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World Record Output (1.5-times higher) Achieved on Microwave Generator for Fusion Reactor
-New Method Applicable to ITER-

Nov. 16 , 2009

JAEA recently developed a new method for increasing the microwave output power from a gyrotron, a microwave generator for heating the plasma, and successfully increased the output power of the gyrotron for the JT-60 by 50%. As a result, the gyrotron has broken the previous world record on high-power microwave generation, 1 MW for more than 1 second, which is the required minimum duration of heating the plasma, and achieved the new world record, 1.5 MW. This makes a huge contribution to the further development of International Thermonuclear Experimental Reactor (ITER) and the JT-60SA (a successor to the JT-60) under construction.

The microwave is used for heating the plasma to a sufficiently high temperature required for the efficient fusion reaction. The gyrotron is a large vacuum tube that accelerates the electron beam in a strong magnetic field and converts the energy to the microwave. Scientists around the world are promoting research and development of the gyrotoron that produces the high-power microwave for more than 1 second. JAEA previously established a “high efficiency operation” mode, and this operation mode reduced heat load on the collector, which received the electron beam after energy conversion, by improving conversion efficiency to the microwave.

It took, however, a few tens of seconds to move into the “high efficiency operation” mode with the conventional method changing the magnetic field intensity with the superconducting coil. The heat load on the collector received during that period was the biggest issue for further increasing the output power and it was needed to develop a new method to reduce the period of time.

So JAEA focused on controlling the electric field intensity to change the electron beam orbit in the gyrotron instead of changing the magnetic field strength. This new method had a significant advantage of reaching the “high efficiency operation” mode in only 0.1 sec. and made it possible to increase the microwave output power by 50%.

This technological development enables us to make a high-powered microwave generator for heating the plasma for fusion reactors. Also it is expected to create a spin-off effect for making a small but high powered ground equipment for a microwave rocket under study.

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