Keith suggested to decrease the voltage by 15 kV for passivation. I tried this way and found the system worked well, and the red light from the chamber looked homogeneous. However the south side randomly missed triggers, I can hear the click from the south thyratrons and see the sparks inside the thyratrons. I thought maybe the trigger circiut board send the noise, so I removed the circiut board. Casually I found the capacitor connected between thyraton CX1585 and CX1622 was very dirty, there was some yellow liqud leaked from the capacitor. I changed this dirty one by a clean one.
So far the passivation has been run well.