Determination of diaphragm opening-times and use of diaphragm particle traps in a hypersonic shock tube
Determination of diaphragm opening-times and use of diaphragm particle traps in hypersonic shock tube
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Molecular line emission models of Herbig-Haro objects. II - HCO(+) emission
We present time-dependent models of the chemistry and temperature of interstellar molecular gas clumps that are exposed to the radiation from propagating stellar-jet shocks. The X-ray, EUV, and FUV radiation from the shock initiates ion chemistry and also heats the gas in the clumps. Using representative parameters, we show that, on the shock transit time between the clumps, the abundances of the ionized molecular species that are produced in the clumps can exceed the values determined from steady state models by several orders of magnitude. Collisional excitation by the heated gas can lead to measurable line emission from several ionized species; as in previous investigations of X-ray-irradiated molecular gas, we find that electron impacts contribute significantly to this process. We apply these results to the interpretation of the HCO(+) line emission that has already been detected in several Herbig-Haro objects. We demonstrate that this picture provides a natural explanation of the fact that the line intensity typically peaks ahead of the associated shock, as well as of the reported low line-center velocities and narrow line widths. We tabulate several diagnostic line intensities of HCO(+) and other molecular species that may be used to infer the physical conditions in the emitting gas.
Wolfire, Mark G.↗
Numerical simulations of time-dependent cosmic ray mediated shocks
Recent research in unsteady shocks that are influenced by nonlinear aspects of diffusive particle acceleration and that involve multidimensional flows is outlined, and some of the difficulties in making further progress are discussed. It is suggested that in many situations it is probably not appropriate to assume steady states for astrophysical CR shocks. This results both from the need to be concerned about the finite rate at which CR pressure builds and modifies a shock and from the existence of instabilities. Even so, it seems likely that CR-modified shocks can develop to a state with substantial CR pressure. The overall acceleration efficiency and the CR particle momentum distribution produced in time-dependent flows typically depend on several details such as the ratio of various time scales and the initial proportion of relativistic to nonrelativistic particles in the CR populations.
Jones, T. W.↗
Pitch angle distributions of energetic protons near the earth's bow shock
Measurements of energetic protons between about 28 and about 145 keV on ISEE-1 upstream and downstream of the earth's bow shock during times of a radial interplanetary magnetic field are presented. The protons exhibited a slight antisunward flow in the spacecraft system in front of the bow shock and a strong flow along the magnetic field in the spacecraft system in the magnetosheath. Compton-Getting transformations of these anisotropies into the plasma frame of reference have been performed. It is argued that the observations can be explained best in terms of particle acceleration by multiple reflection between the bow shock and upstream scattering centers.
Scholer, M.↗
Numerical computation of three-dimensional blunt body flow fields with an impinging shock
A time-marching finite-difference method was used to solve the compressible Navier-Stokes equations for the three-dimensional wing-leading-edge shock impingement problem. The bow shock was treated as a discontinuity across which the exact shock jump conditions were applied. All interior shock layer detail such as shear layers, shock waves, jets, and the wall boundary layer were automatically captured in the solution. The impinging shock was introduced by discontinuously changing the freestream conditions across the intersection line at the bow shock. A special storage-saving procedure for sweeping through the finite-difference mesh was developed which reduces the required amount of computer storage by at least a factor of two without sacrificing the execution time. Numerical results are presented for infinite cylinder blunt body cases as well as the three-dimensional shock impingement case. The numerical results are compared with existing experimental and theoretical results.
Holst, T. L.↗
Central difference TVD and TVB schemes for time dependent and steady state problems
We use central differences to solve the time dependent Euler equations. The schemes are all advanced using a Runge-Kutta formula in time. Near shocks, a second difference is added as an artificial viscosity. This reduces the scheme to a first order upwind scheme at shocks. The switch that is used guarantees that the scheme is locally total variation diminishing (TVD). For steady state problems it is usually advantageous to relax this condition. Then small oscillations do not activate the switches and the convergence to a steady state is improved. To sharpen the shocks, different coefficients are needed for different equations and so a matrix valued dissipation is introduced and compared with the scalar viscosity. The connection between this artificial viscosity and flux limiters is shown. Any flux limiter can be used as the basis of a shock detector for an artificial viscosity. We compare the use of the van Leer, van Albada, mimmod, superbee, and the 'average' flux limiters for this central difference scheme. For time dependent problems, we need to use a small enough time step so that the CFL was less than one even though the scheme was linearly stable for larger time steps. Using a total variation bounded (TVB) Runge-Kutta scheme yields minor improvements in the accuracy.
Jorgenson, P.↗
Central difference TVD and TVB schemes for time dependent and steady state problems
We use central differences to solve the time dependent Euler equations. The schemes are all advanced using a Runge-Kutta formula in time. Near shocks, a second difference is added as an artificial viscosity. This reduces the scheme to a first order upwind scheme at shocks. The switch that is used guarantees that the scheme is locally total variation diminishing (TVD). For steady state problems it is usually advantageous to relax this condition. Then small oscillations do not activate the switches and the convergence to a steady state is improved. To sharpen the shocks, different coefficients are needed for different equations and so a matrix valued dissipation is introduced and compared with the scalar viscosity. The connection between this artificial viscosity and flux limiters is shown. Any flux limiter can be used as the basis of a shock detector for an artificial viscosity. We compare the use of the van Leer, van Albada, mimmod, superbee, and the 'average' flux limiters for this central difference scheme. For time dependent problems, we need to use a small enough time step so that the CFL was less than one even though the scheme was linearly stable for larger time steps. Using a total variation bounded (TVB) Runge-Kutta scheme yields minor improvements in the accuracy.
Jorgenson, P.↗
The time development of a blast wave with shock heated electrons
Accurate approximations are presented for the time development of both edge conditions and internal structures of a blast wave with shock heated electrons, and equal ion and electron temperatures at the shock. The cases considered evolve in cavities with power law ambient densities (including the uniform ambient density case) and have negligible external pressure. Account is taken of possible saturation of the thermal conduction flux. The structures evolve smoothly to the adiabatic structures.
Edgar, R. J.↗
Ar-40/Ar-39 age of the Shergotty achondrite and implications for its post-shock thermal history
Ar-40/Ar-39 measurements are used to determine the age of the Shergotty achondrite and the chronology of the shock event responsible for the complete conversion of its plagioclase to maskelynite is discussed. Apparent ages are found to vary between 240 and 640 million years for the whole rock sample, with a plateau age of 254 million years for a maskelynite separate. The Rb-Sr age of 165 million years determined by Nyquist at al (1978) suggests that the maskelynite as well as the whole rock was incompletely degassed. Argon diffusion characteristics indicate a post-shock cooling time greater than 1000 years and a burial depth greater than 300 m for a thermal model of a cooling ejecta blanket of variable thickness. It is concluded that the shock event which degassed the argon and reset the Rb-Sr systematics occurred between 165 and 250 million years ago when the parent body experienced a collision in the asteroid belt.
Bogard, D. D.↗
Bosch Carbon Catalyst Regeneration in Water III: Experiments for and Related to Thermal Shock
Bosch technology has the potential to close the atmospheric revitalization loop by providing theoretically 100% regeneration of metabolic carbon dioxide into oxygen. The main obstacle to using Bosch technology is over-pressurization issues in the carbon formation reactor. Prior work on Bosch catalyst regeneration established that agitating carbon coated beads in water broke up pressure causing clogs and regenerated the catalyst surface. This process proved to be time consuming with experiments taking at least one hour to regenerate ten grams of carbon coated beads. In an attempt to shorten the processing time, thermally shocking the carbon coated beads prior to mechanical agitation was tested. Agitating the carbon coated beads after exposure to a saturated steam environment was also tested to ensure that the steam generated by thermally shocking the carbon coated beads would not cause adverse effects. The rationale behind thermally shocking the carbon coated beads is that the bead would pull away from the carbon shell due to a difference in the thermal expansion coefficients. The results of this project show that the processing time can be cut in half when compared to previous work, and that saturated steam has little to no effect on regeneration.
Bosch Process↗
Viscous and inertial effects at cosmic-ray shocks
To illustrate the effect of the viscous and inertial terms on the structure of cosmic-ray-modified shocks, an analysis of a time-independent 1D shock is presented in which the pressure of the background fluid and the magnetic-field energy density are negligible compared with the cosmic-ray pressure. The effect of the magnetic field on cosmic-ray transport coefficients is retained. The diffusion, viscous and inertial terms work to 'thicken' the shock. When the average magnetic field is negligible and the cosmic-ray transport is isotropic, diffusion is the dominant effect unless the parameters are such that the scattering time becomes comparable to the characteristic times for velocity change in the fluid frame. For a perpendicular shock, where the diffusion is strongly reduced by the magnetic field, the relative magnitude of the viscous effect is increased by a factor about (omega tau) exp 2, leading to the conclusion that cosmic-ray viscosity can be important to the structure of collisionless MHD shocks. In both cases considered, the viscous and inertial terms become important for those parameter ranges where the diffusion approximation begins to break down.
Jokipii, J. R.↗
Modeling of ion acceleration through drift and diffusion at interplanetary shocks
A test particle simulation designed to model ion acceleration through drift and diffusion at interplanetary shocks is described. The technique consists of integrating along exact particle orbits in a system where the angle between the shock normal and mean upstream magnetic field, the level of magnetic fluctuations, and the energy of injected particles can assume a range of values. The technique makes it possible to study time-dependent shock acceleration under conditions not amenable to analytical techniques. To illustrate the capability of the numerical model, proton acceleration was considered under conditions appropriate for interplanetary shocks at 1 AU, including large-amplitude transverse magnetic fluctuations derived from power spectra of both ambient and shock-associated MHD waves.
Decker, R. B.↗
The 2012 July 23 Backside Eruption: An Extreme Energetic Particle Event?
The backside coronal mass ejection (CME) of 2012 July 23 had a short Sun-to-Earth shock transit time (18.5 hr).The associated solar energetic particle (SEP) event had a greater than 10 MeV proton flux peaking at approximately 5000 pfu, and the energetic storm particle event was an order of magnitude larger, making it the most intense event in the space era at these energies. By a detailed analysis of the CME, shock, and SEP characteristics, we find that the July 23 event is consistent with a high-energy SEP event (accelerating particles to giga-electron volt energies). The times of maximum and fluence spectra in the range 10100 MeV were very hard, similar to those of ground-level enhancement (GLE) events. We found a hierarchical relationship between the CME initial speeds and the fluence spectral indices: CMEs with low initial speeds had SEP events with the softest spectra, while those with the highest initial speeds had SEP events with the hardest spectra. CMEs attaining intermediate speeds result in moderately hard spectra. The July 23 event was in the group of hard-spectrum events. During the July 23 event, the shock speed greater than (2000 km s(exp -1), the initial acceleration (approximately 1.70 km s(exp -2), and the shock-formation height (approximately 1.5 solar radii)were all typical of GLE events. The associated type II burst had emission components from meter to kilometer wavelengths, suggesting a strong shock. These observations confirm that the 2012 July 23 event is likely to be an extreme event in terms of the energetic particles it accelerated.
Gopalswamy, N.↗
Structural Dynamics and Data Analysis
This project consists of two parts, the first will be the post-flight analysis of data from a Delta IV launch vehicle, and the second will be a Finite Element Analysis of a CubeSat. Shock and vibration data was collected on WGS-5 (Wideband Global SATCOM- 5) which was launched on a Delta IV launch vehicle. Using CAM (CAlculation with Matrices) software, the data is to be plotted into Time History, Shock Response Spectrum, and SPL (Sound Pressure Level) curves. In this format the data is to be reviewed and compared to flight instrumentation data from previous flights of the same launch vehicle. This is done to ensure the current mission environments, such as shock, random vibration, and acoustics, are not out of family with existing flight experience. In family means the peaks on the SRS curve for WGS-5 are similar to the peaks from the previous flights and there are no major outliers. The curves from the data will then be compiled into a useful format so that is can be peer reviewed then presented before an engineering review board if required. Also, the reviewed data will be uploaded to the Engineering Review Board Information System (ERBIS) to archive. The second part of this project is conducting Finite Element Analysis of a CubeSat. In 2010, Merritt Island High School partnered with NASA to design, build and launch a CubeSat. The team is now called StangSat in honor of their mascot, the mustang. Over the past few years, the StangSat team has built a satellite and has now been manifested for flight on a SpaceX Falcon 9 launch in 2014. To prepare for the final launch, a test flight was conducted in Mojave, California. StangSat was launched on a Prospector 18D, a high altitude rocket made by Garvey Spacecraft Corporation, along with their sister satellite CP9 built by California Polytechnic University. However, StangSat was damaged during an off nominal landing and this project will give beneficial insights into what loads the CubeSat experienced during the crash. During the year, the MIHS students generated a SolidWorks (CAD software) geometry model of StangSat. This model will be imported into FEMAP (Finite Element Analysis (FEA) Software) and a finite element model wiiJ be created to predict the loads encountered during the crash of this rocket. This analysis will require learning how to import CAD models into the FEM, mesh and add constraints and concentrated masses to represent components inside the CubeSat frame, such as circuit boards, batteries and accelerometers. During the analysis the loads will be varied, in effort to duplicate the damage to the CubeSat. Results will then be peer reviewed and documented.
Luthman, Briana L.↗
A numerical study of the unsteady processes associated with the type IV shock interaction
A time-dependent ADI formulation of the two dimensional Navier-Stokes equations coupled with the total variation diminishing (TVD) scheme is used to examine the type IV shock interaction time accurately. The experimentally measured and computationally calculated unsteadiness of the type IV interaction is shown to be related to the formation and shedding of shear layers in the shock layer, and the frequency of oscillation of the jet is a strong function of the shedding rate of these shear layers. For one particular geometry, an oscillation frequency of 1.4 kHz was calculated. The effects of shock impingement angle and shock strength on the location and magnitude of the peak pressure are also identified. In one case it is shown that a 1-deg change in the impinging shock angle can alter the location of the associated jet by almost 11 deg with a change in the peak surface pressure of 32 percent.
Lind, Charles A.↗
Dependence of 50-keV upstream ion events at IMP 7 and 8 upon magnetic field bow shock geometry
Results are presented for a statistical study of four years (1972-1976) of IMP 7 and 8 observations at approximately 40 R(E) of 50-200 keV upstream ion events measured with the Energetic Particle Experiment. A monotonic increase in the probability of observing upstream particle events is found with a decrease in the angle (theta-Bn) between the interplanetary magnetic field (IMF) and the local shock normal at the point where the IMF intersects the bow shock, independent of the length of time of bow shock connections exceeding approximately 10 min. Approximately equal probabilities are found for observing an event above a given flux from any portion of the bow shock with the same value of theta-Bn, a growth time of the 50-200 keV events of approximately 10 min, a maximum attainable flux of approximately 25,000/sq cm s sr, and a positive correlation between the probability of exceeding a given flux and the 3 hr Kp index. It is concluded that the local structure of the bow shock in the immediate vicinity of the field line connection is the dominant influence in the generation process of energetic upstream particle events and that wave-particle interactions produce a self-throttling mechanism that limits the maximum flux of ions escaping the upstream foreshock.
Mitchell, D. G.↗
The 17 April 2021 Widespread Solar Energetic Particle Event
A complex and long-lasting solar eruption on 17 April 2021 produced a widespread solar energetic particle (SEP) event that was observed by five longitudinally well-separated observers in the inner heliosphere that covered distances to the Sun from 0.42 to 1 au: BepiColombo, Parker Solar Probe, Solar Orbiter, STEREO A, and near-Earth spacecraft. The event was the second widespread SEP event detected in solar cycle 25, and it produced relativistic electrons and protons. It was associated with a long-lasting solar hard X-ray flare that showed multiple hard X-ray peaks over a duration of one hour. The event was further accompanied by a medium-fast coronal mass ejection (CME) with a speed of 880 km s -1 that drove a shock, an extreme ultraviolet wave, and long-lasting and complex radio burst activity that showed four distinct type III burst groups over a period of 40 min. We aim to understand the reason for the wide spread of elevated SEP intensities in the inner heliosphere as well as identify the underlying source regions of the observed energetic electrons and protons. We applied a comprehensive multi-spacecraft analysis of remote-sensing observations and in situ measurements of the energetic particles and interplanetary context to attribute the SEP observations at the different locations to the various potential source regions at the Sun. We used an ENLIL simulation to characterize the complex interplanetary state and its role in the energetic particle transport. The magnetic connection between each spacecraft and the Sun was determined using ballistic backmapping in combination with potential field source surface extrapolations in the lower corona. Using also a reconstruction of the coronal shock front, we then determined the times when the shock establishes magnetic connections with the different observers. Radio observations were used to characterize the directivity of the four main injection episodes, which were then employed in a 2D SEP transport simulation to test the importance of these different injection episodes. A comprehensive timing analysis of the inferred solar injection times of the SEPs observed at each spacecraft suggests different source processes being important for the electron and proton events. Comparison among the characteristics and timing of the potential particle sources, such as the CME-driven shock or the flare, suggests a stronger shock contribution for the proton event and a more likely flare-related source for the electron event. In contrast to earlier studies on widespread SEP events, we find that in this event an important ingredient for the wide SEP spread was the wide longitudinal range of about 110 o covered by distinct SEP injections, which is also supported by our SEP transport modeling.
sun↗
Particle acceleration due to shocks in the interplanetary field: High time resolution data and simulation results
Data were examined from two experiments aboard the Explorer 50 (IMP 8) spacecraft. The Johns Hopkins University/Applied Lab Charged Particle Measurement Experiment (CPME) provides 10.12 second resolution ion and electron count rates as well as 5.5 minute or longer averages of the same, with data sampled in the ecliptic plane. The high time resolution of the data allows for an explicit, point by point, merging of the magnetic field and particle data and thus a close examination of the pre- and post-shock conditions and particle fluxes associated with large angle oblique shocks in the interplanetary field. A computer simulation has been developed wherein sample particle trajectories, taken from observed fluxes, are allowed to interact with a planar shock either forward or backward in time. One event, the 1974 Day 312 shock, is examined in detail.
Kessel, R. L.↗