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Amir Jahromi

Publications and source records attributed to Amir Jahromi.

11 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2023

The Science Performance of JWST as Characterized in Commissioning

This paper characterizes the actual science performance of the James Webb Space Telescope (JWST), as determined from the six month commissioning period. We summarize the performance of the spacecraft, telescope, science instruments, and ground system, with an emphasis on differences from pre-launch expectations. Commissioning has made clear that JWST is fully capable of achieving the discoveries for which it was built. Moreover, almost across the board, the science performance of JWST is better than expected; in most cases, JWST will go deeper faster than expected. The telescope and instrument suite have demonstrated the sensitivity, stability, image quality, and spectral range that are necessary to transform our understanding of the cosmos through observations spanning from near-earth asteroids to the most distant galaxies.

Infrared astronomy↗
NASA NTRS2022

Line Emission Mapper Probing Physics of Cosmic Ecosystems

The Line Emission Mapper (LEM) is an X-ray Probe for the 2030s that will answer the outstanding questions of the Universe’s structure formation. It will also provide transformative new observing capabilities for every area of astrophysics, and to heliophysics and planetary physics as well. LEM’s main goal is a comprehensive look at the physics of galaxy formation, including stellar and black-hole feedback and flows of baryonic matter into and out of galaxies. These processes are best studied in X-rays; as emphasized by the 2020 Decadal Survey, emission-line mapping is the pressing need in this area. LEM will use a large microcalorimeter array/IFU (that builds on Athena XIFU technology developments), covering a 30 × 300 field with 1000 angular resolution, to map the soft Xray line emission from objects that constitute galactic ecosystems. These include supernova remnants, star-forming regions, superbubbles, galactic outflows (such as the Fermi/eROSITA bubbles in the Milky Way and their analogs in other galaxies), the Circumgalactic Medium in the Milky Way and other galaxies, and the Intergalactic Medium at the outskirts and beyond the confines of galaxies and clusters. LEM’s 1–2 eV spectral resolution in the 0.2–2 keV band will make it possible to disentangle the faintest emission lines in those objects from the bright Milky Way foreground, providing groundbreaking measurements of the physics of these plasmas, from temperatures, densities, chemical composition to gas dynamics. While the mission is optimized to provide critical observations that will push our understanding of galaxy formation, LEM will provide transformative capability for all classes of astrophysical objects, from the Earth’s magnetosphere, planets and comets to the interstellar medium and X-ray binaries in nearby galaxies, AGN, and cooling gas in galaxy clusters. In addition to pointed observations, LEM will perform a shallow all-sky survey that will dramatically expand the discovery space.

Ralph Kraft↗
NASA NTRS2020

Optical Design of the EXperiment for Cryogenic Large-Aperture Intensity Mapping (EXCLAIM)

This work describes the optical design of the EXperiment for Cryogenic Large-Aperture Intensity Mapping(EXCLAIM). EXCLAIM is a balloon-borne telescope that will measure integrated line emission from carbonmonoxide (CO) at redshiftsz <1 and ionized carbon ([CII]) at redshiftsz= 2.5−3.5 to probe star forma-tion over cosmic time in cross-correlation with galaxy redshift surveys. The EXCLAIM instrument will observeat frequencies of 420–540 GHz using six microfabricated silicon integrated spectrometers with spectral resolv-ing powerR= 512 coupled to kinetic inductance detectors (KIDs). A completely cryogenic telescope cooledto a temperature below 5 K provides low-background observations between narrow atmospheric lines in thestratosphere. Off-axis reflective optics use a 90-cm primary mirror to provide 4.2′full-width at half-maximum(FWHM) resolution at the center of the EXCLAIM band over a field of view of 22.5′. Illumination of the 1.7 Kcold stop combined with blackened baffling at multiple places in the optical system ensures low (<−40 dB) edgeillumination of the primary to minimize spill onto warmer elements at the top of the dewar.

Thomas Essinger-Hileman↗
NASA NTRS2017

Cryogenic Thermal Conductivity Measurements on Candidate Materials for Space Missions

Spacecraft and instruments on space missions are built using a wide variety of carefully-chosen materials. It is common for NASA engineers to propose new candidate materials which have not been totally characterized at cryogenic temperatures. In many cases a material's cryogenic thermal conductivity must be known before selecting it for a specific space-flight application. We developed a test facility in 2004 at NASA's Goddard Space Flight Center to measure the longitudinal thermal conductivity of materials at temperatures between 4 and 300 Kelvin, and we have characterized many candidate materials since then. The measurement technique is not extremely complex, but proper care to details of the setup, data acquisition and data reduction is necessary for high precision and accuracy. We describe the thermal conductivity measurement process and present results for ten engineered materials, including alloys, polymers, composites, and a ceramic.

James Tuttle↗
NASA NTRS2015

Cryogenic Thermal Absorptance Measurements on Small-Diameter Stainless Steel Tubing

The Mid Infrared Instrument (MIRI) on the James Webb Space Telescope includes a mechanical cryocooler which cools its detectors to their 6 Kelvin operating temperature. The coolant gas flows through several meters of small-diameter stainless steel tubing, which is exposed to thermal radiation from its environment. Over much of its length this tubing is gold-plated to minimize the absorption of this radiant heat. In order to confirm that the cryocooler will meet MIRI's requirements, the thermal absorptance of this tubing was measured as a function of its environment temperature. We describe the measurement technique and present the results.

cryogenics↗
NASA NTRSDate not supplied

Development of an Apparatus and Process for Precision Measurement of Cryogenic Thermal Expansion of Materials

NASA frequently needs thermal contraction data for materials to be used in cryogenic space flight missions. To satisfy this need, we developed an apparatus and a high-precision technique for performing such measurements using a commercial fiber-optic-based position sensor. We describe the measurement process and its verification using a copper sample. We also present data for two materials which we characterized for potential NASA use.

Cryogenic↗
NASA NTRSDate not supplied

A Four-Stage Continuous ADR for Space Missions

The cryogenics group at NASA-Goddard has provided adiabatic demagnetization refrigerators (ADRs) for cooling detectors to sub-Kelvin temperatures in space. These ADRs were single-shot devices that produced cooling at 0.05 K for tens of hours before needing to be recycled. Our group also developed a four-stage laboratory ADR system which holds one stage continuously at 0.05K, or colder, while using the other stages to pump heat from the continuous stage up to a heat sink near 4K. This continuous ADR (CADR) provides a useful cooling power that is more than 10 times greater at 0.050 K than what was required by the single-shot space systems. Over the past several years, this system was updated so that it can withstand the rigors of a launch into space. We describe this development process and report its final results.

Continuous ADR↗
NASA NTRSDate not supplied

Development of an Ultra-Low-Temperature 5-Stage Continuous Adiabatic Demagnetization Refrigerator That Provides Cooling at Two Unique Temperatures

The cryogenics group at NASA-Goddard has built several adiabatic demagnetization refrigerators (ADRs) for cooling detectors to sub-Kelvin temperatures in a lab, balloon, or space environment. The effort presented here describes the development of a new 5-stage adiabatic demagnetization refrigerator capable of providing continuous cooling at 35 mK with a cooling power double that previously demonstrated at this temperature. It will also provide a separate continuous temperature platform near 1 K. This system will be qualified using flight-like conditions, culminating in an ADR that is ready for the rigors of spaceflight by the end of the effort.

ADR↗
NASA NTRSDate not supplied

A Four-Stage Continuous ADR for Space Missions

The cryogenics group at NASA-Goddard has provided adiabatic demagnetization refrigerators (ADRs) for cooling detectors to sub-Kelvin temperatures in space. These ADRs were single-shot devices that produced cooling at 0.05 K for tens of hours before needing to be recycled. Our group also developed a four-stage laboratory ADR system which holds one stage continuously at 0.05K, or colder, while using the other stages to pump heat from the continuous stage up to a heat sink near 4K. This continuous ADR (CADR) provides a useful cooling power that is more than 10 times greater at 0.050 K than what was required by the single-shot space systems. Over the past several years, this system was updated so that it can withstand the rigors of a launch into space. We describe this development process and report its final results.

Continuous ADR↗