### Abstract

In this study the propagation of coherent plasma laments is investigated by means of numerical simulations. The investigations are carried out using both a two-dimensional drift-fluid model which includes the effects of dynamic electron and ion temperatures, and a three-dimensional model derived from first principles, which excludes the effects of dynamic temperatures.

The results from the two-dimensional model reveal that the inclusion of dynamic temperatures has a signicant impact on the propagation of blobs. Especially the inclusion of finite ion temperatures is found to strongly impact the blob propagation. Finite ion temperatures break the up-down symmetry seen for cold ions blobs and causes blobs to propagate faster and remain more coherent.

The results from the three-dimensional model reveals that dynamics along the magnetic field lines in a magnetic connement device also influences the propagation of blobs. A connection to the so-called sheath causes blobs to rotate due to Boltzmann spinning. It is also found that the width of the blob fronts parallel to the magnetic field does not strongly influence the blob propagation, however the parallel extend of the blobs does have an effect. The blobs with larger parallel extend propagate faster than the smaller blobs and they are found to break into smaller fragments at the later stages of propagation. An effect that is not observed for smaller blobs.

Finally we investigate how the so-called scrape-off layer power fall-off length, λ

_{q}, scales with a range of parameters. It is found that coherent structures signicantly influence λ

_{q}, and a simple scaling for how λ

_{q}scales with the electron temperature and the safety factor is found. This scaling is found to compare well with experimental results.

Original language | English |
---|

Place of Publication | Lyngby, Denmark |
---|---|

Publisher | Technical University of Denmark |

Number of pages | 106 |

Publication status | Published - 2018 |

### Keywords

- Coherent filaments
- Plasma blobs
- Drift-fluid equations
- Numerical Modelling
- Scrape-off layer
- Power fall-off length

### Cite this

*Studies of coherent lamentary structures in magnetically conned plasmas*. Lyngby, Denmark: Technical University of Denmark.

}

*Studies of coherent lamentary structures in magnetically conned plasmas*. Technical University of Denmark, Lyngby, Denmark.

**Studies of coherent lamentary structures in magnetically conned plasmas.** / Olsen, Jeppe Miki Busk.

Research output: Book/Report › Ph.D. thesis › Research

TY - BOOK

T1 - Studies of coherent lamentary structures in magnetically conned plasmas

AU - Olsen, Jeppe Miki Busk

PY - 2018

Y1 - 2018

N2 - Thermonuclear fusion has been proposed as a sustainable, clean and safe energy source to meet the energy demands of the future. There are, however, still several challenges that need to be overcome in order to realise a viable fusion power plant. One of the challenges are so-called coherent laments or blobs. These laments constitute a signicant fraction of the transport of plasma towards the outer vessel walls of fusion relevant magnetic connement devices. It is thus crucial for the realisation of a fusion power plant to gain a better understanding of such coherent laments.In this study the propagation of coherent plasma laments is investigated by means of numerical simulations. The investigations are carried out using both a two-dimensional drift-fluid model which includes the effects of dynamic electron and ion temperatures, and a three-dimensional model derived from first principles, which excludes the effects of dynamic temperatures.The results from the two-dimensional model reveal that the inclusion of dynamic temperatures has a signicant impact on the propagation of blobs. Especially the inclusion of finite ion temperatures is found to strongly impact the blob propagation. Finite ion temperatures break the up-down symmetry seen for cold ions blobs and causes blobs to propagate faster and remain more coherent.The results from the three-dimensional model reveals that dynamics along the magnetic field lines in a magnetic connement device also influences the propagation of blobs. A connection to the so-called sheath causes blobs to rotate due to Boltzmann spinning. It is also found that the width of the blob fronts parallel to the magnetic field does not strongly influence the blob propagation, however the parallel extend of the blobs does have an effect. The blobs with larger parallel extend propagate faster than the smaller blobs and they are found to break into smaller fragments at the later stages of propagation. An effect that is not observed for smaller blobs.Finally we investigate how the so-called scrape-off layer power fall-off length, λq, scales with a range of parameters. It is found that coherent structures signicantly influence λq, and a simple scaling for how λq scales with the electron temperature and the safety factor is found. This scaling is found to compare well with experimental results.

AB - Thermonuclear fusion has been proposed as a sustainable, clean and safe energy source to meet the energy demands of the future. There are, however, still several challenges that need to be overcome in order to realise a viable fusion power plant. One of the challenges are so-called coherent laments or blobs. These laments constitute a signicant fraction of the transport of plasma towards the outer vessel walls of fusion relevant magnetic connement devices. It is thus crucial for the realisation of a fusion power plant to gain a better understanding of such coherent laments.In this study the propagation of coherent plasma laments is investigated by means of numerical simulations. The investigations are carried out using both a two-dimensional drift-fluid model which includes the effects of dynamic electron and ion temperatures, and a three-dimensional model derived from first principles, which excludes the effects of dynamic temperatures.The results from the two-dimensional model reveal that the inclusion of dynamic temperatures has a signicant impact on the propagation of blobs. Especially the inclusion of finite ion temperatures is found to strongly impact the blob propagation. Finite ion temperatures break the up-down symmetry seen for cold ions blobs and causes blobs to propagate faster and remain more coherent.The results from the three-dimensional model reveals that dynamics along the magnetic field lines in a magnetic connement device also influences the propagation of blobs. A connection to the so-called sheath causes blobs to rotate due to Boltzmann spinning. It is also found that the width of the blob fronts parallel to the magnetic field does not strongly influence the blob propagation, however the parallel extend of the blobs does have an effect. The blobs with larger parallel extend propagate faster than the smaller blobs and they are found to break into smaller fragments at the later stages of propagation. An effect that is not observed for smaller blobs.Finally we investigate how the so-called scrape-off layer power fall-off length, λq, scales with a range of parameters. It is found that coherent structures signicantly influence λq, and a simple scaling for how λq scales with the electron temperature and the safety factor is found. This scaling is found to compare well with experimental results.

KW - Coherent filaments

KW - Plasma blobs

KW - Drift-fluid equations

KW - Numerical Modelling

KW - Scrape-off layer

KW - Power fall-off length

M3 - Ph.D. thesis

BT - Studies of coherent lamentary structures in magnetically conned plasmas

PB - Technical University of Denmark

CY - Lyngby, Denmark

ER -