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Collisionless zonal-flow dynamics in quasisymmetric stellarators

Journal Article · · Journal of 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 when the quasisymmetry error is small enough.

Sponsoring Organization:
USDOE
Grant/Contract Number:
AC02-05CH11231; SC0024548
OSTI ID:
2507105
Journal Information:
Journal of Plasma Physics, Journal Name: Journal of Plasma Physics Journal Issue: 1 Vol. 91; ISSN 0022-3778
Publisher:
Cambridge University Press (CUP)Copyright Statement
Country of Publication:
United Kingdom
Language:
English

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