Experimental study for microwave-induced thermoacoustic tomography

Microwave-Induced Thermoacoustic Tomography (MI-TAT) is a noninvasive hybrid modality which improves contrast by using thermoelastic wave generation induced by microwave absorption. Ultrasonography is widely used in medical practice as a low-cost alternative and supplement to magnetic resonance imaging (MRI). Although ultrasonography has relatively high image resolution (depending on the ultrasonic wavelength at diagnostic frequencies), it suffers from low image contrast of soft tissues. In this work samples are irradiated with sub- microsecond electromagnetic pulses inducing acoustic waves in the sample that are then detected with an unfocused transducer. The advantage of this hybrid modality is the ability to take advantage of the microwave absorption coefficients which provide high contrast in samples. This in combination with the superior spatial resolution of ultrasound waves is important to providing a low-cost effective imaging technique. Here we propose to use this hybrid imaging technique to image composite materials to further investigate the NDE applications for MI-TAT.</p

Subtraction of correlated noise in global networks of gravitational-wave interferometers

The recent discovery of merging black holes suggests that a stochastic gravitational-wave background is within reach of the advanced detector network operating at design sensitivity. However, correlated magnetic noise from Schumann resonances threatens to contaminate observation of a stochastic background. In this paper, we report on the first effort to eliminate intercontinental correlated noise from Schumann resonances using Wiener filtering. Using magnetometers as proxies for gravitational-wave detectors, we demonstrate as much as a factor of two reduction in the coherence between magnetometers on different continents. While much work remains to be done, our results constitute a proof-of-principle and motivate follow-up studies with a dedicated array of magnetometers

Measurement and subtraction of Schumann resonances at gravitational-wave interferometers

Correlated magnetic noise from Schumann resonances threatens to contaminate the observation of a stochastic gravitational-wave background in interferometric detectors. In previous work, we reported on the first effort to eliminate global correlated noise from the Schumann resonances using Wiener filtering, demonstrating as much as a factor of two reduction in the coherence between magnetometers on different continents. In this work, we present results from dedicated magnetometer measurements at the Virgo and KAGRA sites, which are the first results for subtraction using data from gravitational-wave detector sites. We compare these measurements to a growing network of permanent magnetometer stations, including at the LIGO sites. We show the effect of mutual magnetometer attraction, arguing that magnetometers should be placed at least one meter from one another. In addition, for the first time, we show how dedicated measurements by magnetometers near to the interferometers can reduce coherence to a level consistent with uncorrelated noise, making a potential detection of a stochastic gravitational-wave background possible

Magnetospheric wave injection by modulated HF heating of the auroral electrojet

Modulated High Frequency (HF, 3-30 MHz) heating of the auroral electrojet to generate electromagnetic waves in the Extremely Low Frequency (ELF, 3-3000 Hz) and Very Low Frequency (VLF, 3-30 kHz) bands is investigated in the context of magnetospheric wave injection experiments. The ionospheric heating facility of the High Frequency Active Auroral Research Program (HAARP) is used to excite non-linear amplification of whistler mode waves in the Earth's magnetosphere. Experimental evidence is presented of the first HF heater generated signals experiencing 'ducted' inter-hemispheric propagation and wave-particle interactions resulting in amplification and triggering of free running emissions. The roles of transmitter parameters as well as natural background conditions of the observations are characterized. Dispersion of observed signals is used to determine the magnetospheric propagation paths and associated cold plasma densities. It is found that HAARP induced triggered emissions occur primarily inside the plasmapause and the availability and coupling into magnetospheric 'ducts' is likely one of the limiting factors for observations. Phase and amplitude changes in the observed signals are used to resolve the temporal behavior of the nonlinear resonant current vector that drives amplification. The observed resonant current behavior is discussed in the context of numerical models and used to make inferences about the magnetospheric hot plasma distribution. Ground based capabilities of detection of energetic particle precipitation from the Earth's radiation belts induced by HAARP generated ELF/VLF waves are assessed experimentally and theoretically. A phenomenon of cross-modulation between whistler-mode signals and HF ionospheric heating is observed and investigated as a new method to generate ELF/VLF radiation using an HF ionospheric heater

Experimental Study for Microwave-Induced Thermoacoustic Tomography

Microwave-Induced Thermoacoustic Tomography (MI-TAT) is a noninvasive hybrid modality which improves contrast by using thermoelastic wave generation induced by microwave absorption. Ultrasonography is widely used in medical practice as a low-cost alternative and supplement to magnetic resonance imaging (MRI). Although ultrasonography has relatively high image resolution (depending on the ultrasonic wavelength at diagnostic frequencies), it suffers from low image contrast of soft tissues. In this work samples are irradiated with sub- microsecond electromagnetic pulses inducing acoustic waves in the sample that are then detected with an unfocused transducer. The advantage of this hybrid modality is the ability to take advantage of the microwave absorption coefficients which provide high contrast in samples. This in combination with the superior spatial resolution of ultrasound waves is important to providing a low-cost effective imaging technique. Here we propose to use this hybrid imaging technique to image composite materials to further investigate the NDE applications for MI-TAT.</p

Polarization of Narrowband VLF Transmitter Signals as an Ionospheric Diagnostic Data Set

Very Low Frequency (VLF, 3-30 kHz) transmitter remote sensing has long been used as a simple yet useful diagnostic for the D-region ionosphere (60-90 km). All it requires is a VLF radio receiver that records the amplitude and/or phase of a beacon signal as a function of time. During both ambient and disturbed conditions, the received signal can be compared to predictions from a theoretical model to infer ionospheric waveguide properties like electron density. Amplitude and phase have in most cases been analyzed each as individual data streams, often only the amplitude is used. Scattered field formulation combines amplitude and phase effectively, but does not address how to combine two magnetic field components. We present polarization ellipse analysis of VLF transmitter signals using two horizontal components of the magnetic field. The shape of the polarization ellipse is unchanged as the source phase varies, which circumvents a significant problem where VLF transmitters have an unknown source phase. A synchronized two-channel MSK demodulation algorithm is introduced to mitigate 90 degree ambiguity in the phase difference between the horizontal magnetic field components. Additionally, the synchronized demodulation improves phase measurements during low SNR conditions. Using the polarization ellipse formulation, we take a new look at diurnal VLF transmitter variations, ambient conditions and ionospheric disturbances from solar flares, lightning-ionospheric heating, and lightning-induced electron precipitation, and find differing signatures in the polarization ellipse

Nanoplasmonic Accelerators Towards Tens of TeraVolts per Meter Gradients Using Nanomaterials

Ultra-high gradients which are critical for future advances in high-energy physics, have so far relied on plasma and dielectric accelerating structures. While bulk crystals were predicted to offer unparalleled TV/m gradients that are at least two orders of magnitude higher than gaseous plasmas, crystal-based acceleration has not been realized in practice. We have developed the concept of nanoplasmonic crunch-in surface modes which utilizes the tunability of collective oscillations in nanomaterials to open up unprecedented tens of TV/m gradients. Particle beams interacting with nanomaterials that have vacuum-like core regions, experience minimal disruptive effects such as filamentation and collisions, while the beam-driven crunch-in modes sustain tens of TV/m gradients. Moreover, as the effective apertures for transverse and longitudinal crunch-in wakes are different, the limitation of traditional scaling of structure wakefields to smaller dimensions is significantly relaxed. The SLAC FACET-II experiment of the nano2WA collaboration will utilize ultra-short, high-current electron beams to excite nonlinear plasmonic modes and demonstrate this possibility

PetaVolts per meter Plasmonics: introducing extreme nanoscience as a route towards scientific frontiers

A new class of plasmons has opened access to unprecedentedPetaVolts per meter electromagnetic fields which can transform theparadigm of scientific and technological advances. This includesnon-collider searches in fundamental physics in addition to makingnext generation colliders feasible. PetaVolts per meter plasmonicsrelies on this new class of plasmons uncovered by our work in thelarge amplitude limit of collective oscillations of quantum electrongas. This Fermi gas constituted by “free” conduction bandelectrons is inherent in conductive media endowed with a suitablecombination of constituent atoms and ionic lattice structure. Asthis quantum gas of electrons can be as dense as10$^{24}$ cm$^{-3}$, the coherence limit of plasmonicelectromagnetic fields is extended in our model from the classicalto the quantum domain,0.1√(n$_{0}$(10$^{24}$ cm$^{-3}$)) PVm$^{-1}$. Appropriatelyengineered, structured materials that allow highly tunable materialproperties also make it possible to overcome disruptiveinstabilities that dominate the interactions in bulk media. Theultra-high density of conduction electrons and the existence ofelectronic energy bands engendered by the ionic lattice is onlypossible due to quantum mechanical effects. Based on this framework,it is critical to address various challenges that underlie PetaVoltsper meter plasmonics including stable excitation of plasmons whileaccounting for their effects on the ionic lattice and the electronicenergy band structure over femtosecond timescales. We summarize thechallenges and ongoing efforts that set the strategy for thefuture. Extreme plasmonic fields can shape the future by not onlyopening the possibility of tens of TeV to multi-PeVcenter-of-mass-energies but also enabling novel pathways innon-collider HEP. In view of this promise, our efforts are dedicatedto realization of the immense potential of PV/m plasmonics and itsapplications