A TANGENTIALLY VIEWING VISIBLE TV SYSTEM FOR THE DIII-D DIVERTOR

A video camera system has been installed on the DIII-D tokamak for two -dimensional spatial studies of line emission in the lower divertor re gion. The system views the divertor tangentially at approximately the height of the X point through an outer port. At the tangency plane, th e entire divertor from the inner wall to outside the DIII-D bias ring is viewed with spatial resolution of similar to 1 cm. The image contai ns information from similar to 90 deg of toroidal angle. In a recent u pgrade, remotely controllable filter changers were added which have pr oduced images from nominally identical discharges using different spec tral lines. Software was developed to calculate the response function matrix of the optical system using distributed computing techniques an d assuming toroidal symmetry. Standard sparse matrix algorithms are th en used to invert the three-dimensional images onto a poloidal plane. Spatial resolution of the inverted images is 2 cm; higher resolution s imply increases the size of the response function matrix. Initial resu lts from a series of experiments with multiple identical discharges sh ow that the emission from CII and CIII, which appears along the inner scrape-off layer above and below the X point during ELMing H mode, mov es outward and becomes localized near the X point in radiative diverto r operation induced by deuterium injection. (C) 1997 American Institut e of Physics.