4 research outputs found
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Dependence of fast-ion transport on the nature of the turbulence in the Large Plasma Device
Strong turbulent waves (nn ∼0.5, f ∼5-40 kHz) are observed in the upgraded Large Plasma Device W. Gekelman, H. Pfister, Z. Lucky, J. Bamber, D. Leneman, and J. Maggs, Rev. Sci. Instrum. 62, 2875 (1991) on density gradients produced by an annular obstacle. Energetic lithium ions (E fast / T i 300, fast / s ∼ 10) orbit through the turbulent region. Scans with a collimated analyzer and with probes give detailed profiles of the fast ion spatial distribution and of the fluctuating wave fields. The characteristics of the fluctuations are modified by changing the plasma species from helium to neon and by modifying the bias on the obstacle. Different spatial structure sizes (L s) and correlation lengths (Lcorr) of the wave potential fields alter the fast ion transport. The effects of electrostatic fluctuations are reduced due to gyro-averaging, which explains the difference in the fast-ion transport. A transition from super-diffusive to sub-diffusive transport is observed when the fast ion interacts with the waves for most of a wave period, which agrees with theoretical predictions. © 2011 American Institute of Physics
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Turbulent transport of fast ions in the Large Plasma Device
Strong drift wave turbulence is observed in the Large Plasma Device [H. Gekelman, 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. © 2010 American Institute of Physics
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Measurements of interactions between waves and energetic ions in basic plasma experiments
To measure the transport of fast ions by various types of waves, complementary experiments are conducted in linear and toroidal magnetic fields in the large plasma device and the toroidal plasma experiment. Lithium sources that are immersed in the plasma provide the energetic ions. Spatial scans of collectors measure the transport. Techniques to find the beam and optimize the spatial sensitivity are described. Measurements of Coulomb scattering, resonant interaction with Alfvén waves, and transport by drift-wave and interchange turbulence are summarized. © 2012 IOP Publishing Ltd