Langmuir wave growth and electron bunching: Results from a wave‐particle correlator
Langmuir wave growth and electron bunching: Results from a wave‐particle correlator
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朗缪尔波生长和电子聚束：波粒相关器的结果
DOI：
10.1029/90ja01596
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发表时间：
1991
影响因子：
--
通讯作者：
M. Boehm
中科院分区：
文献类型：
--
作者：
R. Ergun;C. Carlson;J. Mcfadden;J. Clemmons;M. Boehm
最近对高空探测火箭上的极光电子和强烈的朗缪尔波的测量表明，这些波是由色散的低能电子爆发产生的。探空火箭在一次亚暴扩张期间向北发射到晚间极光区，穿过了几个电子能量峰值大于25keV的离散极光弧线。大幅度朗缪尔波出现在大约100ms的爆发中，其幅度大于200 mV/m，只有在增强的低能(0.3-3.0keV)场向电子沉淀期间才能看到。增强的电子通量表现出色散特征，其中高能电子先于低能电子到达。波粒相关器是一种新仪器，它将电子的到达时间与高频波场的相位直接关联起来，在强烈的朗缪尔波爆发期间，它探测到了以波频率聚集的电子。电子聚束事件的幅度只有几个百分点，它提供了对共振电子能量(速度)的直接识别，从而建立了平行波长(约15m)。在电子分布函数出现正斜率的能量处或附近检测到电子聚束事件。在频散爆发期间，朗缪尔波的更多相速度(或波长)随出现正斜率的速度的变化而变化。作者得出的结论是，低能、场定向电子中的速度色散造成了不稳定的电子分布，这是朗缪尔波增长的原因。所提出的增长机制与太阳III型射电爆发期间朗缪尔波的增长机制相似。
Recent measurements of auroral electrons and intense Langmuir waves on a high-altitude sounding rocket show that these waves were produced by dispersive bursts of low-energy electrons. The sounding rocket was launched northward into the evening auroral zone during a substorm expansion and crossed several discrete auroral arcs having electron energy peaks greater than 25 keV. The large-amplitude Langmuir waves, which appeared in {approximately}100-ms bursts and had amplitudes greater than 200 mV/m, were seen only during periods of enhanced low-energy (0.3-3.0 keV), field-aligned electron precipitation. The enhanced electron flux displayed a dispersive signature in which the higher-energy electrons arrived before the lower-energy electrons. A wave-particle correlator, a new instrument that performed a direct correlation of the arrival times of electrons with the phase of the high-frequency wave field, detected electron bunching at the wave frequency during the bursts of intense Langmuir waves. The electron bunching events, which had amplitudes of a few percent, provided a direct identification of the energy (velocity) of the resonant electrons and therefore established the parallel wavelength ({approximately}15 m). The electron bunching events were detected at or near the energy at which a positive slope in the electron distribution function was seen. During a dispersive burst, themore » phase velocity (or wavelength) of the Langmuir waves changed in response to the changing velocity at which the positive slope occured. The authors conclude that the velocity dispersion in the low-energy, field-aligned electrons created the unstable electron distribution that was responsible for Langmuir wave growth. The proposed growth mechanism is similar to that suggested for Langmuir wave growth during solar type III radio bursts.« less