A/N: Kinetic energy = one half mass times velocity squared so long as velocity is much slower than the speed of light. The closer velocity is to light speed the less accurate that equation is. Anyway, this is the result of applying a bit too much thought into using element Zero to make rail guns.
Commander John Shepard stared blankly at the contraption which occupied the small engineering workshop of the Normandy and tried to figure out just why it had Adams giddy and Tali so excited that she was bouncing. There was nothing overly special about it after all, it consisted of what looked like a glass tube with four embedded metal rails that formed an oval track about a meter long and half a meter across. The curved sections that made up the 'top' and 'bottom' of the device looked pretty simple, consisting of clear glass or plastic tube with a set of four metal rails that reinforced the tube. One of the straight sections however, looked like a larger version of what was inside every rifle he'd ever had to take apart. The other straightaway looked like it was covered in some type of coil. In the center was a set of instruments and displays connected to both straightaways, though many more connections ran to the weapon side than the coil side.
All the displays were lit up with data readouts, some he recognized as voltage and current measurements and others that he didn't really understand. It wasn't a static display though, as the readings changed in response to the movement of something he could see inside the tube. A closer look as the object moved slowly through the closer bend showed that it was a cylinder with a cone shaped nose and tail. As it entered the weapon side several lights flashed and one of the readouts that showed a graph dropped instantly as the object shot out of the weapon tunnel moving so fast it was nothing but a blur.
"This will change everything Shepard!" Tali declared with much more enthusiasm than she'd ever shown before. He looked towards her just as the line graph that had fallen jumped back up and passed the previous level. "We've already got the plans and simulations for a more practical ring generator capable of replacing a ship's fusion reactor."
Stunned, Shepard turned to his chief engineer with a questioning look on his face.
The man shook his head amusedly, "She's not kidding or exaggerating sir. I just can't believe no one thought of it before now. It was Tali's brainstorm so I'll let her tell you what we've got here."
He turned towards his favorite combat engineer and smiled, "Ok, so what exactly is this and how will it change the galaxy?"
"Well," She started quietly, "I… Ah, got into a little argument with Jones while we were disassembling that last probe you had us pick up. It had an Ezero based gyroscope stabilizer that was still turning and I told him it was entirely possible that it could still be functioning while he thought we must have inadvertently powered it with our tools. He said that for the gyro to be still running after hundreds of years constituted perpetual motion and thus was physically impossible." She paused here and her head dipped while her bouncing lost some of its vigor as she continued. "I disagreed but he has been here longer so when he told me to drop the foolish notion I did, it isn't my place to challenge him further."
Chief Adams added into the pause, "Something he won't do so callously again, commander. Though in his defense, the idea had been disproven countless times in the past, based on the laws of conversation of energy and thermodynamics."
A click from the machine stole his attention and he turned to see a small fan blow air across a large heatsink. "I'm guessing that you couldn't let that go, could you?"
"No." Tali answered, her voice faltering slightly. "I could, I actually did. I'm used to being dismissed, out of hand, as you might say. But both you and Adams have always listened to my ideas and suggestions so I did some quick work at dinner and Chief Adams was kind enough to help me fine tune the math for my original design and then we built this." She gestured back to the contraption on the workbench.
"So what does it do, exactly?" Shepard asked, a little anxious to get the discussion back on track and finished before they reached the next mission.
Chief Adams answered. "Basically it's a perpetual motion machine in that it will circulate that object indefinitely. The object is actually a powerful permanent magnet. The furthest tunnel is an Eezo enhanced accelerator similar to what is used in every gun on this ship. The magnet has a mass of five hundred grams which is reduced to only five grams by the mass effect field. While inside the field the magnet is accelerated to 50 meters per second, giving it a kinetic energy of six point two five Joules."
Tali continued. "When it leaves the field it retains that velocity despite the increase of mass, just like the metal flakes a rifle fires, so the kinetic energy is increased to six hundred twenty five Joules. The closest tunnel basically has a coil around the track. When the magnet moves thorough it, its magnetic field induces a current in the coils, transforming kinetic energy into electrical energy. It exits the generator tunnel at just a quarter of a meter per second. The generator extracts all but point zero one five Joules of energy from the moving magnet."
Chief Adams took over as Tali paused to take a breath. "Our generator is eighty percent efficient so we get just under five hundred Joules of electrical energy to that circuit board. The Eezo system and accelerator only needs two hundred Joules to accelerate the magnet so we're left with a net gain of three hundred Joules."
"In other words," Tali said brightly, "we turned our weapons technology into free energy!"
Words failed John Shepard for the first time in his career and he stood slack jawed as he stared at the two people whose invention would change the galaxy.
A/N: Perhaps I put just a bit too much thought into this but why not? According to the codex the whole point of using Element Zero in guns of all sizes is that reducing the mass of the projectile allows it to be accelerated to otherwise unobtainable speeds. In practice reducing the mass reduces both the force needed to accelerate the projectile, which makes the gun easier to build, and reduces the energy needed, making the power supply requirements more reasonable. It also breaks the law of conservation of energy.
It does explain how the Citadel can have the keepers survive the long periods of time the station lies unused between cycles and how the relays have the power needed to make nearly infinite speed massless corridors through space though…