Advanced tokamaks seek to achieve a high bootstrap current fraction without
sacrificing fusion power density or fusion gain. Good progress has been ma
de towards the DIII-D research goal of demonstrating a high-beta advanced t
okamak plasma in steady state with a relaxed, fully non-inductive current p
rofile and a bootstrap current fraction greater than 50%. The limiting fact
ors for transport, stability, and current profile control in advanced opera
ting modes are discussed in this paper.