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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Fast and flexible control of beam longitudinal phase space for high-repetition-rate x-ray free-electron lasers

The wide-ranging requirements for the photon properties from multiple beamlines in superconducting based free-electron lasers (FELs) demand more challenging beam manipulation techniques. Shot-by-shot control of electron beam bunch length and peak current at high repetition rate up to megahertz is highly desired. In this paper, we present a comprehensive study of a method based on a 2-m-long normal conducting radio-frequency cavity to achieve fast and flexible control of beam compression and realize the full potential of the facility, including theoretical analysis, beam dynamics simulations, and conceptual cavity design for the Linac Coherent Light Source II and its high-energy upgrade. We illustrate the physical mechanism of the chirping cavity on the control of the final beam compression and propose methods to lower the requirements for the cavity parameters. The application of this method will allow tailored photon properties of individual beamlines to optimize their performance and drastically improve the multiplexing capabilities of a high-repetition rate FEL facility.

42 ENGINEERING↗
DOE OSTI2022

Plasma Processing of SRF Cavities at Jefferson Lab

Jefferson Lab has an ongoing R&D program in plasma processing which is close to going into production pro-cessing in the CEBAF accelerator. Plasma processing is a common technique for removing hydrocarbons from surfaces, which increases the work function and reduces the secondary emission coefficient [1]. The initial focus of the effort is processing C100 cavities by injecting RF power into the HOM coupler ports. The goal will be to improve the operational gradients and the energy margin of the CEBAF linacs by processing cryomodules in situ. Results from processing a cryomodule in the cryomodule test bunker as well as cavity vertical test results will be presented. This work describes the systems and methods used at JLAB for processing cavities using an ar-gon/oxygen gas mixture.

Powers, T.↗
DOE OSTI2024

Successful cleanroom installation of PIP-II SSR2 coupler using robotic arm

To minimize the contamination of SRF cavities, remote installation techniques are needed during the installation of components. Recent work at Fermilab has been performed to begin the process of developing techniques for assembling cavities using robotics. Multiple alignment methods were prototyped including alignment and computer vision methods. Using a remotely controlled robotic arm, the alignment and installation of couplers have been successfully performed on prototype PIP-II SSR2 cavities in a cleanroom. The installation process will be shown to show to demonstrate the potential of future installations on other cavities and cavity ancillaries.

43 PARTICLE ACCELERATORS↗
NASA NTRS1991

Analysis of EM penetration into and scattering by electrically large open waveguide cavities using Gaussian beam shooting

Gaussian beam (GB) representation methods are used to analyze the electromagnetic coupling into and the scattering by a large nonuniform cavity. The aperture field in the cavity is decomposed into beams using the Gabor expansion, and shooting techniques are then employed. The method is illustrated only for the two-dimensional (2-D) case. The GBs are tracked axially using the rules of beam optics which ignore any beam distortion upon reflection at the walls. The effects of beam distortion are not significant for relatively slowly varying waveguide cavities. The field scattered into the exterior by the termination within the cavity is found using a reciprocity integral formulation which requires a knowledge of the beam fields near the termination. Numerical results based on this GB approach are presented and compared with results based on an independent reference solution.

Burkholder, Robert J.↗
NASA NTRS1995

Calculation of three-dimensional (3-D) internal flow by means of the velocity-vorticity formulation on a staggered grid

A method has been developed to accurately compute the viscous flow in three-dimensional (3-D) enclosures. This method is the 3-D extension of a two-dimensional (2-D) method developed for the calculation of flow over airfoils. The 2-D method has been tested extensively and has been shown to accurately reproduce experimental results. As in the 2-D method, the 3-D method provides for the non-iterative solution of the incompressible Navier-Stokes equations by means of a fully coupled implicit technique. The solution is calculated on a body fitted computational mesh incorporating a staggered grid methodology. In the staggered grid method, the three components of vorticity are defined at the centers of the computational cell sides, while the velocity components are defined as normal vectors at the centers of the computational cell faces. The staggered grid orientation provides for the accurate definition of the vorticity components at the vorticity locations, the divergence of vorticity at the mesh cell nodes and the conservation of mass at the mesh cell centers. The solution is obtained by utilizing a fractional step solution technique in the three coordinate directions. The boundary conditions for the vorticity and velocity are calculated implicitly as part of the solution. The method provides for the non-iterative solution of the flow field and satisfies the conservation of mass and divergence of vorticity to machine zero at each time step. To test the method, the calculation of simple driven cavity flows have been computed. The driven cavity flow is defined as the flow in an enclosure driven by a moving upper plate at the top of the enclosure. To demonstrate the ability of the method to predict the flow in arbitrary cavities, results will he shown for both cubic and curved cavities.

Stremel, Paul M.↗
DOE OSTI2025

Mitigation of Pitting on Nitrogen-Doped Niobium Surfaces through Two-Step Electropolishing

Surface processing of niobium superconducting RF cavities used in particle accelerators is crucial for determining their performance. The nitrogen (N)-doping method, developed at Fermilab, enhances the cavities’ quality factor by doping the cavity’s interior surface with N atoms at 800 °C. After N-doping, electropolishing (EP) is employed to remove the niobium nitride phases and attain the desired concentration of interstitial N atoms. This study explores the effects of EP conditions on N-doped niobium samples. The samples were electropolished at 5 to 40 °C and voltages between 3 and 22 V. Different EP voltage ranges produced two types of pits, classified based on their sizes. Larger pits, linked to higher voltages, are also affected by the reaction rate. Pitting could be reduced at a lower temperature and adequate EP voltage. However, to effectively minimize gas evolution forming large-sized pitting, peeling off the top nitride layer before EP might be beneficial. This was achieved through precise low-voltage etching, forming a two-step EP process. The process involves removing the top 100–200 nm layer at a low voltage, followed by standard EP to remove the required material. This two-step EP process effectively mitigated the pitting risk associated with gas evolution on N-doped surfaces.

43 PARTICLE ACCELERATORS↗
NASA NTRS1973

Investigation of solidification in zero-gravity environment; M553 sphere forming experiment. Phase C: Evaluation of Skylab specimens

Results on specimen evaluation and discussion of solidification behavior in each case are reported in the following order: (1) specimen SL-1.6, (2) specimen SL-2.8, (3) specimen SL-2.4, (4) specimen SL-1.10 and (5) specimen SL-1.11. Comparison is made with ground-processed specimens of similar composition, whenever pertinent and meaningful. Among the nondestructive evaluation methods the measurement of sphericity was conducted by micrometric and shadowgraphic techniques. The intricate shape of specimens in some cases appeared difficult to define. In measuring the density, liquid penetration inside cavities that outcrop on the surface was avoided by sealing off these cavities. Among the destructive evaluation methods the use of the Quantimet 720 required particular attention, because of the small difference in contrast between second phases and micropores. With regard to microporosity microvoids in the core of some specimens were so fine that X-ray microradiography had to be used.

Kattamis, T. Z.↗
DOE OSTI2021

Seamless High-Q Microwave Cavities for Multimode Circuit Quantum Electrodynamics

Multimode cavity quantum electrodynamics ---where a two-level system interacts simultaneously with many cavity modes---provides a versatile framework for quantum information processing and quantum optics. Due to the combination of long coherence times and large interaction strengths, one of the leading experimental platforms for cavity QED involves coupling a superconducting circuit to a 3D microwave cavity. In this work, we realize a 3D multimode circuit QED system with single photon lifetimes of $2$ ms and cooperativities of $0.5-1.5\times10^9$ across 9 modes of a novel seamless cavity. We demonstrate a variety of protocols for universal single-mode quantum control applicable across all cavity modes, using only a single drive line. We achieve this by developing a straightforward flute method for creating monolithic superconducting microwave cavities that reduces loss while simultaneously allowing control of the mode spectrum and mode-qubit interaction. We highlight the flexibility and ease of implementation of this technique by using it to fabricate a variety of 3D cavity geometries, providing a template for engineering multimode quantum systems with exceptionally low dissipation. This work is an important step towards realizing hardware efficient random access quantum memories and processors, and for exploring quantum many-body physics with photons.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS1995

Vibration Method for Tracking the Resonant Mode and Impedance of a Microwave Cavity

There has been a concerted effort to improve the microwave heating technique for processing materials at high temperature. Improved optimization of the energy transfer from a microwave source to the material being processed is required. A vibration technique is pre- sented to continuously maintain a mode resonance and impedance match between a constant frequency magnetron source and a resonant cavity.

microwave↗
DOE OSTI2021

THERMAL/STRUCTURAL ANALYSIS OF THE AXION QUANTUM METROLOGY CAVITY AND ITS COMPONENTS

This research was centered around maximizing the capability to cool dielectric material within a containment unit, or Photonic Band Gap (PBG) cavity, designed for detecting axion dark matter and identifying the unit’s thermal properties. There are multiple types of PBG cavities, but the latest version that axion researchers wish to use has been theorized to contain possible issues related to its thermal properties. Thermal conductivity is an issue with the dielectric material because it is made from alumina which is highly insulative. This is important since the research is being done in a cryogenic environment and the thermal noise affects the quantum bit used for detecting the axion to photon conversion process. Therefore, any improvements to this unit should be justified and implemented but are not entirely limited to thermal contact related aspects of PBG cavities. A prospect of using sapphire in place of alumina also exists, but this is a more expensive, less tested, and more elusive material to justify the creation of a full dielectric structure out of sapphire. Thermal aspects of the cavity were analyzed using finite element method (FEM) and an experiment designed to test different thermal joint materials. FEM was used to check the contraction of the cavity during cooling, the contact quality between the dielectric material and cavity wall, theheat flow rate through the assembly, and helps visualize the cavity’s reaction to different design changes. A simple comparison between thermal conductivity curves justified the usage of sapphire over alumina from a thermal property point of view. Thus, the method of experimentation had an additional dielectric material, sapphire, to test with and compare to alumina. The thermal test identified which material is best to use for a thermal joint but also simultaneously found the conductance of the joint and dielectric material as well as an estimate for what the temperature is inside the larger scale cavity since a thermometer cannot be placed inside the PBG when it cools. Initially, the cavity simulation was tested for structural deformation properties and stress distribution since it is made of copper which contracts heavily in comparison to most other materials. The reduction in volume of the cavity was less than anticipated which gave more room for a possible usage of a modified thermal joint for additional contact area and higher conductivity.

43 PARTICLE ACCELERATORS↗
NASA NTRS1982

Finite analytic numerical solution of heat transfer and flow past a square channel cavity

A numerical solution of flow and heat transfer characteristics is obtained by the finite analytic method for a two dimensional laminar channel flow over a two-dimensional square cavity. The finite analytic method utilizes the local analytic solution in a small element of the problem region to form the algebraic equation relating an interior nodal value with its surrounding nodal values. Stable and rapidly converged solutions were obtained for Reynolds numbers ranging to 1000 and Prandtl number to 10. Streamfunction, vorticity and temperature profiles are solved. Local and mean Nusselt number are given. It is found that the separation streamlines between the cavity and channel flow are concave into the cavity at low Reynolds number and convex at high Reynolds number (Re greater than 100) and for square cavity the mean Nusselt number may be approximately correlated with Peclet number as Nu(m) = 0.365 Pe exp 0.2.

Chen, C.-J.↗
NASA NTRS1987

Analysis of the all-specular Linlor baffle design

This paper presents the results of a full three-dimensional analysis of a new type of reflecting baffle vane cavity. The analysis is divided into two separate parts. The first employs advanced geometrical ray tracing techniques to analyze the specular reflecting properties of the cavities. The second part uses deterministic radiation transfer methods to analyze the diffuse scattering properties of the reflecting cavities relative to absorbing ones. In both cases, an operating wavelength of 10.6 microns is initially used. These results are then used to estimate the performance at 2.0 microns.

Greynolds, Alan W.↗
NASA NTRS1981

Finite-analytic numerical solution of heat transfer in two-dimensional cavity flow

Heat transfer in cavity flow is numerically analyzed by a new numerical method called the finite-analytic method. The basic idea of the finite-analytic method is the incorporation of local analytic solutions in the numerical solutions of linear or nonlinear partial differential equations. In the present investigation, the local analytic solutions for temperature, stream function, and vorticity distributions are derived. When the local analytic solution is evaluated at a given nodal point, it gives an algebraic relationship between a nodal value in a subregion and its neighboring nodal points. A system of algebraic equations is solved to provide the numerical solution of the problem. The finite-analytic method is used to solve heat transfer in the cavity flow at high Reynolds number (1000) for Prandtl numbers of 0.1, 1, and 10.

Chen, C.-J.↗
NASA NTRSDate not supplied

Optimization of Variable Depth Acoustic Liners with Grazing Flow

Acoustic liners, typically used as a noise control treatment in the engine nacelles of conventional aircraft, are being considered for noise treatment in the proprotor ducts of a vertical takeoff and landing aircraft. This work considers a new optimization method to design an acoustic liner with variable depth cavities for broadband and low-frequency attenuation. This method, termed the direct optimization method, minimizes the radiated sound from a duct. In this paper, the new method is compared with an existing indirect method to design multiple variable depth acoustic liners. Acoustic impedances of liners designed using both methods are predicted using a semianalytical impedance model and impedance predictions for two designs are compared to experimental results acquired from grazing flow impedance testing. For the work presented here, liners designed using the indirect approach provide improved attenuation spectra over those designed using the direct approach but potential improvements to the performance of the direction optimization method are discussed.

Proprotor↗
NASA NTRS1992

Asymptotic modal analysis of a rectangular acoustic cavity excited by wall vibration

Asymptotic modal analysis, a method that has recently been developed for structural dynamical systems, has been applied to a rectangular acoustic cavity. The cavity had a flexible vibrating portion on one wall, and the other five walls were rigid. Banded white noise was transmitted through the flexible portion (plate) only. Both the location along the wall and the size of the plate were varied. The mean square pressure levels of the cavity interior were computed as a ratio of the result obtained from classical modal analysis to that obtained from asymptotic modal analysis for the various plate configurations. In general, this ratio converged to 1.0 as the number of responding modes increased. Intensification effects were found due to both the excitation location and the response location. The asymptotic modal analysis method was both efficient and accurate in solving the given problem. The method has advantages over the traditional methods that are used for solving dynamics problems with a large number of responding modes.

Peretti, Linda F.↗
NASA NTRS1991

Analytical prediction of EM scattering by complex obstacles within electrically large open cavities

An analytical technique is described for predicting the electromagnetic (EM) scattering by complex obstacles within electrically large open waveguide cavities. This topic is of relevance to EM scattering and EMC type applications. A general open ended waveguide cavity is illustrated and is assumed to be relatively arbitrarily shaped, and the open front end of the cavity is illuminated by an arbitrarily polarized external plane wave field. The interior obstacle is assumed to be located within the cavity near the back end, and it generally contributes significantly to the fields scattered into the exterior by the entire cavity configuration. The present scattering analysis is restricted to within approximately 70 degs from boresight with respect to the open front end; outside of this region, the scattering by the external features of the cavity are generally more significant than from the interior of the cavity. The scattering analysis is composed of two main parts. One analysis is of the coupling of the incident plane wave field, via the open front end using the high frequency ray or beam shooting methods. The other analysis deals with separately obtaining the plane wave scattering characteristics of the interior obstacle. Thus the present analysis represents a hybrid combination of an asymptotic high frequency ray/beam method for tracking the fields through the cavity, together with any suitable method for obtaining a plane wave characterization of the interior obstacle.

Pathak, Prabhakar H.↗
DOE OSTI2023

Enhancing SRF cavity stability and minimizing detuning with data-driven resonance control based on dynamic mode decomposition

Effective resonance control of superconducting radio frequency (SRF) cavities is critical for large machines like LCLS-II, as failure to achieve proper control can result in increased RF power consumption, higher cryogenic heat loads, and increased costs. To address this challenge, we have developed a machine learning (ML) model based on the dynamic mode decomposition method to represent the forced cavity dynamics. Using this model, we designed a model predictive controller (MPC) and demonstrated through simulation that the MPC can effectively stabilize the amplitude and phase of SRF cavities using only a frequency actuator, even in the presence of multiple mechanical modes. The lightweight and explicit ML model makes the controller suitable for direct implementation on field-programmable gate arrays, unlocking the full potential of SRF linacs like LCLS-II, enabling higher beam power and energy, and also serving as an advanced motion controller for various applications, such as photon beamlines and storage rings.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗