Two dimensional imaging of the plasma response to externally launched fast waves in preheated spherical tokamaks

We have considered the problem of the consistent determination of the global electromagnetic field for Alfvènic modes in inhomogeneous, magnetized, resistive, finite aspect ratio plasmas in the presence of externally launched radio frequency (RF) waves. The "global" approach consists of the simultaneous treatment of the plasma-vacuum-external RF source-vacuum-metal wall configuration with the appropriate consideration of wave propagation; transmission, absorption, and mode conversion; in this, no simplifying approximations or small parameter expansions are used. Thus, the basic physics of arbitrary aspect ratio and noncircular cross section, axially symmetric tokamaks in the preheated stage and in the presence of externally (antenna) launched RF waves is adequately described; it rigorously holds, in particular, for the low aspect ratio (spherical) tokamaks mentioned above. As a study case, we considered the START-device (Sykes et al., 1983; Sykes 1994; Wilson, 1994).