You stuck up on energy. Mass is charge is gravity. You cant have mass without charge. When you have a vaccumm tube, the so called space charge, is ON THE GLASS. The charge in a vaccum, is coming from the glass, like getting shocked when you touch the glass on your tv. You cant have a charge in a vaccum there is no vaccum. there is mass  around the vaccum where the charge coming from. Maybe the three current thing is bullshit. but it makes sense to me, to explain how electrical power generation works, becuase there are three entities, of radiation pressure, which is what electricity really is. Talking about it as if there are two things, only current and voltage, leaves out something big. the trouble is everyone is brainwashed, and you cant explain the difference, between the current is generation and the current in usage. These are separate entities. This termonology is a dogmatic religeon. There is no energy coming from the atom. It is radiating from it, just like a piece of uranium radiates into you and gives you cancer. There is no difference, is terms of what is atomicly happening, when you have electricity, then when you have nuclear decay. Its all radioation, just electricty, happens to be prodcuing less of it.