The tomographic diagnostic developed for the beam generated in the SPIDER facility (100 keV, 50 A prototype negative ion source for the ITER neutral beam injector) will characterize the two-dimensional density distribution of the particles. The diagnostic will measure the emission of H?(or D?) radiation in a plane perpendicular to the beam propagation direction, with a set of 3127 lines of sight, covering the whole beam. The simulations described in the paper show that one of the most limiting causes of the maximum achievable resolution of the diagnostic is the instrumental noise. To reduce its impact on the image reconstruction, a filtering technique operating in the spatial domain has been adapted and implemented in the tomography code. This technique, originally developed for the application to radar imaging and based on a local statistics method [1], is applied to the simulated tomographic reconstruction of the SPIDER beam, and the main results are reported in this paper. Different experimental beam configurations have been simulated, corresponding to several operating conditions of the ion source (e.g. ideal uniform beam; beam with a linear variation of density; beam having some beamlet groups obstructed, representing a malfunctioning mode of the source). Reconstructions are made by adding different levels of random noise, up to 20%, uniformly distributed in the line integrated signals. The application of the spatial filter results in a clear amelioration of the reconstruction, with an important reduction of the reconstruction errors, allowing to better identify the beam uniformity level even when noise affects the signals. These simulations represent a first and encouraging attempt to reduce instrumental noise effects in the SPIDER tomography system, by implementing in the tomographic inversion code a post-processing algorithm that does not significantly increase the processing time. References 1 J.S. Lee, Speckle suppression and analysis for synthetic aperture radar image, Optical Engineering 25 (5), 636-646 (1986)
An Image Filtering Technique For SPIDER Visible Tomography
Matteo Agostini;Matteo Brombin;Roberto Pasqualotto;Gianluigi Serianni
2013
Abstract
The tomographic diagnostic developed for the beam generated in the SPIDER facility (100 keV, 50 A prototype negative ion source for the ITER neutral beam injector) will characterize the two-dimensional density distribution of the particles. The diagnostic will measure the emission of H?(or D?) radiation in a plane perpendicular to the beam propagation direction, with a set of 3127 lines of sight, covering the whole beam. The simulations described in the paper show that one of the most limiting causes of the maximum achievable resolution of the diagnostic is the instrumental noise. To reduce its impact on the image reconstruction, a filtering technique operating in the spatial domain has been adapted and implemented in the tomography code. This technique, originally developed for the application to radar imaging and based on a local statistics method [1], is applied to the simulated tomographic reconstruction of the SPIDER beam, and the main results are reported in this paper. Different experimental beam configurations have been simulated, corresponding to several operating conditions of the ion source (e.g. ideal uniform beam; beam with a linear variation of density; beam having some beamlet groups obstructed, representing a malfunctioning mode of the source). Reconstructions are made by adding different levels of random noise, up to 20%, uniformly distributed in the line integrated signals. The application of the spatial filter results in a clear amelioration of the reconstruction, with an important reduction of the reconstruction errors, allowing to better identify the beam uniformity level even when noise affects the signals. These simulations represent a first and encouraging attempt to reduce instrumental noise effects in the SPIDER tomography system, by implementing in the tomographic inversion code a post-processing algorithm that does not significantly increase the processing time. References 1 J.S. Lee, Speckle suppression and analysis for synthetic aperture radar image, Optical Engineering 25 (5), 636-646 (1986)I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
