Helium Ionization Energy

The Helium Ionization Energy is the energy required to remove from atom one mole of electrons with subsequent production of positively charged ion of Helium.
He -> He⁺ + e^-
This process can be repeated many times, but the energy cost is increased dramatically. The general equation for the Helium is:
He^N+ -> He^(N+1)+ + e^-