Numerical simulation of a high-brightness lithium ion gun for a Zeeman polarimetry on JT-60U

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

A lithium ion gun is under construction for a lithium beam Zeeman polarimetry on JT-60U. The performance of the prototype ion gun has been estimated by the numerical simulation taking the space charge effects into account. The target values of the ion gun are the beam energy of 30 keV, the beam current of 10 mA and the beam divergence angle within 0.13 degrees. The low divergence is required for the geometry of the Zeeman polarimetry on JT-60U where the observation area is 6m away from the neutralizer. The simulation results show the beam loss of 50% caused by the clash to the electrode such as an cathode and the neutralizer. Moreover, the beam transport efficiency from the neutralizer to the observation area is low due to the broadening of the divergence angle. The total beam efficiency is about 5%. Extracted current profile affects the beam property and efficiency. The peaked profile achieves better efficiency than the hollow one. As a result, beam current of 1mA is obtained at the observation area by the simulation for the prototype ion gun.