It seems I didn’t understand this correctly myself. I think what you’re trying to achieve is transparency for the sphere?
In that case you would need to change material to translucent so you get access to opacity pin, then use scalar parameter to control the value. Value of 0.01 might be a bit to low and you might think it’s completely translucent (it’s not but it’s really hard to make out, suggest using something like .1 or 0.05).
I tried to make it work just by using Alpha but it doesn’t seem to work that way. Perhaps a material guru can clarify this. 
Apologies for confusion, I learned something new today. 
Hope that works for you.