CALIBRATION AND TEST OF THE TANGENTIAL PHASE-CONTRAST IMAGING DIAGNOSTIC ON CDX-U

A novel CO, laser-based tangential imaging diagnostic was completely c alibrated and the system was tested on CDX-U plasmas. It was shown tha t localized, two-dimensional images of the plasma electron density flu ctuations in the tokamak core can be obtained from a tangential imagin g beam [E. Lo, J. Wright, and R. Nazikian, Rev. Sci. Instrum. 66, 1180 (1995)]. A variation of the Zernike phase mirror is used. Test measur ements made on sound waves verify that the system will image phase var iations placed at the object plane. An absolute sensitivity of approxi mate to 1 x 10(7) cm(-3)/root Hz was determined. A series of plasma me asurements made on CDX-U is described. Results show that the plasma fl uctuations are two to three orders of magnitude above the noise floor of the diagnostic. It is also verified that a high-pass cut-off wave n umber (from approximate to 1 to 8 cm(-1)) for the fluctuations can be selected by translating the phase mirror. The density fluctuation k sp ectrum is measured and found to peak at approximate to 1-3 cm(-1). (C) 1997 American Institute of Physics.