Excitation of strong Langmuir turbulence in plasmas near critical density: Application to HF heating of the ionosphere
Excitation of strong Langmuir turbulence in plasmas near critical density: Application to HF heating of the ionosphere
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DOI：
10.1029/ja095ia12p21221
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发表时间：
1990-12
影响因子：
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通讯作者：
D. Dubois;H. Rose;D. Russell
中科院分区：
文献类型：
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作者：
D. Dubois;H. Rose;D. Russell
本文介绍了强相干辐射束在临界密度附近激发的等离子体中强朗缪尔湍流的广泛研究结果。高频加热实验的标称参数意味着电离层等离子体处于这种状态。大量的实验数据存在，特别是从高频增强波动水平的非相干散射雷达（ISR）测量。通过对Zakharov模型和相关理论的长期模拟，我们得到了一些新的结论和认识：（1）在静止的电离层中，线性参数不稳定性可能只在加热器开启后的最初几毫秒内起作用，但也有可能在先前存在的密度涨落中空穴子“直接成核”;（2）这两种可能性都导致朗缪尔坍缩;（4）成核-坍缩-烧毁方案解释了早期低占空比实验中观测到的ISR等离子体线功率谱的几个特征，并预测了新的特征;（5）在低占空比加热实验中，早期得到的ISR谱与非关联空泡事件的谱是一致的;（6）这些谱包含一个“自由模”峰，它是由于坍缩的空穴辐射自由朗缪尔波引起的，这个峰最近被观测到;（7）在较长时间的强光谱中观察到尖锐的光谱峰，高占空比或CW加热可以出现在STIM模型中从时空空穴相关性，提供过密域存在和布拉格共振条件得到满足;（8）关联模型可以解释所有尖锐的特征，包括衰变线、级联、窄振荡双流不稳定线和反斯托克斯线，这些模型不涉及参数不稳定性;（9）ISR谱的特征结构在相对于地磁场的角度范围上比弱湍流预测的情况下保持得更宽;（10）等离子体线的高度依赖性与观测一致，而不假设大尺度密度变化;加热器能量的非线性吸收率远大于碰撞吸收，吸收的能量主要进入超热电子。
Results are presented for an extensive study of strong Langmuir turbulence (SLT) in plasmas excited near the critical density by intense coherent radiation beams. The nominal parameters for HF heating experiments imply that the ionospheric plasma is in such a state. A large body of experimental data exists, particularly from incoherent scatter radar (ISR) measurements of HF-enhanced fluctuation levels. Long-time simulations of Zakharov's model of SLT and related theoretical arguments have led to new conclusions and insights: (1) linear parametric instabilities may play a role only during the first few milliseconds after heater turn-on in a quiescent ionosphere, but there is also the possibility of “direct nucleation” of cavitons in preexisting density fluctuations; (2) both possibilities lead to Langmuir collapse; (3) the turbulence is sustained by nucleation of trapped electric fields in burnt-out density cavities from previous collapses; (4) the nucleation-collapse-burnout scenario explains several features of the observed ISR plasma line power spectra in early-time, low-duty cycle experiments and predicts new features; (5) ISR spectra obtained at early times in low-duty cycle heating experiments are consistent with the spectra of uncorrelated caviton events; (6) these spectra contain a “free mode” peak which is due to the radiation of free Langmuir waves by collapsing cavitons; this peak has recently been observed; (7) sharp spectral peaks observed in strong spectra in longer-time, high-duty cycle or CW heating can arise in the SLT model from spatio-temporal caviton correlations, provided overdense domains exist and a Bragg resonance condition is satisfied; (8) correlation models can explain all the sharp features including the decay line, the cascade, the narrow oscillating two-stream instability line, and the anti-Stokes line; these models do not involve parametric instabilities; (9) the characteristic structure of the ISR spectrum is maintained over a much wider range of angles relative to the geomagnetic field than is the case for weak turbulence predictions; (10) the altitude dependence of the plasma line is consistent with observation without postulating large-scale density modifications; and (11) the nonlinear absorption rate of heater energy is much larger than collisional absorption, the absorbed energy going mainly into suprathermal electrons.