Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Kink Instability”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2018

Statistical Analysis of Torus and Kink Instabilities in Solar Eruptions

A recent laboratory experiment of ideal magnetohydrodynamic instabilities revealed four distinct eruption regimes readily distinguished by the torus instability (TI) and helical kink instability (KI) parameters. To establish its observational counterpart, we collected 38 solar flares (stronger than GOES-class M5 in general) that took place within 45° of disk center during 2011–2017, 26 of which are associated with a halo or partial halo coronal mass ejection (CME; i.e., ejective events), while the others are CME-less (i.e., confined events). This is a complete sample of solar events satisfying our selection criteria detailed in the paper. For each event, we calculate a decay index n of the potential strapping field above the magnetic flux rope (MFR) in and around the flaring magnetic polarity inversion line (a TI parameter) and the unsigned twist number T(sub w) of the nonlinear force-free field lines forming the same MFR (a KI parameter). We then construct an n–T(sub w) diagram to investigate how the eruptiveness depends on these parameters. We find that (1) T(sub w) appears to play little role in discriminating between confined and ejective events; (2) the events with n ≳ 0.8 are all ejective, and all confined events have n ≲ 0.8. However, n ≳ 0.8 is not a necessary condition for eruption because some events with n ≲ 0.8 also erupted. In addition, we investigate the MFR’s geometrical parameters, apex height, and distance between footpoints, as a possible factors for the eruptiveness. We briefly discuss the difference of the present result for solar eruptions with that of the laboratory result in terms of the role played by magnetic reconnection.

Solar activity↗
NASA NTRS1994

Coalescence of two current loops with a kink instability simulated by a three-dimensional electromagnetic particle code

We have studied the dynamics of a coalescence of current loops using three-dimensional electromagnetic (EM) particle simulation code. Our focus is the investigation of such kinetic processes as energy trasnfer, heating particles, and electromagnetic emissions associated with a current loop coalescence which cannot be studied by MHD simulations. First, the two loops undergo a pinching oscillation due to a pressure imbalance between the inside and outside of the current loop. During the pinching oscillation, a kinetic kink instability is excited and electrons in the loops are heated perpendicularly to an ambient magnetic field. Next, the two current loops collide and coalesce, while at the same time a helical structure grows further. Subsequently, the perturbed current, which is due to these helically bunched electrons, can drive a whistler instability. It should be noted in this case that the whistler wave is excited by the kinetic kink instability and not a beam instability. After the coalescence of two helical loops, tilting motions can be observed in the direction of left-hand rotation, and the helical structure will relax resulting in strong plasma heating mostly in the direction perpendicular to the ambient magnetic field. It is also shown that high-frequency electromagnetic waves can be emitted from the region where the two loops coalesce and propagate strongly in the direction of the electron drift velocity. These processes may be important in understanding heating mechansims for coronal loops as well as radio wave emission mechanisms from active regions of solar plasmas.

Nishikawa, K.-I.↗
NASA NTRS1977

Observation of a kink instability in a solar flare

The morphological evolution of XUV flare emissions is studied for a solar flare observed during the Skylab mission, and observational evidence is found for a possible identification of a kink or helical instability in a magnetic flux loop associated with the flare. The evolution of the loop as seen in 256-A He II emission is described, showing that the kink instability lasted about 2 to 4 min, caused the flux tube to wriggle, and produced lateral motion of the loop in the observations with theoretical calculations of the kink instability reveals a close correspondence between observed and theoretical values of such parameters as critical current for instability and growth rate.

Cheng, C.-C.↗
NASA NTRS2017

Prominence Eruption Initiated by Helical Kink Instability of an Embedded Flux Rope

We study the triggering mechanism of a limb-prominence eruption and the associated coronal mass ejection (CME) near AR 12342 using Solar Dynamics Observatory and Large Angle and Spectrometric Coronagraph/Solar Heliospheric Observatory observations. The prominence is seen with an embedded flux thread (FT) at one end and bifurcates from the middle to a different footpoint location. The morphological evolution of the FT is similar to that of an unstable flux rope (FR), which we regard as a prominence-embedded FR. The FR twist exceeds the critical value. In addition, the morphology of the prominence plasma in 304 Å images marks the helical nature of the magnetic skeleton, with a total of 2.96 turns along arc length. The potential field extrapolation model indicates that the critical height of the background magnetic field gradient falls within the inner corona (105 Mm), which is consistent with the extent of coronal plasma loops. These results suggest that the helical kink instability in the embedded FR caused the slow rise of the prominence to the height of the torus instability domain. Moreover, the differential emission measure analysis unveils heating of the prominence plasma to coronal temperatures during an eruption, suggesting reconnection-related heating underneath the upward rising embedded FR. The prominence starts with a slow rise motion of 10 km s(exp. -1), which is followed by fast and slow acceleration phases that have an average acceleration of 28.9 m s(exp. -2) and 2.4 m s(exp. -2) in C2 and C3 field of view, respectively. As predicted by previous numerical simulations, the observed synchronous kinematic profiles of the CME leading edge and the core support the involved FR instability in the prominence initiation.

Vemareddy, P.↗
NASA NTRS1983

Evidence for helical kink instability in the Venus magnetic flux ropes

Empirical models of the magnetic field structure of flux ropes found in the Venus ionosphere are seen as suggesting that the ropes are unstable to long-wavelength (more than 100 km) helical-kink perturbations. The onset of such an instability can explain the apparent volume distribution of flux ropes with altitude, as well as their orientation as a function of altitude. In the subsolar region, the fraction of volume occupied by flux ropes increases from approximately 20 percent at high altitudes to more than 50 percent at low altitudes; this is a greater increase than would be expected if ropes convect downward as simple straight horizontal cylinders. The helical kink instability raises the fractional volume occupied by ropes by turning the originally straight, horizontal flux tubes into corkscrew-shaped structures as they convect to lower altitudes. It is noted that this instability also explains why high altitude ropes tend to be horizontal and low altitude ropes appear to have almost any orientation.

Elphic, R. C.↗
NASA NTRS1989

Nonlinear twist-kink instability of a coronal loop

Three-dimensional magnetoinductive particle simulations are used to demonstrate that the mechanical twisting motion applied to a magnetized plasma column induces a current aligned to the external magnetic field direction, pinches the plasma and magnetic fields, and stores the energy in poloidal magnetic fields. As the twist motion continues, the field lines locally begin to wrap around the plasma more than one revolution. A strong MHD instability sets in that is a mixture of kink and ballooning modes, releasing the magnetic energy and causing destruction of coherent column structure and flows of turbulent plasma. A similar episode ensues, exhibiting relaxation oscillations. The buildup of poloidal fields and structure and its sudden release driven by the twist motion may be a model for the solar coronal loop dynamics which exhibits a slow energy buildup with some photospheric motion and a sudden energy release by flares.

Zaidman, E. G.↗
NASA NTRS1990

The kink instability in infinite cylindrical flux tubes - Eigenvalues for power-law twist profiles

Simple, accurate methods of calculating ideal MHD instability eigenvalues for infinitely long cylindrical tubes with twist function T(r) are developed. The results show that the most rapidly growing and energetic instabilities occur in the Gold-Hoyle v = 0 field, with the instability progressively weakening with increasing v. However, the maximum force eigenvalue is always small, so that even in the Gold-Hoyle case only a small proportion of the available magnetic energy can be released in the linear phase. The results also confirm that the linear pinch is remarkably weak yet relatively resistant to line-tying. It is shown that the weakness of the force eigenvalue implies that the influence of uniform gas pressure on stability is negligible. Implications for the energy-release mechanism in solar flares are discussed.

Craig, I. J. D.↗
NASA NTRS2013

High-Speed Imaging of the First Kink Mode Instability in a Magnetoplasmadynamic Thruster

One of the biggest challenges to efficient magnetoplasmadynamic thruster (MPDT) operation is the onset of high-frequency voltage oscillations as the discharge current is increased above a threshold value. The onset regime is closely related to magnetohydrodynamic instabilities known as kink modes. This work documents direct observation of the formation and quasi-steady state behavior of an argon discharge plasma in a MPDT operating at discharge currents of 8 to 10 kA for a pulse length of approximately 4 ms. A high-speed camera images the quasi-steady-state operation of the thruster at 26,143 fps with a frame exposure time of 10 micro s. A 0.9 neutral density filter and 488-nm argon line filter with a 10-nm bandwidth are used on separate trials to capture the time evolution of the discharge plasma. Frame-by-frame analysis of the power flux incident on the CCD sensor shows both the initial discharge plasma formation process and the steady-state behavior of the discharge plasma. Light intensity levels on the order of 4-6 W/m2 indicate radial and azimuthal asymmetries in the concentration of argon plasma in the discharge channel. The plasma concentration exhibits characteristics that suggest the presence of a helical plasma column. This helical behavior has been observed in previous experiments that characterize plasma kink mode instabilities indirectly. Therefore, the direct imaging of these plasma kink modes further supports the link between MPDT onset behavior and the excitation of the magnetohydrodynamic instabilities.

Walker, Jonathan A.↗
NASA NTRSDate not supplied

Indirect Magnetic Measurements on the Aerodynamic Heating Facility (AHF)

The arc jet complex at NASA Ames Research Center (ARC) investigates various thermal protection systems (TPS) and their performance in high enthalpy flow environments to improve heat shields used in atmospheric entry. The arc jet operates by inducing an arc between two electrodes and passing the heated gas through a supersonic nozzle. The arc plasma is typically a partially ionized air mixture at low temperature (< 2 eV) but operates for long periods of time (up to 30 min) at high power (< 60 MW). However, simulations using the in-house ARC Heater Simulator (ARCHeS) code predict that the arc is still unstable to MHD instabilities, primarily the kink instability, which limit the operational envelope of the facility [1]. Consequently, it is important to better characterize these instabilities to improve facility stability and extend operational ranges. Due to the high enthalpy and long timescales (i.e., minutes) arc diagnostics must be non-invasive (i.e., optical or magnetic). This work will cover the development of tri-axial magnetic hall sensors for arc jet instabilities and subsequent 3D characterization of arc motion. The latest results describing the kink instability amplitude, frequency and wavelength will be presented and represent the first measurements of this instability in a NASA arc jet facility. References: [1] Meurisse, J. (2018). 3D Unsteady Model of Arc Heater Plasma Flow Using the ARC Heater Simulator (ARCHeS), APS Gaseous Electronics Conference, 2018: APS.

Sebastian Vicente Colom↗
NASA NTRS2020

Preliminary Measurements of the Motion of Arcjet Current Channel Using Inductive Magnetic Probes

This paper covers the design and first measurements of non-perturbative, external inductive magnetic diagnostics for arcjet constrictors which can measure the motion of the arc current channel. These measurements of arc motion are motivated by previous simulations using the ARC Heater Simulator (ARCHeS), which predicted unsteady arc motion due to the magnetic kink instability. Measurements of the kink instability are relevant to characterizing motion of the enthalpy profile of the arcjet, the arcjet operational stability, and electrode damage due to associated arc detachment events. These first measurements indicate 4 mm oscillations at 0.5-2 kHz of the current profile.

Haw, Magnus A.↗
NASA NTRS2020

Preliminary Measurements of the Motion of Arcjet Current Channel Using Inductive Magnetic Probes

This paper covers the design and first measurements of non-perturbative, external inductive magnetic diagnostics for arcjet constrictors which can measure the motion of the arc current-channel. These measurements of arc motion are motivated by previous simulations using the ARC Heater Simulator (ARCHeS), which predicted unsteady arc motion due to the magnetic kink instability. Measurements of the kink instability are relevant to characterizing motion of the enthalpy profile of the arcjet, the arcjet operational stability, and electrode damage due to associated arc detachment events. These first measurements indicate $\pm4$ mm oscillations at 0.5-2 kHz of the current profile.

Haw, Magnus A.↗
NASA NTRS2010

3D Relativistic Magnetohydrodynamic Simulations of Current-Driven Instability: Instability of a Static Column - 1

We have investigated the development of current-driven (CD) kink instability through three-dimensional relativistic MHD simulations. A static force-free equilibrium helical magnetic configuration is considered in order to study the influence of the initial configuration on the linear and nonlinear evolution of the instability. We found that the initial configuration is strongly distorted but not disrupted by the kink instability. The instability develops as predicted by linear theory. In the non-linear regime the kink amplitude continues to increase up to the terminal simulation time, albeit at different rates, for all but one simulation. The growth rate and nonlinear evolution of the CD kink instability depends moderately on the density profile and strongly on the magnetic pitch profile. The growth rate of the kink mode is reduced in the linear regime by an increase in the magnetic pitch with radius and the non-linear regime is reached at a later time than for constant helical pitch. On the other hand, the growth rate of the kink mode is increased in the linear regime by a decrease in the magnetic pitch with radius and reaches the non-linear regime sooner than the case with constant magnetic pitch. Kink amplitude growth in the non-linear regime for decreasing magnetic pitch leads to a slender helically twisted column wrapped by magnetic field. On the other hand, kink amplitude growth in the non-linear regime nearly ceases for increasing magnetic pitch.

Mizuno, Yosuke↗
NASA NTRSDate not supplied

Magnetic Measurements of Arc Instabilities in Segmented Arc Heater Column

The Aerodynamic Heating Facility (AHF) at NASA Ames Research Center (ARC) generates high enthalpy, supersonic flow environments for ground testing of NASAheat shield materials. This arc jet heater operates by passing a DC arc (<3200A,<2500V) through a gas column (~10cm diameter, 2m length) and ejecting the heatedgas through a supersonic nozzle into a test chamber. The arc plasma is a partially ionized air mixture at low temperature (< 2eV) but needs to be stable for long test times (up to 30min) at high power (< 20MW). Currently, the operational envelope of the facility is limited by arc instabilities including the kink instability. Consequently, it is of interest to characterize these instabilities to better understand facility limits and inform methods to extend stable operational ranges. Due to the high enthalpy and long timescales (i.e., minutes) diagnostics must be non-invasive. This work will cover the development of two sets of magnetic sensors: differential B-dot sensors and tri-axial magnetic hall sensors and will describe initial measurements of arc motion usingthese sensors.

Kink instability↗
NASA NTRSDate not supplied

Magnetic Measurements of Arc Instabilities in Segmented Arc Heater Column

The Aerodynamic Heating Facility (AHF) at NASA Ames Research Center (ARC) generates high enthalpy, supersonic flow environments for ground testing of NASAheat shield materials. This arc jet heater operates by passing a DC arc (<3200 A,<2500 V) through a gas column (~6 cm diameter, 2 m length) and ejecting the heated gas through a supersonic nozzle into a test chamber. The arc plasma is a partially ionized air mixture at low temperature (< 2 eV) but needs to be stable for long test times (up to 30 min) at high power (< 20 MW). Currently, the operational envelope of the facility is limited by arc instabilities including the kink instability. Consequently, it is of interest to characterize these instabilities to better understand facility limits and inform methods to extend stable operational ranges. Due to the high enthalpy and long timescales (i.e., minutes) diagnostics must be non-invasive. This work will cover the development of two sets of magnetic sensors: differential B-dot sensors and tri-axial magnetic hall sensors and will describe initial measurements of arc motion using these sensors.

Kink instability↗
NASA NTRS2013

Observations from Hinode and SDO of a Twisting and Writhing Start to a Solar-filament-eruption Cascade

Active region eruption of 1 June 2011. Ejective eruption. GOES class C4.1 flare. SDO/AIA, various filters (94, 131, 171, 193, 211, 304, 335 Ang.) High time cadence (24 s) and high spatial resolution (0 .6 pixels). SDO/HMI line-of-sight magnetograms. Hinode observed the onset, and the later decay phase. There are two filament eruptions (filament 1 and filament 2). Filament 1 has slow rise with steps, as in several previous cases. GOES "episodes" play role of "microflares" in other events; that is, filament jumps <=> intensity peaks. Episode 1 brightening: Accompanied by filament 1 s initial motions. (Rest of talk.) Filament 1 becomes unstable, and.. Episode 2 brightening: Flare ribbons following filament 1 s fast liftoff. This destabilizes neighboring filament 2, and... Episode 3 brightening: Flare ribbons of whole system following filament 2 s eruption.Something leads to reconnection; not totally clear what. Reconnection -> twisted flux rope in approx.20 min; episode 1 microflare (flare ribbons; TC) and filament jump. Twist -> writhe, via kink instability; filament-trajectory plateau, approx. 20 min. Writhe -> jump and eruption of filament 1, via instability; episode 2 microflare (flare ribbons; TC). (E.g., Williams et al.) First eruption -> second filament eruption (episode 3 flare ribbons; TC). (E.g., Sterling, Moore; Liu et al.; Torok et al.; Schrijver & Title.). Estimate amount of free energy in newly-twisted field (cf. Moore 1988): where we have taken L and r = 50, 3 arcsec. Energy of the total system is likely 1030 ergs or more. So "no" is answer to question. Additional energy comes from remainder of sheared large loop, shear (free energy) of second filament, etc. (Normally assumed situation.) Some history of twist-induced instability in filament eruptions: e.g., Sakurai, Torok & Kliem, Fan & Gibson, Gilbert et al., van Driel-Gesztelyi et al. Criterion : Kink instability for line-tied tube (Hood & Priest): 2.5pi; for Titov & Demoulin loop (Torok et al): approx.3.5pi We observe here: approx.1.5 turns (3.0pi) over ~50. => consistent with kink instability acting. (Cf. Srivastava et al. (2010): Small flare seen in TRACE and Hinode: approx.6.0pi)

Sterling, Alphonse C.↗
NASA NTRS2012

A Parametric Study of Erupting Flux Rope Rotation: Modeling the 'Cartwheel CME' on 9 April 2008

The rotation of erupting filaments in the solar corona is addressed through a parametric simulation study of unstable, rotating flux ropes in bipolar force-free initial equilibrium. The Lorentz force due to the external shear-field component and the relaxation of tension in the twisted field are the major contributors to the rotation in this model, while reconnection with the ambient field is of minor importance, due to the field's simple structure. In the low-beta corona, the rotation is not guided by the changing orientation of the vertical field component's polarity inversion line with height. The model yields strong initial rotations which saturate in the corona and differ qualitatively from the profile of rotation vs. height obtained in a recent simulation of an eruption without preexisting flux rope. Both major mechanisms writhe the flux rope axis, converting part of the initial twist helicity, and produce rotation profiles which, to a large part, are very similar within a range of shear-twist combinations. A difference lies in the tendency of twist-driven rotation to saturate at lower heights than shear-driven rotation. For parameters characteristic of the source regions of erupting filaments and coronal mass ejections, the shear field is found to be the dominant origin of rotations in the corona and to be required if the rotation reaches angles of order 90 degrees and higher; it dominates even if the twist exceeds the threshold of the helical kink instability. The contributions by shear and twist to the total rotation can be disentangled in the analysis of observations if the rotation and rise profiles are simultaneously compared with model calculations. The resulting twist estimate allows one to judge whether the helical kink instability occurred. This is demonstrated for the erupting prominence in the "Cartwheel CME" on 9 April 2008, which has shown a rotation of approximately 115 deg. up to a height of 1.5 Solar R above the photosphere. Out of a range of initial equilibria which include strongly kink-unstable (Phi = 5 pi), weakly kink-unstable (Phi = 3.5 pi), and kink-stable (Phi = 2.5 pi) configurations, only the evolution of the weakly kink-unstable flux rope matches the observations in their entirety.

initiation and propagation↗
NASA NTRS2005

Shape and Reconnection of the Exploding Magnetic Field in the Onset of CMEs

From chromospheric and coronal images and line-of-sight and vector magnetograms of magnetic regions that produce CMEs, and from chromospheric and coronal movies of the onsets of CME eruptions, it appears that the magnetic field that explodes to drive the CME is initially the strongly sheared core of a magnetic arcade encasing a polarity dividing line in the magnetic flux. Before or during the onset of the explosion, the sheared core field becomes a flux rope, often carrying chromospheric material within it. For the erupting flux rope to drive the explosion, that is, for its magnetic energy content to decrease in the explosion, the flux rope's cross-sectional area must increase faster than its length. For instance, for isotropic expansion, the area increases as the square of the length, and the magnetic energy content of the flux rope decreases as the inverse of the length. The instability that initiates the eruption of the flux rope might be an ideal MHD kink instability, or might involve runaway tether-cutting reconnection. The reconnection begins below the flux rope (internal to the arcade) when the overall field configuration of the region is effectively that of a single bipole. When the flux rope resides in a multi- bipolar configuration having a magnetic null above the flux rope, the runaway tether- cutting reconnection might begin either below the flux rope or at the null above (external to) the arcade. We present examples of observed CME onsets that illustrate the above alternatives. In each example, reconnection below the flux rope begins early in the eruption. This indicates that internal tether cutting reconnection (classic tether-cutting reconnection) is important in unleashing the CME explosion in all cases, including those in which the explosion may be triggered by MHD kinking or by external reconnection (classic breakout reconnection).

Moore, R. L.↗
NASA NTRS1994

Loop heating by D.C. electric current and electromagnetic wave emissions simulated by 3-D EM particle zone

We have shown that a current-carrying plasma loop can be heated by magnetic pinch driven by the pressure imbalance between inside and outside the loop, using a 3-dimensional electromagnetic (EM) particle code. Both electrons and ions in the loop can be heated in the direction perpendicular to the ambient magnetic field, therefore the perpendicular temperature can be increased about 10 times compared with the parallel temperature. This temperature anisotropy produced by the magnetic pinch heating can induce a plasma instability, by which high-frequency electromagnetic waves can be excited. The plasma current which is enhanced by the magnetic pinch can also excite a kinetic kink instability, which can heat ions perpendicular to the magnetic field. The heating mechanism of ions as well as the electromagnetic emission could be important for an understanding of the coronal loop heating and the electromagnetic wave emissions from active coronal regions.

Sakai, J. I.↗