Session C04: Applied Physics & Instrumentation

Investigation of fatigue fracture behavior based on optical interferometry

This study explores the physical mechanism of fatigue failure using electronic speckle pattern interferometry (ESPI) and a wave theory of deformation and fracture. ESPI visualizes the displacement field of solid objects under deformation. Our numerical analysis indicates the reduction in Poisson's ratio plays a role in the transition from fatigue deformation to fracture. The ESPI data support this proposition. In this presentation, we will discuss various findings in the above research that can lead to a new paradigm of the fatigue fracture mechanism.   

2D Multi-mode Iso-thermally Stratified Compressible Rayleigh-Taylor instability with Low Atwood Number

The flow compressibility through the strength of the background stratification has been reported to have a stabilization effect in single-mode Rayleigh-Taylor instability (RTI) at Atwood numbers less than 0.05. This work extends the study of such effects on the low Atwood number (A=0.04) 2D RTI to the multi-mode perturbation using direct numerical simulations, DNS. We study the growth of the RTI, mixing, energetics, and the vortical dynamics of the flow with different Mach and Reynolds numbers. In addition, we present a detailed analysis of our DNS to study how compressibility plays a role in the transport of Turbulent Kinetic Energy, TKE, of the multi-mode 2D RTI.   

Line narrowing of polycrystalline Cr:ZnS/Se laser oscillation due to suppression of spatial hole burning in non-selective twisted mode cavities

Current work reports on comparative laser characterization of Cr:ZnS/Se polycrystalline gain media in non-selective linear polarized and twisted mode cavities. The work aimed to identify the mechanism of the spectral broadening of continuous-wave Cr:ZnS/ZnSe lasers in the non-selective cavity. Randomly polarized Er-fiber laser operating at 1567 nm with 10W maximum power utilized as a pumping source. By adjusting the orientation of intracavity waveplates with respect to intracavity polarizer, the switching between linear polarized and twisted cavity mode was realized. We demonstrated that in the presence of a spatial hole burning effect in the gain element, the spectral output of the Cr:ZnS/Se lasers in non-selective cavities is broadened to ~20-50 nm. It was shown that suppression of the spatial hole burning in the gain element could be realized by enabling circular polarization of the laser radiation in the gain element in the so-called "twisted mode" cavity. In this cavity, narrow-line oscillations with linewidth limited by wavemeter resolution (~90 pm) were demonstrated using the same laser crystals without any selective elements.   

Effect of low Earth orbit radiation levels of decay characteristics of thermographic phosphors

The authors have investigated the effects of the environment outside of the Earth’s protective atmosphere on the decay characteristics of thermographic phosphor powders and phosphor composites. Phosphor thermometry is a versatile, accurate, noncontact and rapid method of thermometry that uses the luminescent properties of phosphors to measure temperature [1] This precise, remote, and instantaneous method of thermometry covers temperatures ranging from cryogenic to 1700 C and potentially beyond [2]. The temperature dependent information can be inferred by measuring the decay characteristics of the emitted signal, and/ or the decay intensity [3]. The study presented here focuses on evaluating the effect of atomic oxygen and UV radiation on the excitation / emission characteristics of La₂O₂S: Eu and Mg₃F₂GeO₄: Mn thermographic phosphors. Samples were flown on MISSE-Aegis Aerospace Inc and after a 6 month duration returned to Earth for evaluation and characterization. Post exposure tests ranged from -50 to 250 C for luminescence excited by 365 and 405 nm.  It is expected that decay time should be a sensitive indicator of radiation damage.  Examination and comparison of results of decay time versus temperature for both exposed and unexposed samples appears to indicate no discernible change for these characteristics within measurement uncertainty.  This suggests little or no damage to the thermographic phosphors.

    

Novel Microwave Plasma Synthesis of High Entropy Borides

This research focuses on the benefits of microwave-induced plasma as a means to synthesize high entropy transition metal borides. This synthesis route allows rapid heating/cooling rates and investigation into potential heating mechanisms and reaction pathways offered by MW-plasma. The microwave plasma approach relies on metal oxide thermal reduction (borothermal or boro/carbothermal) for precursor powders containing metal oxides with graphite, boron, and B₄C as reducing agents. This precursor powder mixture allows efficient microwave energy absorption contributing to rapid and uniform sample heating. The results show that boro/carbothermal reduction coupled with MW-plasma results in higher measured hardness compared to previous studies and when compared to the borothermal reduction approach.  The potential interactions of the low-temperature microwave plasma with the precursor powder will be discussed in the context of metal oxide thermal reduction methods and mechanical properties.

    

Characterization of a modified printed optical particle spectrometer for aerosol sampling systems.

The printed optical particle spectrometer (POPS) is a light-weight, low-cost instrument for aerosol number concentrations and size distributions measurements. Here we report on modifications of the POPS (Handix Scientific) to facilitate its use in multi-instrument aerosol sampling systems. The flow system is modified by replacing the internal pump with a needle valve and a vacuum pump. The instrument is integrated into closed flow systems by routing the sheath flow from filtered inlet air. A high-precision multichannel analyzer card (MCA) is added to sample the analog pulse signal. The MCA card is polled at 10 Hz frequency using an external data acquisition system and removes the count rate limitation of 10000 particles s^-1 associated with the POPS internal system. The MCA card enables integration of the POPS into larger setups that require precise time stamping and clock synchronization, especially in field. The 90/10 rise and fall times were measured to be 0.17 s and 0.41 s at 5 cm^-3 s^-1 and provide a sampling frequency of ~1-2 Hz below which the amplitude of measured fluctuations is captured with > 70% efficiency. We also integrated the POPS into the dual tandem DMA system, which generates dimer particles. We anticipate that this version will extend utilization of the POPS.

    

Fast-timing measurements using LaBr3(Ce) detectors in the neutron-rich N = 20 region

Variations in the proton and neutron numbers inside the nucleus lead to changes in the nuclear shell structure. Nuclear transition rates are sensitive indicators of those changes, so-called “nuclear shell evolution”, which depend in part on knowledge of the level lifetimes. Radioactive nuclei were implanted into a CeBr₃ scintillator coupled to a Position-Sensitive Photomultiplier Tube (PSPMT) as part of a β decay experiment in the neutron-rich N = 20 region conducted at the National Superconducting Cyclotron Laboratory (NSCL). This allowed for correlating the decays to the implanted ions using spatial and temporal techniques. 15 LaBr₃(Ce) detectors, providing fast timing measurement and γ radiation detection, were used to generate time-difference spectra for β-delayed γ radiation following a decay event to measure half-lives. In the neutron-rich N = 20 region, corrections for the energy-dependent time-walk effects and validation results will be provided.   

Setup of a Simulated EPICS /Phoebus Systems with Alarms for the Mu2e Cosmic Ray Veto

The Cosmic Ray Veto System (CRV) for the Mu2e Experiment is well under construction.  A set of software to simulate the electronics of the CRV readout and controls has been setup at the University of South Alabama.  This software set, which includes the programs EPICS, ZooKeeper and Kafka is needed to define variables and alarm conditions for the program Phoebus.  This program, Phoebus, is the graphical user interface (GUI) that expert shifters will use to monitor and control the CRV.  The advantage of setting up the user GUI before electronics installation is that the layout can be studied by the CRV group and revised into an optimal display.  More process variables that are related to the CRV can be added upon request.  Eventually, this upper-level shifter GUI will be interfaced with the actual Input/Output Control that will be installed with the electronics. This talk will summarize the implementation of this local system.

    

Tabletop detector for detecting dark massive particles with a crystal pendulum and laser doppler vibrometer.

The detectors of dark matter (DM) particles employ liquid noble gases, superheated liquid, crystals, etc. but DM is not yet directly detected. Galactic and extragalactic PeV-energy (10¹⁵ eV) gamma rays with zero rest masses are known. However, PeV mass-energy particles with non-zero rest mass have not yet been detected because of the lack of detectors for particles of approximately 100 times the total collision energy of the Large Hadron Collider. Here, we report an alternative detector for neutral massive particles (MP) of PeV energy by using a pendulum with a microgram crystalline bob. It does not need electromagnetic, nuclear, or chemical interaction between the detector and the particle. The linear momentum of PeV energy MP   propagating with a cosmic speed of ~249 km/s is enough to start oscillations of such micro-pendulum. The amplitude and speed of crystal-bob oscillations are detected with a laser-doppler vibrometer. These data are compared with theoretical calculations of the amplitude of forced oscillations of the crystal-bob, which are initiated by a periodic force due to energetic MP hitting the crystal. It allows the estimate of the mass of these MP. In our experiments, this tabletop instrument detected MP from the Sun and the center of our galaxy. The detected solar MP-particles have average mass-energy of (3.1 ±1) ×10¹⁵ (eV/C²) = (5.5 ±1.8) ×10^-21 kg, which is several orders of magnitude bigger than a nucleon mass. The uncovered MP particles contribute to the masses of our galaxy and universe.