The X-ray Integral Field Unit (X-IFU) is an instrument of European Space Agency’s future NewAthena space observatory, with the goal to provide high-energy resolution (<4 eV at X-ray energies up to 7 keV) and high-spatial resolution (9 in.) spectroscopic imaging over the X-ray energy range from 200 eV to 12 keV, by means of an array of ∼1500 transition-edge sensors (TESs) read out via superconducting quantum interference device time-division multiplexing (TDM). A TDM-based laboratory test bed has been assembled at Netherlands Institute for Space Research, hosting an array of 75×75 μm2 TESs that are read out via 2-column × 32-row TDM. A system component that is critical to high-performance operation is the wiring harness that connects the room-temperature electronics to the cryogenic readout componentry. We report here on our characterization of such a test bed, whose harness has a length close to what was envisioned for X-IFU, which allowed us to achieve a co-added energy resolution at a level of 2.7-eV full width half maximum at 6 keV via 32-row readout. In addition, we provide an outlook on the integration of TDM readout into the X-IFU focal plane assembly development model.
The Line Emission Mapper (LEM) is a Probe mission concept developed in response to NASA’s Astrophysics Probe Explorer (APEX) Announcement of Opportunity. LEM has a single science instrument composed of a large-area, wide-field X-ray optic and a microcalorimeter X-ray imaging spectrometer in the focal plane. LEM is optimized to observe low-surface-brightness diffuse X-ray emission over a 30′ equivalent diameter field of view with 1.3 and 2.5 eV spectral resolution in the 0.2−2.0 keV band. Our primary scientific objective is to map the thermal, kinetic, and elemental properties of the diffuse gas in the extended X-ray halos of galaxies, the outskirts of galaxy clusters, the filamentary structures between these clusters, the Milky Way star-formation regions, the Galactic halo, and supernova remnants in the Milky Way and Local Group. The combination of a wide-field optic with 18′′ angular resolution end-to-end and a microcalorimeter array with 1.3 eV spectral resolution in a 5′ × 5′ inner array (2.5 eV outside of that) offers unprecedented sensitivity to extended low-surface-brightness X-ray emission. This allows us to study feedback processes, gas dynamics, and metal enrichment over seven orders of magnitude in spatial scales, from parsecs to tens of megaparsecs. LEM will spend approximately 11% of its five-year prime science mission performing an All-Sky Survey, the first all-sky X-ray survey at high spectral resolution. The remainder of the five-year science mission will be divided between directed science (30%) and competed General Observer science (70%). LEM and the NewAthena/XIFU are highly complementary, with LEM’s optimization for soft X-rays, large FOV, 1.3 eV spectral resolution, and large grasp balancing the NewAthena/X-IFU’s broadband sensitivity, large effective area, and unprecedented spectral resolving power at 6 keV. In this presentation, we will provide an overview of the mission architecture, the directed science driving the mission design, and the broad scope these capabilities offer to the entire astrophysics community.
The X-ray Integral Field Unit (X-IFU) instrument is the high-resolution X-ray spectrometer of the ESA Athena X-ray Observatory. X-IFU will deliver spectra from 0.2 to 12 keV with a spectral resolution requirement of 4 eV (3 eV design goal) up to 7 keV from 5" pixels, with a hexagonal field of view of 4' equivalent diameter. The main sensor array and its associated detection chain is one of the major functional chains of the X-IFU instrument, and is the main contributor to XIFU performance. CNES (Centre National d’Études Spatiales) is the prime contractor for the X-IFU and leads the project development and procurement aspects within the X-IFU Consortium; additional major partners of the main detection chain are NASA-GFSC, SRON, VTT, APC, NIST, IRAP, and IAP. The detection chain design for X-IFU has evolved in the past few years in order to secure the performances and development costs, in the frame of the New Athena mission. New TES pixels are implemented with slower time constant and a reduced sensitivity to magnetic field. The slower time constant directly allows an increase of the MUX factor and a reduction of the number of channels, together with the decrease of the number of proximity electronics boxes, or warm front end electronics (WFEE). The cryostat outer vessel temperature is now a 50 K thermal interface, cooled passively thanks to L-shaped thermal shield (L-grooves). This has a direct impact of the cryo-harness between the 4 K core interface and the WFEE interface. In the past years, we have performed early demonstration on the critical components in order to secure the detection chain design and performances. This paper presents the progress done on early demonstrations (warm electronics, cryo-harness breadboarding,...), while providing an update to the detection-chain design description.
We have obtained NASA funding to build and demonstrate Transition Edge Sensor (TES) based kilopixel arrays with the properties that match the requirements for cryogenic far-infrared space missions: the arrays are very closely tileable in one direction and have only a moderate gap in the other direction. This array architecture can meet the sampling- and pixel number requirement of ~ 104 pixels. Many details of the architecture have already been demonstrated individually, and the detector board will be optimized for the use of the latest cryogenic bump bonded NIST 2-D time domain SQUID readout multiplexers with a high density fanout scheme. Additionally, we use flex-lines that are very similar to those developed at Princeton University for the ACT project. We already have a pixel design that exceeds the continuum sensitivity requirements for a cryogenic space mission.
The line emission mapper (LEM) is a probe-class mission concept that is designed to detect x-ray emission lines from hot ionized gas (T > 106 K) that will enable us to test galaxy evolution theories. It will permit us to study the effects of stellar and black-hole feedback and flows of baryonic matter into and out of galaxies. The key to being able to study the hot gases that are otherwise invisible to current imaging x-ray spectrometers is that the energy resolution is sufficient to use cosmological redshift to separate extragalactic source lines from foreground Milky Way emission. LEM incorporates a large-format microcalorimeter array instrument called the LEM microcalorimeter spectrometer (LMS) with a light-weight x-ray optic with 10” half power diameter angular resolution. The LMS microcalorimeter array has pixels with 15″ pixel pitch over a 33′ field of view (FOV) optimized for the 0.3 to 2 keV energy band. The central 7′ region of the array has an energy resolution of 1.3 eV at 1 keV and the rest of the FOV has 2.5 eV energy resolution at 1 keV. The array will be read out with state-of-the-art time-division multiplexing. We present an overview of the LMS instrument, including details of the entire detection chain, the focal plane assembly, as well as the cooling system and overall mechanical and thermal design. For each of the key technologies, we discuss the current technology readiness level and the plan to advance them to be ready for flight. We also describe the current system design and our estimate for the mass, power, and data rate of the instrument. The design details presented concentrate primarily on the unique aspects of the LMS design compared with prior missions and confirm that the type of microcalorimeter instrument needed for LEM is not only feasible but also technically mature.
The flight of the Micro-X sounding rocket on July 22, 2018, marked the first operation of transition-edge sensors and their superconducting quantum interference device readouts in space. The instrument combines the microcalorimeter array with an imaging mirror to take high-resolution spectra from extended X-ray sources. The first flight target was the Cassiopeia A supernova remnant. Although a rocket pointing malfunction led to no time on-target, data from the flight were used to evaluate the performance of the instrument and demonstrate the flight viability of the payload. The instrument successfully achieved a stable cryogenic environment, executed all flight operations, and observed X-rays from the on-board calibration source. The flight environment did not significantly affect the performance of the detectors compared with ground operation. The flight provided an invaluable test of the impact of external magnetic fields and the instrument configuration on detector performance. This flight provides a milestone in the flight readiness of these detector and readout technologies, both of which have been selected for future X-ray observatories.
We present the conceptual design of the modular detector and readout system for the Cosmic Microwave Background – Stage four (CMB-S4) ground-based survey experiment. CMB-S4 will map the cosmic microwave background (CMB) and the millimeter-wave sky to unprecedented sensitivity, using 500,000 superconducting detectors observing from Chile and Antarctica to map over 60% of the sky. The fundamental building block of the detector and readout system is a detector module package operated at 100 mK, which is connected to a readout and amplification chain that carries signals out to room temperature. It uses arrays of feedhorn-coupled orthomode transducers (OMT) that collect optical power from the sky onto dc-voltage-biased transition-edge sensor (TES) bolometers. The resulting current signal in the TESs is then amplified by a two-stage cryogenic Superconducting Quantum Interference Device (SQUID) system with a time-division multiplexer to reduce wire count, and matching room-temperature electronics to condition and transmit signals to the data acquisition system. Sensitivity and systematics requirements are being developed for the detector and readout system over wide range of observing bands (20 to 300 GHz) and optical powers to accomplish CMB-S4’s science goals. While the design incorporates the successes of previous generations of CMB instruments, CMB-S4 requires an order of magnitude more detectors than any prior experiment. This requires fabrication of complex superconducting circuits on over 10 m2 of silicon, as well as significant amounts of precision wiring, assembly and cryogenic testing
The X-IFU (x-ray integral field unit) onboard the large ESA mission Athena (advanced telescope for high energy astrophysics), planned to be launched in the mid 2030s, will be a cryogenic x-ray imaging spectrometer operating at 55 mK. It will provide unprecedented spatially resolved high-resolution spectroscopy (2.5 eV FWHM up to 7 keV) in the 0.2-12 keV energy range thanks to its array of TES (transition edge sensors) microcalorimeters of more than 2k pixel. The detection chain of the instrument is developed by an international collaboration: the detector array by NASA/GSFC, the cold electronics by NIST, the cold amplifier by VTT, the WFEE (warm front-end electronics) by APC, the DRE (digital readout electronics) by IRAP and a focal plane assembly by SRON. To assess the operation of the complete readout chain of the X-IFU, a 50 mK test bench based on a kilo-pixel array of microcalorimeters from NASA/GSFC has been developed at IRAP in collaboration with CNES. Validation of the test bench has been performed with an intermediate detection chain entirely from NIST and Goddard. Next planned activities include the integration of DRE and WFEE prototypes in order to perform an end-to-end demonstration of a complete X-IFU detection chain.
The x-ray integral field unit (X-IFU) instrument is the high-resolution x-ray spectrometer of the ESA Athena x-ray observatory. X-IFU will deliver spectra from 0.2 to 12 keV with a spectral resolution of 2.5 eV up to 7 keV from 5" pixels, with a hexagonal field of view of 5' equivalent diameter. The main sensor array and its associated detection chain is one of the major sub-systems of the X-IFU instrument, and is the main contributor to X-IFU’s performance. CNES (the French Space Agency) is leading the development of X-IFU; additional major partners are NASA-GFSC, SRON, VTT, APC, NIST, and IRAP. This paper updates the B-phase definition of the X-IFU detection chain. The readout is based on time-division multiplexing (TDM). The different sub-components of the detection chain (the main sensor array, the cold electronics stages, and the warm electronics) require global design optimization in order to achieve the best performance. The detection chain’s sensitivity to the EMI/EMC environment requires detailed analysis and implementation of dedicated design solutions. This paper focuses on these aspects while providing an update to the detection-chain design description.
With its first flight in 2018, Micro-X became the first program to fly Transition-Edge Sensors and their SQUID readouts in space. The science goal was a high-resolution, spatially resolved X-ray spectrum of the Cassiopeia A Supernova Remnant. While a rocket pointing error led to no time on target, the data was used to demonstrate the flight performance of the instrument. The detectors observed X-rays from the on-board calibration source, but a susceptibility to external magnetic fields limited their livetime. Accounting for this, no change was observed in detector response between ground operation and flight operation. This paper provides an overview of the first flight performance and focuses on the upgrades made in preparation for reflight. The largest changes have been upgrading the SQUIDs to mitigate magnetic susceptibility, synchronizing the clocks on the digital electronics to minimize beat frequencies, and replacing the mounts between the cryostat and the rocket skin to improve mechanical integrity. As the first flight performance was consistent with performance on the ground, reaching the instrument goals in the laboratory is considered a strong predictor of future flight performance.
CNES (French Space Agency) is in charge of the development of the X-IFU instrument for Athena. The main sensor array detection chain sub-system of the X-IFU instrument is one of the major sub-subsystem of the instrument, as the main contributor to the performance. This sub-system involves major partners of the X-IFU instrument, e.g GFSC, SRON, VTT, APC, and IRAP. The purpose of this paper is to present the baseline of the definition of the X-IFU detection chain in the frame at end of phase A/beginning of phase B. The readout is based on Time Domain Multiplexing (TDM). There are strong design issues which couple the different sub-components of the detection chain (the main sensor array, the cold electronics stages, and the warm electronics). The detection chain environment (thermal, mechanical and EMI/EMC environment) also requires a transverse analysis. This paper focuses on those aspects while providing design description of the sub-components of the detection chain.
SQUID Time-Division Multiplexing (TDM) is a technique for the readout of arrays of Transition-Edge Sensors (TESs) for x-ray and gamma-ray science. TDM has been deployed in many recent 250-pixel-scale instruments including at synchrotron light sources and particle-accelerator facilities, as well as in table-top experiments. Two TES spectrometers employing TDM readout will soon be deployed to electron-beam ion-trap facilities.
TDM is also under development as a back-up readout option for the X-ray Integral Field Unit (X-IFU) of the Athena satellite mission. The 3,840 TES pixels of the X-IFU will enable efficient, high resolution spectroscopy (2.5 eV FWHM at 7 keV) of extended astrophysical sources. Multiplexing factors of 40 or more sensors per readout column are planned for the X-IFU. To advance the maturity of TDM readout for Athena, we are creating a focal-plane assembly for the readout of 960 TES pixels in a 24 column by 40 row configuration. We will describe the design and experimental progress on this technology demonstrator.
In a TDM system, each dc-biased TES has its own first-stage SQUID. Rows of these first-stage-SQUIDs are turned on and off sequentially such that the signal from only one TES at a time per readout column is passed to a series-array SQUID, to a room-temperature preamplifier, and to digital-feedback electronics. Recent implementations of TDM have a row period of 160 ns and non-multiplexed amplifier noise of 0.19 micro-Phi_0/sqrt(Hz) referred to the first-stage SQUID.
Some benchmark demonstrations of TDM with x-ray TES sensors include achievement of 2.55 eV FWHM energy resolution at 5.9 keV in a 32-row, 1-column configuration. Here, the fastest slew rates in the TES currents were similar to those of the X-IFU “LPA2” detector model. We have also achieved 2.72 eV FWHM resolution in a 32-row, 6-column configuration that contained 144 high-quality TESs that were similar to the much faster X-IFU “LPA1” pixels. We will describe on-going efforts to read out TDM arrays at the 6x32 scale and larger, as well as efforts to improve the performance of TDM system subcomponents. We will also describe system-level performance metrics such as cross-talk.
SQUID Code-Division Multiplexing (CDM) is closely related to TDM but has important performance advantages. CDM and TDM operation are similar with the main difference being that in CDM, all TESs are observed by the multiplexer at all times, with the polarity of the TES signals switched between rows. Because all TESs are observed by the multiplexer at all times, the sqrt(N_rows) noise-aliasing degradation inherent to TDM is eliminated.
We are developing flux-summing CDM to be drop-in compatible with existing TDM systems. The most recent CDM implementation has a nonmultiplexed noise level of 0.17 micro-Phi_0/sqrt(Hz) referred to the first-stage SQUID and a row period of 160 ns. We have demonstrated 2.77 eV FWM resolution at 5.9 keV in 32-row, 1-column CDM test.
Micro-X is a sounding rocket borne X-ray telescope that utilizes transition edge sensors to perform imaging
spectroscopy with a high level of energy resolution. Its 2.1m focal length X-ray optic has an effective area of 300
cm2, a field of view of 11.8 arcmin, and a bandpass of 0.1–2.5 keV. The detector array has 128 pixels and an
intrinsic energy resolution of 4.5 eV FWHM. The integration of the system has progressed with functional tests
of the detectors and electronics complete, and performance characterization of the detectors is underway. We
present an update of ongoing progress in preparation for the upcoming launch of the instrument.
The focal plane of the X-ray integral field unit (X-IFU) for ESA’s Athena X-ray observatory will consist of ~ 4000 transition edge sensor (TES) x-ray microcalorimeters optimized for the energy range of 0.2 to 12 keV. The instrument will provide unprecedented spectral resolution of ~ 2.5 eV at energies of up to 7 keV and will accommodate photon fluxes of 1 mCrab (90 cps) for point source observations. The baseline configuration is a uniform large pixel array (LPA) of 4.28” pixels that is read out using frequency domain multiplexing (FDM). However, an alternative configuration under study incorporates an 18 × 18 small pixel array (SPA) of 2” pixels in the central ~ 36” region. This hybrid array configuration could be designed to accommodate higher fluxes of up to 10 mCrab (900 cps) or alternately for improved spectral performance (< 1.5 eV) at low count-rates. In this paper we report on the TES pixel designs that are being optimized to meet these proposed LPA and SPA configurations. In particular we describe details of how important TES parameters are chosen to meet the specific mission criteria such as energy resolution, count-rate and quantum efficiency, and highlight performance trade-offs between designs. The basis of the pixel parameter selection is discussed in the context of existing TES arrays that are being developed for solar and x-ray astronomy applications. We describe the latest results on DC biased diagnostic arrays as well as large format kilo-pixel arrays and discuss the technical challenges associated with integrating different array types on to a single detector die.
Four astrophysics missions are currently being studied by NASA as candidate large missions to be chosen in the 2020 astrophysics decadal survey.1 One of these missions is the “X-Ray Surveyor” (XRS), and possible configurations of this mission are currently under study by a science and technology definition team (STDT). One of the key instruments under study is an X-ray microcalorimeter, and the requirements for such an instrument are currently under discussion. In this paper we review some different detector options that exist for this instrument, and discuss what array formats might be possible. We have developed one design option that utilizes either transition-edge sensor (TES) or magnetically coupled calorimeters (MCC) in pixel array-sizes approaching 100 kilo-pixels. To reduce the number of sensors read out to a plausible scale, we have assumed detector geometries in which a thermal sensor such a TES or MCC can read out a sub-array of 20-25 individual 1” pixels. In this paper we describe the development status of these detectors, and also discuss the different options that exist for reading out the very large number of pixels.
The Transition-edge EBIT Microcalorimeter Spectrometer (TEMS) is a 1000-pixel array instrument to be delivered
to the Electron Beam Ion Trap (EBIT) facility at the Lawrence Livermore National Laboratory (LLNL)
in 2015. It will be the first fully operational array of its kind. The TEMS will utilize the unique capabilities of
the EBIT to verify and benchmark atomic theory that is critical for the analysis of high-resolution data from
microcalorimeter spectrometers aboard the next generation of x-ray observatories. We present spectra from the
present instrumentation at EBIT, as well as our latest results with time-division multiplexing using the current
iteration of the TEMS focal plane assembly in our test platform at NASA/GSFC.
One of the instruments on the Advanced Telescope for High-Energy Astrophysics (Athena) which was one of the three
missions under study as one of the L-class missions of ESA, is the X-ray Microcalorimeter Spectrometer (XMS). This
instrument, which will provide high-spectral resolution images, is based on X-ray micro-calorimeters with Transition
Edge Sensor (TES) and absorbers that consist of metal and semi-metal layers and a multiplexed SQUID readout. The
array (32 x 32 pixels) provides an energy resolution of < 3 eV. Due to the large collection area of the Athena optics, the XMS instrument must be capable of processing high counting rates, while maintaining the spectral resolution and a low deadtime. In addition, an anti-coincidence detector is required to suppress the particle-induced background. Compared to the requirements for the same instrument on IXO, the performance requirements have been relaxed to fit into the much more restricted boundary conditions of Athena.
In this paper we illustrate some of the science achievable with the instrument. We describe the results of design studies for the focal plane assembly and the cooling systems. Also, the system and its required spacecraft resources will be given.
The Micro-X High Resolution Microcalorimeter X-ray Imaging Rocket is a sounding rocket experiment
that will
combine a transition-edge-sensor X-ray-microcalorimeter array with a conical imaging mirror to
obtain high- spectral-resolution images of extended X-ray sources. The target for Micro-X’s first
flight (slated for January
2013) is the Puppis A supernova remnant. The Micro-X observation of the bright eastern knot of
Puppis A will obtain a line-dominated spectrum with up to 27,000 counts collected in 300 seconds at
2 eV resolution across the 0.3-2.5 keV band. Micro-X will determine the thermodynamic and
ionization state of the plasma, search for line shifts and broadening associated with dynamical
processes, and seek evidence of ejecta enhancement. We describe the progress made in developing
this payload, including the detector, cryogenics, and electronics
assemblies.
One of the instruments on the International X-ray Observatory (IXO), under study with NASA, ESA and JAXA, is the
X-ray Microcalorimeter Spectrometer (XMS). This instrument, which will provide high spectral resolution images, is
based on X-ray micro-calorimeters with Transition Edge Sensor thermometers. The pixels have metallic X-ray absorbers
and are read-out by multiplexed SQUID electronics. The requirements for this instrument are demanding. In the central
array (40 x 40 pixels) an energy resolution of < 2.5 eV is required, whereas the energy resolution of the outer array is
more relaxed (≈ 10 eV) but the detection elements have to be a factor 16 larger in order to keep the number of read-out
channels acceptable for a cryogenic instrument. Due to the large collection area of the IXO optics, the XMS instrument
must be capable of processing high counting rates, while maintaining the spectral resolution and a low deadtime. In
addition, an anti-coincidence detector is required to suppress the particle-induced background.
In this paper we will summarize the instrument status and performance. We will describe the results of design studies for
the focal plane assembly and the cooling systems. Also the system and its required spacecraft resources will be given.
Micro-X is a rocket-borne X-ray telescope which will use an array of Transition Edge Sensor (TES) microcalorimeters
to obtain high resolution soft X-ray spectra of extended astronomical sources. The microcalorimeter array consists of
128 pixels with a size of 590 μm × 590 μm each. The TESs are read out with a time-division Superconducting Quantum
Interference Device (SQUID) multiplexing system. The instrument's front end assembly, which contains the
microcalorimeter array and two SQUID amplification stages, is located at the focal point of a conically approximated
Wolter mirror with a focal length of 2100 mm and a point spread function of 2.4 arcmin half-power diameter. The
telescope's effective area amounts to ~ 300 cm2 at 1 keV. The TES array is cooled with an Adiabatic Demagnetization
Refrigerator. The first flight of Micro-X is scheduled for 2011, and will likely target a Si knot in the Puppis A supernova
remnant. The time available for the observation above an altitude of 160 km will be in excess of 300 seconds. The
design, manufacturing and assembly of the flight hardware has recently been completed, and system testing is underway.
We describe the final design of the Micro-X instrument, and report on the overall status of the project.
The Atacama Cosmology Telescope (ACT) is designed to measure temperature anisotropies of the cosmic microwave background (CMB) at arcminute resolution. It is the first CMB experiment to employ a 32×32 close-packed array of free-space-coupled transition-edge superconducting bolometers. We describe the organization of the telescope systems and software for autonomous, scheduled operations. When paired with real-time data streaming and display, we are able to operate the telescope at the remote site in the Chilean Altiplano via the Internet from North America. The telescope had a data rate of 70 GB/day in the 2007 season, and the 2008 upgrade to three arrays will bring this to 210 GB/day.
The Atacama Cosmology Telescope is a six meter, off-axis Gregorian telescope for measuring the cosmic microwave background at arcminute resolutions. The Millimeter Bolometer Array Camera (MBAC) is its current science instrument. Erected in the Atacama Desert of Chile in early 2007, it saw first light with the MBAC on 22 October 2007. In this paper we review its performance after one month of observing, focusing in particular on issues surrounding the alignment of the optical system that impact the sensitivity of the experiment. We discuss the telescope motion, pointing, and susceptibility to thermal distortions. We describe the mirror alignment procedure, which has yielded surface deviations of 31 μm rms on the primary and 10 μm rms on the secondary. Observations of planets show that the optical performance is consistent with the telescope design parameters. Preliminary analysis measures a solid angle of about 215 nanosteradians with a full width at half maximum of 1.44 arcminutes at 145 GHz.
The Atacama Cosmology Telescope (ACT) aims to measure the Cosmic Microwave Background (CMB) temperature
anisotropies on arcminute scales. The primary receiver for ACT is the Millimeter Bolometer Array
Camera (MBAC). The MBAC is comprised of three 32×32 transition edge sensor (TES) bolometer arrays, each
observing the sky with an independent set of band-defining filters. The MBAC arrays will be the largest pop-up
detector arrays fielded, and among the largest TES arrays built. Prior to its assembly into an array and installation
into the MBAC, a column of 32 bolometers is tested at ~ 0.4 K in a quick-turn-around dip probe. In
this paper we describe the properties of the ACT bolometers as revealed by data from those tests, emphasizing
a characterization that accounts for both the complex impedance and the noise as a function of frequency.
The Atacama Cosmology Telescope observes the Cosmic Microwave Background with arcminute resolution
from the Atacama desert in Chile. For the first observing season one array of 32 x 32 Transition Edge
Sensor (TES) bolometers was installed in the primary ACT receiver, the Millimeter Bolometer Array Camera
(MBAC). In the next season, three independent arrays working at 145, 220 and 280 GHz will be installed in
MBAC. The three bolometer arrays are each coupled to a time-domain multiplexer developed at the National
Institute of Standard and Technology, Boulder, which comprises three stages of superconducting quantum
interference devices (SQUIDs). The arrays and multiplexers are read-out and controlled by the Multi Channel
Electronics (MCE) developed at the University of British Columbia, Vancouver.
A number of experiments plan to use the MCE as read-out electronics and thus the procedure for tuning the
three stage SQUID system is of general interest. Here we describe the automated array tuning procedures and
algorithms we have developed. During array tuning, the SQUIDs are biased near their critical currents. SQUID
feedback currents and lock points are selected to maximize linearity, dynamic range, and gain of the SQUID
response curves. Our automatic array characterization optimizes the tuning of all three stages of SQUIDs by
selecting over 1100 parameters per array during the first observing season and over 2100 parameters during the
second observing season. We discuss the timing, performance, and reliability of this array tuning procedure
as well as planned and recently implemented improvements.
The 6-meter Atacama Cosmology Telescope will map the cosmic microwave background at millimeter wavelengths.
The commissioning instrument for the telescope, the Millimeter Bolometer Array Camera, is based on a
refractive optical system which simultaneously images three separate fields of view at three different frequencies:
145, 220, and 280 GHz. Each frequency band contains around twelve individual optical elements at five different
temperature stages ranging from 300 K to 300 mK and a 32 x 32 array of Transition Edge Sensor bolometers at
300 mK. We discuss the design of the close-packed on-axis optical design of the three frequencies. The thermal
design and performance of the system are presented in the context of the scientific requirements and observing
schedule. A major part of the design was the incorporation of multiple layers of magnetic shielding. We discuss
the performance of the 145 GHz optical system in 2007 and the implementation of the additional two frequency
channels in 2008.
The Micro-X High Resolution Microcalorimeter X-ray Imaging Rocket is sounding rocket experiment that will combine a transition-edge-sensor X-ray-microcalorimeter array with a conical imaging mirror to obtain high-spectral-resolution images of extended and point X-ray sources. Our first target is the Puppis A supernova remnant, which will be observed in January 2011. The Micro-X observation of the bright eastern knot of Puppis A will obtain a line-dominated spectrum with up to 90,000 counts collected in 300 seconds at 2 eV resolution across the 0.3-2.5 keV band. Micro-X will utilize plasma diagnostics to determine the thermodynamic and ionization state of the plasma, to search for line shifts and broadening associated with dynamical processes, and seek evidence of ejecta enhancement. We describe the progress made in developing this payload, including the detector, cryogenics, and electronics assemblies. A detailed modeling effort has been undertaken to design a rocket-bourne adiabatic demagnetization refrigerator with sufficient magnetic shielding to allow stable operation of transition edge sensors, and the associated rocket electronics have been prototyped and tested.
The Millimeter Bolometer Array Camera (MBAC) was commissioned in the fall of 2007 on the new 6-meter
Atacama Cosmology Telescope (ACT). The MBAC on the ACT will map the temperature anisotropies of the
Cosmic Microwave Background (CMB) with arc-minute resolution. For this first observing season, the MBAC
contained a diffraction-limited, 32 by 32 element, focal plane array of Transition Edge Sensor (TES) bolometers
for observations at 145 GHz. This array was coupled to the telescope with a series of cold, refractive, reimaging
optics. To meet the performance specifications, the MBAC employs four stages of cooling using closed-cycle
3He/4He sorption fridge systems in combination with pulse tube coolers. In this paper we present the design of
the instrument and discuss its performance during the first observing season. Finally, we report on the status
of the MBAC for the 2008 observing season, when the instrument will be upgraded to a total of three separate
1024-element arrays at 145 GHz, 220 GHz and 280 GHz.
Following our development of a superconducting transition-edge-sensor (TES) microcalorimeter design that en-
ables reproducible, high performance (routinely better than 3 eV FWHM energy resolution at 6 keV) and is
compatible with high-fill-factor arrays, we have directed our efforts towards demonstrating arrays of identical
pixels using the multiplexed read-out concept needed for instrumenting the Constellation-X X-ray Microcalorime-
ter Spectrometer (XMS) focal plane array. We have used a state-of-the-art, time-division SQUID multiplexer
system to demonstrate 2
×8 multiplexing (16 pixels read out with two signal channels) with an acceptably modest
level of degradation in the energy resolution. The average resolution for the 16 multiplexed pixels was 2.9 eV,
and the distribution of resolution values had a relative standard deviation of 5%. The performance of the array
while multiplexed is well understood. The technical path to realizing multiplexing for the XMS instrument on
the scale of 32 pixels per signal channel includes increasing the system bandwidth by a factor of four and reducing
the non-multiplexed SQUID noise by a factor of two.
In this paper we discuss the characteristics of a uniform 8
×8 array and its performance when read out non-
multiplexed and with various degrees of multiplexing. We present data acquired through the readout chain from
the multiplexer electronics, through the real-time demultiplexer software, to storage for later signal processing.
We also report on a demonstration of real-time data processing. Finally, because the multiplexer provides
unprecedented simultaneous access to the pixels of the array, we were able to measure the array-scale uniformity
of TES calorimeter parameters such as the individual thermal conductances and superconducting transition
temperatures of the pixels. Detector uniformity is essential for optimal operation of a multiplexed array, and
we found that the distributions of thermal conductances, transition temperatures, and transition slopes were
sufficiently tight to avoid significant compromises in the operation of any pixel.
Micro-X is a proposed sounding rocket experiment that will combine a transition-edge-sensor X-ray-microcalorimeter array with a conical imaging mirror to obtain high-spectral-resolution images of extended and point X-ray sources. We describe the payload and the science targeted by this mission including the discussion of three possible Micro- X targets: the Puppis A supernova remnant, the Virgo Cluster, and Circinus X-1. For example, a Micro-X observation of the bright eastern knot of Puppis A will obtain a line-dominated spectrum with 90,000 counts collected in 300 seconds at 2 eV resolution across the 0.3-2.5 keV band. Micro-X will utilize plama diagnostics to determine the thermodynamic and ionization state of the plasma, to search for line shifts and broadening associated with dynamical processes, and seek evidence of ejecta enhancement. For clusters of galaxies, Micro-X can uniquely study turbulence and the temperature distribution function. For binaries, Micro-X's high resolution spectra will separate the different processes contributing to the Fe K lines at 6 keV and give a clear view of the geometry of the gas flows and circumstellar gas.
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