It has been mentioned that high frequency AC moves near the surface of the conductor. Because of this, almost all coaxial cables for high power utilize a hollow conductor. The large coax cables you see on broadcast and cell towers utilize a hollow center conductor made of copper. Looks just like soft copper tubing for plumbing. For RF, the surface area determines current carrying capacity.
Just another note in this good discussion.
Electronics and electricity are fun! (diodes are like check valves except when they are voltage regulators or capacitors) Fun stuff!