A multijunction launcher was designed and constructed to improve the directivity of launched waves with a narrow wave number spectrum by dividing each main waveguide into three secondary waveguides. The coupling characteristics agree fairly well with theory, and a power of up to 2 MW was obtained after a few days of conditioning. The dependence of the current drive efficiency ηCD (= neIRFR/PLH) on the wave spectrum was studied by changing the phase difference between the adjacent main waveguides. It was found that high current drive efficiency is obtained by waves interacting with fast electrons as far into the plasma as the waves travel. A maximum current drive efficiency of 2.8 × 1019 A·W−1·m−2 was achieved with this launcher at a plasma current of 1 MA. The efficiency of the multijunction launcher was higher by 40% than that of the previous conventional launcher on JT-60.
Quasi-optical grill mounted in hyperguide