Power loading of electrons ejected from the JT-60 negative ion source

Hanada, Masaya; Ikeda, Yoshitaka; Kamada, Masaki; Grisham, L. R.*

Power loading of the electrons ejected from the negative ion accelerator to the beam-line was first measured in the negative-ion-based neutral beam injector on JT-60U. At 0.3 Pa of the operating pressure in the arc chamber, the heat flux and the total power load for the single segment were about 8 W/cm and 27 kW for the D ion beam of 300 keV, 3.4 A, respectively. The normalized total power loading on the electron dump was no more than 2.6% of the electric power in the acceleration power supply. About 70% of the total power is originated by the electrons stripped from D ions due to the collisions with residual gas molecules in the accelerator. The calculation of the stripped electron trajectories shows that the electrons stripped in the second acceleration gap are the main origin of the power loading in the beam-line.