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Results of a 2-column by 8-row multiplexing demonstration using a Goddard array and NIST SQUID multiplexing electronics at NIST. The black points show histograms of MnK-alpha X-rays from an 55Fe source for each pixel acquired simultaneously, with vertical offsets for clarity and fits overlaid in blue/red. The mean energy resolution is 2.93 eV and the variation on this is only 0.02 eV. Adapted from Kilbourne et al., 2008. (Click theimage for a larger view)
The XMS microcalorimeter array consists of a high-performance core array, surrounded by a field-of-view extension.
The focal plane consists of a core 40 × 40 array of 300 × 300 μm pixels with spectral resolution of 2.5 eV, corresponding to a 2 × 2 arcmin field of view with 3 arcsec pixels. This core array is surrounded by an outer 52 × 52 array of 600 × 600 μm pixels (2,304 pixels total in the outer array) that extends the field of view to 5 × 5 arcmin with better than 10 eV resolution.
The arrays are fabricated using standard micro-electronic techniques. The pixels use Mo/Au bilayer superconducting films deposited on Si wafers with silicon nitride films. The X-ray absorbing elements are formed by electroplating Au/Bi films that are patterned so they provide a high array filling factor (95%), but only contact a small, non-active area of each TES to avoid electrical or chemical interaction with the sensors.
Since, TES thermometers use the extremely rapid change in electrical resistance in the narrow temperature range (<1 mK) of a superconducting transition, to achieve this performance, the detector must be cooled to 0.05 K and electrically biased into the superconducting transition at (~ 0.1 μK).
Imaging TES detectors will have at least eight imaging elements per pair of TES. Position information will be obtained by comparing the relative signals on the two TESs, while energy will be inferred by summing the signals. Both parts of the focal plane will be read using multiplexed inductively coupled superconducting quantum-interference devices (SQUIDs) amplifiers. In total, there will be ~1800 TES microcalorimeters that will be read out using a SQUID multiplexer.
For more information, refer to
Multiplexed readout of uniform arrays of TES X-ray, Caroline Kilbourne et al., SPIE 2008
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