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Turbulent inward pinch of plasma confined by a levitated dipole magnet

Nature Physics 6, 207–212 (2010) | Download Citation

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Abstract

The rearrangement of plasma as a result of turbulence is among the most important processes that occur in planetary magnetospheres and in experiments used for fusion energy research. Remarkably, fluctuations that occur in active magnetospheres drive particles inward and create centrally peaked profiles. Until now, the strong peaking seen in space has been undetectable in the laboratory because the loss of particles along the magnetic field is faster than the net driven flow across the magnetic field. Here, we report the first laboratory measurements in which a strong superconducting magnet is levitated and used to confine high-temperature plasma in a configuration that resembles planetary magnetospheres. Levitation eliminates field-aligned particle loss, and the central plasma density increases markedly. The build-up of density characterizes a sustained turbulent pinch and is equal to the rate predicted from measured electric-field fluctuations. Our observations show that dynamic principles describing magnetospheric plasma are relevant to plasma confined by a levitated dipole.

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Acknowledgements

The authors acknowledge the technical expertise of R. Lations, P. Michael, J. Minervini, D. Strahan and A. Zhukovsky that has been required for the design and successful operation of the LDX superconducting magnets. LDX is a joint research project of Columbia University and the Massachusetts Institute of Technology and is supported by the USDOE Office of Fusion Energy Sciences with Grants DE-FG02-98ER54458 and DE-FG02-98ER54459.

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Affiliations

  1. Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA

    • A. C. Boxer
    • , R. Bergmann
    • , J. L. Ellsworth
    • , J. Kesner
    •  & P. Woskov

  2. Department of Applied Physics and Applied Mathematics, Columbia University, New York, New York 10027, USA

    • D. T. Garnier
    •  & M. E. Mauel

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Contributions

A.B. constructed the interferometer array and parameterized the density profile. R.B. constructed and installed the probe array. J.E. installed and analysed optical measurements. P.W. installed and calibrated the radiometers. D.G. designed and implemented the dipole levitation system and supervised operation of the experimental facility. M.E.M. noted the time-evolution of the inward particle pinch, modelled the relationship between edge fluctuations and diffusion and drafted the article. All authors participated in the planning and execution of experiments, discussed the experimental results and commented on the manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to M. E. Mauel.

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https://doi.org/10.1038/nphys1510

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