Numerical simulation of auroral cyclotron maser processes
Numerical simulation of auroral cyclotron maser processes
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DOI：
10.1088/0741-3335/50/7/074011
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发表时间：
2008-07
影响因子：
2.2
通讯作者：
D. Speirs;S. McConville;K. Gillespie;K. Ronald;A. Phelps;A. Cross;R. Bingham;C. Robertson;C. Whyte;I. Vorgul;R. A. Cairns;B. Kellett
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文献类型：
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作者：
D. Speirs;S. McConville;K. Gillespie;K. Ronald;A. Phelps;A. Cross;R. Bingham;C. Robertson;C. Whyte;I. Vorgul;R. A. Cairns;B. Kellett
结果从一个马蹄形的速度分布的电子束辐射发射的数值调查。这一过程与发生在地球磁层极地地区的极光千米辐射现象有关。在极光带的这些区域，粒子加速进入地球偶极子不断增加的磁场，通过磁矩守恒发展出马蹄形的速度分布。理论上已经表明，这种分布对于回旋脉泽不稳定性来说是不稳定的。建立了一个二维粒子模拟程序模型，模拟了一个实验室实验，在该实验中，电子束受到明显的磁压缩，并与相互作用波导的TE模发生共振。电子束能量为75-85千电子伏，磁压缩因子高达30和电子回旋频率为4.42和11.7 GHz的结果。在11.7 GHz下，观察到TE 03模式的束波耦合，并获得20 kW的RF输出功率，对应于1.3%的RF转换效率。在4.42 GHz，TE 01模式的激发观察到的RF输出功率为35千瓦的回旋波失谐为2%。这对应于2.6%的RF转换效率。在这两种情况下，PiC粒子的速度分布表明，一个马蹄形的速度分布和随后的行动回旋脉泽不稳定性的明确形成。获得的RF转换效率也与AKR发电效率的估计值相当。
Results are presented from a numerical investigation of radiation emission from an electron beam with a horseshoe-shaped velocity distribution. This process is relevant to the phenomenon of auroral kilometric radiation (AKR) which occurs in the polar regions of the Earth's magnetosphere. In these regions of the auroral zone, particles accelerated into the increasing magnetic field of the Earth's dipole develop a horseshoe-shaped velocity distribution through conservation of magnetic moment. It has been shown theoretically that this distribution is unstable to a cyclotron maser instability. A 2D particle-in-cell (PIC) code model was constructed to simulate a scaled laboratory experiment in which an electron beam subject to significant magnetic compression may be studied and brought into resonance with TE modes of an interaction waveguide. Results were obtained for electron beam energies of 75–85 keV, magnetic compression factors of up to 30 and electron cyclotron frequencies of 4.42 and 11.7 GHz. At 11.7 GHz, beam–wave coupling was observed with the TE03 mode and an RF output power of 20 kW was obtained corresponding to an RF conversion efficiency of 1.3%. At 4.42 GHz, excitation of the TE01 mode was observed with an RF output power of 35 kW for a cyclotron-wave detuning of 2%. This corresponds to an RF conversion efficiency of 2.6%. In both cases PiC particle velocity distributions show the clear formation of a horseshoe-shaped velocity distribution and subsequent action of a cyclotron maser instability. The RF conversion efficiencies obtained are also comparable with estimates for the AKR generation efficiency.