Surely thay can't be proposing that a field be PROJECTED to that distance from the spaceship - the energy demand to generate such a field would be collossal.

Perhaps they are proposing a co-travelling literal shield that would fly that distance away, interposed between the spacecraft and the Sun. A MUCH smaller system could then generate a local magnetic field large enough to block-out direct particles from the Sun.

Of course, such a shield would be useless against cosmic rays, but they are a steady and tolerable background. It is the intense particle flux of solar storms that must be blocked.