hydrogen ions so the can be accelerated to high speed with very little power, then increase their gravitic mass until the inevitably fuse into a cloud of an atom with an atomic number and atomic mass in the zillions, then shut "the magic field" off and watch the giant atoms fission releasing considerable energy to their surroundings.
Duuuude!!! You have the kernel of an awesome SF novel here...what you describe seems to be the recipe for a "Big Bang" and the plot could involve a scientist trying to recreate the Big Bang and make a whole new universe.
Using satellite data, researchers from the Woods Hole Oceanographic Institute (WHOI) set out to more accurately answer that question -- and found out that it's 320 million cubic miles.
So, what were the earlier estimates? I'm on Slashdot => I did not RTFA.