Consider a hollow conducting tube with a highly positively charged object close to one of its ends. The medium between the conducting tube and the charged object is strong enough to prevent an electric breakdown. Now, if I pass protons through the tube, they don't feel any force from the charged object as they are inside a conductor. (Since there is a hole, the charges feel a negligible force on them. The hole is small enough so that only a negligible or tiny part of the electric field enters the hollow region inside of it.) When the particles exit the tube, they now feel a large force on them as they are near the charged object.
The induced surface charge will alter the electric field. Now, all the electric field lines are perpendicular to the conductors surface and the side of the tube closer to the charged body has a negative charge.
Can the particles leave the conducting tube, or will they be attracted to the conductors negative charge that is induced. If they do leave, they will be accelerated to relativistic speeds, assuming the charged body is charged enough.). So, where is this energy coming from? Since the larger the number of protons that pass through the tube, the more energy is required to accelerate them. I am assuming that the protons would actually collide with the surface of the conductor just after they leave it, unless they have sufficient kinetic energy to start with. Even then, I don't understand where that potential energy between the charged body and the protons is coming from or how it is created all of a sudden.