Electron beam-generated whistler waves are widely found in the Earth's space plasma environment and are intricately involved in a number of phenomena. Here we study the linear growth of whistler eigenmodes excited by a finite gyrating electron beam, to facilitate the interpretation of relevant experiments on beam-generated whistler waves in the Large Plasma Device at UCLA. A linear instability analysis for an infinite gyrating beam is first performed. It is shown that whistler waves are excited through a combination of cyclotron resonance, Landau resonance and anomalous cyclotron resonance, consistent with our experimental results. By matching the whistler eigenmodes inside and outside the beam at the boundary, a linear growth rate is obtained for each wave mode and the corresponding mode structure is constructed. These eigenmodes peak near the beam boundary, leak out of the beam region and decay to zero far away from the beam.
The solar wind in the inner heliosphere has been observed by Parker Solar Probe (PSP) to exhibit abundant wave activities. The cyclotron wave modes in the sense of ions or electrons are among the most crucial wave components. However, their origin and evolution in the inner heliosphere close to the Sun remain mysteries. Specifically, it remains unknown whether it is an emitted signal from the solar atmosphere or an eigenmode growing locally in the heliosphere due to plasma instability. To address and resolve this controversy, we must investigate the key quantity of the energy change rate of th…
Whistler mode wave is a fundamental perturbation of electromagnetic fields and plasmas in various environments including planetary space, laboratory and astrophysics. The origin and evolution of the waves are a long-standing question due to the limited instrumental capability in resolving highly variable plasma and electromagnetic fields. Here, we analyse data with the high time resolution from the multi-scale magnetospheric spacecraft in the weak magnetic environment (i.e., foreshock) enabling a relatively long gyro-period of whistler mode wave. Moreover, we develop a novel approach to separa…
The recent simulations showed that the whistler heat flux instability, which presumably produces the most of quasi-parallel coherent whistler waves in the solar wind, is not efficient in regulating the electron heat conduction. In addition, recent spacecraft measurements indicated that some fraction of coherent whistler waves in the solar wind may propagate anti-parallel to the electron heat flux, being produced due to a perpendicular temperature anisotropy of suprathermal electrons. We present analysis of properties of parallel and anti-parallel whistler waves unstable at electron heat fluxes…
The hot beaming (or strahl) electrons responsible for the main electron heat-flux in the solar wind are believed to be self-regulated by the electromagnetic beaming instabilities, also known as the heat-flux instabilities. Here we report the first quasi-linear theoretical approach of the whistler unstable branch able to characterize the long-term saturation of the instability as well as the relaxation of the electron velocity distributions. The instability saturation is not solely determined by the drift velocities, which undergo only a minor relaxation, but mainly from a concurrent interactio…
Thermalization and heating of plasma flows at shocks result in unstable charged-particle distributions which generate a wide range of electromagnetic waves. These waves, in turn, can further accelerate and scatter energetic particles. Thus, the properties of the waves and their implication for wave-particle interactions are critically important for modeling energetic particle dynamics in shock environments. Whistler-mode waves, excited by the electron heat flux or a temperature anisotropy, arise naturally near shocks and foreshock transients. As a result, they can often interact with supra-the…
In this paper, we report the novel experimental observation of both unstable and stable Toroidicity-induced Alfvén Eigenmodes (TAEs) measured simultaneously in a JET tokamak plasma. The three-ion-heating scheme (D-DNBI-3He) is employed to accelerate deuterons to MeV energies, thereby destabilizing TAEs with toroidal mode numbers n = 3-5, each decreasing in mode amplitude. At the same time, the Alfvén Eigenmode Active Diagnostic resonantly excites a stable n = 6 TAE with total normalized damping rate $-γ/ω_0 \approx$ 1%-4%. Hybrid kinetic-MHD modeling with codes NOVA-K and MEGA both find eigenm…
Kinetic instabilities in a dense plasma of a continuous ECR discharge in a mirror magnetic trap at the GISMO setup are studied. We experimentally define unstable regimes and corresponding plasma parameters, where the excitation of electromagnetic emission is observed, accompanied by the precipitation of energetic electrons from the magnetic trap. Comprehensive experimental study of the precipitating electron energy distribution and plasma electromagnetic emission spectra, together with theoretical estimates of the cyclotron instability increment proves that under the experimental conditions th…
Rotational Fresnel drag - or orbital Faraday rotation - in a rotating magnetised plasma is uncovered and studied analytically for Trivelpiece-Gould and Whistler-Helicon waves carrying orbital angular momentum (OAM). Plasma rotation is shown to introduce a non-zero phase shift between OAM-carrying eigenmodes with opposite helicities, similarly to the phase-shift between spin angular momentum eigenmodes associated with the classical Faraday effect in a magnetised plasma at rest. By examining the dispersion relation for these two low-frequency modes in a Brillouin rotating plasma, this Faraday-Fr…
Transport equations for electron thermal energy in the high $β_e$ intracluster medium (ICM) are developed that include scattering from both classical collisions and self-generated whistler waves. The calculation employs an expansion of the kinetic electron equation along the ambient magnetic field in the limit of strong scattering and assumes whistler waves with low phase speeds $V_w\sim{v}_{te}/β_e\ll{v}_{te}$ dominate the turbulent spectrum, with $v_{te}$ the electron thermal speed and $β_e\gg1$ the ratio of electron thermal to magnetic pressure. We find: (1) temperature-gradient-driven whis…
The conventional ion temperature gradient or η_i mode is known to propagate in the ion diamagnetic direction. Investigation of a generic drift fluid model with warm ions and adiabatic electrons, reveals that as η_i decreases, the propagation characteristics of the unstable mode may change drastically, the mode frequency first decreases in magnitude, and reaches zero for a critical η_i. But as η_i goes down further, the mode begins to propagate in the electron diamagnetic direction. The lower toroidal mode number perturbations are more prone to reversal in propagation direction. Even for η_i=0,…
A comprehensive numerical study has been conducted in order to investigate the stability of beam-driven, sub-cyclotron frequency compressional (CAE) and global (GAE) Alfvén Eigenmodes in low aspect ratio plasmas for a wide range of beam parameters. The presence of CAEs and GAEs has previously been linked to anomalous electron temperature profile flattening at high beam power in NSTX experiments, prompting further examination of the conditions for their excitation. Linear simulations are performed with the hybrid MHD-kinetic initial value code HYM in order to capture the general Doppler-shifted…
Comprehensive evaluation of the linear stability of Alfvén eigenmodes driven by alpha particles in an ITER baseline scenario
阿尔文本征模的线性稳定性在聚变产生的α粒子的存在下进行了彻底评估的两个变种的ITER基线方案，这在他们的核心和基座温度显着不同。一个系统的方法，考虑所有可能的本征模为一个给定的磁平衡，并确定其增长率由于α粒子驱动器和朗道阻尼燃料离子，氦灰和电子。这种广泛的稳定性研究是有效地进行，通过使用一个专门的工作流程，从混合MHD漂移动力学代码$\mbox{CASTOR-K}$（Borba D.和Kerner W. 1999 J. Comput.物理学${\bf 153}$ 101; Nabais F. ${\it et\,al}$ 2015血浆科学技术${\bf 17}$ 89），其可以快速评估本征模的线性增长率。结果发现，在上述ITER方案中增长最快的不稳定性是核心本地化，低剪切环形阿尔文本征模。最大的增长率发生在具有较高的核心温度的方案变体中，其具有最高的α粒子密度和密度梯度，对于具有环形模式数$n\approx30$的本征模式。虽然这些本征模遭受显着的辐射阻尼，这也是评估，它们的增长率仍然大于那些最不稳定的本征模中发现的ITER基线方案的变化与较低的核心温度，有$n\approx15$，不受辐射阻尼。
Neutral-beam-driven, sub-cyclotron compressional (CAE) and global (GAE) \Alfven eigenmodes are routinely excited in spherical tokamaks such as NSTX(-U) and MAST, have been observed on the conventional aspect ratio tokamak DIII-D, and may be unstable in ITER burning plasmas. Their presence has been experimentally linked to the anomalous flattening of electron temperature profiles at high beam power in NSTX, potentially limiting fusion performance. A detailed understanding of CAE/GAE excitation, therefore, is vital to predicting (and ultimately controlling) their effects on plasma confinement. T…
Important efforts are currently made for understanding the so-called kinetic instabilities, driven by the anisotropy of different species of plasma particles present in the solar wind and terrestrial magnetosphere. These instabilities are fast enough to efficiently convert the free energy of plasma particles into enhanced (small-scale) fluctuations with multiple implications, regulating the anisotropy of plasma particles. In this paper we use both linear and quasilinear (QL) frameworks to describe complex unstable regimes, which realistically combine different temperature anisotropies of elect…
In this paper, we develop a model to describe the generalized wave-particle instability in a quasi-neutral plasma. We analyze the quasi-linear diffusion equation for particles by expressing an arbitrary unstable and resonant wave mode as a Gaussian wave packet, allowing for an arbitrary direction of propagation with respect to the background magnetic field. We show that the localized energy density of the Gaussian wave packet determines the velocity-space range in which the dominant wave-particle instability and counter-acting damping contributions are effective. Moreover, we derive a relation…
Recently-proposed tokamak concepts use magnetic fields up to 12 T, far higher than in conventional devices, to reduce size and cost. Theoretical and computational study of trends in plasma behavior with increasing field strength is critical to such proposed devices. This paper considers trends in Alfvén eigenmode (AE) stability. Energetic particles, including alphas from D-T fusion, can destabilize AEs, possibly causing loss of alpha heat and damage to the device. AEs are sensitive to device magnetic field via the field dependence of resonances, alpha particle beta, and alpha orbit width. We d…
