Collisionless zonal-flow dynamics in quasisymmetric stellarators
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arXiv
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| Format: | Preprint |
| Publié: |
2024
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| _version_ | 1866909475340812288 |
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| author | Zhu, Hongxuan Lin, Z. Bhattacharjee, A. |
| author_facet | Zhu, Hongxuan Lin, Z. Bhattacharjee, A. |
| contents | The linear collisionless plasma response to a zonal-density perturbation in quasisymmetric stellarators is studied, including the geodesic-acoustic-mode oscillations and the Rosenbluth--Hinton residual flow. While the geodesic-acoustic-mode oscillations in quasiaxisymmetric configurations are similar to tokamaks, they become non-existent in quasi-helically symmetric configurations when the effective safety factor in helical-angle coordinates is small. Compared with concentric circular tokamaks, the Rosenbluth--Hinton residual is also found to be multiplied by a geometric factor $\mathcal{C}$ that arises from the flux-surface averaged classical polarization. Using the near-axis-expansion framework, we derive an analytic expression for $\mathcal{C}$, which varies significantly among different configurations. These analytic results are compared with numerical simulation results from the global gyrokinetic particle-in-cell code GTC, and good agreement with the theoretical Rosenbluth--Hinton residual level is achieved only when the quasisymmetry error is small enough. Since zonal flows can be important for regulating turbulent transport, these results suggest a possible relation between the transport level and the stellarator geometric parameters via nonlinear interactions with zonal flows. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2407_19592 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | Collisionless zonal-flow dynamics in quasisymmetric stellarators Zhu, Hongxuan Lin, Z. Bhattacharjee, A. Plasma Physics The linear collisionless plasma response to a zonal-density perturbation in quasisymmetric stellarators is studied, including the geodesic-acoustic-mode oscillations and the Rosenbluth--Hinton residual flow. While the geodesic-acoustic-mode oscillations in quasiaxisymmetric configurations are similar to tokamaks, they become non-existent in quasi-helically symmetric configurations when the effective safety factor in helical-angle coordinates is small. Compared with concentric circular tokamaks, the Rosenbluth--Hinton residual is also found to be multiplied by a geometric factor $\mathcal{C}$ that arises from the flux-surface averaged classical polarization. Using the near-axis-expansion framework, we derive an analytic expression for $\mathcal{C}$, which varies significantly among different configurations. These analytic results are compared with numerical simulation results from the global gyrokinetic particle-in-cell code GTC, and good agreement with the theoretical Rosenbluth--Hinton residual level is achieved only when the quasisymmetry error is small enough. Since zonal flows can be important for regulating turbulent transport, these results suggest a possible relation between the transport level and the stellarator geometric parameters via nonlinear interactions with zonal flows. |
| title | Collisionless zonal-flow dynamics in quasisymmetric stellarators |
| topic | Plasma Physics |
| url | https://arxiv.org/abs/2407.19592 |