Modeling of ultra-short-pulse reflectometry

Pulsed reflectometry using both ordinary (O) and extraordinary (X) modes ca n provide time- and space-resolved measurements of the electron density, th e magnitude of the magnetic field, the magnetic shear as a function of radi us, and information on density and magnetic fluctuations. Such a diagnostic also yields the current profile from the curl of the magnetic field. This research addresses theoretical issues associated with the use of pulsed ref lectometry with particular emphasis on applications in the Sustained Sphero mak Physics Experiment (SSPX) at the Lawrence Livermore National Laboratory [E. B. Hooper et al., "Sustained Spheromak Physics Experiment,'' in Procee dings of the 17th International Atomic Energy Agency (IAEA) Fusion Energy C onference, Yokohama, Japan, October 19-24, 1998, Lawrence Livermore Nationa l Laboratory Report UCRL-JC-132034 (September 29, 1998)]. Simulation result s are presented for O- and X-mode mixed-polarization reflectometry and line ar mode conversion in two spatial dimensions. The profile reconstruction al gorithms depend on Wentzel-Kramers-Brillouin-Jeffreys (WKBJ) formulae for g roup delays and linear mode conversion, which agree reasonably well with di rect numerical solutions of the wave equation. Reconstructions of the elect ron density and modulus of the magnetic field are relatively robust in the presence of two-dimensional electron density and magnetic perturbations of the plasma. (C) 1999 American Institute of Physics. [S1070-664X(99)90205-7] .