Abstract
Strong drift wave turbulence is observed in the Large Plasma Device [H. Gekelman et al., Rev. Sci. Instrum. 62, 2875 (1991)] on density gradients produced by a plate limiter. Energetic lithium ions orbit through the turbulent region. Scans with a collimated ion analyzer and with Langmuir probes give detailed profiles of the fast ion spatial distribution and the fluctuating fields. The fast ion transport decreases rapidly with increasing fast ion gyroradius. Unlike the diffusive transport caused by Coulomb collisions, in this case the turbulent transport is nondiffusive. Analysis and simulation suggest that such nondiffusive transport is due to the interaction of the fast ions with stationary two-dimensional electrostatic turbulence.
Highlights
The influence of microturbulence on fast ion behavior in plasmas has attracted growing interest in fusion and space physics
Confinement of fast ions is a critical issue in fusion experiments approaching ignition,[1] and many space and astrophysical problemssee, e.g., Ref. 2 and references thereindepend on understanding fast ion dynamics in a turbulent medium
Many fast ion transport measurements in tokamaks are consistent with classical theory, yielding lower-level diffusion compared to thermal ions.[3]
Summary
The influence of microturbulence on fast ion behavior in plasmas has attracted growing interest in fusion and space physics. We report direct measurements of fast ion transport in the presence of drift wave turbulence. The approach discussed in this paper was to launch test-particle fast ion beams with narrow initial width in phase space and to have the fast ion gyro-orbit overlap with the turbulent potential structure of the drift wave. This allows study of fast ion transport in phase space with time and space resolution This technique has been used in previous studies of fast ion classical diffusion[22] and of resonance with shear Alfvén wavesSAW.[23,24]. The energy and time dependencies of the fast ion transport in drift wave turbulence are studied on a relatively short time scale compared to the turbulence correlation time c.
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