High-fidelity optical transfer system for two dimensional imaging of density distribution of a pure electron plasma

A simple-structured imaging system is constructed for observing two-dimensional electron density distributions over a wide dynamic range and with a high spatial resolution. It consists of a phosphor plate, an image-transfer lens system and a charge-coupled-device (CCD) camera. The reliable operation of the CCD camera for experiments in a strong magnetic field (<2.2 T) requires positioning the camera at a large distance from the plasma trap. We successfully introduce a three-lens system for transferring the phosphor images to the camera with a low distortion and a high optical efficiency. The luminosity distribution of the CCD camera image is observed to be proportional to the axially integrated two-dimensional distribution of electrons. This proportionality is confirmed over a wide dynamic range of 15 : 60000 in the counting at each pixel of the CCD. On the basis of the linear relationship, a quantitative analysis is demonstrated for image data obtained from a vortex experiment encompassing the fluctuation level of 15 in the background and the peak value exceeding 30000 of an electron clump.