Algorithms for correcting geometric distortions in delay-line anodes

Time-delay anodes are typically used in conjunction with microchannel plates to provide photon counting and two- dimensional imaging. The anode and associated electronics are used to compute the centroid of the charge cloud from the microchannel plate stack. The computation is done in analog circuitry and reported as a digital value. The analog nature of the time-delay anode makes them susceptible to variations in the correlation between physical space and the reported digital value. These variations, both local and global, must be corrected as part of the data reduction of scientific data. If left uncorrected in spectral data, for example, these variations would result in inaccurate wavelength identifications and distorted spectral line profiles. This work describes successful algorithms for correcting the dominant distortions present in a time-delay anode; geometric (local) and thermal (global) distortions. These algorithms were developed as part of the data reduction pipelines for the Cosmic Origins Spectrograph (COS), a fourth generation instrument for the Hubble Space Telescope, and the Far Ultraviolet Spectroscopic Explorer (FUSE).