Development of a high-brightness and low-divergence lithium neutral beam for a Zeeman polarimetry on JT-60U

Kojima, Atsushi; Kamiya, Kensaku; Iguchi, Harukazu*; Fujita, Takaaki; Kakiuchi, Hideto*; Kamada, Yutaka

A high-brightness and low-divergence neutral lithium beam is obtained for a Zeeman polarimetry of edge plasmas on JT-60U. In order to achieve high-brightness and low divergence angle simultaneously, the beam optics is designed after detailed numerical simulation taking the space charge effects into account. The newly-developed ion gun is operated on a test stand which simulates the diagnostic arrangement on JT-60U. The ion beam current of 10 mA is successfully extracted from the electron beam heated ion source. A sodium vapor neutralizer neutralizes the collimated ion beam fully at the temperature of 300C. The neutral lithium beam is transported for 6.5 m long from the neutralizer. The HWHM radius of 26 mm and the equivalent beam current of 3 mA with the beam divergence angle of 0.2 degree are obtained. Those parameters satisfy the requirements of the Zeeman polarimetry. Furthermore, a long pulse extraction with a current of 10 mA and duration of 50 seconds is attained.