New aspects of whistler waves driven by an electron beam studied by a 3-D electromagnetic code

We have restudied electron beam driven whistler waves with a 3-D electromagnetic particle code. In the initialisation of the beam-plasma system, “quiet start” conditions were approached by including the poloidal magnetic field due to the current carried by beam electrons streaming along a background magnetic field. The simulation results show electromagnetic whistler wave emissions and electrostatic beam modes like those observed in the Spacelab 2 electron beam experiment. It has been suggested in the past that the spatial bunching of beam electrons associated with the beam mode may directly generate whistler waves. However, the simulation results indicate several inconsistencies with this picture: (1) the parallel (to the background magnetic field) wavelength of the whistler wave is longer than that of the beam instability, (2) the parallel phase velocity of the whistler wave is smaller than that of the beam mode, and (3) whistler waves continue to be generated even after the beam mode space charge modulation looses its coherence. The complex structure of the whistler waves in the vicinity of the beam suggest that the transverse motion (gyration) of the beam and background electrons is involved in the generation of the whistler waves.     

相对论电子束的哨声不稳定性

本文根据相对论粒子与电磁波的共振特性, 讨论了相对论电子束的反常迴旋共振产生的哨声不稳定性.满足共振条件的粒子在动量空间位于一组双曲线上.对于具有损失锥分布的相对论电子束, 相对论效应的共振特性提高了哨声不稳定性的阈值, 对ω～0.5Ω_e频段的哨声影响最大.这种作用在背景参数ω_e～Ω_e时最为显著, 并随ω_e/Ω_e增大而减小.      

无碰撞电流片哨声波不稳定性

通过数值求解文献[4]中物理模型A得到的一般形式的色散关系,讨论了无碰撞电流片低频波不稳定性问题.结果表明,哨声波能被无碰撞电流片直接激发.在中性片上(z/di=0),在较宽的波数范围内,斜哨声波是可以传播的,但它基本上是稳定的.在离子惯性区内(z/di<1,电子惯性区外),斜传播的哨声波是不稳定的.在离子惯性区边缘(z/di=1),斜传播的哨声波仍然是不稳定的,增长率更大,不稳定的波频率范围更高.此外,朝向中性片方向传播(kzdi<0)的哨声波比离开中性片方向传播(kzdi>0)的哨声波有更大的增长率.     

Injection of 40-kHz-modulated electron beam from the satellite: II. Excitation of electrostatic and whistler waves

Beam-plasma interaction effects are studied during the active space experiment with electron and Xe-ion beam injections in an ionospheric plasma. Permanent 40-kHz-modulated electron beam injection occurs simultaneously with a xenon-ion beam injected by the Hall-type plasma thruster operating in a square-pulse mode (100/50 s for a job/pause duration). The unusual behavior of the background charged particle fluxes and wave activity stimulated during the beam-plasma interaction have been registered by the scientific instruments onboard Intercosmos-25 station (IK-25) and Magion-3 subsatellite. The longitudinal and electromagnetic wave instabilities and their mutual relationship are considered in order to explain the observed effects. The excitation of electrostatic waves by the electron injection has been considered for different resonance conditions near the linear stability boundary. Beam-driven electromagnetic instability is responsible for the backward-propagating whistler waves excited via cyclotron resonance. Competition of these two beam instabilities is one of the subjects of the present study.     

Study of VLF wave with relativistic effect in Saturn magnetosphere in the presence of parallel A.C. electric field

Cassini radio and plasma wave surveys aim to study radio emissions, plasma waves, thermal plasma and dust near Saturn. Using the characteristic solution and dynamics method, the influence of electron beam on the loss cone and bi-Maxwellian distribution of whistler mode waves in the parallel alternating electric field and magnetic field is studied. The dispersion relation and the growth rate of Saturn's magnetic layer were deduced and calculated in detail. Parameter analysis is performed by changing the parameters of the plasma like number density, AC frequency, temperature anisotropy, etc. The influence of AC frequency on Doppler shift and the comparative study of growth rate of oblique and parallel propagating waves are analyzed using generalized distribution function. We found temperature anisotropy ${\text{A}}_{\text{T}}=1.25$ can explain the linear spatiotemporal growth rate of whistler mode waves. It provides the majority of the observed frequency integral power. It can be seen that the effective parameters for the generation of Whistler mode waves are not only temperature anisotropy, but also the relativistic factors discussed in the results and discussion section, and the AC field frequency and width of the loss cone distribution function.     

Acceleration of energetic particles by whistler waves in active space experiment with charged particle beams injection

In this paper the investigation of wave-particle interaction during simultaneous injection of electron and xenon ion beams from the satellite Intercosmos-25 (IK-25) carried out using the data of the double satellite system with subsatellite Magion-3 (APEX). Results of active space experiment devoted to the beam-plasma instability are partially presented in the paper Baranets et al. (2007). A specific feature of the experiment carried out in orbits 201, 202 was that charged particle flows were injected in the same direction along the magnetic field lines B₀ so the oblique beam-into-beam injection have been produced. Results of the beam-plasma interaction for this configuration were registered by scientific instruments mounted on the station IK-25 and Magion-3 subsatellite. Main attention is paid to study the electromagnetic and longitudinal waves excitation in different frequency ranges and the energetic electron fluxes disturbed due to wave-particle interaction with whistler waves. The whistler wave excitation on the 1st electron cyclotron harmonic via normal Doppler effect during electron beam injection in ionospheric plasma are considered.     

Pitch angle diffusion as seen by CRRES

Lifetimes and pitch angle distributions of radiation belt electrons injected into the slot region are determined from CRRES/MEA particle flux measurements. The dominant loss mechanism is presumed to be pitch angle scattering due to whistler waves, for which a theoretical formulation is available. The empirical lifetimes are compared to those from recent calculations, which rely on model whistler wave parameters. CRRES measurements of cyclotron-frequency electric fields are also presented and compared to the wave model.     

哨声模合声波与地球同步轨道高能电子通量增强事件事例研究

局部加速机制是磁暴期间地球外辐射带高能电子通量增强事件发生的重要原 因. 此加速机制需要两个基本条件, 一是存在种子电子, 二是存在能与种子 电子产生共振的加速波动, 包括哨声模合声波. 通过对2004-2006年 Pi1地磁脉动持续时间与种子电子通量的相关性分析, 更明确提出Pi1地磁脉 动的持续时间可以作为种子电子通量的指示剂. 通过对三个磁暴事例地球同 步轨道的种子电子通量、高能电子通量及哨声模合声波变化情况的分析, 发 现在高能电子通量较强的事例中, 均观测到较高的种子电子通量和较强的 哨声模合声波, 这在一定程度上验证了哨声模合声波对种子电子的回旋加速 机制, 且合声波强度与高能电子通量有正的相关性.      

Whistler waves in plasmas with time-varying magnetic field: Laboratory investigation

Modulation of whistler waves in a plasma with time-dependant magnetic field perturbations was investigated experimentally. The experiments were performed on large “Krot” device, which was specially designed to study space plasma physics phenomena. It is shown that magnetic field variations on the wave propagation path can lead to splitting of initially continuous whistler wave into the sequence of bursts, whose repetition rate corresponds to magnetic field perturbation period. The frequency inside each burst is changing from its front edge to the back edge. Relative shift of the wave frequency can be as large as the relative magnetic disturbance. Distortion of whistler wave frequency spectrum after its passing through magnetically disturbed areas can be used as a diagnostics for low-frequency magnetic field variations. The applicability of our laboratory results to space plasma is discussed.     

调制电子束弛豫长度对哨声波辐射的影响

在发射调制电子束的主动空间试验中,电子束与背景等离子体的线性和非线性相互作用将产生哨声波辐射.影响辐射特性的因素很多,调制电子束的弛豫长度是其中一个重要因素.本文研究了呈指数衰减的调制电子束弛豫长度对电子束产生的哨声波辐射特性的影响.结果表明,当电子束弛豫长度与背景等离子体非均匀特征尺度相当时,有利于提高调制电子束产生的波辐射强度.      

An investigation into the roles of ECH and whistler mode waves in the formation of “pancake” electron distributions using data from the CRRES satellite

Electron pitch angle distributions sharply peaked at 90° pitch angle were first recorded in the energy range 50 eV < E < 500 eV by the GEOS-1 and GEOS-2 spacecraft in 1977/8, from the plasmapause out to geostationary orbit. At the time they were explained as the remnants of pitch angle diffusion driven solely by Electron Cyclotron Harmonic (ECH) waves. Here we use observations by instruments on board the CRRES spacecraft to study these distributions in more detail. The pancake distributions are now seen to develop from injected distributions that are nearly isotropic in velocity space, on a time scale that is greater than 2 hours. The freshly injected distributions are associated with strong ECH and whistler mode waves suggesting that the pancake distributions are likely to be caused by a combination of both wave types. Our results suggest that whistler mode waves play a dominant role in the formation of pancake distributions outside L = 6.0, whereas inside L = 6.0 and, in particular, in the vicinity of the plasmapause, the ECH waves also play a significant role. Consequently both types of waves should be considered in any attempt to explain the diffuse aurora and the variation with L taken into account.     

哨声模波通过低纬电离层传播的某些特征

本文采用IGRF(1980)模型进行了哨声模三维射线跟踪计算, 研究了夜间哨声通过低纬电离层传播的射线与波法的特征.着重讨论了形成非导管哨声可透射路径的条件、射线的聚焦效应及射线的低纬截止.数值计算得到路径终纬度截止约在倾角纬度10.7°N.      

哨声波的自聚焦(Ⅱ)——当磁层对波有放大作用时的讨论

本文指出, 当磁层对波有放大作用时, 哨声波的自聚焦容易发生;当磁层对波有吸收时, 哨声波的自聚焦不容易发生.      

磁纬10°以下哨声路径纬度和所需抬升因子积分中值的估算方法

本文采用国际地磁参考场(1980IGRF,n=8)磁力线经验公式和三层模式电离层,结合哨声波沿磁力线传播所需电子浓度的横向梯度,给出了磁纬10°以下哨声路径纬度和所需抬升因子积分中值的估算方法;从而得出:(1)哨声色散值D不仅与电离层N_mF2正相关,而且与h_mF2也有明显相关性.当路径纬度ф₉₀≤10.5°(IGRF,n=8,下同)时,D与h_mF2负相关;>12时,正相关;在10.5°—12°之间时,正或负相关取决于路径顶点高度与h_m之差值.估算表明,三亚(磁纬7.04°N)收到的哨声中路径纬度ф₉₀≤10.5。的占94.5%,D与h_mF2负相关,这与观测结果一致.(2)所需抬升因子积分中值一般在7—31%之间.      

哨声波的自聚焦

本文分析和计算了由于有质动力所导致的哨声波的自聚焦现象。结果表明,对磁层内的中等强度哨声和强哨声自聚焦是可能的。从而这种自聚焦现象可能是哨声导管传播的一种非线性机制。      

磁层哨声波的丝化不稳定性

本文分析了磁层内哨声波的丝化不稳定性,并计算了增长率.结果表明,对于L(?)4和电场强度约1mV/m的哨声波最大增长率约0.13/1000km,对应最大增长率的横向波长约400km(赤道位置).并进而指出,这种丝化不稳定性有可能是多路径哨声形成的一种非线性机制.      

Rocket borne electron accelerator results pertaining to the beam plasma discharge

Three flights of rocket borne electron accelerators have yielded some results concerning the Beam Plasma Discharge (BPD). The first flight, E||B, from Churchill carrying an accelerator of 2 and 4 keV electrons, produced a spectrum of whistler mode waves which was identical with that produced in a large vacuum chamber, and which we know to be an indicator of BPD. The second, Echo V, launched from Poker Flat, Alaska, carrying an accelerator of 25–35 keV electrons, produced wave emissions at 3–3.5 MHz observed on the ground. Our interpretation is that BPD was not or was weakly produced. In the third flight, NB³-II launched from Churchill with an accelerator of 2, 4 and 8 keV electrons, wave emissions well above the ambient plasma frequency were observed from a separated payload, but very close to the beam, and are interpreted as demonstrating BPD.     

A model for stochastic acceleration of electrons during geomagnetic storms

The theory of resonant diffusion is extended to fully relativistic plasmas, and we examine resonant interactions between electrons and electromagnetic R mode (whistler) and L-mode (EMIC) waves. Resonant diffusion curves are constructed for plasma parameters representative of the Earth's storm time magnetosphere, both inside and outside the plasmapause. EMIC waves can resonate with electrons > 1 MeV, but the energies remain nearly constant along the diffusion curves. Storm-time EMIC waves can induce rapid pitch—angle scattering, but the waves are ineffective for stochastic acceleration of elections. Substantial energy change can occur along the diffusion curves for interactions between resonant electrons and whistler—mode waves, especially in regions of low plasma density. Specifically, whistlers can accelerate electrons from energies near 100 keV to above 1 MeV outside the plasmapause. A model is proposed comprising energy diffusion by whistler-mode chorus and pitch-angle scattering by EMIC waves to account for the gradual acceleration of electrons over the region 4 ≤ L ≤ 6 during the recovery phase of a geomagnetic storm.     

Siple VLF transmissions and their magnetospheric effects observed at Halley,Antarctica

Halley (75.5°S, 26.7°W, L = 4.3) is well placed for reception of subionospheric signals from the Siple transmitter. Occasionally a two-hop magnetospheric response to such signals can be observed. The data presented here are relevant to the problems of the radiation and propagation of VLF waves in the polar earth/ionosphere waveguide, duct stimulation and ducted wave amplification and the growth of triggered emissions. An upper sideband emission 20–40 Hz higher in frequency than the transmitted pulse was often received at a similar strength to, and simultaneously with the two-hop whistler mode echo.     

The waves observed in the ARAKS-North Experiment

Experimental results of the wave measurements over frequency range 0.1 – 5.0 MHz during the first launch of the ARAKS Experiment (26.01.75) are reported. The dynamics of spectra of the whistler mode and plasma mode emission stimulated by high energy electron beam is described.