EMP energy can possibly gained by trying to put the 2 poles of the supermagnets onto eachother on high-rotating speed. The energy-burst that should follow must be 'caught' and used to give the spaceship speed. Because this happens constantly under high speed,the spaceship should get energy-bursts so quickly,that the spaceship will constantly have a very high average speed. Ofcourse, we must be able to control and manage the entire proces,so we can also slow down and stop the spaceship. Other options might be Vacuum energy and Manipulated spacetimes. Also BTC travel has other options