All of it in the relativistic kinetic energy of the beam. The energy in the superconductor magnets is a whole chapter of its own; their energy dissipating into heat is what makes the Helium boil off during a quench.

Also static magnetic fields don't "do" work, by that I mean, that you can not extract energy from a magnetic field by sending particles through it: The Lorentz force is perpendicular to both the movement of the particle through the field, and perpendicular to the field itself. Hence taking the inner=scalar=dot product of the force vectors and trajectories they come out as 0, i.e. no work is done.

You need dynamic magnetic fields to do work.