Characteristics of monotonic sheaths near a wall with grazing magnetic incidence
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arXiv
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| Format: | Preprint |
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2025
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| _version_ | 1866911102990811136 |
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| author | Geraldini, Alessandro Ewart, Robert J. Brunner, Stephan Parra, Felix I. |
| author_facet | Geraldini, Alessandro Ewart, Robert J. Brunner, Stephan Parra, Felix I. |
| contents | We consider a magnetised plasma in contact with an absorbing planar wall, where the angle $α$ between the magnetic field and the wall is small, $α\ll 1$ (in radians) and the system is symmetric tangential to the wall. The finite ratio $γ$ of the characteristic electron gyroradius $ρ_{\rm e}$ to the Debye length $λ_{\rm D}$, $γ= ρ_{\rm e} / λ_{\rm D}$, is retained via a grazing-incidence ($α\ll 1$) gyrokinetic treatment [1,2]. Building on a previously developed iterative scheme [2,3] to solve for the steady-state electrostatic potential in the quasineutral magnetic presheath of width $\sim ρ_{\rm S}$, we developed a scheme that simultaneously solves for both the presheath and the non-neutral Debye sheath of width $\sim λ_{\rm D}$ in the limit $λ_{\rm D} / ρ_{\rm S} \rightarrow 0$. The code, called GYRAZE, thus provides the energy-angle distribution of ions at the wall and the velocity distributions of electrons reflected by the wall for different values of wall potential. A monotonic electrostatic potential profile, assumed in this work, can only exist for magnetic field angles larger than a critical value [3]. While the critical angle is shown here to significantly increase with $γ$, it is still typically smaller than the magnetic field angle at divertor targets of a fusion device. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2508_09067 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Characteristics of monotonic sheaths near a wall with grazing magnetic incidence Geraldini, Alessandro Ewart, Robert J. Brunner, Stephan Parra, Felix I. Plasma Physics We consider a magnetised plasma in contact with an absorbing planar wall, where the angle $α$ between the magnetic field and the wall is small, $α\ll 1$ (in radians) and the system is symmetric tangential to the wall. The finite ratio $γ$ of the characteristic electron gyroradius $ρ_{\rm e}$ to the Debye length $λ_{\rm D}$, $γ= ρ_{\rm e} / λ_{\rm D}$, is retained via a grazing-incidence ($α\ll 1$) gyrokinetic treatment [1,2]. Building on a previously developed iterative scheme [2,3] to solve for the steady-state electrostatic potential in the quasineutral magnetic presheath of width $\sim ρ_{\rm S}$, we developed a scheme that simultaneously solves for both the presheath and the non-neutral Debye sheath of width $\sim λ_{\rm D}$ in the limit $λ_{\rm D} / ρ_{\rm S} \rightarrow 0$. The code, called GYRAZE, thus provides the energy-angle distribution of ions at the wall and the velocity distributions of electrons reflected by the wall for different values of wall potential. A monotonic electrostatic potential profile, assumed in this work, can only exist for magnetic field angles larger than a critical value [3]. While the critical angle is shown here to significantly increase with $γ$, it is still typically smaller than the magnetic field angle at divertor targets of a fusion device. |
| title | Characteristics of monotonic sheaths near a wall with grazing magnetic incidence |
| topic | Plasma Physics |
| url | https://arxiv.org/abs/2508.09067 |