### Abstract

Ideal magnetohydrodynamics relaxation is the topology-conserving reconfiguration of a magnetic field into a lower energy state where the net force is zero. This is achieved by modeling the plasma as perfectly conducting viscous fluid. It is an important tool for investigating plasma equilibria and is often used to study the magnetic configurations in fusion devices and astrophysical plasmas. We study the equilibrium reached by a localized magnetic field through the topology conserving relaxation of a magnetic field based on the Hopf fibration in which magnetic field lines are closed circles that are all linked with one another. Magnetic fields with this topology have recently been shown to occur in non-ideal numerical simulations. Our results show that any localized field can only attain equilibrium if there is a finite external pressure, and that for such a field a Taylor state is unattainable. We find an equilibrium plasma configuration that is characterized by a lowered pressure in a toroidal region, with field lines lying on surfaces of constant pressure. Therefore, the field is in a Grad-Shafranov equilibrium. Localized helical magnetic fields are found when plasma is ejected from astrophysical bodies and subsequently relaxes against the background plasma, as well as on earth in plasmoids generated by, e.g., a Marshall gun. This work shows under which conditions an equilibrium can be reached and identifies a toroidal depression as the characteristic feature of such a configuration.

Original language | English |
---|---|

Article number | 072110 |

Pages (from-to) | 1-11 |

Number of pages | 11 |

Journal | Physics of Plasmas |

Volume | 24 |

Issue number | 7 |

Early online date | 6 Jul 2017 |

DOIs | |

Publication status | Published - Jul 2017 |

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### Cite this

*Physics of Plasmas*,

*24*(7), 1-11. [072110]. https://doi.org/10.1063/1.4990076

}

*Physics of Plasmas*, vol. 24, no. 7, 072110, pp. 1-11. https://doi.org/10.1063/1.4990076

**Ideal relaxation of the Hopf fibration.** / Smiet, Christopher Berg; Candelaresi, Simon; Bouwmeester, Dirk.

Research output: Contribution to journal › Article

TY - JOUR

T1 - Ideal relaxation of the Hopf fibration

AU - Smiet, Christopher Berg

AU - Candelaresi, Simon

AU - Bouwmeester, Dirk

N1 - S.C. acknowledges financial support from the UK's STFC (Grant No. ST/K000993). This work was supported by NWO VICI 680-47-604 and the NWO graduate programme. The authors acknowledge support from the Edinburgh Mathematical Societies research support fund. We gratefully acknowledge the support of NVIDIA Corporation with the donation of one Tesla K40 GPU used for this research.

PY - 2017/7

Y1 - 2017/7

N2 - Ideal magnetohydrodynamics relaxation is the topology-conserving reconfiguration of a magnetic field into a lower energy state where the net force is zero. This is achieved by modeling the plasma as perfectly conducting viscous fluid. It is an important tool for investigating plasma equilibria and is often used to study the magnetic configurations in fusion devices and astrophysical plasmas. We study the equilibrium reached by a localized magnetic field through the topology conserving relaxation of a magnetic field based on the Hopf fibration in which magnetic field lines are closed circles that are all linked with one another. Magnetic fields with this topology have recently been shown to occur in non-ideal numerical simulations. Our results show that any localized field can only attain equilibrium if there is a finite external pressure, and that for such a field a Taylor state is unattainable. We find an equilibrium plasma configuration that is characterized by a lowered pressure in a toroidal region, with field lines lying on surfaces of constant pressure. Therefore, the field is in a Grad-Shafranov equilibrium. Localized helical magnetic fields are found when plasma is ejected from astrophysical bodies and subsequently relaxes against the background plasma, as well as on earth in plasmoids generated by, e.g., a Marshall gun. This work shows under which conditions an equilibrium can be reached and identifies a toroidal depression as the characteristic feature of such a configuration.

AB - Ideal magnetohydrodynamics relaxation is the topology-conserving reconfiguration of a magnetic field into a lower energy state where the net force is zero. This is achieved by modeling the plasma as perfectly conducting viscous fluid. It is an important tool for investigating plasma equilibria and is often used to study the magnetic configurations in fusion devices and astrophysical plasmas. We study the equilibrium reached by a localized magnetic field through the topology conserving relaxation of a magnetic field based on the Hopf fibration in which magnetic field lines are closed circles that are all linked with one another. Magnetic fields with this topology have recently been shown to occur in non-ideal numerical simulations. Our results show that any localized field can only attain equilibrium if there is a finite external pressure, and that for such a field a Taylor state is unattainable. We find an equilibrium plasma configuration that is characterized by a lowered pressure in a toroidal region, with field lines lying on surfaces of constant pressure. Therefore, the field is in a Grad-Shafranov equilibrium. Localized helical magnetic fields are found when plasma is ejected from astrophysical bodies and subsequently relaxes against the background plasma, as well as on earth in plasmoids generated by, e.g., a Marshall gun. This work shows under which conditions an equilibrium can be reached and identifies a toroidal depression as the characteristic feature of such a configuration.

UR - http://www.scopus.com/inward/record.url?scp=85022193429&partnerID=8YFLogxK

U2 - 10.1063/1.4990076

DO - 10.1063/1.4990076

M3 - Article

VL - 24

SP - 1

EP - 11

JO - Physics of Plasmas

JF - Physics of Plasmas

SN - 1070-664X

IS - 7

M1 - 072110

ER -