The Experts below are selected from a list of 68427 Experts worldwide ranked by ideXlab platform
Orkan M. Umurhan - One of the best experts on this subject based on the ideXlab platform.
-
interacting vorticity waves as an Instability Mechanism for magnetohydrodynamic shear instabilities
Journal of Fluid Mechanics, 2015Co-Authors: Eyal Heifetz, Julian Mak, Jonas Nycander, Orkan M. UmurhanAbstract:The interacting vorticity wave formalism for shear flow instabilities is extended here to the magnetohydrodynamic (MUD) setting, to provide a mechanistic description for stabilising and destabilisi ...
-
Interacting vorticity waves as an Instability Mechanism for MHD shear instabilities
Journal of Fluid Mechanics, 2015Co-Authors: Eyal Heifetz, Julian Mak, Jonas Nycander, Orkan M. UmurhanAbstract:The interacting vorticity wave formalism for shear flow instabilities is extended here to the magnetohydrodynamic (MHD) setting, to provide a mechanistic description for the stabilising and destabilising of shear instabilities by the presence of a background magnetic field. The interpretation relies on local vorticity anomalies inducing a non-local velocity field, resulting in action-at-a-distance. It is shown here that the waves supported by the system are able to propagate vorticity via the Lorentz force, and waves may interact; existence of Instability then rests upon whether the choice of basic state allows for phase-locking and constructive interference of the vorticity waves via mutual interaction. To substantiate this claim, we solve the Instability problem of two representative basic states, one where a background magnetic field stabilises an unstable flow and the other where the field destabilises a stable flow, and perform relevant analyses to show how this Mechanism operates in MHD.
V R Romanovskii - One of the best experts on this subject based on the ideXlab platform.
-
Current Instability Mechanisms in high-temperature superconductors cooled by liquid coolant
Superconductor Science and Technology, 2009Co-Authors: V R RomanovskiiAbstract:The Instability of the steady current state in high-temperature superconductors (Bi2Sr2CaCu2O8, Bi2Sr2Ca2Cu3O8 and YBa2Cu3O7) cooled by a liquid refrigerant (helium, hydrogen and nitrogen) is studied. It is shown that the Mechanism of the current Instability depends on the type of coolant. Firstly, the destruction of stable current states may occur after transition of the cooling conditions on the surface of the superconductor from the nucleate to film boiling regimes. This Instability Mechanism is more probable for superconductors cooled by liquid helium. Secondly, the current Instability may occur due to the disruption of the stable formation of the voltage–current characteristic of a superconductor even in the nucleate boiling regime of cooling. Such regimes are most probable when liquid nitrogen cools the superconductor. The necessary criteria allowing one to determine the influence of the properties of superconductor and coolant on the current Instability Mechanism are formulated.
-
Current Instability Mechanisms in liquid-coolant-cooled high-temperature superconductors
Technical Physics, 2009Co-Authors: V R RomanovskiiAbstract:The stable current distribution in Bi2Sr2CaCu2O8, Bi2Sr2Ca2Cu3O8, and YBa2Cu3O7 high-temperature superconductors depending on conditions of cooling thereof by liquid cryocoolants—helium, hydrogen, and nitrogen, respectively—is studied. It is shown that the current Instability Mechanism may change in going from one coolant to another. Consequently, stable states may be disturbed, first, when the conditions of cooling the superconductor surface change from nucleate boiling to film boiling. Such a thermal Mechanism of stable current state disturbance is observed largely when a superconductor is cooled by liquid helium. Second, even for the nucleate boiling of a liquid coolant, current Instability may result from the stable formation of the voltage-current characteristic of the superconductor. This type of injected current stability disturbance is most likely when a superconductor is cooled by liquid nitrogen. Criteria for determining a current Instability Mechanism in relation to the properties of the superconductor and coolant are given.
Erik P. Gilson - One of the best experts on this subject based on the ideXlab platform.
-
Experimental confirmation of the standard magnetorotational Instability Mechanism with a spring-mass analogue
Communications Physics, 2019Co-Authors: Derek M. H. Hung, Eric G. Blackman, Kyle J. Caspary, Erik P. GilsonAbstract:Magnetorotational Instability (MRI) has long been considered a possible Mechanism to transport angular momentum allowing fast accretion in astrophysical objects, but its standard form with a vertical magnetic field has never been experimentally verified. The authors present an experimental demonstration of a spring-mass analogue of the standard MRI using water as working fluid and a spring to mimic the action of magnetic fields. The magnetorotational Instability (MRI) has long been considered a plausibly ubiquitous Mechanism to destabilize otherwise stable Keplerian flows to support radially outward transport of angular momentum. Such an efficient transport process would allow fast accretion in astrophysical objects such as stars and black holes to release copious kinetic energy that powers many of the most luminous sources in the universe. But the standard MRI under a purely vertical magnetic field has heretofore never been directly measured despite numerous efforts over more than a decade. Here we report an unambiguous laboratory demonstration of the spring-mass analogue to the standard MRI by comparing motion of a spring-tethered ball within different rotating flows. The experiment corroborates the theory: efficient outward angular momentum transport manifests only for cases with a weak spring in quasi-Keperian flow. Our experimental method accomplishes this in a new way, thereby connecting solid and fluid mechanics to plasma astrophysics.
-
experimental confirmation of the standard magnetorotational Instability Mechanism with a spring mass analogue
arXiv: Instrumentation and Methods for Astrophysics, 2018Co-Authors: Derek M. H. Hung, Eric G. Blackman, Kyle Caspary, Erik P. GilsonAbstract:The Magnetorotational Instability (MRI) has long been considered a plausibly ubiquitous Mechanism to destabilize otherwise stable Keplerian flows to support radially outward transport of angular momentum. Such an efficient transport process would allow fast accretion in astrophysical objects such as stars and black holes to release copious kinetic energy that powers many of the most luminous sources in the universe. But the standard MRI under a purely vertical magnetic field has heretofore never been directly measured despite numerous efforts over more than a decade. Here we report an unambiguous laboratory demonstration of the spring-mass analogue to the standard MRI by comparing motion of a spring-tethered ball within different rotating flows. The experiment corroborates the theory: efficient outward angular momentum transport manifests only for cases with a weak spring in quasi-Keperian flow. Our experimental method accomplishes this in a new way, thereby connecting solid and fluid mechanics to plasma astrophysics.
Derek M. H. Hung - One of the best experts on this subject based on the ideXlab platform.
-
Experimental confirmation of the standard magnetorotational Instability Mechanism with a spring-mass analogue
Communications Physics, 2019Co-Authors: Derek M. H. Hung, Eric G. Blackman, Kyle J. Caspary, Erik P. GilsonAbstract:Magnetorotational Instability (MRI) has long been considered a possible Mechanism to transport angular momentum allowing fast accretion in astrophysical objects, but its standard form with a vertical magnetic field has never been experimentally verified. The authors present an experimental demonstration of a spring-mass analogue of the standard MRI using water as working fluid and a spring to mimic the action of magnetic fields. The magnetorotational Instability (MRI) has long been considered a plausibly ubiquitous Mechanism to destabilize otherwise stable Keplerian flows to support radially outward transport of angular momentum. Such an efficient transport process would allow fast accretion in astrophysical objects such as stars and black holes to release copious kinetic energy that powers many of the most luminous sources in the universe. But the standard MRI under a purely vertical magnetic field has heretofore never been directly measured despite numerous efforts over more than a decade. Here we report an unambiguous laboratory demonstration of the spring-mass analogue to the standard MRI by comparing motion of a spring-tethered ball within different rotating flows. The experiment corroborates the theory: efficient outward angular momentum transport manifests only for cases with a weak spring in quasi-Keperian flow. Our experimental method accomplishes this in a new way, thereby connecting solid and fluid mechanics to plasma astrophysics.
-
experimental confirmation of the standard magnetorotational Instability Mechanism with a spring mass analogue
arXiv: Instrumentation and Methods for Astrophysics, 2018Co-Authors: Derek M. H. Hung, Eric G. Blackman, Kyle Caspary, Erik P. GilsonAbstract:The Magnetorotational Instability (MRI) has long been considered a plausibly ubiquitous Mechanism to destabilize otherwise stable Keplerian flows to support radially outward transport of angular momentum. Such an efficient transport process would allow fast accretion in astrophysical objects such as stars and black holes to release copious kinetic energy that powers many of the most luminous sources in the universe. But the standard MRI under a purely vertical magnetic field has heretofore never been directly measured despite numerous efforts over more than a decade. Here we report an unambiguous laboratory demonstration of the spring-mass analogue to the standard MRI by comparing motion of a spring-tethered ball within different rotating flows. The experiment corroborates the theory: efficient outward angular momentum transport manifests only for cases with a weak spring in quasi-Keperian flow. Our experimental method accomplishes this in a new way, thereby connecting solid and fluid mechanics to plasma astrophysics.
Eyal Heifetz - One of the best experts on this subject based on the ideXlab platform.
-
interacting vorticity waves as an Instability Mechanism for magnetohydrodynamic shear instabilities
Journal of Fluid Mechanics, 2015Co-Authors: Eyal Heifetz, Julian Mak, Jonas Nycander, Orkan M. UmurhanAbstract:The interacting vorticity wave formalism for shear flow instabilities is extended here to the magnetohydrodynamic (MUD) setting, to provide a mechanistic description for stabilising and destabilisi ...
-
Interacting vorticity waves as an Instability Mechanism for MHD shear instabilities
Journal of Fluid Mechanics, 2015Co-Authors: Eyal Heifetz, Julian Mak, Jonas Nycander, Orkan M. UmurhanAbstract:The interacting vorticity wave formalism for shear flow instabilities is extended here to the magnetohydrodynamic (MHD) setting, to provide a mechanistic description for the stabilising and destabilising of shear instabilities by the presence of a background magnetic field. The interpretation relies on local vorticity anomalies inducing a non-local velocity field, resulting in action-at-a-distance. It is shown here that the waves supported by the system are able to propagate vorticity via the Lorentz force, and waves may interact; existence of Instability then rests upon whether the choice of basic state allows for phase-locking and constructive interference of the vorticity waves via mutual interaction. To substantiate this claim, we solve the Instability problem of two representative basic states, one where a background magnetic field stabilises an unstable flow and the other where the field destabilises a stable flow, and perform relevant analyses to show how this Mechanism operates in MHD.
