Jet outflow of metallic plasma into a vacuum
Jet outflow of metallic plasma into vacuum and applicability of metallic plasma jets in heat transfer studies of plasma flow to solid wall and aerodynamic studies of plasma flows
Chekalin, E. K.↗
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The Structure of the Electron Outflow Jet in Collisionless Magnetic Reconnection
Particle-in-cell simulations and analytic theory are applied to the study of the electron outflow jet in collisionless magnetic reconnection. In these jets, which have also been identified in spacecraft observations, electron flow speeds in thin layers exceed the ExB drift, suggesting that electrons are unmagnetized. In this study, we find the surprising result that the electron flow jets can be explained by a combination of EjcB drifts and of diamagnetic effects, through the combination of the gradients of particle pressure and of the magnetic field. In a suitably rotated coordinate system, the electron motion is readily decomposed into ExB drift and the motion to support the required current density, consistent with electron gyrotropy. This process appears to be nondissipative.
Hesse, Michael↗
Outflows, Jets and Shocks in the Orion Nebula
The rich young cluster of stars associated with the Orion Nebula provides a unique laboratory for the study of plasma phenomena. We see five types of flows and shocks. Photoablation outflow from the proplyds nearest theta (exp 1) Ori C form nearly stationary shocks with the high velocity wind from that star. Microjets, with scales of less than 10 (exp 4) AU, are seen around some 20 low mass stars. Isolated jets, with high velocities and scales of about, 104 AU, are less numerous but common. One also sees the shocks formed when these jets impinge on the ionized nebular gas and the neutral gas in the foreground lid. The final type of object is the stationary shock formed by the interaction from the stellar wind that arises during disk formation with the ambient, gas flowing away from the main body of the nebula.
ODell, C. R.↗
The Formation of Electron Outflow Jets with Power-law Energy Distribution in Guide-field Magnetic Reconnection
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H. Che↗
Secondary jet interaction with emphasis on outflow and jet location.
Data were obtained concerning a model which utilized a two-dimensional sonic jet. It was found that outflow and jet location significantly influence the magnitude and behavior of the secondary jet interaction forces. Continued refinements in jet interaction analyses which do not account for outflow are of limited usefulness in the design of control systems for supersonic and hypersonic vehicles. The jet total back pressure ratio increases with either jet pressure ratio or freestream Mach number.
Hefner, J. N.↗
A Three Parsec-Scale Jet-Driven Outflow from Sgr A
The compact radio source Sgr A* is coincident with a 4x 10(exp 6) solar Mass black hole at the dynamical center of the Galaxy and is surrounded by dense orbiting ionized and molecular gas. We present high resolution radio continuum images of the central 3' and report a faint continuous linear structure centered on Sgr A*. This feature is rotated by 28 deg in PA with respect to the Galactic plane. A number of weak blobs of radio emission with X-ray counterparts are detected along the axis of the linear structure. In addition, the continuous linear feature appears to be terminated symmetrically by two linearly polarized structures at 8.4 GHz, approx 75" from Sgr A*. The linear structure is best characterized by a mildly relativistic jet-driven outflow from Sgr A*, and an outflow rate 10(exp 6) solar M / yr. The near and far-sides of the jet are interacting with orbiting ionized and molecular gas over the last 1-3 hundred years and are responsible for the origin of a 2" hole, the "minicavity", where disturbed kinematics, enhanced FeII/III line emission, and diffuse X-ray gas have been detected. The estimated kinetic luminosity of the outflow is approx 1.2 X 10(exp 41) erg/s which can produce the Galactic center X-ray flash that has recently been identified
Yusef-Zadeh, F.↗
Jets, mass outflows and disks associated with young stellar objects
Over the past 3 years, a series was obtained of the CCD images of regions surrounding young stellar objects (YSO's) located in a variety of environments with the goal of providing a census of the properties of mass outflows associated these objects. A catalog describing the optical morphology and kinematics of 38 mass outflows associated with young stellar objects (YSOs) was completed. The direct detection was reported of disks surrounding HL Tau and LI551/IRS 5 -- both sources of optical jets and large-scale mass outflows. In each case, the disk dimensions are on the order of several hundred astronomical units and the disk dust masses approximately 10 to the -7th power solar masses. A program aimed at indirect detection of circumstellar disks associated with YSOs was started. The technique involves comparison of an observed bolometric luminosity (L(bol)) with an independent measure of the true luminosity (L(spec)) of a YSO which derives from the observed strengths of surface-gravity-sensitive spectral features.
Strom, S. E.↗
A numerical study of the outflow layer of tropical cyclones
Numerical simulations of idealized tropical cyclones with special emphasis on the outflow layer are presented. The quasi-steady state outflow layers of weak and strong cyclones are found to exhibit similar characteristics. The circulations are anticyclonic and asymmetric about the center; the outflow layer is dominated by a narrow, elongated outflow-jet contributing up to 50 percent of the angular momentum transport; the air particles in the outflow jet mostly originate from the lower level. Secondary circulations are found to influence the relative humidity and the potential vorticity at the outflow levels. In order to study the effect of upper tropospheric forcings, two variational numerical experiments using cumulus convection as the major link between the upper-level forcing and the tropical cyclone's response are conducted.
Shi, Jainn-Jong↗
Particle-in-Cell Simulation of Collisionless Driven Reconnection with Open Boundaries
First results are discussed from an ongoing study of driven collisionless reconnection using a 2 1/2-dimensional electromagnetic particle-in-cell simulation model with open inflow and outflow boundaries. An extended electron diffusion region (EEDR) is defined as that region surrounding a reconnecting neutral line in which the out-of-plane nonideal electric field is positive. It is shown that the boundaries of this region in the directions of the outflow jets are at the positions where the electrons make the transition from unfrozen meandering motion in the current sheet to outward drifting with the magnetic field in the outflow jets; a turning length scale is defined to mark these positions, The initial width of the EEDR in the inflow directions is comparable to the electron bounce width. Later. as shoulders develop to form a two-scale structure. thc EEDR width expands to the ion bounce width scale. The inner portion of the EEDR or the electron diffusion region proper remains at the electron bounce width. Two methods are introduced for predicting the reconnection electric field using the dimensions of the EEDR. These results are interpreted as further evidence that the EEDR is the region that is relevant to understanding the electron role in the neutral line vicinity.
Kimas, Alex↗
The IRS 1 circumstellar disk, and the origin of the jet and CO outflow in B5
We report the discovery of the inner edge of the high velocity CO outflow associated with the bipolar jet originating from IRS 1 in Barnard 5 and the first ever resolution of its circumstellar disk in the 2.6 mm dust continuum and C18O. From high spatial resolution observations made with the Owens Valley Millimeter Array we are able to locate the origin of the outflow to within approximately 500 AU on either side of IRS 1 and apparently at the edge of, or possibly within, its circumstellar disk. The orientation of the continuum disk is perpendicular to the highly collimated jet outflow recently seen in optical emission at much farther distances. The disk has been detected in C18O giving a disk mass approximately 0.16 M (solar). Our HCO+ and HCN maps indicate significant chemical differentiation in the circumstellar region on small scales with HCO+ tracing an extended disk of material. The 12CO interferometer maps of the outflow show two conelike features originating at IRS 1, the blue one fanning open to the northeast and the red one to the southwest. The vertices of the cones are on either side of the circumstellar disk and have a projected opening angle of about 90 degrees. The intrinsic opening angle is in the range of 60 degrees-90 degrees which leads to significant interaction between outflow and infall.
NASA Center JPL↗
Magnetically driven jets and winds: Exact solutions
We present a general class of self-similar solutions of the full set of MHD equations that include matter flow, electromagnetic fields, pressure, and gravity. The solutions represent axisymmetric, time-independent, nonrelativistic, ideal, magnetohydrodynamic, collimated outflows (jet and winds) from magnetized accretion disks around compact objects. The magnetic field extracts angular momentum from the disk, accelerates the outflows perpedicular to the disk, and provides collimation at large distances. The terminal outflow velocities are of the order of or greater than the rotational velocity of the disk at the base of the flow. When a nonzero electric current flows along the jet, the outflow radius oscillates with axial distance, whereas when the total electric current is zero (with the return current flowing across the jet's cross section), the outflow radius increase to a maximum and then decreases. The method can also be applied to relativistic outflows.
Contopoulos, J.↗
Nimbus-7 total ozone observations of western North Pacific tropical cyclones
The Nimbus-7 Total Ozone Mapping Spectrometer (TOMS) was used to map the distribution of total ozone around western North Pacific tropical cyclones from 1979 to 1982. The strong correlation between total ozone distribution and tropopause height found in the subtropical and midlatitudes made it possible for TOMS to monitor the propagation of upper-tropospheric waves and the mutual adjustment between these waves and tropical cyclones during their interaction. Changes in these total ozone patterns reflect the 3D upper-tropospheric transport processes that are involved in tropical cyclone intensity and intensity and motion changes. The total ozone distributions indicate that: (1) the mean upper-tropospheric circulations associated with western North Pacific and Atlantic tropical cyclones are similar; (2) more intense tropical cyclones have higher tropopauses around their centers; (3) more intense tropical cyclones have higher tropopauses on the anticyclonic-shear side of their outflow jets, which indicate that the more intense tropical cyclones have stronger outflow channels than less intense systems; (4) tropical cyclones that intensify (do not intensify) are within 10 deg (15 deg) latitude of weak (strong) upper-tropospheric troughs that are moderately rich (very rich) in total ozone; and (5) tropical cyclones turn to the left (right) when they move within approximately 15 deg latitude downstream of an ozone-poor (ozone-rich) upper-tropospheric ridge (trough).
Stout, John↗
Experimental Measurement of RCS Jet Interaction Effects on a Capsule Entry Vehicle
An investigation was made in NASA Langley Research Center s 31-Inch Mach 10 Tunnel to determine the effects of reaction-control system (RCS) jet interactions on the aft-body of a capsule entry vehicle. The test focused on demonstrating and improving advanced measurement techniques that would aid in the rapid measurement and visualization of jet interaction effects for the Orion Crew Exploration Vehicle while providing data useful for developing engineering models or validation of computational tools used to assess actual flight environments. Measurements included global surface imaging with pressure and temperature sensitive paints and three-dimensional flow visualization with a scanning planar laser induced fluorescence technique. The wind tunnel model was fabricated with interchangeable parts for two different aft-body configurations. The first, an Apollo-like configuration, was used to focus primarily on the forward facing roll and yaw jet interactions which are known to have significant aft-body heating augmentation. The second, an early Orion Crew Module configuration (4-cluster jets), was tested blowing only out of the most windward yaw jet, which was expected to have the maximum heating augmentation for that configuration. Jet chamber pressures and tunnel flow conditions were chosen to approximate early Apollo wind tunnel test conditions. Maximum heating augmentation values measured for the Apollo-like configuration (>10 for forward facing roll jet and 4 for yaw jet) using temperature sensitive paint were shown to be similar to earlier experimental results (Jones and Hunt, 1965) using a phase change paint technique, but were acquired with much higher surface resolution. Heating results for the windward yaw jet on the Orion configuration had similar augmentation levels, but affected much less surface area. Numerical modeling for the Apollo-like yaw jet configuration with laminar flow and uniform jet outflow conditions showed similar heating patterns, qualitatively, but also showed significant variation with jet exit divergence angle, with as much as 25 percent variation in heat flux intensity for a 10 degree divergence angle versus parallel outflow. These results along with the fabrication methods and advanced measurement techniques developed will be used in the next phase of testing and evaluation for the updated Orion RCS configuration.
Buck, Gregory M.↗
Electron Jet of Asymmetric Reconnection
We present Magnetospheric Multiscale observations of an electron-scale current sheet and electron outflow jet for asymmetric reconnection with guide field at the subsolar magnetopause. The electron jet observed within the reconnection region has an electron Mach number of 0.35 and is associated with electron agyrotropy. The jet is unstable to an electrostatic instability which generates intense waves with E(sub parallel lines) amplitudes reaching up to 300 mV/m and potentials up to 20% of the electron thermal energy. We see evidence of interaction between the waves and the electron beam, leading to quick thermalization of the beam and stabilization of the instability. The wave phase speed is comparable to the ion thermal speed, suggesting that the instability is of Buneman type, and therefore introduces electron-ion drag and leads to braking of the electron flow. Our observations demonstrate that electrostatic turbulence plays an important role in the electron-scale physics of asymmetric reconnection.
Khotyaintsev, Yu. V.↗
Significant and Variable Linear Polarization During the Prompt Optical Flash of GRB 160625B
Measurement of polarized light provides a direct probe of magnetic fields in collimated outflows (jets) of relativistic plasma from accreting stellar-mass black holes at cosmological distances. These outflows power brief and intense flashes of prompt gamma-rays known as Gamma Ray Bursts (GRBs), followed by longer-lived afterglow radiation detected across the electromagnetic spectrum. Rapid-response polarimetric observations of newly discovered GRBs have probed the initial afterglow phase. Linear polarization degrees as high as Π∼30% are detected minutes after the end of the prompt GRB emission, consistent with a stable, globally ordered magnetic field permeating the jet at large distances from the central source. In contrast, optical and gamma-ray observations during the prompt phase led to discordant and often controversial results, and no definitive conclusions on the origin of the prompt radiation or the configuration of the magnetic field could be derived. Here we report the detection of linear polarization of a prompt optical flash that accompanied the extremely energetic and long-lived prompt gamma-ray emission from GRB 160625B. Our measurements probe the structure of the magnetic field at an early stage of the GRB jet, closer to the central source, and show that the prompt GRB phase is produced via fast cooling synchrotron radiation in a large-scale magnetic field advected from the central black hole and distorted from dissipation processes within the jet.
High-energy astrophysics↗
Significant and Variable Linear Polarization During the Prompt Optical Flash of GRB 160625B
Measurement of polarized light provides a direct probe of magnetic fields in collimated outflows (jets) of relativistic plasma from accreting stellar-mass black holes at cosmological distances. These outflows power brief and intense flashes of prompt gamma-rays known as Gamma Ray Bursts (GRBs), followed by longer-lived afterglow radiation detected across the electromagnetic spectrum. Rapid-response polarimetric observations of newly discovered GRBs have probed the initial afterglow phase. Linear polarization degrees as high as Π∼30% are detected minutes after the end of the prompt GRB emission, consistent with a stable, globally ordered magnetic field permeating the jet at large distances from the central source. In contrast, optical and gamma-ray observations during the prompt phase led to discordant and often controversial results, and no definitive conclusions on the origin of the prompt radiation or the configuration of the magnetic field could be derived. Here we report the detection of linear polarization of a prompt optical flash that accompanied the extremely energetic and long-lived prompt gamma-ray emission from GRB 160625B. Our measurements probe the structure of the magnetic field at an early stage of the GRB jet, closer to the central source, and show that the prompt GRB phase is produced via fast cooling synchrotron radiation in a large-scale magnetic field advected from the central black hole and distorted from dissipation processes within the jet.
High-energy astrophysics↗
Simulations of Solar Jets Confined by Coronal Loops
Coronal jets are collimated, dynamic events that occur over a broad range of spatial scales in the solar corona. In the open magnetic field of coronal holes, jets form quasi-radial spires that can extend far out into the heliosphere, while in closed-field regions the jet outflows are confined to the corona. We explore the application of the embedded-bipole model to jets occurring in closed coronal loops. In this model, magnetic free energy is injected slowly by footpoint motions that introduce twist within the closed dome of the jet source region, and is released rapidly by the onset of an ideal kink-like instability. Two length scales characterize the system: the width (N) of the jet source region and the footpoint separation (L) of the coronal loop that envelops the jet source. We find that both the conditions for initiation and the subsequent dynamics are highly sensitive to the ratio L/N. The longest-lasting and most energetic jets occur along long coronal loops with large L/N ratios, and share many of the features of open-field jets, while smaller L/N ratios produce shorter-duration, less energetic jets that are affected by reflections from the far-loop footpoint. We quantify the transition between these behaviors and show that our model replicates key qualitative and quantitative aspects of both quiet Sun and active-region loop jets. We also find that there connection between the closed dome and surrounding coronal loop is very extensive: the cumulative reconnected flux at least matches the total flux beneath the dome for small L/N, and is more than double that value for large L/N.
Wyper, P. F.↗
The IRS 1 Circumstellar Disk, and the Origin of the Jet and CO Outflow n B5
We report on the discovery of the inner edge of the high velocity CO outflow associated with the bipolar jet originating from IRS 1 in Barnard 5 andf the first ever resolution of its circumstellar disk in the 2.6mm dust continuum and CO isotopes.
CO↗