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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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At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Calculation of RF sheath properties from surface wave-fields: a post-processing method

In ion cyclotron range of frequency (ICRF) experiments in fusion research devices, radio frequency (RF) sheaths form where plasma, strong RF wave fields and material surfaces coexist. These RF sheaths affect plasma material interactions such as sputtering and localized power deposition, as well as the global RF wave fields themselves. RF sheaths may be modeled by employing a sheath boundary condition (BC) in place of the more customary conducting wall BC; however, there are still many ICRF computer codes that do not implement the sheath BC. In this paper we present a method for post-processing results obtained with the conducting wall BC. The post-processing method produces results that are equivalent to those that would have been obtained with the RF sheath BC, under certain assumptions. We found the post-processing method is also useful for verification of sheath BC implementations and as a guide to interpretation and understanding of the role of RF sheaths and their interactions with the waves that drive them.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

RF-Net 2: fast inference of virus reassortment and hybridization networks

Abstract Motivation A phylogenetic network is a powerful model to represent entangled evolutionary histories with both divergent (speciation) and convergent (e.g. hybridization, reassortment, recombination) evolution. The standard approach to inference of hybridization networks is to (i) reconstruct rooted gene trees and (ii) leverage gene tree discordance for network inference. Recently, we introduced a method called RF-Net for accurate inference of virus reassortment and hybridization networks from input gene trees in the presence of errors commonly found in phylogenetic trees. While RF-Net demonstrated the ability to accurately infer networks with up to four reticulations from erroneous input gene trees, its application was limited by the number of reticulations it could handle in a reasonable amount of time. This limitation is particularly restrictive in the inference of the evolutionary history of segmented RNA viruses such as influenza A virus (IAV), where reassortment is one of the major mechanisms shaping the evolution of these pathogens. Results Here, we expand the functionality of RF-Net that makes it significantly more applicable in practice. Crucially, we introduce a fast extension to RF-Net, called Fast-RF-Net, that can handle large numbers of reticulations without sacrificing accuracy. In addition, we develop automatic stopping criteria to select the appropriate number of reticulations heuristically and implement a feature for RF-Net to output error-corrected input gene trees. We then conduct a comprehensive study of the original method and its novel extensions and confirm their efficacy in practice using extensive simulation and empirical IAV evolutionary analyses. Availability and implementation RF-Net 2 is available at https://github.com/flu-crew/rf-net-2. Supplementary information Supplementary data are available at Bioinformatics online.

Markin, Alexey (ORCID:0000000332809050)↗
DOE OSTI2022

High-Sensitivity rf Detection Using an Optically Pumped Comagnetometer Based on Natural-Abundance Rubidium with Active Ambient-Field Cancellation

To detect a specific radio-frequency (rf) magnetic field, rf optically pumped magnetometers (OPMs) require a static magnetic field to set the Larmor frequency of the atoms equal to the frequency of interest. However, unshielded and variable magnetic field environments (e.g., an rf OPM on a moving platform) pose a problem for rf OPM operation. Here, we demonstrate the use of a natural-abundance rubidium vapor to make a comagnetometer to address this challenge. Our implementation builds upon the simultaneous application of several OPM techniques within the same vapor cell. First, we use a modified implementation of an OPM variometer based on 87 Rb to detect and actively cancel unwanted external fields at frequencies ≲60 Hz using active feedback to a set of field control coils. In this experiment, we exploit this stabilized field environment to implement a high-sensitivity rf magnetometer using 85 Rb. Using this approach, we demonstrate the ability to measure rf fields with a sensitivity of approximately 9 fT Hz -1/2 inside a magnetic shield in the presence of an applied field of approximately 20 μT along three mutually orthogonal directions. This demonstration opens up a path toward completely unshielded operation of a high-sensitivity rf OPM.

47 OTHER INSTRUMENTATION↗
DOE OSTI2013

Pressurized H 2 rf Cavities in Ionizing Beams and Magnetic Fields

A major technological challenge in building a muon cooling channel is operating RF cavities in multi-tesla external magnetic fields. We report the first experimental characterization of a high pressure gas-filled 805 MHz RF cavity for use with intense ionizing beams and strong external magnetic fields. RF power consumption by beam-induced plasma was investigated with hydrogen and deuterium gases with pressures between 20 and 100 atm and peak RF gradients between 5 and 50 MV/m. The energy absorption per ion pair-RF cycle ranges from 10-18 to 10-16 J. The low pressure case agrees well with an analytical model based on electron and ion mobilities. Varying concentrations of oxygen gas were investigated to remove free electrons from the cavity and reduce the RF power consumption. Measurements of the electron attachment time to oxygen and rate of ion-ion recombination were also made. Additionally, we demonstrate the operation of the gas-filled RF cavity in a solenoidal field of up to 3 T, finding no major magnetic field dependence. These results indicate that a high pressure gas-filled cavity is potentially a viable technology for muon ionization cooling.

Chung, M.↗
DOE OSTI2014

SU-E-T-558: An Exploratory RF Pulse Sequence Technique Used to Induce Differential Heating in Tissues Containing Iron Oxide Nanoparticles for a Possible Hyperthermic Adjuvant Effect to Radiotherapy

Purpose: In pre-clinical trials of cancer thermotherapy, hyperthermia can be induced by exposing localized super-paramagnetic iron oxide nanoparticles (SPION) to external alternating magnetic fields generated by a solenoid electrical circuit (Zhao et al., Theranostics 2012). Alternatively, an RF pulse technique implemented in a regular MRI system is explored as a possible hyperthermia induction technique . Methods: A new thermal RF pulse sequence was developed using the Philips pulse programming tool for the 3T Ingenia MRI system to provide a sinusoidal magnetic field alternating at the frequency of 1.43 kHz (multiples of sine waves of 0.7 ms period) before each excitation RF pulse for imaging. The duration of each thermal RF pulse routine was approximately 3 min, and the thermal pulse was applied multiple times to a phantom that contains different concentrations (high, medium and low) of SPION samples. After applying the thermal pulse each time, the temperature change was estimated by measuring the phase changes in the T1-weighted inversion-prepared multi-shot turbo field echo (TFE) sequence (TR=5.5 ms, TE=2.7 ms, inversion time=200 ms). Results: The phase values and relative differences among them changed as the number of applied thermal RF pulses increased. After the 5th application of the thermal RF pulse, the relative phase differences increased significantly, suggesting the thermal activation of the SPION. The increase of the phase difference was approximately linear with the SPION concentration. Conclusion: A sinusoidal RF pulse from the MRI system may be utilized to selectively thermally activate tissues containing super-paramagnetic iron oxide nanoparticles.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

Monitoring local heating around an interventional MRI antenna with RF radiometry

Purpose: Radiofrequency (RF) radiometry uses thermal noise detected by an antenna to measure the temperature of objects independent of medical imaging technologies such as magnetic resonance imaging (MRI). Here, an active interventional MRI antenna can be deployed as a RF radiometer to measure local heating, as a possible new method of monitoring device safety and thermal therapy. Methods: A 128 MHz radiometer receiver was fabricated to measure the RF noise voltage from an interventional 3 T MRI loopless antenna and calibrated for temperature in a uniformly heated bioanalogous gel phantom. Local heating (ΔT) was induced using the antenna for RF transmission and measured by RF radiometry, fiber-optic thermal sensors, and MRI thermometry. The spatial thermal sensitivity of the antenna radiometer was numerically computed using a method-of-moment electric field analyses. The gel’s thermal conductivity was measured by MRI thermometry, and the localized time-dependent ΔT distribution computed from the bioheat transfer equation and compared with radiometry measurements. A “H-factor” relating the 1 g-averaged ΔT to the radiometric temperature was introduced to estimate peak temperature rise in the antenna’s sensitive region. Results: The loopless antenna radiometer linearly tracked temperature inside a thermally equilibrated phantom up to 73 °C to within ±0.3 °C at a 2 Hz sample rate. Computed and MRI thermometric measures of peak ΔT agreed within 13%. The peak 1 g-average temperature was H = 1.36 ± 0.02 times higher than the radiometric temperature for any media with a thermal conductivity of 0.15–0.50 (W/m)/K, indicating that the radiometer can measure peak 1 g-averaged ΔT in physiologically relevant tissue within ±0.4 °C. Conclusions: Active internal MRI detectors can serve as RF radiometers at the MRI frequency to provide accurate independent measures of local and peak temperature without the artifacts that can accompany MRI thermometry or the extra space needed to accommodate alternative thermal transducers. A RF radiometer could be integrated in a MRI scanner to permit “self-monitoring” for assuring device safety and/or monitoring delivery of thermal therapy.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

Nanostructured crystals of fluorite phases Sr{sub 1−x}R{sub x}F{sub 2+x} (R Are Rare Earth Elements) and their ordering: 10. Ordering under spontaneous crystallization and annealing of Sr{sub 1−x}R{sub x}F{sub 2+x} Alloys (R = Tb-Lu, Y) with 23.8–36.1 mol % RF{sub 3}

The products of spontaneous crystallization (at a cooling rate of ∼200 K/min) of Sr{sub 1−x}R{sub x}F{sub 2+x} melts in the homogeneity range of the fluorite phase have been investigated. Thirty-two irrational compositions with 23.8–36.1 mol % RF{sub 3} and eight rational Sr{sub 2}RF{sub 7} compositions are obtained. With respect to the RF{sub 3} content, these compositions form five groups: (1) Sr{sub 0.762}R{sub 0.238}F{sub 2.238} (23.8% RF{sub 3}), (2) Sr{sub 0.744}R{sub 0.256}F{sub 2.256} (25.6%), (3) Sr{sub 0.718}R{sub 0.282}F{sub 2.282} (28.2%), (4) Sr{sub 2}RF{sub 7} (33.3%), and (5) Sr{sub 0.639}R{sub 0.361}F{sub 2.361} (36.1%). R = Tb-Lu, Y for all groups. Quenching melts of group 5 with R = Tb, Dy, and Ho leads to the formation of ordered phases with the trigonal distortion of the rhβ-Na{sub 7}Zr{sub 6}F{sub 31} type, while for melts of group 5 with R = Lu, quenching yields a phase of the trigonal rhα′-Sr{sub 4}Lu{sub 3}F{sub 17} type. In group 5 with R = Y, Er, Tm, or Yb and in groups 1–4 with all REEs, fluorite phases are formed. Annealing at 900 ± 20°C for 96 h with subsequent cooling at a rate of ∼200 K/min expands the variety of ordered phases: a phase with a new r type of orthorhombic distortion is formed in group 1 with R = Lu, in group 2 with R = Tm or Lu, and in group 3 with R = Ho-Lu, Y; a t-Sr{sub 2}RF{sub 7} phase with tetragonal distortion is formed in group 4 with R = Tb-Er, Y; and a phase of trigonal rhα′ type is formed in group 5 with R = Y, Yb, or Lu. A fluorite phase arises in group 1 with R = Tb-Lu, Y as a result of quenching and annealing. The tendency to ordering becomes more pronounced with an increase in the RF{sub 3} content and REE atomic number. The annealing conditions do not provide equilibrium or the completely ordered state of all alloys.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

IBS for RHIC operation below transition energy and various RF systems

Following first successful runs in RHIC at low energies for physics (Beam Energy Scan I) there is a strong interest in further low-energy RHIC operation in the range of γ=4-10 but with higher luminosity (Beam Energy Scan II). An electron cooling was proposed to increase luminosity at these low energies. Both transverse and longitudinal Intra-beam Scattering (IBS) can be counteracted with electron cooling. In addition, the phase-space density of the hadron beams can be further increased by providing stronger cooling. Unfortunately, the defining intensity limitation for low energies in RHIC is expected to be the space charge. Experimental studies of the space-charge effects and beam lifetime in RHIC were reported. Additional limitations at low energies and their possible mitigations were discussed. It was suggested that better luminosity performance may be expected by using lower frequency RF system and longer bunches compared to the baseline 28 MHz RF, which is being used for RHIC operation with heavy ions. Recently, even lower frequency RF of 4.5 MHz was proposed for future low-energy RHIC operation. Although low-frequency RF systems in RHIC (either 9 or 4.5 MHz) seem to address possible limitations of beam lifetime observed at low energies, the resulting ion beam temperatures in beam rest frame get further from an equilibrium which lead to a much stronger longitudinal IBS. This would put stronger requirement on electron cooling system under consideration. However, operation below transition energy allows us to exploit an IBS feature that drives the transverse and longitudinal beam temperatures towards equilibrium by minimizing the longitudinal diffusion rate using larger longitudinal beam emittance and larger RF voltage. Such studies were performed before to explore IBS redistribution at low energies for the 28 and 56 MHz RHIC RF systems. This Note presents results of similar studies for newly proposed 4.5 and 9 MHz RF systems.

43 PARTICLE ACCELERATORS↗
DOE OSTI2024

On forced RF generation of CW magnetrons for SRF accelerators

CW magnetrons, initially developed for industrial RF heaters, were suggested to power RF cavities of superconducting accelerators due to their higher efficiency and lower cost of RF power per Watt than used traditionally klystrons, IOTs or solid-state amplifiers. RF amplifiers driven by a master oscillator serve as coherent RF sources. CW magnetrons are regenerative RF generators with a huge regenerative gain to start up reliably with self-excitation even if the tube is powered by a DC power supply. This causes regenerative instability with a large noise when a magnetron operates with the anode voltage above the threshold of self-excitation. Traditionally for stabilization of magnetrons is used injection locking by a signal PLock ≤ -20 dB or less then of the magnetron power PMag. Then the magnetron generates the injection locked oscillations and generates noise. This may preclude use of standard CW magnetrons in some SRF accelerators. We developed briefly described below a mode for forced coherent RF generation of CW magnetrons when the magnetron startup is provided by the injected forcing signal and the regenerative noise is suppressed. The mode is most suitable for powering high Q-factor SRF cavities.

Kazakevich, G.↗
NASA NTRS2004

The Use of RF Waves in Space Propulsion Systems

This paper will review the ways in which RF and microwave radiation may be used in the design of electric propulsion systems for spacecraft. RF power has been used or proposed in electric propulsion systems to ionize, to heat, and to accelerate the propellant, or to produce plasma used to inflate a magnetic field for solar sail purposes. Direct RF propulsion using radiation pressure or ponderomotive forces is impractical owing to efficiency considerations. Examples of various systems that have been developed or proposed will be reviewed. The Variable Specific Impulse Magnetoplasma Rocket (VASIMR) uses RF for producing, heating and accelerating plasma. Inductive RF and microwave ion thruster schemes use e-m waves to ionize the plasma, which is then accelerated by use of dc grids. The details of the VASIMR, an inductive RF thruster, and a microwave ion thruster are discussed and contrasted with related RF systems.

Bering, Edgar A., III↗
NASA NTRS2007

RF Performance of Membrane Aperture Shells

This paper provides an overview of recent results establishing the suitability of Membrane Aperture Shell Technology (MAST) for Radio Frequency (RF) applications. These single surface shells are capable of maintaining their figure with no preload or pressurization and minimal boundary support, yet can be compactly roll stowed and passively self deploy. As such, they are a promising technology for enabling a future generation of RF apertures. In this paper, we review recent experimental and numerical results quantifying suitable RF performance. It is shown that candidate materials possess metallic coatings with sufficiently low surface roughness and that these materials can be efficiently fabricated into RF relevant doubly curved shapes. A numerical justification for using a reflectivity metric, as opposed to the more standard RF designer metric of skin depth, is presented and the resulting ability to use relatively thin coating thickness is experimentally validated with material sample tests. The validity of these independent film sample measurements are then confirmed through experimental results measuring RF performance for reasonable sized doubly curved apertures. Currently available best results are 22 dBi gain at 3 GHz (S-Band) for a 0.5m aperture tested in prime focus mode, 28dBi gain for the same antenna in the C-Band (4 to 6 GHz), and 36.8dBi for a smaller 0.25m antenna tested at 32 GHz in the Ka-Band. RF range test results for a segmented aperture (one possible scaling approach) are shown as well. Measured antenna system actual efficiencies (relative to the unachievable) ideal for these on axis tests are generally quite good, typically ranging from 50 to 90%.

Flint, Eirc M.↗
NASA NTRS2018

Development of an Optical Slice for an RF and Optical Software Defined Radio

A key component in the Integrated Radio and Optical Communications project at the National Aeronautics and Space Administration's (NASA) Glenn Research Center (GRC) is the radio frequency (RF) and optical software defined radio (SDR). A NASA RF SDR might consist of a general purpose processor to run the Space Telecommunications Radio System (STRS) Architecture for radio command and control, a reconfigurable signal processing device such as a field programmable gate array (FPGA) which houses the waveform, and a digital to analog converter for (DAC) transmitting data. Prior to development, SDR architecture trades on how to combine the RF and optical elements were studied. A modular architecture with physically separate RF and optical hardware slices was chosen and the optical slice of an SDR was designed and developed. The Harris AppSTAR("TM") platform, which consists of an FPGA processing platform with a mezzanine card targeted for RF communications, was used as the base platform in prototyping the optical slice. A serially concatenated pulse position modulation (SCPPM) optical waveform was developed. The waveform follows the standard described in the Consultative Committee for Space Data Systems (CCSDS) Optical Communions Coding and Synchronization Red Book. A custom optical mezzanine printed circuit board card was developed at NASA GRC for optical transmission. The optical mezzanine card replaces the DAC, which is used in the transmission of RF signals. This paper describes RF and optical SDR architecture trades, the Harris AppSTAR("TM") platform, the design of the SCPPM waveform, and the development of the optical mezzanine card.

optical communications↗
NASA NTRS2018

Development of an Optical Slice for an RF and Optical Software Defined Radio

A key component in the Integrated Radio and Optical Communications project at the National Aeronautics and Space Administration's (NASA) Glenn Research Center (GRC) is the radio frequency (RF) and optical software defined radio (SDR). A NASA RF SDR might consist of a general purpose processor to run the Space Telecommunications Radio System (STRS) Architecture for radio command and control, a reconfigurable signal processing device such as a field programmable gate array (FPGA) which houses the waveform, and a digital to analog converter (DAC) for transmitting data. Prior to development, SDR architecture trades on how to combine the RF and optical elements were studied. A modular architecture with physically separate RF and optical hardware slices was chosen and the optical slice of an SDR was designed and developed. The Harris AppSTARTM platform, which consists of an FPGA processing platform with a mezzanine card targeted for RF communications, was used as the base platform in prototyping the optical slice. A serially concatenated pulse position modulation (SCPPM) optical waveform was developed. The waveform follows the standard described in the Consultative Committee for Space Data Systems (CCSDS) Optical Communications Coding and Synchronization Red Book. A custom optical mezzanine printed circuit board card was developed at NASA GRC for optical transmission. The optical mezzanine card replaces the DAC, which is used in the transmission of RF signals. This paper describes RF and optical SDR architecture trades, the Harris AppSTAR platform, the design of the SCPPM waveform, and the development of the optical mezzanine card.

Nappier, Jennifer M.↗
DOE OSTI2014

Boosting Deuteron Polarization in HD Targets: Experience of moving spins between H and D with RF methods during the E06-101 experiment at Jefferson Lab

Solid HDice targets are polarized by bringing the HD crystal to thermal equilibrium at low temperature and high magnetic field, typically 10-20 mK and 15 Tesla, at Jefferson Lab. In this regime, due to its smaller magnetic moment, the resulting polarization for D is always at least three times smaller than for H. The controlled amount of polarizing catalysts, o-H2 and p-D2, used in the process of reaching a frozen-spin state, further limit the maximum achievable D polarization. Nonetheless, H and D polarizations can be transferred from one to the other by connecting the H and D sub-states of the HD system with RF. In a large target, the RF power needed for such transitions is effectively limited by non-uniformities in the RF field. High efficiency transfers can require substantial RF power levels, and a tuned-RF circuit is needed to prevent large temperature excursions of the holding cryostat. In this paper, we compare the advantages and limitations of two different RF transfer methods to increase D polarization, Forbidden Adiabatic and Saturated Forbidden RF Transitions. The experience with the HD targets used during the recently completed E06-101 experiment in Hall-B of Jefferson Lab is discussed.

Wei, Xiangdong↗
DOE OSTI2019

COMMISSIONING UPDATE ON RF STATION #5 OF AWA

The RF system of Argonne Wakefield Accelerator (AWA) facility has grown over the years from one RF power station into 4 RF power stations. The demanding for RF power keeps growing as the capability of AWA con-tinues to grow. Now the 5th RF station is needed to fulfill the RF power needs of AWA facility. Some details regard-ing the construction and commissioning of the 5th RF sta-tion of AWA facility are documented in this paper.

Liu, W.↗
DOE OSTI2026

Final Technical Report - Center for Simulation of Fusion Relevant RF Actuators

We have developed a suite of 3D electromagnetic field solvers, both FEM and FDTD based, that account for the RF antenna and vacuum vessel geometries with unprecedented accuracy. Workflows were developed that make it possible to translate CAD models for the antenna and vacuum vessel to physics meshes for RF wave simulation. Nonlinear RF sheath formation has been incorporated self-consistently as a boundary condition in these solvers. We have also carried out extensive studies of the impact of RF sheaths on the ion energy angle distribution at plasma-material interfaces, using high fidelity particle-in-cell codes. Comprehensive simulation models were developed to assess the impact of blob-like edge turbulence on RF wave propagation and the impact of the RF ponderomotive force on the plasma scrape-off layer (SOL). A fluid transport solver for the far-SOL was also developed which accounts for the high parallel to perpendicular heat anisotropy on an unstructured mesh, thus making it possible to precisely represent an antenna structure in the presence of edge transport. Finally we have developed a hierarchy of core wave propagation and absorption models that self-consistently combine continuum Fokker Planck and Monte Carlo treatments of fast ion evolution with ICRF full-wave field solvers and continuum Fokker Planck treatments of fast electron evolution with both full-wave and ray tracing models.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2019

Nanosecond rf-Power Switch for Gyrotron-Driven Millimeter-Wave Accelerators

The development of alternative mm-wave high-gradient, >200 MV/m, accelerating structures offers a promising path to reduce the cost and footprint of future TeV-scale linear colliders, as well as linacs for industrial, medical, and security applications. The major factor limiting accelerating gradient is vacuum rf breakdown. The probability of such breakdowns increases with pulse length. For reliable operation, millimeter-wave structures require nanoseconds-long pulses at the megawatt level. This power is available from gyrotrons, which have a minimum pulse length on the order of microseconds. To create shorter pulses and to reliably detect rf breakdowns, we developed the following devices: a laser-based rf switch capable of selecting 10 ns long pulses out of the microseconds long gyrotron pulses, thus enabling the use of the gyrotrons as power sources for mm-wave high-gradient linacs, and a shot-to-shot sub-THz spectrometer with high-frequency resolution, capable of detecting pulse shortening due to rf breakdowns. We will describe the principle of operation of these devices and their achieved parameters. Here, we also report on the experimental demonstration of these devices with the high-power gyrotron at the Massachusetts Institute of Technology. In the experiments, we demonstrate nanosecond rf power modulation, shot-to-shot measurements of the pulse spectra, and detection of rf breakdowns.

43 PARTICLE ACCELERATORS↗
DOE OSTI2026

Center for Integrated Simulation of Fusion Relevant RF Actuators

This project was part of the “Center for Integrated Simulation of Fusion Relevant RF Actuators” SciDAC-4 project, led by Dr. Paul Bonoli (MIT). Rather than use an acronym (CISFRRFA), the project will be referred to in this document as the “RF-SciDAC4”. The larger SciDAC-4 project goals were to: 1. Develop an integrated simulation of the antenna + sheath + scrape-off-layer + core plasma system which fully utilizes leadership class computing resources to move towards a quantitative predictive capability for the response to RF power. 2. Work closely with the SciDAC-4 Whole Device Modeling (WDM) community to make both our new code development efforts, as well as the established hierarchy of RF tools, available within their environment, and to utilize WDM technologies to implement the couplings below. 3. Validate this predictive capability on appropriately diagnosed experiments including dedicated RF test stands, linear devices, and existing tokamaks. 4. Use these tools to inform design of robust, impurity-mitigating RF heating and current drive sources for future fusion devices.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗