Inertial Electrostatic Confinement
The Cathode Space, Where it All Happens: A More Rigourous Explanation.
Originally by Dr. Robert Hirsch. 
1. Take Poisson's Equation in Spherical Coordinates. (Equation
2. Set the virtual anode equal to ground, the same as the actual anode.
Apply Conservation of Energy to Protons and Electrons. (Equations
3. Apply Conservation of Charge to get the ion currents. (Equation
4. Now, normalize the potential and radius. (ra being the anode radius.)
5. Rewrite Equation 1 in terms of R and f.
(Equations 5, 6, 7)
Its just that simple!