron pulses with increasing power and pulse length have been performed in the load and are reported. The maximum equivalent power load reached in the tests was ~ 1.8 MW for 15 s while the longest pulse was 300 s, at ~ 1 MW. During the experiments, the temperatures of either the load or the preload were monitored using thermocouples and multiple infrared cameras. The results of the tests are described in the paper.

Validation Experiments on the 2-MW CW 170-GHz Load for the European ITER Gyrotron

The development of high-power gyrotrons needs matched loads with good performance capable of absorbing and measuring powers as high as 1 MW in the International Thermonuclear Experimental Reactor (ITER) and higher (up to two times) in the future devices, such as the DEMOnstrating fusion power reactor. At Istituto di Fisica del Plasma - Consiglio Nazionale delle Ricerche IFP-CNR (Milan), several spherical loads were developed, all with identical absorbing geometry but different heat removal systems for operations with pulselengths (PLs) from a few milliseconds to continuous wave (CW). A dummy load designed for 2-MW CW 170-GHz operations has been constructed in the frame of the development program of the European gyrotron for ITER. The first prototype hemisphere of this load, joined with an uncoated one, has been successfully tested with long pulses and under vacuum using the gyrotron for ITER of the National Institutes for Quantum and Radiological Science and Technology in Naka. The symmetry of the system is such that the equivalent power (EP) load of the absorbing (coated) hemisphere is doubled when the second one is reflective (uncoated), with an almost unchanged distribution with respect to a fully coated load. The tests demonstrate the capability of the IFP-CNR load to withstand and measure radiation at an EP in an excess of 1.5MW. Experiments involving gyrotron pulses with increasing power and PL have been performed in the load and are reported. The maximum EP load reached in the tests was

Development of a Real‐time Modulation Control System on the JT‐60U ECRF System

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Oscillation Control of the JT-60U High Power Gyrotron by Controlling the Anode Voltage

MW for 15 s while the longest pulse was 300 s, at

Recent Results from the Development of the Electron Cyclotron Heating System for JT-60SA toward High-Power Long-Pulse Operations ∗)

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

MW. During the experiments, the temperatures of either the load or the preload were monitored using thermocouples and multiple infrared cameras, while a pressure sensor and a hydrophone have been used for the monitoring of cavitation phenomena and water boiling in the cooling circuits. The results achieved in the tests are described in this paper.

Progress in ECRF antenna development for JT-60SA

A real‐time modulation control system was developed for studying the effectiveness of modulated Electron Cyclotron Current Drive (ECCD) on the stabilization of Neoclassical Tearing Modes (NTMs). The phase and duty cycle tracking was enabled with high accuracy even if the NTM frequency varied during ECCD. A characteristic of an anode voltage modulation for modulating the gyrotron oscillation that caused the time variation of the phase and duty cycle was also taking into account. It was shown that the phase and duty cycle could be kept the target values within 50 ms even if the frequency varied by 1 kHz/s or higher at a frequency of around 5 kHz. Then, NTM stabilization experiments with modulated ECCD for m/n = 2/1 NTM was successfully performed in JT‐60U.

Development of a linear motion antenna for the JT-60SA ECRF system

Tne JT-60U gyrotron has a triode electron gun, which enables to control its oscillation output by adjusting its anode voltage. The output was successfully recovered by anode voltage control when it was terminated. Moreover, the output was modulated at 0.7 MW up to 500 Hz with modulation factor 80 %.