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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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300 records · Page 17
All sourcesNASA NTRSDOE OSTI
NASA NTRS2018

2.0 um Wavelength Injection Seed Semiconductor Laser for Lidar Transmitter for Global-Scale Measurements of CO2

Many of the high accuracy Earth science survey missions are planned to use laser-based remote sensing instruments. The 2-μm laser wavelength is of particular interest due to the presence of many CO2 and H20 absorption lines in its vicinity1. Transmitter architectures are typically composed of an optically pumped, frequency-stable, solid-state seed laser and a high-power optical amplifier.2, 3 Taking advantage of the reliability and relative simplicity of semiconductor lasers, this architecture can substantially improve by replacing the solid-state light source with semiconductor lasers of comparable performance. This approach will greatly improve the system reliability, and will simplify instrument integration and space qualification. There are currently very limited semiconductor lasers operating in the 2-m range with performance satisfactory enough for use as an injection seed in a laser absorption spectrometer. Optimally, seed lasers producing greater than 50 mW of continuous-wave (CW), with frequency jitter of less than 1 MHz are desired to reliably resolve the CO2 absorption lines near 2-µm. In this paper, we report the demonstration of high-power, single-longitudinal-mode laterally coupled distributed feedback (LC-DFB) lasers at 2.05 µm wavelength. We measured more than 80 mW of CW power at -10 ºC for devices with a 4-µm-wide ridge and 2-mm-long cavity.

Fradet, Mathieu↗
NASA NTRS2019

An upgraded G-band differential absorption radar system for future airborne studies

A proof-of-concept, 170 GHz frequency-modulated, continuous-wave (FMCW) radar has been developed for measuring water vapor profiles within the cloudy boundary layer from an airborne platform. The measurement concept exploits the differential absorption accrued by two or more transmitted frequencies in the vicinity of the 183 GHz water absorption line to retrieve range-resolved humidity profiles, so-called differential absorption radar (DAR). The upgraded system design includes important considerations for monostatic radar operation with an open fuselage viewport (i.e. no radome). The radar features an all-solid-state tansmitter with > 0:4 W continuous transmit power, a 60 cm primary aperture and corresponding 58 dB antenna gain, and more than 80 dB transmit/receive isolation, enabling near thermal-noise-limited sensitivity with a 8 dB noise figure receiver. Ice-cloud radar returns are detected beyond 8 km in height from the ground, demonstrating the high sensitivity of the system. In addition to in-cloud humidity profiling capabilities, deployment of a water vapor DAR from an airborne platform enables measurements of total column water vapor (TCWV) for all weather and surface scenarios. Precision estimates and potential biases for future TCWV measurements are discussed.

Monje, Raquel↗
NASA NTRSDate not supplied

Modeling Electro-Optic Frequency Comb Generation as a Pump Source for Quantum Communications

The Quantum Communications group at NASA GRC is focused on developing technologies and system architectures to enable future space-based quantum networks. High-repetition rate pulsed pump lasers are needed because the signal on the quantum channel cannot be amplified, hence entanglement generation rates can only be increased through high-rate pumping. Additionally, tunability in center frequency, pulse width, and repetition rate allows for a wider parameter space over which to optimize quantum channel frequency conversion efficiency, joint spectral engineering, and channel synchronization for high-fidelity entanglement swapping –a necessary stepping-stone towards quantum repeater development. One of the most flexible methods for high-repetition rate pulse generation is through spectral shaping–generating a frequency comb from a continuous-wave(CW)laser using electro-optic modulators (EOMs). As a result, this project focuses on analytically modeling and simulating the effects various EOMs such as phase and intensity modulators have on a CW source. Generating a tunable frequency comb as the pump source allows us to conveniently fine-tune the central frequency, repetition rate, and the spectral shape of our source to match the strict optimal parameters for any given entanglement source considered in the future. These models and simulations are to be used for comparison purposes for future experiments as well as for providing the Quantum Communications group a convenient tool to understand the effects of manipulating various parameters have on the outgoing frequency comb.

Electro-optic modulator↗
NASA NTRSDate not supplied

Volume Raycasting of GNSS Signals through Ground Structure Lidar for UAV Navigational Guidance and Safety Estimation

Autonomous UAS navigation at low altitudes is often hindered by degradation of GNSS position estimates. The line of sight from the UAS to orbital satellites may be intersected by foliage (which attenuates the received signal) and by buildings (which block the signal). Since the geometric ray from the presumed UAS position to each GNSS satellite orbital location is predictable, if a 3D survey of ground structures is available, the degree of blockage of each GNSS signal can be estimated. In this study we show raycasting from a UAS location to GNSS satellites at two flight locations: one with overlying structures and bordered by tall trees, and another in an arboreal canyon bordered by tall trees. We confirm the intermittent blockage of satellites in the first location sufficient to lose GNSS position fix. We demonstrate low-altitude GNSS fidelity forecasting via the raycasting method at the second location that can be used to plan navigable flight locations and altitudes. Finally, we match the GNSS signal strength with raycast-derived foliage obstruction depth at hundreds of observation times from 55 recordings collected over 14 days from November 2018 to February 2021 at the second location. This matching confirms that signal attenuation varies with the depth of foliage blockage along a saturating exponential curve, as found in prior continuous-wave RF studies. The exponent and saturation value are species dependent and therefore vary from site to site; once determined empirically, they can be used to characterize foliage along a particular flight path, and refine GNSS fidelity forecasts of flights along that path. The techniques described in this study show the feasibility of a survey method to construct low-altitude navigation safety maps and forecasts.

Navigation↗
DOE OSTI2020

History of gradient advances in SRF

Radio frequency (RF) superconductivity has become a key technology for many modern particle accelerators. One of its most salient features of this technology is the ability of superconducting RF cavities to deliver high accelerating gradients in continuous-wave and long-pulse modes of operation. However, reaching the current state of the technology was not an easy fit. Over many years scientists and engineers had to overcome several serous performance limitations. In this paper, I attempt to the best of my knowledge to trace the history of accelerating gradients evolution in the field of superconducting radio frequency. I will restrict the scope to primary innovations along with some of the ensuing developments in developing cavities made of bulk niobium. But I will not cover all the many applications and findings over the subsequent decades of progress that were based on the primary discoveries and inventions. I will also not cover a number of other important topics in the history of cavity developments, such as the drive for higher Q values, or the push for lower cavity costs via Nb/Cu cavities or large grain Nb cavities.

43 PARTICLE ACCELERATORS↗
DOE OSTI2022

Design of a high-power compact SRF linac for industrial applications of e-beam irradiation

Fermilab has developed a novel concept for an industrial electron linac using Nb3Sn coating technology and conduction cooling. These conduction-cooled linacs can generate electron beam energies up to 10 MeV in continuous-wave operation and reach higher power (>=1 MW) by combing several modules. Compact and light enough to mount on mobile platforms, our machine is anticipated to enable new in-situ environmental remediation applications such as waste-water treatment for urban areas, X-ray medical device sterilization, and innovative pavement applications. We highlight a few aspects of a 1 MW design of such a machine in this paper. A detailed plan is in Dhuley et al. (2022) Phys. Rev. Accel. Beams 25, 041601.

43 PARTICLE ACCELERATORS↗
DOE OSTI2023

High-Performance Accelerator Modeling: Toward Improving Controls and Diagnostics for High-Brightness Beams in Experiment

One of the main charges of beam physics is to improve the overall beam quality delivered to experiments and applications, which is generally quantified by the beam brightness. High brightness beams have numerous applications, including x-ray free electron lasers and ultrafast electron diffraction (UED). To these ends, this thesis details efforts to use high-performance models --- high-fidelity models that execute quickly --- for controls and diagnostics. To demonstrate the generality of these techniques, this thesis focuses on three of the most successful photoinjector designs currently used worldwide: the UCLA/SLAC/BNL-type high-gradient S-band gun, the continuous-wave high-repetition rate VHF APEX gun and the L-band DESY-PITZ-type gun. Work will be shown from Pegasus (UCLA), HiRES (LBNL) and FAST (FNAL).Specifically, data-driven models for online virtual diagnostics are presented, in this case, in the context of UED at HiRES, leading to a temporal resolution improvement. Methods for improving the fidelity of physics-based models are discussed, with examples at HiRES, Pegasus and FAST. Markov-chain Monte Carlo analysis is applied to match simulations, in the context of photocathode studies at HiRES and Pegasus. Lastly, the augmentation of online model-based predictions with model-independent optimization is explored in a fluctuating environment at Pegasus and HiRES. A central theme of this dissertation is working with parameter fluctuations when modeling an accelerator beamline. Long-term drifts and shot-to-shot jitter exist in every accelerator to a varying degree and therefore play an important role in every chapter of this dissertation. This thesis attempts to address the issues associated with these fluctuations when trying to develop faithful model representations of the system.

43 PARTICLE ACCELERATORS↗
DOE OSTI2024

Nb 3 Sn Superconducting Cavities by Bronze Routes for Accelerator Stewardship

This project explored the challenges of making Nb 3 Sn superconducting radio-frequency (SRF) cavities by bronze routes. The SRF research community has prioritized Nb 3 Sn for many reasons, including the possibility to operate linacs for stewardship applications in continuous-wave mode with compact cryogenic systems. Existing Nb 3 Sn approaches use a cavity body made of niobium and apply tin to the polished cavity interior, a starting point that contains the main costs of present niobium cavity technology. Further complexity is then added because a high vacuum and temperature >1100 °C must be used to prevent formation of undesirable Nb-Sn phases, de-gas interstitial contaminants, and maintain the high purity of the Nb body. The project sought a more cost-effective solution for the same performance opportunities by exploiting the Cu-Sn-Nb diffusion reactions used to make Nb 3 Sn superconducting wires for magnets, which can be carried out at ~700 °C and are compatible with much cheaper copper cavity bodies. The project also sought understanding of the materials science and factors that affect superconducting properties. The project has impacted SRF cavity technology by demonstrating feasibility of alternative routes that enable compact, high-power electron accelerators for energy, security, environment, medical, and commercial applications.

43 PARTICLE ACCELERATORS↗
DOE OSTI2024

A Low-Cost, Reconfigurable UWB Microwave Radar Front-End for Fine Resolution Nadir-Looking Measurements of Snow and Layered Media

This paper presents a reconfigurable, low-cost ultra-wideband microwave radar front-end and radar demonstrator designed for nadir-looking measurements of layered media (e.g. snow or vegetation) from either a fast-moving ground-based platform or a C-3 class unmanned aerial system (UAS). The radar demonstrator uses a frequency modulated continuous-wave (FMCW) architecture and can be configured to operate in either the 2-8 GHz or in the 12-18 GHz range, providing fine vertical resolution while offering a significantly reduced weight, size, and power consumption with respect to prior implementations. We have demonstrated the operation of the system in the 2-8 GHz and 12-18 GHz bands in the laboratory; in the 2-8 GHz band using a surface-based setup in Antarctica; and in the 2.6-7 GHz band on local flight tests onboard an Aurelia X6 Pro UAS equipped with 3-D printed antennas. This paper provides an overview of the radar front-end and demonstrator design and implementation and a summary of the different tests completed to document their performance.

UWB radar, UAS-borne radar, snow-probing radar.↗
DOE OSTI2025

Compensating for Amplifier Non-Linearity in a SEL Controller

The Self-Excited Loop (SEL) architecture, used in some continuous-wave (CW) superconducting linacs, relies on a positive feedback mechanism that requires carefully defined operating limits to ensure stable operation. These limits are typically derived from amplifier calibration, which characterizes the relationship between forward power and DAC drive. However, amplifier non-linearity often prevents a simple linear fit of this characteristic, introducing errors that can compromise stability. To address this, we present a modified calibration procedure that incorporates amplifier non-linearity into the SEL framework. The approach is validated with test data from a 32 kW solid-state amplifier (SSA) and a cavity emulator developed for the Fermilab PIP-II linac.

Raman, S. [Fermilab] (ORCID:0009000735937206)↗
DOE OSTI2025

Design of a 915 MHz conduction-cooled cryomodule

High-power, compact, continuous-wave (CW) linear electron accelerators with beam energies of up to 10 MeV are being considered for possible industrial applications. Conduction-cooled, superconducting radio-frequency (SRF) technology allows operating such machines at high electrical efficiency, thereby reducing the operating cost significantly. A prototype conduction-cooled SRF cryomodule has been designed and components are currently being manufactured. The cryomodule features a two-cell, 915 MHz SRF cavity, two cryocoolers, a fundamental power coupler, two magnetic shields, a thermal shield and warm-to-cold transitions. The cryomodule has been designed to be able to provide an energy gain of 3.5 MeV to a CW electron beam with a current of 5 mA. This contribution focusses on thermal and mechanical design aspects of the cryomodule.

Ciovati, G. [Old Dominion Univ., Norfolk, VA (Unit↗
NASA NTRS2007

Multilaser Herriott Cell for Planetary Tunable Laser Spectrometers

Geometric optics and matrix methods are used to mathematically model multilaser Herriott cells for tunable laser absorption spectrometers for planetary missions. The Herriott cells presented accommodate several laser sources that follow independent optical paths but probe a single gas cell. Strategically placed output holes located in the far mirrors of the Herriott cells reduce the size of the spectrometers. A four-channel Herriott cell configuration is presented for the specific application as the sample cell of the tunable laser spectrometer instrument selected for the sample analysis at Mars analytical suite on the 2009 Mars Science Laboratory mission.

continuous-wave↗