Finding Kinetic Energy of Ions Leaving a Charged Plate

[straki02]

I need to know how to find the kinetic energy of ions leaving a charged plate. I figure I can find the electric potential energy, but all i know is the power being supplied to the plate and the plate's cross-sectional area. Any ideas? Thanks in advance!

 

[mfb]

How do ions leave that plate?
How does the power supply work (what is powered)?
Electric potential energy relative to what?