If this worked like OsakanOne suggested, with the system pushing and attracting in waves, the confinement would pretty much be assured to fall apart.
OsakanOne is also wrong about how magnetism works. Confined plasma will not clash and end up merely passing through one another. Magnetism is a very weak force at a distance and sense the only thing holding the plasma together is a magnetic field the beam will act more like a cutting torch than a saber (this technology is used in some arc wielding devices today and they most certainly do not 'clash' against eachother).
If you want to make a light saber, just go ahead and add in an 'electrostatic shield' or a physical component.