  A spherical tokamak (ST) with a plasma center column (PCC) can be formed via
driven magnetic relaxation of a screw pinch plasma. An ST-PCC could in
principle eliminate many problems associated with a material center column, a
key weakness of the ST reactor concept. This work summarizes the design space
for an ST-PCC in terms of flux amplification, aspect ratio, and elongation,
based on the zero-beta Taylor-relaxed analysis of Tang & Boozer [Phys. Plasmas
13, 042514 (2006)]. The paper will discuss (1) equilibrium and stability
properties of the ST-PCC, (2) issues for an engineering design, and (3) key
differences between the proposed ST-PCC and the ongoing Proto-Sphera effort in
Italy.
