Determination of the two-dimensional density distribution in a tokamak plasma using phase-imaging interferometry (invited)

Conventional interferometer systems used on fusion devices are typically limited to approximately ten channels or views, thus precluding the use of tomographic reconstruction techniques. Instead, a priori assumptions have to be made in order to obtain the electron density distribution. To overcome these problems, interferometer systems have been developed at the University of California, Los Angeles (UCLA), which use imaging techniques to provide many channels per probe beam. Using a two-dimensional, 40-channel, imaging far infrared (FIR) interferometer measurements have been made of the density distribution in the minor cross section of the UCLA Microtor tokamak. The heterodyne interferometer consists of two probe beams expanded so as to completely fill orthogonal views of the plasma cross section. These views are then imaged onto two 20-channel, linear microbolometer detector arrays. Using data from this system, the spatial electron density distribution in a tokamak plasma has been recovered for the first time using tomographic reconstruction techniques.