Microstructural development in chemically vapor-deposited (CVD) high-purity beta-SiC during neutron and self-ion irradiation at elevated temperatures was studied. The CVD SiC samples were examined by ...transmission electron microscopy following neutron irradiation to 4.5–7.7
×
10
25 n/m
2 (
E
>
0.1
MeV) at 300 and 800
°C and 5.1
MeV Si
2+ ion irradiation up to ∼200
dpa at 600–1400
°C. The evolution of various irradiation-produced defects including black spot defects, dislocation loops, network dislocations, and cavities was characterized as a function of irradiation temperature and fluence. It was demonstrated that the black spot defects and small dislocation loops continue to dominate at relatively low temperatures (<∼800
°C), whereas they grow into Frank faulted loops and finally develop into dislocation networks at a higher temperature (1400
°C). Substantial cavity formation on grain boundaries and stacking faults was confirmed after ion irradiation at 1400
°C. These observations were discussed in relation with the known irradiation phenomena in SiC, such as low temperature swelling and cavity swelling.
•Impact of control blade position on the deformation behavior of SiC-SiC channel box was analyzed.•Large gradients in fast neutron flux up to 35–40% will develop across the channel box.•The bending ...behavior of the channel box depends strongly on the control blade position.•The stress development in the channel box for the three positions of control blade was analyzed.
This article describes the analysis of distortion of a silicon carbide fiber-reinforced, silicon carbide matrix (SiC-SiC) composite channel box under in-reactor conditions of a boiling water reactor (BWR). The BWR core has significant gradients in the fast neutron flux across the channel box due to the presence of water rods within the fuel assemblies, and these gradients increase further with the insertion of control blades. As a result of the temperature and neutron flux dependent irradiation-induced swelling of SiC, the SiC-SiC composite channel box can undergo distortion. In this work, we evaluate the SiC-SiC channel box distortion for three different control blade positions. This analysis is based on the neutron flux and temperature distributions in the BWR core calculated using the neutronics code MPACT and thermal-hydraulics code CTF. This calculation is coupled through temperature feedback. Subsequently, we have performed structural analysis based on the calculated neutron flux and temperature distributions to determine the deformation and stress development in the channel box. The structural analysis was performed using the fuel performance modeling code BISON and the commercial finite element analysis software Abaqus. The results indicate that large gradients in fast neutron flux (up to 35–40% across a single axial level) will develop across the channel box. Due to these gradients, the channel box will undergo time-dependent bending for all the control blade positions in the assembly. The time-dependent bowing behavior is dominated by the transient swelling of SiC-SiC material under non-uniform neutron flux, and changes with variation in the control blade position. The bending will cause temporary interference between the channel box and control blade, and the interference is expected to be most severe for the fully inserted control blade position. The developed stresses due to differential swelling in the channel box exceed the proportional limit stress of the material, which may cause matrix microcracking in the channel box. However, the stresses remain below the tensile strength of the material, and therefore, development of a full, through-thickness crack in the channel box is not expected. Further work is recommended to explore and evaluate the mitigation strategies.
Accelerated ion irradiation, especially ‘dual-beam’ irradiation, is a useful technique for experimental exploration of irradiation effects and validation of irradiation effect models, because of the ...unique controllability in irradiation conditions including the helium production rate. In this work, the effects of irradiation and helium implantation on microstructural evolution, hardness and plastic deformation behavior in Fe–15Cr–20Ni model austenitic ternary alloy and Fe–8
∼
9Cr–2W reduced-activation martensitic steels were studied through combined applications of ion irradiation, nano-indentation, focused ion-beam microprocessing and transmission electron microscopy. Systematic data on irradiation hardening are presented for broad irradiation conditions. Influences of helium implantation on irradiation-induced microstructural and nano-indentation hardness changes were not detected in the Fe–8
∼
9Cr–2W steels, while they were significant in the Fe–15Cr–20Ni alloy. The interaction behavior of dislocation loops with moving dislocations and the strength of the loops as obstacles to dislocation motion are also discussed for these two material classes based on the hardness, and the irradiated and indented microstructures.
Saturn chorus intensity variations Menietti, J. D.; Schippers, P.; Katoh, Y. ...
Journal of geophysical research. Space physics,
September 2013, Letnik:
118, Številka:
9
Journal Article
Recenzirano
Odprti dostop
Whistler mode chorus plasma wave emissions have been observed at Saturn near the magnetic equator and the source region. During crossings of the magnetic equator along nearly constant L shells, the ...Cassini Radio and Plasma Wave Science Investigation often observes a local decrease in whistler mode intensity and bandwidth closest to the magnetic equator, where linear growth appears to dominate, with nonlinear structures appearing at higher latitudes and higher frequencies. We investigate linear growth rate using the Waves in a Homogeneous, Anisotropic, Multi‐component Plasma dispersion solver and locally observed electron phase space density measurements from the Electron Spectrometer sensor of the Cassini Plasma Spectrometer Investigation to determine the parameters responsible for the variation in chorus intensity and bandwidth. We find that a temperature anisotropy (T⊥/T∥ ~ 1.3) can account for linear spatiotemporal growth rate of whistler mode waves, which provides a majority of the observed frequency‐integrated power. At the highest frequencies, intense, nonlinear, frequency‐drifting structures (drift rates ~ 200 Hz/s) are observed a few degrees away from the equator and can account for a significant fraction of the total power. Chorus emission at higher frequencies is distinct from lower frequency whistler mode emission and is sometimes correlated with simultaneously observed low‐frequency electromagnetic ion cyclotron waves. These electromagnetic ion cyclotron waves appear to modulate a slow frequency drift (~15 Hz/s) which develops into nonlinear growth with much larger frequency drift associated only with the higher‐frequency chorus.
Key Points
Tprp/Tpar ~ 1.3 can account for spatiotemporal growth of waves
Nonlinear chorus intensity may be correlated with EMIC wave period
Electron distribution shows pitch angle dependence at low energy
In the upcoming JAXA/ERG satellite mission, Wave Particle Interaction Analyzer (WPIA) will be installed as an onboard software function. We study the statistical significance of the WPIA for ...measurement of the energy transfer process between energetic electrons and whistler-mode chorus emissions in the Earth's inner magnetosphere. The WPIA measures a relative phase angle between the wave vector E and velocity vector v of each electron and computes their inner product W, where W is the time variation of the kinetic energy of energetic electrons interacting with plasma waves. We evaluate the feasibility by applying the WPIA analysis to the simulation results of whistler-mode chorus generation. We compute W using both a wave electric field vector observed at a fixed point in the simulation system and a velocity vector of each energetic electron passing through this point. By summing up W sub(i) of an individual particle i to give W sub(int), we obtain significant values of W sub(int) as expected from the evolution of chorus emissions in the simulation result. We can discuss the efficiency of the energy exchange through wave-particle interactions by selecting the range of the kinetic energy and pitch angle of the electrons used in the computation of W sub(int). The statistical significance of the obtained W sub(int) is evaluated by calculating the standard deviation sigma sub(W) of W sub(int). In the results of the analysis, positive or negative W sub(int) is obtained at the different regions of velocity phase space, while at the specific regions the obtained W sub(int) values are significantly greater than sigma sub(W), indicating efficient wave-particle interactions. The present study demonstrates the feasibility of using the WPIA, which will be on board the upcoming ERG satellite, for direct measurement of wave-particle interactions.
The Io tail aurora extends for approximately 100 degrees downstream in longitude from the Io footprint aurora. Observations indicate that the brightness of the Io tail aurora continuously decreases ...along the footpath while its peak altitude remains constant. According to the quasi‐steady theoretical frame, this suggests that the field‐aligned voltage is constant while the parallel current density decreases in the downstream direction. The mechanism that realizes the current‐voltage relationship of the Io tail aurora remains unresolved. In this paper, we apply a new multimagnetofluid code to the Io‐Jupiter system to clarify the origin of the current‐voltage relationship. The code solves a set of equations that includes the electron convection term in Ohm's law, which enables us to simulate the current‐driven ion acoustic instability in the fluid frame. The instability forms a transition layer at a high altitude, which accelerates the magnetospheric electrons and blocks the magnetospheric ions, leading to the formation of a density depleted region called an auroral cavity. We find that if the ionospheric proton density decreases at the same rate as the parallel current density, the timescale on which the transition layer disappears is consistent with the longitudinal extent of the tail aurora, and the potential gap is constant all along the tail. We discuss the possibility that the fringe, wideband repetitive bursts of the Io‐related Jovian decametric radiation, is excited in the auroral cavity.
Key Points
We simulated the ion acoustic instability in the fluid frame
We reproduced the constant voltage with decreasing parallel current density
We suggest that the Io‐DAM fringes are excited in the auroral cavity
The fine structure of nonlinear drifting‐frequency chorus is observed at Saturn by the Cassini Radio and Plasma Wave Investigation. During a high‐inclination orbit in which Cassini is at ...near‐constant L‐shell within about 10° of the magnetic equator, moderately intense nonlinear chorus is observed. Cassini observed a region of intense chorus and large bandwidth a few degrees on either side of the magnetic equator, with lower intensities and bandwidths observed nearest the magnetic equator. Using the observed plasma wave spectra and electron phase space distribution, we have measured plasma parameters within or near the chorus generation region and evaluated the theoretical value of the frequency sweep rate, ∂f/∂t, based on the nonlinear wave growth theory of Omura et al. and the backward wave oscillator theory of Trakhtengerts. Both theories produce rates that are within a factor of 2 of the observed values, but the nonlinear wave growth theory values are closer to the observations for the cases examined. The work presented is consistent with nonlinear theory in the generation of chorus, but also reveals a distinct region of weaker or linear chorus growth nearest to the magnetic equator at Saturn.
Key PointsChorus wave growth appears linear nearest the magnetic equator.Nonlinear chorus with frequency drift occurs away from the magnetic equator.Frequency drift rates are consistent with nonlinear theory.
We investigate the type IV burst event observed byAMATERAS on 2011 June 7, and reveal that themain component of the burstwas emitted from the plasmoid eruption identified in the EUVimages of the ...Solar Dynamics Observatory (SDO)/AIA. We show that a slowly drifting narrowband structure (SDNS) appeared in the burst's spectra. Using statistical analysis, we reveal that the SDNS appeared for a duration of tens to hundreds of milliseconds and had a typical bandwidth of 3MHz. To explain the mechanism generating the SDNS, we propose wave-wave coupling between Langmuir waves and whistler-mode chorus emissions generated in a post-flare loop, which were inferred from the similarities in the plasma environments of a post-flare loop and the equatorial region of Earth's inner magnetosphere. We assume that a chorus element with a rising tone is generated at the top of a post-flare loop. Using the magnetic field and plasma density models, we quantitatively estimate the expected duration of radio emissions generated from coupling between Langmuir waves and chorus emissions during their propagation in the post-flare loop, and we find that the observed duration and bandwidth properties of the SDNS are consistently explained by the proposed generation mechanism. While observations in the terrestrial magnetosphere show that the chorus emissions are a group of large-amplitude wave elements generated naturally and intermittently, the mechanism proposed in the present study can explain both the intermittency and the frequency drift in the observed spectra.
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