They use electricity to produce an incredibly powerful magnetic force. (aren't you an engineer?)
Electricity and magnetism are linked forces
* All electric forces produce their own magnetic fields - (example, an electromagnet)
* Movement of magnetic fields produces electricity (dunno really how to word it) (ex, a generator)
They work by very different principals the railgun by the Lorentz force where the Gauss cannon / Coil Gun works through a series of electromagnets activated in series to accelerate the projectile down the barrel.
64MJ is still in the roadmap, but it slipped lower on the priority list. The initial plan was to ramp up to 64MJ with Lab weapons, then from there develop into a "production" weapon. But with the funding being threatened, Carr and others chose to make a run at getting a practical weapon to the fleet sooner and ramp up the power afterward. As he points out, at the 33+ MJ figure they can have a practical at-sea demonstrator by FY2019. To get to 64MJ (and fit in existing ships) they'd need 3-5 more years to shrink the power system.
I do wonder what the rationale was for pursuing a railgun as opposed to a coil gun.
Sorry, I missed this. A coilgun of 33MJ would be heavier and more complex than a 33MJ railgun, with less muzzle energy. They're great from a durability standpoint, but switching and resistance issues are their own developmental nightmare. Coils at lower power/velocity, however, have real potential. DARPA's working on a coilgun vehicle mortar, for example.
In case anyone was wondering about Railgun and FEL in the Budget released today:
The Railgun program's budget is more than doubled to support testing of 2 prototypes and development of the pulsed power system and rapid fire technology. Projectile development is also pressing ahead.
FEL's budget is harder to parse since its part of an umbrella program, though that umbrella's budget has been halved so its clearly not in as good shape as Railgun. FEL will continue "Phase II" which is development of the 100kw demonstrator, however, so its not dead. Mostly it seems to have been stretched out in favor of Railgun and an interest in getting Solid State Lasers to the fleet faster than FEL can be ready.