It's like an ion drive. Here's the steps: 1. Start with a metal rod. 2. Remove one atom from the rod. 3. Remove electron from atom. 4. Now that the ato

It's like an ion drive. Here's the steps: 1. Start with a metal rod. 2. Remove one atom from the rod. 3. Remove electron from atom. 4. Now that the atom is charged, shoot it out the back of the engine really fast using electrical repulsion. 5. Shoot the electron out the back (using a different pipe) so that the exhaust doesn't come back at you due to electrostatic attraction. 6. Now you have the rod, with one less atom. Repeat. A whole ton of times. Steps 2&3 might happen simultaneously, not entirely sure the mechanism but generally an electrical arc is violent, it will spallate and ionize a few atoms here and there. Not having a tank is huge, and the first ionization energy of many metal ions is far far lower than noble gases, which are what is commonly used in normal ion drives