Investigation of dual mode (O-X) correlation reflectometry for determination of magnetic field strength

A new method to measure the internal magnetic field in a plasma, based on crosscorrelation of ordinary (O) mode and extraordinary (X) mode reflectometer signals originating from naturally occurring turbulence, is investigated. This method relies on identifying the O- and X-mode frequency pair (f(o), f(x)) where cross-correlation is maximum. Maximum cross-correlation is found to occur at an X-mode frequency slightly lower than the right-hand cut-off frequency. It is shown that the magnetic field strength can be determined from reflectometer data interpreted via a one-dimensional model, given estimates of the k-spectral width of the electrostatic plasma turbulence, and the electron density gradient scale length.