Development of a local internal magnetic field measurement via dual mode (O-X) correlation reflectometry

A new method to measure the local magnetic field strength internal to a plasma is described using cross correlation of ordinary (O) and extraordinary (X) mode reflectometer signals originating from the naturally occurring turbulence present in all plasmas. This method relies on determination of the peak cross correlation between O- and X-mode signals, which are then assumed to originate from the same spatial location. Since the density at cutoff is known from the incident O- mode frequency, the magnetic field may be determined from the X-mode frequency. This method is expected to be widely applicable to many magnetic confinement devices, including those with magnetic fields less than or equal to 0.2-0.3 T, where application of other diagnostics may be difficult. (C) 1999 American Institute of Physics. [S0034-6748(99)56201-1].