Engineering topics
Publications and source records attributed to Bock, James J..
This Snowmass 2021 White Paper describes the Cosmic Microwave Background Stage 4 project CMB-S4, which is designed to cross critical thresholds in our understanding of the origin and evolution of the Universe, from the highest energies at the dawn of time through the growth of structure to the present day. We provide an overview of the science case, the technical design, and project plan.
CMB-S4—the next-generation ground-based cosmic microwave background (CMB) experiment—is set to significantly advance the sensitivity of CMB measurements and enhance our understanding of the origin and evolution of the universe. Among the science cases pursued with CMB-S4, the quest for detecting primordial gravitational waves is a central driver of the experimental design. This work details the development of a forecasting framework that includes a power-spectrum-based semianalytic projection tool, targeted explicitly toward optimizing constraints on the tensor-to-scalar ratio, r, in the presence of Galactic foregrounds and gravitational lensing of the CMB. This framework is unique in its direct use of information from the achieved performance of current Stage 2–3 CMB experiments to robustly forecast the science reach of upcoming CMB-polarization endeavors. The methodology allows for rapid iteration over experimental configurations and offers a flexible way to optimize the design of future experiments, given a desired scientific goal. To form a closed-loop process, we couple this semianalytic tool with map-based validation studies, which allow for the injection of additional complexity and verification of our forecasts with several independent analysis methods. We document multiple rounds of forecasts for CMB-S4 using this process and the resulting establishment of the current reference design of the primordial gravitational-wave component of the Stage-4 experiment, optimized to achieve our science goals of detecting primordial gravitational waves for r > 0.003 at greater than 5σ, or in the absence of a detection, of reaching an upper limit of r < 0.001 at 95% CL.
We study the stellar halos of 0.2 ≲ $z$ ≲ 0.5 galaxies with stellar masses spanning $M$* ~ 10 10.5 to 10 12 $M$ ⊙ (approximately $L$* galaxies at this redshift) using imaging data from the Cosmic Infrared Background Experiment (CIBER). A previous CIBER fluctuation analysis suggested that intra-halo light (IHL) contributes a significant portion of the near-infrared extragalactic background light (EBL), the integrated emission from all sources throughout cosmic history. In this work, we carry out a stacking analysis with a sample of ~30,000 Sloan Digital Sky Survey (SDSS) photometric galaxies from CIBER images in two near-infrared bands (1.1 and 1.8 $μ$m) to directly probe the IHL associated with these galaxies. We stack galaxies in five sub-samples split by brightness and detect an extended galaxy profile beyond the instrument point-spread function (PSF) derived by stacking stars. We jointly fit a model for the inherent galaxy light profile plus large-scale one- and two-halo clustering to measure the extended galaxy IHL. We detect nonlinear one-halo clustering in the 1.8 $μ$m band at a level consistent with numerical simulations. Furthermore, by extrapolating the fraction of extended galaxy light, we measure to all galaxy mass scales, we find ~30%/15% of the total galaxy light budget from galaxies is at radius $r$ > 10/20 kpc, respectively. These results are new at near-infrared wavelengths at the $L$* mass scale and suggest that the IHL emission and one-halo clustering could have appreciable contributions to the amplitude of large-scale EBL background fluctuations.
SPHEREx, the Spectro-Photometer for the History of the Universe, Epoch of Reionization, and ices Explorer, isa NASA MIDEX mission planned for launch in 2024. SPHEREx will carry out the first all-sky spectral survey at wavelengths between 0.75μm and 5μm with spectral resolving power ~40 between 0.75 and 3.8μm and ~120 between 3.8 and 5μm At the end of its two-year mission, SPHEREx will provide 14 billion 0.75-to-5μm spectra of each 6."2 x 6."2 pixel on the sky. This paper updates an earlier description of SPHEREx presenting changes made during the mission's Preliminary Design Phase, including a discussion of instrument integration and test flow and a summary of the data processing, analysis, and distribution plans.
Thermal Kinetic-Inductance Detectors (TKIDs) combine the excellent noise performance of traditional bolometers with a radio frequency multiplexing architecture that enables the large detector counts needed for the next generation of millimeter-wave instruments. In this paper, we first discuss the expected noise sources in TKIDs and derive the limits where the phonon noise contribution dominates over the other detector noise terms: generation–recombination, amplifier, and two-level system noise. Second, we characterize aluminum TKIDs in a dark environment. We present measurements of TKID resonators with quality factors of about 10 5 at 80 mK. We also discuss the bolometer thermal conductance, heat capacity, and time constants. These were measured by the use of a resistor on the thermal island to excite the bolometers. These dark aluminum TKIDs demonstrate a noise equivalent power, NEP = 2 × 10 − 17 W / Hz , with a 1 / f knee at 0.1 Hz, which provides background noise limited performance for ground-based telescopes observing at 150 GHz.
We present a final report on our program to raise the Technology Readiness Level (TRL) of enhanced charge‐coupled‐device (CCD) detectors capable of meeting the requirements of X‐ray grating spectrometers (XGS) and wide‐field X‐ray imaging instruments for small, medium, and large missions. Because they are made of silicon, all X‐ray CCDs require blocking filters to prevent corruption of the Xray signal by out‐of‐band, mainly optical and near‐infrared (near‐IR) radiation. Our primary objective is to demonstrate technology that can replace the fragile, extremely thin, free‐standing blocking filter that has been standard practice with a much more robust filter deposited directly on the detector surface. High‐performance, back‐illuminated CCDs have flown with free‐standing filters (e.g., one of our detectors on Suzaku), and other relatively low‐performance CCDs with directly deposited filters have flown (e.g., on the X‐ray Multi‐mirror Mission‐Newton, XMM‐Newton Reflection Grating Spectrometer, RGS). At the inception of our program, a high‐performance, back‐illuminated CCD with a directly deposited filter has not been demonstrated. Our effort will be the first to show such a filter can be deposited on an X‐ray CCD that meets the requirements of a variety of contemplated future instruments. Our principal results are as follows: i) we have demonstrated a process for direct deposition of aluminum optical blocking filters on back‐illuminated MIT Lincoln Laboratory CCDs. Filters ranging in thickness from 70 nm to 220 nm exhibit expected bulk visible‐band and X‐ray transmission properties except in a small number (affecting ≲ 1% of detector area) of isolated detector pixels ("pinholes"), which show higher‐than‐expected visible‐band transmission; ii) these filters produce no measurable degradation in soft‐X‐ray spectral resolution, demonstrating that direct filter deposition is compatible with the MIT Lincoln Laboratory back‐illumination process; iii) we have shown that under sufficiently intense visible and near‐IR illumination, out‐of‐band light can enter the detector through its sidewalls and mounting surfaces, compromising detector performance. This 'sidewall leakage' has been observed, for example, by a previous experiment on the International Space Station during its orbit‐day operations. We have developed effective countermeasures for this sidewall leakage; iv) we developed an exceptionally productive collaboration with the Regolith X‐ray Imaging Spectrometer (REXIS) team. REXIS is a student instrument now flying on the Origins Spectral Interpretation Resource Identification Security - Regolith Explorer (OSIRIS‐REx) mission. REXIS students participated in our filter development program, adopted our technology for their flight instrument, and raised the TRL of this technology beyond our initial goals. This Strategic Astrophysics Technology (SAT) project, a collaboration between the MKI and MIT Lincoln Laboratory, began July 1, 2012, and ended on June 30, 2018.
We present measurements of the auto- and cross-frequency correlation power spectra of the cosmic (sub)millimeter background at: 250, 350, and 500 microns (1200, 860, and 600 GHz) from observations made with the Balloon-borne Large Aperture Submillimeter Telescope, BLAST; and at 1380 and 2030 microns (218 and 148 GHz) from observations made with the Atacama Cosmology Telescope, ACT. The overlapping observations cover 8.6 deg(sup 2) in an area relatively free of Galactic dust near the south ecliptic pole (SEP). The ACT bands are sensitive to radiation from the CMB, the Sunyaev-Zel'dovich (SZ) effect from galaxy clusters, and to emission by radio and dusty star-forming galaxies (DSFGs), while the dominant contribution to the BLAST bands is from DSFGs. We confirm and extend the BLAST analysis of clustering with an independent pipeline, and also detect correlations between the ACT and BLAST maps at over 25(sigma) significance, which we interpret as a detection of the DSFGs in the ACT maps. In addition to a Poisson component in the cross-frequency power spectra, we detect a clustered signal at 4(sigma), and using a model for the DSFG evolution and number counts, we successfully fit all our spectra with a linear clustering model and a bias that depends only on red shift and not on scale. Finally, the data are compared to, and generally agree with, phenomenological models for the DSFG population. This study represents a first of its kind, and demonstrates the constraining power of the cross-frequency correlation technique to constrain models for the DSFGs. Similar analyses with more data will impose tight constraints 011 future models.
We report the performance of the flight bolometer arrays for the Spectral and Photometric Imaging REceiver (SPIRE) instrument to be on board of the Herschel Space Observatory (HSO). We describe the test setup for the flight Bolometric Detector Assembly (BDA) that allows the characterization of its performance, both dark and optical, in one instrument’s cool down. We summarize the laboratory procedure to measure the basic bolometer parameters, optical response time, optical efficiency of bolometer and feedhorn, dark and optical noise, and the overall thermal conductance of the BDA unit. Finally, we present the test results obtained from the two flight units, Spectroscopic Long Wavelength (SLW) and Spectroscopic Short Wavelength (SSW).
We present a near-infrared (3.5-5 micron) search for the integrated emission from low-mass stars and/or brown dwarfs in the halo of the nearby edge-on spiral galaxy NGC 4565. The observation was made with a liquid-helium-cooled rocket-borne telescope using a 256 x 256 InSb array with a pixel scale of 17". Images of NGC 4565 were successfully obtained with sensitivity near the natural background limit. Our search reveals no evidence of a faint halo around the galaxy, in contrast with the previous reports of a halo around NGC 5907. The lower limit of the mass-to-light ratio for the halo of NGC 4565 is 260 (2 delta) in solar units at 3.5-5 microns. This implies that hydrogen-burning stars do not contribute significantly to the mass of the dark halo in NGC 4565.
The high sensitivity of large format InSb arrays can be used to obtain deep images of the sky at 3-5 micrometers. In this spectral range cool or highly redshifted objects (e.g. brown dwarfs and protogalaxies) which are not visible at shorter wavelengths may be observed. Sensitivity at these wavelengths in ground-based observations is severly limited by the thermal flux from the telescope and from the earth's atmosphere. The Near Infrared Faint-Object Telescope Experiment (NIFTE), a 50 cm cooled rocket-borne telescope combined with large format, high performance InSb arrays, can reach a limiting flux less than 1 micro-Jy(1-sigma) over a large field-of-view in a single flight. In comparison, the Infrared Space Observatory (ISO) will require days of observation to reach a sensitivity more than one order of magnitude worse over a similar area of the sky. The deep 3-5 micrometer images obtained by the rocket-borne telescope will assist in determining the nature of faint red objects detected by ground-based telescopes at 2 micrometers, and by ISO at wavelengths longer than 5 micrometers.
We give a detailed description of the design and flight performance of an instrument onboard the S-520-15 rocket of the Institute of Space and Astronautical Science. The isntrument, consisting of a near-infrared spectrometer and a far-infrared photometer at the focus of a 10 cm liquid-helium cooled telescope, was designed to observe both the brightness and distribution of diffuse emission with high sensitivity. The rocket was successfully launched and the instrument observed near-infrared and far-infrared continuum emission, as well as (C II) 157.7 micrometer line emission from regions at high Galactic latitude. We also give a brief description of the design and performance of an onboard attitude control system.