A Real-Time Imaging Diagnostic for Electron Cyclotron Heating Systems

In this presentation we describe a spectroscopic diagnostic capable of imaging high frequency waves (>50 GHz) in real time with sub-mm spatial resolution. The diagnostic relies on measuring passive D_β optical emission and requires a minimum wave electric field magnitude of ~500 V/cm. These requirements limit the technique to the edge plasma and yield an optimal response when implemented to diagnose the microwave beam of electron cyclotron heating systems. The diagnostic was specifically designed to investigate electron cyclotron beam scattering from turbulence. This effect is important because it can lead to a substantial increase in the power required to stabilize neoclassical tearing modes. The dynamic Stark effect is used to extract the electric field vector from the D_boptical emission. This effect produces a satellite structure in the spectrum. For high frequency waves, individual satellite intensities can be imaged using ultra-narrow bandpass filtered cameras. The electric field vector is determined from the intensity ratio of two satellites in two orthogonal polarization states. The details associated with the diagnostic and its application for physics studies will be discussed.