Very fun idea. Let's think about this: The L1 point is unstable. This means that if you put a spacecraft there and it starts to drift away, it will not come back. So you don't have to expend much energy to keep a spacecraft at the L1 point, but you do have to be active about it. It's just like balancing a stick on your hand. It's not hard and once you have it balanced just right you don't have to move your hand around much to keep it there. But if you stop actively balancing it, it will fall over.

So think about the solar wind shield: Its purpose is to deflect charged particles coming from the sun so they don't hit Mars and strip away its atmosphere (and give its residents cancer). Can you do this without having the solar wind exert huge forces on your shield? Maybe?

Certainly if the shield were a literal physical shield, the forces generated by radiation pressure would be enormous. You'd have to be firing some kind of propulsion device towards the sun at all times to keep from being blown away from the L1 point.

But would the magnetic shield work the same? All it has to do is deflect the particles to the side, right? It doesn't have to bounce them back towards the sun. So at face value, it's not obvious to me that conservation of momentum would kill you...

That's all I've got. Thanks!