SLAC microresonator RF (SMuRF) electronics: A tone-tracking readout system for superconducting microwave resonator arrays.

We describe the newest generation of the SLAC Microresonator RF (SMuRF) electronics, a warm digital control and readout system for microwave-frequency resonator-based cryogenic detector and multiplexer systems, such as microwave superconducting quantum interference device multiplexers (µmux) or microwave kinetic inductance detectors. Ultra-sensitive measurements in particle physics and astronomy increasingly rely on large arrays of cryogenic sensors, which in turn necessitate highly multiplexed readout and accompanying room-temperature electronics. Microwave-frequency resonators are a popular tool for cryogenic multiplexing, with the potential to multiplex thousands of detector channels on one readout line. The SMuRF system provides the capability for reading out up to 3328 channels across a 4-8 GHz bandwidth. Notably, the SMuRF system is unique in its implementation of a closed-loop tone-tracking algorithm that minimizes RF power transmitted to the cold amplifier, substantially relaxing system linearity requirements and effective noise from intermodulation products. Here, we present a description of the hardware, firmware, and software systems of the SMuRF electronics, comparing achieved performance with science-driven design requirements. In particular, we focus on the case of large-channel-count, low-bandwidth applications, but the system has been easily reconfigured for high-bandwidth applications. The system described here has been successfully deployed in lab settings and field sites around the world and is baselined for use on upcoming large-scale observatories.

Depth-dependent valence stratification driven by oxygen redox in lithium-rich layered oxide.

Lithium-rich nickel-manganese-cobalt (LirNMC) layered material is a promising cathode for lithium-ion batteries thanks to its large energy density enabled by coexisting cation and anion redox activities. It however suffers from a voltage decay upon cycling, urging for an in-depth understanding of the particle-level structure and chemical complexity. In this work, we investigate the Li1.2Ni0.13Mn0.54Co0.13O2 particles morphologically, compositionally, and chemically in three-dimensions. While the composition is generally uniform throughout the particle, the charging induces a strong depth dependency in transition metal valence. Such a valence stratification phenomenon is attributed to the nature of oxygen redox which is very likely mostly associated with Mn. The depth-dependent chemistry could be modulated by the particles' core-multi-shell morphology, suggesting a structural-chemical interplay. These findings highlight the possibility of introducing a chemical gradient to address the oxygen-loss-induced voltage fade in LirNMC layered materials.

Soft X-ray spectroscopy with transition-edge sensors at Stanford Synchrotron Radiation Lightsource beamline 10-1.

We present results obtained with a new soft X-ray spectrometer based on transition-edge sensors (TESs) composed of Mo/Cu bilayers coupled to bismuth absorbers. This spectrometer simultaneously provides excellent energy resolution, high detection efficiency, and broadband spectral coverage. The new spectrometer is optimized for incident X-ray energies below 2 keV. Each pixel serves as both a highly sensitive calorimeter and an X-ray absorber with near unity quantum efficiency. We have commissioned this 240-pixel TES spectrometer at the Stanford Synchrotron Radiation Lightsource beamline 10-1 (BL 10-1) and used it to probe the local electronic structure of sample materials with unprecedented sensitivity in the soft X-ray regime. As mounted, the TES spectrometer has a maximum detection solid angle of 2 × 10-3 sr. The energy resolution of all pixels combined is 1.5 eV full width at half maximum at 500 eV. We describe the performance of the TES spectrometer in terms of its energy resolution and count-rate capability and demonstrate its utility as a high throughput detector for synchrotron-based X-ray spectroscopy. Results from initial X-ray emission spectroscopy and resonant inelastic X-ray scattering experiments obtained with the spectrometer are presented.

Synthesis of a copper-supported triplet nitrene complex pertinent to copper-catalyzed amination.

Terminal copper-nitrenoid complexes have inspired interest in their fundamental bonding structures as well as their putative intermediacy in catalytic nitrene-transfer reactions. Here, we report that aryl azides react with a copper(I) dinitrogen complex bearing a sterically encumbered dipyrrin ligand to produce terminal copper nitrene complexes with near-linear, short copper-nitrenoid bonds [1.745(2) to 1.759(2) angstroms]. X-ray absorption spectroscopy and quantum chemistry calculations reveal a predominantly triplet nitrene adduct bound to copper(I), as opposed to copper(II) or copper(III) assignments, indicating the absence of a copper-nitrogen multiple-bond character. Employing electron-deficient aryl azides renders the copper nitrene species competent for alkane amination and alkene aziridination, lending further credence to the intermediacy of this species in proposed nitrene-transfer mechanisms.

Surface-to-Bulk Redox Coupling through Thermally Driven Li Redistribution in Li- and Mn-Rich Layered Cathode Materials.

Li- and Mn-rich (LMR) layered cathode materials have demonstrated impressive capacity and specific energy density thanks to their intertwined redox centers including transition metal cations and oxygen anions. Although tremendous efforts have been devoted to the investigation of the electrochemically driven redox evolution in LMR cathode at ambient temperature, their behavior under a mildly elevated temperature (up to ∼100 °C), with or without electrochemical driving force, remains largely unexplored. Here we show a systematic study of the thermally driven surface-to-bulk redox coupling effect in charged Li1.2Ni0.15Co0.1Mn0.55O2. We for the first time observed a charge transfer between the bulk oxygen anions and the surface transition metal cations under ∼100 °C, which is attributed to the thermally driven redistribution of Li ions. This finding highlights the nonequilibrium state and dynamic nature of the LMR material at deeply delithiated state upon a mild temperature perturbation.

Lynx x-ray microcalorimeter.

Lynx is an x-ray telescope, one of four large satellite mission concepts currently being studied by NASA to be a flagship mission. One of Lynx's three instruments is an imaging spectrometer called the Lynx x-ray microcalorimeter (LXM), an x-ray microcalorimeter behind an x-ray optic with an angular resolution of 0.5 arc sec and ∼2 m2 of area at 1 keV. The LXM will provide unparalleled diagnostics of distant extended structures and, in particular, will allow the detailed study of the role of cosmic feedback in the evolution of the Universe. We discuss the baseline design of LXM and some parallel approaches for some of the key technologies. The baseline sensor technology uses transition-edge sensors, but we also consider an alternative approach using metallic magnetic calorimeters. We discuss the requirements for the instrument, the pixel layout, and the baseline readout design, which uses microwave superconducting quantum interference devices and high-electron mobility transistor amplifiers and the cryogenic cooling requirements and strategy for meeting these requirements. For each of these technologies, we discuss the current technology readiness level and our strategy for advancing them to be ready for flight. We also describe the current system design, including the block diagram, and our estimate for the mass, power, and data rate of the instrument.

Use of Transition Models to Design High Performance TESs for the LCLS-II Soft X-Ray Spectrometer.

We are designing an array of transition-edge sensor (TES) microcalorimeters for a soft X-ray spectrometer at the Linac Coherent Light Source at SLAC National Accelerator Laboratory to coincide with upgrades to the free electron laser facility. The complete spectrometer will have 1000 TES pixels with energy resolution of 0.5 eV full-width at half-maximum (FWHM) for incident energies below 1 keV while maintaining pulse decay-time constants shorter than 100 µs. Historically, TES pixels have often been designed for a particular scientific application via a combination of simple scaling relations and trial-and-error experimentation with device geometry. We have improved upon this process by using our understanding of transition physics to guide TES design. Using the two-fluid approximation of the phase-slip line model for TES resistance, we determine how the geometry and critical temperature of a TES will affect the shape of the transition. We have used these techniques to design sensors with a critical temperature of 55 mK. The best sensors achieve an energy resolution of 0.75 eV FWHM at 1.25 keV. Building upon this result, we show how the next generation of sensors can be designed to reach our goal of 0.5 eV resolution.

L-edge spectroscopy of dilute, radiation-sensitive systems using a transition-edge-sensor array.

We present X-ray absorption spectroscopy and resonant inelastic X-ray scattering (RIXS) measurements on the iron L-edge of 0.5 mM aqueous ferricyanide. These measurements demonstrate the ability of high-throughput transition-edge-sensor (TES) spectrometers to access the rich soft X-ray (100-2000 eV) spectroscopy regime for dilute and radiation-sensitive samples. Our low-concentration data are in agreement with high-concentration measurements recorded by grating spectrometers. These results show that soft-X-ray RIXS spectroscopy acquired by high-throughput TES spectrometers can be used to study the local electronic structure of dilute metal-centered complexes relevant to biology, chemistry, and catalysis. In particular, TES spectrometers have a unique ability to characterize frozen solutions of radiation- and temperature-sensitive samples.

Prototype phantoms for characterization of ultralow field magnetic resonance imaging.

PURPOSE: Prototype phantoms were designed, constructed, and characterized for the purpose of calibrating ultralow field magnetic resonance imaging (ULF MRI) systems. The phantoms were designed to measure spatial resolution and to quantify sensitivity to systematic variation of proton density and relaxation time, T1 . METHODS: The phantoms were characterized first with conventional magnetic resonance scanners at 1.5 and 3 T, and subsequently with a prototype ULF MRI scanner between 107 and 128 µT . RESULTS: The ULF system demonstrated a 2-mm spatial resolution and, using T1 measurements, distinguished aqueous solutions of MnCl2 differing by 20 µM [Mn(2+) ]. CONCLUSION: The prototype phantoms proved well-matched to ULF MRI applications, and allowed direct comparison of the performance of ULF and clinical systems.

Evidence of galaxy cluster motions with the kinematic Sunyaev-Zel'dovich effect.

Using high-resolution microwave sky maps made by the Atacama Cosmology Telescope, we for the first time present strong evidence for motions of galaxy clusters and groups via microwave background temperature distortions due to the kinematic Sunyaev-Zel'dovich effect. Galaxy clusters are identified by their constituent luminous galaxies observed by the Baryon Oscillation Spectroscopic Survey, part of the Sloan Digital Sky Survey III. We measure the mean pairwise momentum of clusters, with a probability of the signal being due to random errors of 0.002, and the signal is consistent with the growth of cosmic structure in the standard model of cosmology.

Detection of the power spectrum of cosmic microwave background lensing by the Atacama Cosmology Telescope.

We report the first detection of the gravitational lensing of the cosmic microwave background through a measurement of the four-point correlation function in the temperature maps made by the Atacama Cosmology Telescope. We verify our detection by calculating the levels of potential contaminants and performing a number of null tests. The resulting convergence power spectrum at 2° angular scales measures the amplitude of matter density fluctuations on comoving length scales of around 100 Mpc at redshifts around 0.5 to 3. The measured amplitude of the signal agrees with Lambda cold dark matter cosmology predictions. Since the amplitude of the convergence power spectrum scales as the square of the amplitude of the density fluctuations, the 4σ detection of the lensing signal measures the amplitude of density fluctuations to 12%.

Evidence for dark energy from the cosmic microwave background alone using the Atacama Cosmology Telescope lensing measurements.

For the first time, measurements of the cosmic microwave background radiation (CMB) alone favor cosmologies with w = -1 dark energy over models without dark energy at a 3.2-sigma level. We demonstrate this by combining the CMB lensing deflection power spectrum from the Atacama Cosmology Telescope with temperature and polarization power spectra from the Wilkinson Microwave Anisotropy Probe. The lensing data break the geometric degeneracy of different cosmological models with similar CMB temperature power spectra. Our CMB-only measurement of the dark energy density Ω(Λ) confirms other measurements from supernovae, galaxy clusters, and baryon acoustic oscillations, and demonstrates the power of CMB lensing as a new cosmological tool.

Electrical and optical measurements on the first SCUBA-2 prototype 1280 pixel submillimeter superconducting bolometer array.

SCUBA-2 is a submillimeter camera being built for the James Clerk Maxwell Telescope in Hawaii. Bringing CCD style imaging to the submillimeter for the first time, with over 10000 pixels, it will provide a revolutionary improvement in sensitivity and mapping speed. We present results of the first tests on a prototype 1280 pixel SCUBA-2 subarray; the full instrument will be made up of eight such subarrays. The array is made up of transition edge sensor (TES) detectors, with Mo/Cu bilayers as the sensing element. To keep the number of wires reasonable, a multiplexed readout is used. Unlike previous TES arrays, an in-focal plane multiplexer configuration is used, in which the multiplexing elements are located beneath each pixel. To achieve the required performance, the detectors are operated at a temperature of approximately 120 mK. We describe the results of a basic electrical and optical characterization of the array, demonstrating that it is fully operational. Noise measurements were made on several pixels and gave a noise equivalent power below 2.5 x 10(-17) W HZ(-0.5), within the requirements for SCUBA-2. The construction of the testbed used to carry out these measurements is also described.