The Atacama Cosmology Telescope was designed to measure small-scale anisotropies in the cosmic microwave background and detect galaxy clusters through the Sunyaev-Zel'dovich effect. The instrument is ...located on Cerro Toco in the Atacama Desert, at an altitude of 5190 m. A 6 m off-axis Gregorian telescope feeds a new type of cryogenic receiver, the Millimeter Bolometer Array Camera. The receiver features three 1000-element arrays of transition-edge sensor bolometers for observations at 148 GHz, 218 GHz, and 277 GHz. Each detector array is fed by free space millimeter-wave optics. Each frequency band has a field of view of approximately 22' X 26'. The telescope was commissioned in 2007 and has completed its third year of operations. We discuss the major components of the telescope, camera, and related systems, and summarize the instrument performance.
At NASA Goddard Space Flight Center, we have previously demonstrated a kilo-pixel array of transition-edge sensor (TES) microcalorimeters capable of meeting the energy resolution requirements of the ...future X-ray Integral Field Unit (X-IFU) instrument that is being developed for the Advanced Telescope for High ENergy Astrophysics (ATHENA) observatory satellite. The TES design in this array was a square device with side length of <inline-formula><tex-math notation="LaTeX">50 \,\mathrm{\upmu }\mathrm{m}</tex-math></inline-formula>. Here, we describe studies of TES designs with small variations of the dimensions, exploring lengths, parallel to the current direction, ranging from <inline-formula><tex-math notation="LaTeX">75 \,\mathrm{\upmu }\mathrm{m}</tex-math></inline-formula> to <inline-formula><tex-math notation="LaTeX">50 \,\mathrm{\upmu }\mathrm{m}</tex-math></inline-formula> and widths, perpendicular to the current direction, ranging from <inline-formula><tex-math notation="LaTeX">50 \,\mathrm{\upmu }\mathrm{m}</tex-math></inline-formula> to <inline-formula><tex-math notation="LaTeX">15 \,\mathrm{\upmu }\mathrm{m}</tex-math></inline-formula>. We describe how these changes impact transition properties, thermal conductance and magnetic field sensitivity. In particular, we show that using a TES with a length of <inline-formula><tex-math notation="LaTeX">50 \,\mathrm{\upmu }\mathrm{m}</tex-math></inline-formula> and width of <inline-formula><tex-math notation="LaTeX">30 \,\mathrm{\upmu }\mathrm{m}</tex-math></inline-formula> may be a promising route to reduce the maximum time-derivative of the TES current in an X-ray pulse and reduce the sensitivity of the TES to magnetic field.
Time-division multiplexing (TDM) is the backup readout technology for the X-ray Integral Field Unit (X-IFU), a 3168-pixel X-ray transition-edge sensor (TES) array that will provide imaging ...spectroscopy for european space agency's Athena satellite mission. X-IFU design studies are considering readout with a multiplexing factor of up to 40. We present data showing 40-row TDM readout (32 TES rows + 8 repeats of the last row) of TESs that are of the same type as those being planned for X-IFU, using measurement and analysis parameters within the ranges specified for X-IFU. Single-column TDM measurements have best-fit energy resolution of (1.91 ± 0.01) eV for the Al Kα complex (1.5 keV), (2.10 ± 0.02) eV for Ti Kα (4.5 keV), (2.23 ± 0.02) eV for Mn Kα (5.9 keV), (2.40 ± 0.02) eV for Co Kα (6.9 keV), and (3.44 ± 0.04) eV for Br Kα (11.9 keV). Three-column measurements have best-fit resolution of (2.03 ± 0.01) eV for Ti Kα and (2.40 ± 0.01) eV for Co Kα. The degradation due to the multiplexed readout ranges from 0.1 eV at the lower end of the energy range to 0.5 eV at the higher end. The demonstrated performance meets X-IFU's energy-resolution and energy-range requirements. True 40-row TDM readout, without repeated rows, of kilopixel scale arrays of X-IFU-like TESs is now under development.
The Athena mission and its X-ray Integral Field Unit (X-IFU) instrument will be positioned at the Sun-Earth Lagrange point L1, where it will be subject to particles from the solar wind with energy ...below 0.1 MeV, and from galactic cosmic rays and solar flares with energies up to hundreds of MeV for protons and GeVs for heavier ions. Some of these particles will go through the satellite and hit the focal plane assembly and hence the detectors. These detectors will be TES (Transition-edge sensor) microcalorimeters, flown for the first time in such an environment. In order to ensure the performance of this type of detector throughout the duration of such a mission, it is critical to study the impact of the radiation on their behavior. Indeed, although a lot of reference material exist for semiconductor-based photodetectors such as CCDs and CISs, little is currently known about the impact of radiation on TES detectors. These energetic events could cause local heating or damage to the detectors and affect their performance. In this work, we describe how we designed a test campaign to assess the impact of L1 radiation on TES detectors for Athena/X-IFU-like missions and present the results of the tests, for a maximum dose of 4.3 krad(Si)). Analysis includes assessing changes in the pulse shapes and energy resolution of the detectors measured at 55 mK after several radiation dose steps performed at 4 K.
The X-ray Integral Field Unit on Athena will be subject to a cosmic-ray induced thermal background on orbit, with energy depositions into the detector wafer leading to thermal bath fluctuations. Such ...fluctuations have the potential to degrade energy resolution performance of the transition-edge sensor based microcalorimeter. This problem was previously studied in simulations that modeled thermal bath fluctuations induced by cosmic-ray events and evaluated the resulting energy resolution degradation due to a simulated timeline of such events. Now taking an experimental approach, we present results using a collimated Am-241 alpha particle source to deposit a known energy to specific locations on the detector wafer. Thermal pulses induced by the alpha particle energy depositions are measured at various detector pixels for several different experimental configurations, including for energy deposited into the inter-pixel structure of the wafer, as well as the frame area outside the pixel array. Further, we also test both with and without a thick backside heatsinking metallization layer that is baselined for the instrument. In each case results are compared to expectations based on the thermal model developed for the previous study.
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