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Due to a malfunctioning high-gain antenna, the Galileo spacecraft is transmitting all its data through a low-gain antenna, and the data rate will seldom exceed 100 bits per second during its two-year tour of Jupiter's satellites.
This presentation contains notes for a 30 minute lecture that is part of an AIAA Special Session titled, Pressure Gain Combustion Overview: Principles, Operation, and Applications. The presentation covers an introduction to Pressure Gain Combustion (PGC) and the devices used to implement it. The concept of PGC is discussed on a thermodynamic basis, the performance benefits are demonstrated, and methods of implementation are described. These include devices such as Resonant Pulse Combustors, Internal Combustion Wave Rotors, Pulse Detonation Engines, and Rotating Detonation Engines.
The high gain antenna for the Cassini spacecraft is a lightweight, large surface area structural element, and therefore its dynamic characteristics are noticeably altered by air mass effects...This paper describes the method ultimately used to quantify these effects on the Cassini HGA (High Gain Antenna).
The VIIRS instruments on board the SNPP and NOAA-20 (N20) satellites have 14 reflective solar bands covering a spectral range from 412 nm to 2250 nm. Three of these are imaging bands (I bands) with a nadir spatial resolution of 375 m and 11 are moderate resolution bands (M bands) with a resolution of 750 m. The higher resolution in the I bands is achieved by a combination of more detectors, with the I bands having twice as many detectors of half the size for every M band detector, and a higher data rate, with the I bands having two sub-samples for every sample of M band data. To ensure calibration accuracy, any systematic difference in the response of the two sub-samples needs to be monitored and corrected in the calibrated products. In this paper, we use the solar diffuser calibrations to monitor the gain differences between the two sub-samples of the I bands both as a function of time and signal level. We find gain differences of about 0.1% for I1, 0.3% for I2, and <0.1% for I3 that are mostly constant over the range of signal values available in the SD calibration. These values are mostly consistent throughout the mission for both instruments. The results are remarkably similar for the two VIIRS instruments, including a slightly out-of-family behavior seen in a few detectors. We discuss possible causes for the difference and the impact on the aggregated Earth view images.
4H-SiC Low Gain Avalanche Detectors (LGADs) have been fabricated and characterized. The devices employ a circular mesa design with low-resistivity contacts and an SiO 2 passivation layer. The I–V and C–V characteristics of the 4H-SiC LGADs are compared with complementary 4H-SiC PiN diodes to confirm a high breakdown voltage and low leakage current. Both LGADs and PiN diodes were irradiated with alpha particles from a $^{210}_{84}$Po source. The charge collected by each device was compared, and it was observed that low-gain charge carrier multiplication is achieved in the 4H-SiC LGAD.
We propose and demonstrate construction of highly uniform, multilayered superstructures of CdSe/CdZnS core/shell colloidal nanoplatelets (NPLs) using liquid interface self-assembly. These NPLs are sequentially deposited onto a solid substrate into slabs having monolayer-precise thickness across tens of cm(2) areas. Because of near-unity surface coverage and excellent uniformity, amplified spontaneous emission (ASE) is observed from an uncharacteristically thin film having 6 NPL layers, corresponding to a mere 42 nm thickness. Furthermore, systematic studies on optical gain of these NPL superstructures having thicknesses ranging from 6 to 15 layers revealed the gradual reduction in gain threshold with increasing number of layers, along with a continuous spectral shift of the ASE peak (similar to 18 nm). These observations can be explained by the change in the optical mode confinement factor with the NPL waveguide thickness and propagation wavelength. This bottom-up construction technique for thickness-tunable, three-dimensional NPL superstructures can be used for large-area device fabrication.
Auger decay of multiple excitons represents one of the main obstacles to photonic applications of semiconductor quantum dots (QDs). These non-radiative processes are particularly detrimental to the performance of QD-based electroluminescent and lasing devices. Here, we demonstrate that by using semiconductor quantum shells with an “inverted” QD geometry, it is possible to inhibit Auger recombination, allowing extraordinary improvements to their multi-exciton characteristics. Additionally, we show that quantum shells result in ultralong biexciton lifetimes (>10 ns), and an associated biexciton quantum yield of up to 81%. Furthermore, the energy-dispersive architecture of quantum shells leads to exciton-exciton repulsion, which splits the single-exciton and bi-exciton optical transitions. In this regime, quantum shells produce the longest optical gain lifetime reported for colloidal QDs to date (> 6 ns) over a broad amplification bandwidth. Therefore, the employment of quantum shells in optically- or electrically-pumped gain media can lead to a substantial improvement in device performance.
We demonstrate large area (25 000 μm2) Al-rich AlGaN-based avalanche photodiodes (APDs) grown on single crystal AlN substrates operating with differential (the difference in photocurrent and dark current) signal gain of 100 000 at 90 pW (<1 μW cm−2) illumination with very low dark currents <0.1 pA at room temperature under ambient light. The high gain in large area AlGaN APDs is attributed to a high breakdown voltage at 340 V, corresponding to very high breakdown fields ∼9 MV cm−1 as a consequence of low threading and screw dislocation densities < 103 cm−2. The maximum charge collection efficiency of 30% was determined at 255 nm, corresponding to the bandgap of Al0.65Ga0.35N, with a response of 0.06 A/W. No response was detected for λ > 280 nm, establishing solar blindness of the device.
In this work, we report on a theoretical study of second-harmonic generation (SHG) in plasmonic nanostructures interacting with two-level quantum emitters (QEs) under incoherent energy pump. We generalize the driven-dissipative Tavis–Cummings model by introducing the anharmonic surface plasmon-polariton (SPP) mode coupled to QEs and examine physical properties of corresponding SPP-QE polariton states. Our calculations of the SHG efficiency for strong QE-SPP coupling demonstrate orders of magnitude enhancement facilitated by the polariton gain. We further discuss time-domain numerical simulations of SHG in a square lattice comprising Ag nanopillars coupled to QEs utilizing a fully vectorial nonperturbative nonlinear hydrodynamic model for conduction electrons coupled to Maxwell–Bloch equations for QEs. The simulations support the idea of gain enhanced SHG and show orders of magnitude increase in the SHG efficiency as the QEs are tuned in resonance with the lattice plasmon mode and brought above the population inversion threshold by incoherent pumping. By varying pump frequency and tuning QEs to a localized plasmon mode, we demonstrate further enhancement of the SHG efficiency facilitated by strong local electric fields. The incident light polarization dependence of the SHG is examined and related to the symmetries of participating plasmon modes.
MagLIF experiments [M.R. Gomez et al., Phys. Plasmas 22, 056306 (2015)] on Z have demonstrated the basic principles of Magneto-Inertial Fusion (MIF) for wall confined plasmas. Other MIF schemes have been proposed based on the liner implosion of closed field magnetically confined plasmas such as Field Reversed Configurations (FRCs) [T. P. Intrator et al., Phys. Plasmas 15, 042505 (2008)]. We present a semi-analytical model of liner driven FRC implosions that predicts the fusion gain of such systems. The model predicts a fusion gain near unity for an FRC imploded by a liner driven by the Z Machine. We show that FRCs could be formed and imploded at the Z facility using the AutoMag liner concept [S. A. Slutz et al., Phys. Plasmas 24, 012704 (2017)]. Furthermore, an initial bias magnetic field can be supplied by the external magnets used in MagLIF experiments. The reverse field is then supplied by an AutoMag liner, which has helical conducting paths imbedded in an insulating substance. Experiments [Shipley et al., Phys. Plasmas 26, 052705 (2019)] have demonstrated that AutoMag can generate magnetic fields greater than 30 Tesla inside of the liner. We have performed 2D Radiation MHD simulations of the formation and implosion of an FRC, which are in good agreement with the analytical model. The FRC formation process could be studied on small pulsed power machines delivering about 1 MA.
When an inertial confinement fusion implosion is compressed, it maintains thermonuclear density and temperatures for a very short time scale, about 100 ps. The Gamma Reaction History diagnostic measures the time evolution of the fusion burn, but its temporal resolution is limited by the use of a photomultiplier tube (PMT) to amplify the photon signal. Multichannel plate-based PMTs have a fast (~120 ps) full-width at half-max impulse response function (IRF), but the time scale is similar to the incoming physics signal. An analysis routine is used to remove the effect of the PMT IRF and infer the incident fusion burnwidth. With the National Ignition Facility achieving ignition and creating much brighter signals, the PMTs are run at gains three orders of magnitude lower than nominal operation. Calibration at these settings shows the PMT IRFs get ~15% wider. Taking the gain-dependent IRF can affect the inferred nuclear burnwidths by up to ~15%.
Optical parametric amplifiers require a seed energy at the spectral range of interest for amplification. In the case of pulsed laser systems, seed pulse characteristics such as spectral energy density and spectral uniformity influence laser system design and performance. In this letter, we present the design and modeling of a few micro-joules, wavelength-tunable, femtosecond parametric amplifier system. We employ a gain-managed nonlinear fiber amplifier output as the seed pulse. This seed pulse is relatively uniform across its bandwidth from 1010 to 1180 nm. Its spectral energy density averages 600 pJ/nm, 30 times higher than conventional counterparts. The overall amplification gain is 175, and the conversion efficiency is 17.5%. The inherent quasi-linear chirp of the seed pulse is utilized to alter the output wavelength. Our tunable femtosecond laser is an enabling technology for high-demand applications such as time-resolved spectroscopy, nonlinear and advanced material research, and biomedical imaging and microscopy modalities.
We quantify the calibration requirements for systematic uncertainties for next-generation ground-based observatories targeting the large-angle B-mode polarization of the Cosmic Microwave Background, with a focus on the Simons Observatory (SO). We explore uncertainties on gain calibration, bandpass center frequencies, and polarization angles, including the frequency variation of the latter across the bandpass. We find that gain calibration and bandpass center frequencies must be known to percent levels or less to avoid biases on the tensor-to-scalar ratio r on the order of Δ r∼10-3, in line with previous findings. Polarization angles must be calibrated to the level of a few tenths of a degree, while their frequency variation between the edges of the band must be known to O(10) degrees. Given the tightness of these calibration requirements, we explore the level to which residual uncertainties on these systematics would affect the final constraints on r if included in the data model and marginalized over. We find that the additional parameter freedom does not degrade the final constraints on r significantly, broadening the error bar by O(10%) at most. We validate these results by reanalyzing the latest publicly available data from the collaboration within an extended parameter space covering both cosmological, foreground and systematic parameters. Finally, our results are discussed in light of the instrument design and calibration studies carried out within SO.
Abstract Gas electron Multipliers (GEM) are a new generation of gaseous avalanche devices in the Micro Pattern Gaseous Detector (MPGD) category. GEMs are widely used in both nuclear and high energy experiments as well as in medical science. Several parameters define the performance of these types of devices under various experimental conditions. This article focuses on the study of effective gain and Ion Back Flow (IBF) in both triple and quadruple GEM detectors. Effective gain and IBF are two of the most important parameters in determining the performance of GEM detectors.
Abstract Low gain avalanche detectors (LGADs) deliver excellent timing resolution, which can mitigate mis-assignment of vertices associated with pileup at the High Luminosity LHC and other future hadron colliders. The most highly irradiated LGADs will be subject to 2.5 × 10 15 n eq cm -2 of hadronic fluence during HL-LHC operation; their performance must tolerate this. Hamamatsu Photonics K.K. and Fondazione Bruno Kessler LGADs have been irradiated with 400 and 500 MeV protons respectively in several steps up to 1.5 × 10 15 n eq cm -2 . Measurements of the acceptor removal constants of the gain layers, evolution of the timing resolution and charge collection with damage, and inter-channel isolation characteristics, for a variety of design options, are presented here.
Argon fluoride (ArF) is currently the shortest wavelength laser that can credibly scale to the energy and power required for high gain inertial fusion. ArF's deep ultraviolet light and capability to provide much wider bandwidth than other contemporary inertial confinement fusion (ICF) laser drivers would drastically improve the laser target coupling efficiency and enable substantially higher pressures to drive an implosion. Our radiation hydrodynamics simulations indicate gains greater than 100 are feasible with a sub-megajoule ArF driver. Our laser kinetics simulations indicate that the electron beam-pumped ArF laser can have intrinsic efficiencies of more than 16%, versus about 12% for the next most efficient krypton fluoride excimer laser. We expect at least 10% ‘wall plug' efficiency for delivering ArF light to target should be achievable using solid-state pulsed power and efficient electron beam transport to the laser gas that was demonstrated with the U.S. Naval Research Laboratory's Electra facility. These advantages could enable the development of modest size and lower cost fusion power plant modules. This would drastically change the present view on inertial fusion energy as being too expensive and the power plant size too large.
The Resolve instrument aboard the X-ray Imaging and Spectroscopy Mission (XRISM) is a 36-pixel microcalorimeter spectrometer that provides nondispersive spectroscopy with ∼ 5 eV spectral resolution in the soft X-ray waveband. Resolve has a requirement to provide an absolute energy-scale calibration of ± 2 eV from 0.3 to 12 keV. We describe our ground calibration strategy and results of a subset of the ground calibration campaigns, including a discussion of improvements in the energy scale ground calibration compared with Hitomi’s. These improvements include calibration of the low-energy band below 4 keV with the instrument in the flight dewar and the dewar aperture door open, which was not performed for Hitomi, and thorough measurements over an extended high-energy waveband to 22 keV. We also developed an improved technique for gain calibration of “mid-res” secondary events, which have suppressed gain due to proximity to a preceding X-ray event (18 to 70 ms) on the same pixel. We provide a discussion of the on-orbit energy scale monitoring campaigns and an assessment of the Resolve energy scale uncertainties, a key parameter for astrophysics analysis. Energy-scale calibration approaches for future space-based instruments, including the X-ray Integral Field Unit on Athena and microcalorimeter spectrometers proposed or under discussion for future X-ray observatory concepts, have heritage in the calibration of XRISM. We briefly comment on lessons learned from Resolve calibration that are relevant for these future instruments.
Vascular plant pathogens travel long distances through host veins, leading to life-threatening, systemic infections. In contrast, nonvascular pathogens remain restricted to infection sites, triggering localized symptom development. The contrasting features of vascular and nonvascular diseases suggest distinct etiologies, but the basis for each remains unclear. Here, we show that the hydrolase CbsA acts as a phenotypic switch between vascular and nonvascular plant pathogenesis. cbsA was enriched in genomes of vascular phytopathogenic bacteria in the family Xanthomonadaceae and absent in most nonvascular species. CbsA expression allowed nonvascular Xanthomonas to cause vascular blight, while cbsA mutagenesis resulted in reduction of vascular or enhanced nonvascular symptom development. Phylogenetic hypothesis testing further revealed that cbsA was lost in multiple nonvascular lineages and more recently gained by some vascular subgroups, suggesting that vascular pathogenesis is ancestral. Our results overall demonstrate how the gain and loss of single loci can facilitate the evolution of complex ecological traits.