Impact of GEM foil hole geometry on GEM detector gain
Detailed 3D imaging of Gas Electron Multiplier (GEM) foil hole geometry was realized. Scanning White Light Interferometry was used to examine six topological parameters of GEM foil holes from both sides of the foil. To study the effect of the hole geometry on detector gain, the ANSYS and Garfield ++ software were employed to simulate the GEM detector gain on the basis of SWLI data. In particular, the effective gain in a GEM foil with equally shaped holes was studied. The real GEM foil holes exhibited a 4% lower effective gain and 6% more electrons produced near the exit electrode of the GEM foil than the design anticipated. Our results indicate that the GEM foil hole geometry affects the gain performance of GEM detectors.
2D GEM based imaging detector readout capabilities from perspective of intense soft x-ray plasma radiation.
A detecting system based on the Gas Electron Multiplier (GEM) technology is considered for tokamak plasma radiation monitoring. In order to estimate its capabilities in processing and recording intense photon flux (up to ∼0.1 MHz/mm2), the imaging effectiveness of GEM detectors was tested with different patterned anode planes (i.e., different signal readouts): a simple hexagonal readout structure and three structures with interconnected electrodes (XY square, XY rectangular, and UXV). It was found that under intense photon flux, all the readouts fail to account for a considerable amount of the incoming signals due to mostly photon position determination ambiguity and overlapped signals. Analysis of the signals that can be used to determine photon position and energy unambiguously showed that the UXV readout structure is more effective among the readouts with interconnected electrodes. Along with similar spatial resolution and accuracy, the UXV based layout could be considered as a quite promising base of the interconnected anode electrodes configuration, keeping in mind that the photon rate capability has to be improved for the final application.
DEM generation from new VIR sensors: IKONOS, ASTER and Landsat-7
DEM generation is a living R&D topic since new-launched satellite images can be used to generate stereoscopic images. Using a coplanarity equation model developed at CCRS and an automatic matching method developed at PCI, DEMs are generated with new VIR stereo data. Accuracy of 4.9 m with high-resolution IKONOS images, and 33 m and 101 m with medium-resolution ASTER and Landsat-7 ETM/sup +/ images respectively are obtained. The same matching accuracy of one-pixel is translated into worse results with Landsat due to a small B/H ratio of 0.15.