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A DIII-D high-beta H-mode discharge, with Ip = 850 kA, Bt = 2.1 T ne = 4 1019 m−3, has been designed to validate full wave modeling of helicon waves by optimizing the expected response of the Phase Contrast Imaging diagnostic. Helicon waves have been predicted to have high current drive efficiency off-axis without facing the accessibility issues of lower-hybrid waves. To test these predictions experimentally, DIII-D has recently commissioned a high-power helicon antenna. To confidently predict the behavior of helicon waves in future devices, measurements of their fundamental properties and validation against models will be essential. Phase contrast imaging (PCI) is an absolutely calibrated internal reference interferometer able to measure density fluctuations with radial wavenumbers kR between 1.5 cm−1 and 20 cm−1. For helicon waves 2 cm−1< kR< 10 cm−1 is expected, allowing PCI to measure their envelope and wavenumber spectrum. This makes PCI a powerful tool for the validation of state-of-the-art models, like the AORSA full wave code. AORSA is used to compute the density perturbations measured by the PCI with 2D calculations corresponding to 11 different toroidal mode numbers combined to resolve the trajectory of the helicon wave in 3D. This is necessary because the waves travel 120 degrees toroidally from the antenna to the PCI. A cold plasma finite element model (CPFEM) [4] is used to predict propagation through the scrape-off layer. The result of the CPFEM model is connected to AORSA by creating an artificial Gaussian antenna on the last closed flux surface. PCI shows best results for waves with small vertical wavenumbers kz. Modeling the helicon waves for several past DIII-D experiments shows that kz is minimized if the intersection of the helicon and the PCI laser beams occurs in the midplane. For such an optimized scenario the predicted signal level is two orders of magnitude larger than the background density fluctuations arising from broadband turbulence. [ABSTRACT FROM AUTHOR]

Low-power (∼100 W) helicon wave (fast waves in the lower hybrid range of frequencies) experiments were conducted on the LArge Plasma Device (LAPD) at UCLA to study wave propagation and coupling properties with a 10-element comb-line traveling wave antenna. Helicon waves are launched unidirectionally along the long axis of the machine from the inductively coupled antenna modules. Varying the launch frequency within the passband of the antenna selects the principal normalized parallel wavenumber n∥. The accessible diagnostic suite and simplified geometry of the LAPD make it well equipped to conduct this systematic study of the comb-line antenna coupling and wave propagation in the plasma. With well resolved spatial and temporal measurements of density, fields, and antenna power, wave power in the plasma was measured across a range of tunable parameters. These parameters included the background magnetic field (B0=0.7-2 kG), plasma density (∼1010 – 1012 cm−3), wave launch direction (sign of n∥), launcher angle (0 to 45 degrees with respect to B0), antenna power (∼ 10−3 -102 W), and launch frequency (461-491 MHz, thereby changing n∥ in the range 2<|n∥ |<4). Across the range of densities there are times during the discharge where both the fast (helicon) and slow ('lower hybrid wave') branches may simultaneously propagate in the plasma core. An extensive data set was obtained to characterize the wave coupling and propagation. [ABSTRACT FROM AUTHOR]

The aim of this paper is to propose the use of passive acoustic monitoring (PAM) as a noninvasive method to investigate the state of communities and ecosystems. PAM operates through the study and characterization of the soundscape of an area. One of the three components of the soundscape (beside geophony and biophony) is anthrophony, which is the collection of sounds produced by human activities. This kind of sounds can have effects on natural environments and natural population. In this study, recording instruments and sampling techniques have been used to acquire and collect sound data for long periods (two weeks) in a natural terrestrial ecosystem (Ticino Park) which is affected by road and rail traffic noise. The analysis conducted studied the trends of the eco-acoustic indices belonging to three measurement sites to detect the presence of characteristic trends and to evaluate the influence of the two anthropogenic noise sources at different distances. [ABSTRACT FROM AUTHOR]

Seabirds are perhaps the most imperiled group of birds. They can readily transit between air and water and enact key behaviors in both habitats. With this amphibious lifestyle, they likely face unique auditory constraints in air, underwater, and even subterranean. Unfortunately, like many other birds, anthropogenic noise seems to be a stressor, yet we have few data on seabird hearing abilities and noise impacts. Here we examined the hearing in the Atlantic puffin, Fratercula arctica . Hearing tests were conducted in-air in a portable semi-anechoic crate using physiological, auditory evoked potential (AEP) methods with temporarily wild-caught, sedated birds. Hearing data were quite clear and provided an auditory curve that was not unlike AEP hearing thresholds in other birds. Lowest measured thresholds were found at 1-2 kHz with a gradual increase in AEP-thresholds at lower frequencies and a steeper increase at higher frequencies. Responses were measurable from 0.5 to 6 kHz. Obtaining auditory data for seabirds is particularly valuable considering their conservation status, population-level declines, and a minimal understanding of how they may use or be influenced by their acoustic habitat. These data show sensitive in-air hearing, and supports concerns about coastal noise which could have clear ecologically relevant consequences. [ABSTRACT FROM AUTHOR]

The goal of this research is to design and fabricate a very sensitive MEMS-based magnetic field sensor for space applications. The challenge is to reach the required sensitivity: measuring magnetic fields from a few nT to about 60000nT with sub-nano Tesla accuracy. The device studied in this paper is based on a classical resonating Xylophone Bar Magnetometer (XBM). It consists of a free-free beam supported in the nodal points of the fundamental transverse mode of vibration. A sinusoidal current at the vibration frequency is supplied via the nodal supports. In the presence of an external magnetic field, this current results in a sinusoidal Lorentz force that puts the XBM in vibration at its fundamental frequency. Two different materials are proposed to fabricate this device: the first one is Poly-SiGe and the second is Nickel. The paper will present multi-physics simulations to evaluate the response of the SiGe-XBM and the Ni-XBM. Following these studies, devices with several support lengths and shapes were designed and fabricated in poly-SiGe and Nickel. Increasing the quality factor by a dedicated design of the support and using the intrinsic properties of the material, the new magnetometer will have improved accuracy and resolution and will meet the requirements for space applications. [ABSTRACT FROM PUBLISHER]