Architecture of Planetary Systems Predicted from Protoplanetary Disks Observed with ALMA. I. Mass of the Possible Planets Embedded in the Dust Gap

Recent ALMA observations have identified a variety of dust gaps in protoplanetary disks, which are commonly interpreted to be generated by unobserved planets. Predicting mass of such embedded planets is of fundamental importance in comparing those disk architectures with the observed diversity of exoplanets. The prediction, however, depends on the assumption that whether the same gap structure exists in the dust component alone or in the gas component as well. We assume a planet can only open a gap in the gas component when its mass exceeds the pebble isolation mass by considering the core-accretion scenario. We then propose two criteria to distinguish if a gap is opened in the dust disk alone or the gas gap as well when observation data on the gas profile is not available. We apply the criteria to 35 disk systems with a total of 55 gaps compiled from previous studies and classify each gap into four different groups. The classification of the observed gaps allows us to predict the mass of embedded planets in a consistent manner with the pebble isolation mass. We find that outer gaps are mostly dust alone, while inner gaps are more likely to be associated with a gas gap as well. The distribution of such embedded planets is very different from the architecture of the observed planetary systems, suggesting that significant inward migration is required in their evolution.

The study of instabilities role of plasma in the high-voltage discharge formation initiated by optical radiation at high pressures in high-voltage optically triggered switches

The paper presents the experimental results of triggering a high-voltage gas gap by YAG: Nd3+ laser radiation. The gas gap was used as the primary switch of a high-current pulsed e-beam RADAN-type accelerator. As a result, an operating regime when the instability and delay time appeared to be minimal was experimentally found. The developed gas gap and the found operating regimes sustain the switching instability no more than 0.3 ns. The physical mechanisms determining the switch-on delay and the obtained level of instability are discussed.

Cylindricity Sensitivity Thermal Model of the AGR-5/6/7 Experiment in the Advanced Test Reactor

The AGR-5/6/7 experiment is currently being irradiated in the Advanced Test Reactor (ATR) at the Idaho National Laboratory and is approximately 70% complete. Several fuel and material irradiation experiments have been planned for the U.S. Department of Energy Advanced Gas Reactor Fuel Development and Qualification Program, which supports the development and qualification of tristructural isotropic (TRISO)-coated particle fuel for use in high-temperature gas-cooled reactors. The goals of these experiments are to provide irradiation performance data to support fuel process development, qualify fuel for normal operating conditions, support development of fuel performance models and codes, and provide irradiated fuel and materials for post-irradiation examination and safety testing. Originally planned and named as separate fuel experiments, but subsequently combined into a single test train, AGR-5/6/7 is testing low-enriched uranium oxycarbide TRISO fuel. The AGR-5/6/7 test train has five capsules with thermocouples and independent gas control mixtures. Unique to this paper is a sensitivity study concerning the cylindricity of the graphite holders containing the fuel compacts and their eccentricity in relation to the stainless-steel capsule walls. Each capsule has small nubs on the outside used for centering the graphite holder inside the stainless-steel capsule with a small gas gap used to control temperature. Due to machining tolerances of these nubs, and vibration wearing the nubs down when the experiment is running in the reactor, the possibility exists that the holder may move around radially. Each capsule is equipped with several thermocouples placed at various radii and depths within each graphite holder. This paper will show the sensitivity of offsetting the graphite holder for various radii in 45-degree increments around the circle with the objective of minimizing the difference between the measured thermocouples and the modeled thermocouple temperatures. Separate gas mixtures of helium/neon are introduced into this gas gap between the holder and capsule wall and changed as necessary to maintain the desired thermocouple temperatures to keep the fuel compacts at a constant temperature as the nuclear reactor conditions change. The goal of the sensitivity study is to find a radius and an angle to offset the holder from perfectly centered for each of the five capsules separately. The complex thermal model includes fission heating, gamma heating, radiation heat transfer, and heat transfer via conduction and radiation across the control gaps. Subroutines linked to the thermal model offer an easy method to offset the graphite holder from the capsule walls without remeshing the entire model.

Study on the Effect of Structure Parameters on NO Oxidation in DBD Reactor under Oxygen-Enriched Condition

To improve NO oxidation and energy efficiency, the effect of dielectric barrier discharge reactor structure on NO oxidation was studied experimentally in simulated diesel exhaust at atmospheric pressure. The mixture of 15% O2/N2 (balance)/860 ppm NOX (92% NO + 8% NO2) was used as simulated diesel exhaust. The results show that DBD reactor with 100-mm electrode length has the highest oxidation degree of NOX and energy efficiency. NO oxidation efficiency is promoted and the generation of NO is inhibited significantly by increasing the inner electrode diameter. Increasing the inner electrode diameter not only improve the E/N, but also makes the distribution of E/N more concentrated in the gas gap. The secondary electron emission coefficient (γ) of electrode material is closely related to electron energy and cannot be considered as a constant, which causes the different performance of electrode material for NO oxidation under different gas gap conditions. Compared with the rod electrode, the screw electrode has a higher electric field strength near the top of the screw, which promotes the generation of N radicals and inhibits the generation of O radicals. Rod electrode has a higher NO oxidation and energy efficiency than screw electrode under oxygen-enriched condition.

Metal Hydride Compressors with Gas-Gap Heat Switches: Concept, Development, Testing, and Space Flight Operation for the Planck Sorption Cryocoolers

Two closed-cycle cryogenic refrigerators were used to generate temperatures of ~18 K via evaporation of liquid hydrogen at the interfaces with radiofrequency and infrared sensors on an Earth-orbiting spacecraft that measured the anisotropy of the cosmic microwave background (CMB) during the European Space Agency (ESA) Planck Mission from June 2009 until October 2013. The liquid hydrogen phase was continuously generated in each Planck Sorption Cryocooler (PSC) by coupling a Joule–Thomson (J–T) expander to hydrogen gas initially pressurized to nominally 3000 kPa (i.e., ~30 bar) and subsequently discharged at pressure of 30 kPa (i.e., ~0.3 bar) by desorption and absorption using LaNi4.78Sn0.22Hx contained in six individual sorbent beds. The pressures were varied by alternately heating and cooling this hydride that included temperature modulation with an integrated Gas-Gap Heat Switch (GGHS). The novel GGHS used the low-pressure hydride ZrNiHx to vary thermal conductance between the bed containing the LaNi4.78Sn0.22Hx sorbent and the rest of the compressor system. The design features and development of these hydride components are described along with details of fabrication and assembly. The results obtained during extended laboratory testing are also summarized. The predictions from this preflight testing are compared to the performance observed while operating in orbit during the Planck Mission. This review ends with a summary of lessons learned and recommendations for improved systems.