Measurements of the radial profile of magnetic field in the Gas-Dynamic Trap using a motional Stark effect diagnostic

We have implemented a spectral motional Stark effect diagnostic for spatially localized measurements of magnetic field on the Gas-Dynamic Trap (GDT) magnetic mirror device. A 7 A, 40 keV diagnostic neutral hydrogen beam was focused to a current density of 0.25 A/cm(2) in the measurement volume, allowing achievement of a radial resolution of 4.5 cm by viewing the beam at 45degrees with a well-defined light collection chord. The entire Stark spectrum was recorded by a spectrometer with a charge-coupled device detector. Analysis of the splitting of the components of the Stark spectrum directly results in a measurement of local \B\. When operated with deuterium heating neutral beam injection into a hydrogen target plasma, the GDT axial magnetic field is strongly perturbed by plasma diamagnetic effects. Thus,. measurement of the radial pro file of the perturbed magnetic field, combined with equilibrium modeling, will yield an,estimate of the plasma beta. (C) 2003 American Institute of Physics.