How to Accelerate Protons

In the same way a surfer needs to catch a wave to ride it, they need to be in the right spot and already going at the right speed. If you just dropped electrons into any random spot in the plasma, they would become part of the plasma. But if you set up this wave and then inject particles at the right place with the right speed, they can ride the wave generated by the plasma without becoming part of the Plasma.