Exponential Frequency Spectrum in Magnetized Plasmas

Pace, D. C.; Shi, Meixuan; Maggs, J. E.; Morales, G. J.; Carter, Troy

doi:10.1103/physrevlett.101.085001

Cited by 29 publications

(35 citation statements)

References 17 publications

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“…Some of the observations were highlighted in Ref. 20 and are expanded in detail in the present manuscript which also includes new modeling features. The two experiments are performed in the Large Plasma Device ͑LAPD-U͒ ͑Ref.…”

Section: Introductionmentioning

confidence: 87%

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Exponential frequency spectrum and Lorentzian pulses in magnetized plasmas

et al. 2008

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Two different experiments involving pressure gradients across the confinement magnetic field in a large plasma column are found to exhibit a broadband turbulence that displays an exponential frequency spectrum for frequencies below the ion cyclotron frequency. The exponential feature has been traced to the presence of solitary pulses having a Lorentzian temporal signature. These pulses arise from nonlinear interactions of drift-Alfvén waves driven by the pressure gradients. In both experiments the width of the pulses is narrowly distributed resulting in exponential spectra with a single characteristic time scale. The temporal width of the pulses is measured to be a fraction of a period of the drift-Alfvén waves. The experiments are performed in the Large Plasma Device ͑LAPD-U͒ ͓W. Gekelman et al., Rev. Sci. Instrum. 62, 2875 ͑1991͔͒ operated by the Basic Plasma Science Facility at the University of California, Los Angeles. One experiment involves a controlled, pure electron temperature gradient associated with a microscopic ͑6 mm gradient length͒ hot electron temperature filament created by the injection a small electron beam embedded in the center of a large, cold magnetized plasma. The other experiment is a macroscopic ͑3.5 cm gradient length͒ limiter-edge experiment in which a density gradient is established by inserting a metallic plate at the edge of the nominal plasma column of the LAPD-U. The temperature filament experiment permits a detailed study of the transition from coherent to turbulent behavior and the concomitant change from classical to anomalous transport. In the limiter experiment the turbulence sampled is always fully developed. The similarity of the results in the two experiments strongly suggests a universal feature of pressure-gradient driven turbulence in magnetized plasmas that results in nondiffusive cross-field transport. This may explain previous observations in helical confinement devices, research tokamaks, and arc plasmas.

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Section: Introductionmentioning

confidence: 87%

“…It has the largest temperature and the smallest temperature gradient. It is in this region where low frequency oscillations corresponding to thermal waves 37 are localized. These are the low frequency oscillations that appear at the start of the third stage, close to t = 5 ms in the Fig.…”

Section: Temperature Filament Experimentsmentioning

confidence: 96%

Exponential frequency spectrum and Lorentzian pulses in magnetized plasmas

et al. 2008

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“…The threshold corresponds to the ExB velocity imparted by the modes exceeding the phase velocity of the modes (approximately the diamagnetic drift velocity). The experimental observations [16][17][18] and the model results [19] also show that the value of the parameter τ is a fraction (1/4 to 1/5) of the wave period of the drift-modes.…”

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confidence: 94%

“…The procedure works technically, but it fails to provide a connection to an underlying physical process. This Letter emphasizes that recent insight into this issue has emerged from transport experiments in magnetized plasmas, both in a basic linear device [16,17] and in a stellarator, toroidal configuration [18]. In these completely different experiments, fluctuations in the plasma pressure are observed to follow an exponential frequency dependence for frequencies below the ion cyclotron frequency.…”

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confidence: 99%