Observation of a Parametric Instability Near the Lower Hybrid Frequency.

Hooke, W. M.; Bernabei, S.

doi:10.2172/4640186

1972

DOI: 10.2172/4640186

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Observation of a Parametric Instability Near the Lower Hybrid Frequency.

W. M. Hooke¹,

S. Bernabei²

Abstract: We have observed a parametric instability at frequencies close to and somewhat above the lower hybrid resonance frequency. The threshold for this decay occurs when the rf electron drift velocity is of the order of the ion sound speed.

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“…13 In a real plasma, a second parametric instability driven by the electric field of the excited lower hybrid waves-i.e., (E fe XB 0 ) y drift-may occur in the pump direction. 7 This problem is now under investigation by means of two-dimensional simulation.…”

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Parametric Instabilities and Anomalous Heating of Plasmas near the Lower Hybrid Frequency

1972

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It is shown both by theory and by computer experiments that a plasma subjected to a long-wavelength electric field oscillating near the lower hybrid frequency causes parametric instabilities which lead to an anomalous heating of both ions and electrons. Because the instability threshold is much lower than that for the corresponding electron plasma-wave problem, the saturation of the electric field can be much higher.Plasma heating by anomalous absorption of a large-amplitude external electromagnetic wave has been of considerable theoretical and experimental interest. 1 " 5 We show by theory and by computer simulations that an electric field perpendicular to a dc magnetic field and oscillating at a frequency above but near the lower hybrid frequency can excite, at extremely low thresholds, decay and purely growing parametric instabilities. 2 These result in short-wavelength lower hybrid waves and ion waves and lead to a substantial plasma heating. This driving field might be associated with a whistler wave, with a lower hybrid wave propagating nearly perpendicular to a magnetic field, 6 * 7 or even with grids in the plasma. Such instabilities may occur naturally in shock-heated plasmas and Earth's magnetosphere. 8 We consider the stability of a homogeneous plasma embedded in a uniform magnetic field Bjz and an oscillatory electric field JEQ^ cos(oo 0 t) in the dipole approximation; u> 0 is chosen close to the lower hybrid frequency co LH =o> /)i /(l + <*)p e 2 / tyj 2 ) 172 , where 0 is near w Pe or £l e , lt4 ion dynamics cannot be neglected in € ±1 , and this allows the excited highfrequency waves to heat ions directly. 9 Equation (1) exhibits both decay and purely growing or two-stream-type instabilities. Using Eqs.(1) and (2) the minimum threshold 2 for the decay of the pump at co 0 into a lower hybrid wave at ii fSfe'V? Vi/i M e 2 V e 2 X\{ l/2 and an acoustic wave at oo s = kc s is given by Above threshold where damping is not important the...

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Parametric Instabilities and Anomalous Heating of Plasmas near the Lower Hybrid Frequency

1972

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Observation of a Parametric Instability Near the Lower Hybrid Frequency.

Abstract: We have observed a parametric instability at frequencies close to and somewhat above the lower hybrid resonance frequency. The threshold for this decay occurs when the rf electron drift velocity is of the order of the ion sound speed.

Cited by 1 publication

References 1 publication

Parametric Instabilities and Anomalous Heating of Plasmas near the Lower Hybrid Frequency

Parametric Instabilities and Anomalous Heating of Plasmas near the Lower Hybrid Frequency

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