Maybe this has already been mentioned as a possible Defender fix, but I would go with:
Linked Ion Cannon
Cannon Upgrade (not a secondary weapon)
TIE Defender Only
3 Points
When you attack with your primary weapon, if the attack hits, the defender receives one Ion token.
Maybe it could be 2 points, and maybe 2 ion tokens, but you get the idea.
--mjg
+ 