I am sorry but I might still not understand your question. I will answer to the best of my ability but if I did in fact misunderstand you please ask again.

The plasma is refered to as the plasma inside a tokamak reactor that will produce energy from fusion reactions. The walls I talk about are the walls of the tokamak reactor which are of course in contact with the plasma inside the tokamak vacuum vessel.

If you want to understand better feel free to read the posts I posted in the Guide to fusion I mention in the post.