Ion pickup by the intrinsic low-frequency Alfvén waves with a spectrum

Ion pickup by a monochromatic low-frequency Alfvén wave, which propagates along the background magnetic field, has recently been investigated in a low beta plasma (Lu and Li 2007 Phys. Plasmas 14 042303). In this paper, the monochromatic Alfvén wave is generalized to a spectrum of Alfvén waves with random phase. It finds that the process of ion pickup can be divided into two stages. First, ions are picked up in the transverse direction, and then phase difference (randomization) between ions due to their different parallel thermal motions leads to heating of the ions. The heating is dominant in the direction perpendicular to the background magnetic field. The temperatures of the ions at the asymptotic stage do not depend on individual waves in the spectrum, but are determined by the total amplitude of the waves. The effect of the initial ion bulk flow in the parallel direction on the heating is also considered in this paper.     

Effects of Heavy Ions on Kinetic Alfvén Waves

Kinetic Alfvén Wave (KAW) is one of the low-frequency electromagnetic fluctuations that are identified extensively in space plasmas by in situ observations of satellites and has been an interesting topic for discussion widely in the fields of laboratory, space, and astrophysical plasmas because of its potential importance in plasma particle energization. Some satellite observations show that the number density ratio of the oxygen ions to the ambient plasma is 30%～50%, sometimes, even as high as 80%. In this paper, effects of heavy ion species on KAWs are studied in a low-beta plasma. The results show that heavy ions not only considerably reduce the propagation speed of KAWs, but also remarkably influence the parallel component of perturbed electric field of KAWs (to the ambient magnetic field). The ratio of parallel to perpendicular components of perturbed field decreases (or increases) with the heavy ion abundance for KAWs dominated by the electron inertial length (or by ion acoustic gyroradius). In particular, the resonant condition of KAWs with thermal electrons is modified by the heavy ion species.     

低频Alfvén波多波相干加热粒子模拟

采用粒子模拟方法,考察多支沿背景磁场方向传播的低频Alfvén波对磁化等离子体的加热过程,研究不同频率的多支低频Alfvén波相干加热.结果表明可以通过调整波的频率比实现对非共振加热过程和随机加热过程这两个阶段的强化.符合相干共振条件的多波加热会强化低频Alfvén波对粒子拾取,进而强化非共振加热,明显提高加热效率.在多波加热的过程中,如果多支波之间的频率差足够小,则多波在调制过程中会形成波包.波包的出现标志着粒子各向异性的强化,从而提升随机加热效率.     

Influence of Ion Nonlinear Polarization Drift and Warm Ions on Solitary Kinetic Alfvén Wave

Considering the effects of ion nonlinear polarization drift and warm ions, we adopt two-fluid model to results derived in this paper indicate that dip SKAW and hump SKAW both exist in a wide range in magnetosphere(for the pressure parameter β ~ 10-5 ~ 0.01, where βis the ratio of thermal pressure to magnetic pressure, i.e.region 1 > β > me/mi. These results are different from previous ones. That indicates that the effects of ion nonlinear polarization drift and warm ions are important and they cannot be neglected. The SKAW has an electric field parallel to the ambient magnetic field, which makes the SKAW take an important role in the acceleration and energization of field-aligned charged particles in magnetic plasmas. And the SKAW is also important for the heating of a local plasma.So it makes a novel physical mechanism of energy transmission possible.     

Numerical Simulation of Solitary Kinetic Alfvén Waves

Using the two-fluid model in the case of α〉〉1 （α= β/2Q, β is the ratio of thermal pressure to magnetic pressure, and Q = me/mi ）, we numerically investigate the interactions between two solitary kinetic Alfvén waves （SKAWs） and between an SKAW and a density discontinuity. The results show that the two SKAWs would remain in their original shapes and propagate at their initiating speeds, which indicates that SKAWs behave just like standard solitons. The simulation also shows that SKAWs will reflect and refract when crossing a discontinuity and propagating into a higher density region. The transmission wave is an SKAW with increasing density, and the reverberation is a disturbance with lower amplitude.     

Effects of Charge in Heavy Ions on Solitary Kinetic Alfvén Waves in Double-Ion Plasmas

After the charge of heavy ions is considered, a Sagdeev equation is obtained for the solitary kinetic lfvén waves (SKAWs) in a low-β (m_e/m_p « β « or m_p/m_e » α » 1), three-component (electrons, protons, and highly charged heavy ions) plasma. Numerical results show that the charge number q of heavy ions can cause the width of the solitary structure to decrease, but increase for the maximum of electron density n_em≤ 1.2 and the initial abundance of heavy ions C_b0 ≤ 0.1. The parallel phase speed of the waves increases with larger q.     

Effect of Kinetic Alfvén Waves on Electron Transport in an Ion-Scale Flux Rope

At the Earth's magnetopause, the electron transport due to kinetic Alfvén waves(KAWs) is investigated in an ion-scale flux rope by the Magnetospheric Multiscale mission. Clear electron dropout around 90° pitch angle is observed throughout the flux rope, where intense KAWs are identified. The KAWs can effectively trap electrons by the wave parallel electric field and the magnetic mirror force, allowing electrons to undergo Landau resonance and be transported into more field-aligned directions. The pitch angle range for the trapped electrons is estimated from the wave analysis, which is in good agreement with direct pitch angle measurements of the electron distributions. The newly formed beam-like electron distribution is unstable and excites whistler waves,as revealed in the observations. We suggest that KAWs could be responsible for the plasma depletion inside a flux rope by this transport process, and thus be responsible for the formation of a typical flux rope.     

Effects of the Safety Factor on Ion Temperature Gradient Modes

In the previous models for the ion temperature(ITG)driven instability,the safety factor (r) is introduced into the model through the wavenumber or relative derivative,such sa kθ=lq(r)/r and △1=ik1=(Rq)^-1э/эθ.since the safety factor     

低频Alfvén波对等离子体非共振加热与随机加热的粒子模拟

采用粒子模拟方法,研究沿背景磁场方向传播的低频Alfvén波对磁化等离子体加热的物理过程.模拟结果表明:离子在垂直和平行于背景磁场的方向都得到明显的加热,在非共振加热阶段,垂直方向比平行方向的加热效果更加显著,形成温度各向异性;在随机加热阶段,垂直和平行方向的温度最终达到饱和且趋于一致.加热过程中,离子所获得动力学温度的最大值由外加磁场能量密度与等离子体密度的比值决定,与Alfvén波的频率及振幅无关;离子在平行于背景磁场方向上被加速,并最终获得相当于Alfvén波相速度大小的流速.     

Discrete Alfvn eigenmodes in international thermonuclear experimental reactor operations with negative magnetic shear

Discrete Alfvén eigenmodes in steady-state operation scenarios with negative magnetic shear in the international thermonuclear experimental reactor are investigated in this paper. These magnetohydrodynamic eigenmodes are trapped by the α -induced potential wells along the magnetic field line. Here α =-q²Rdβ/d r with q being the safety factor, β the ratio between plasma and magnetic pressures, and R the major radius, and r the minor radius. Due to negligible continuum damping via wave energy tunneling, these Alfvén eigenmodes could be readily destabilized by energetic particles.     

An approximate solution of the DKP equation under the Hulthén vector potential

Using the analytical NU technique as well as an acceptable physical approximation to the centrifugal term, the bound-state solutions of the Duffin-Kemmer-Petiau equation are obtained for arbitrary quantum numbers. The solutions appear in terms of the Jacobi Polynomials. Various explanatory figures and tables are included to complete the study.     

The Temperature Effects on the Ion Trap Quantum Computer

We consider one source of decoherence for a quantum computer composed of many trapped ions due to the thermal effects of the system in the presence of laser-ion interaction.The upper limit of the temperature at which the logical gate operations could be carried out reliably is given,and our result is agreement with the experiment.     

Nonlinear Coupling of Reversed Shear Alfvén Eigenmode and Toroidal Alfvén Eigenmode during Current Ramp

Two novel nonlinear mode coupling processes for reversed shear Alfvén eigenmode(RSAE) nonlinear saturation are proposed and investigated. In the first process, the RSAE nonlinearly couples to a co-propagating toroidal Alfvén eigenmode(TAE) with the same toroidal and poloidal mode numbers, and generates a geodesic acoustic mode. In the second process, the RSAE couples to a counter-propagating TAE and generates an ion acoustic wave quasi-mode. The condition for the two processes to occur is favored during current ramp. Both the processes contribute to effectively saturate the Alfvénic instabilities, as well as nonlinearly transfer of energy from energetic fusion alpha particles to fuel ions in burning plasmas.     

Electron Acceleration by a Finite-Amplitude Solitary Kinetic Alfvén Wave

The electron acceleration by a finite-amplitude solitary kinetic Alfvén wave (SKAW) in the low-β magnetized plasma is presented. It is found that the electron can be efficiently accelerated in both the parallel and the transverse directions of ambient magnetic field by a finite-amplitude SKAW up to several tenfold Alvén velocity within the time 0.08μs. These results are greatly different from the case of the electron accelerated by a small-amplitude SKAW.     

MHD spectroscopy through detecting toroidal Alfvén eigenmodes and Alfvén wave cascades

Toroidal Alfvén eigenmodes and a new class of modes, the Alfvén cascades, excited by energetic ions are observed in the JET tokamak. Measurements of these Alfvén instabilities are used to solve the inverse problem of identifying the plasma parameters using the dependence of the Alfvén spectrum on equilibrium parameters.     

Topological constraints on solar loop plasma instabilities and Alfvén waves

Inhomogeneous plasmas-solar instabilities-are investigated by using the techniques of classical differential geometry for curves, where the Frenet torsion and curvature describe completely the motion of a curve. In our case, the Frenet frame changes in time and also depends upon the other coordinates, taking into account the inhomogeneity of the plasma. The exponential perturbation method, so commonly used to describe cosmological perturbations, is applied to the magnetohydrodynamic (MHD) plasma equations to find modes describing Alfvén wave propagation in the medium of planar loops. Stability is investigated in the imaginary axis of the spectra of complex frequencies ω, i.e. m (ω) ≠ 0. A pratical guide for experimental solar physicists is given by computing the twist of force-free solar loops, which generalizes the Parker formula relating the twist to the Frenet torsion. In our expression the twist of the solar loops also depends on the abnormality of the normal vector of the frame.      

Exact bound state solutions of the Klein--Gordon particle in Hulthén potential

In this paper, the Klein-Gordon equation with the spherical symmetric Hulthén potential is turned into a hypergeometric equation and is solved in the framework of function analysis exactly. The corresponding bound state solutions are expressed in terms of the hypergeometric function, and the energy spectrum of the bound states is obtained as a solution to a given equation by boundary constraints.     

Observation of odd toroidal Alfvén eigenmodes

Experimental evidence is presented for the existence of the theoretically predicted odd toroidicity induced Alfvén eigenmode (TAE) from the simultaneous appearance of odd and even TAEs in a normal shear discharge of the joint European torus. The modes are observed in low central magnetic shear plasmas created by injecting lower hybrid current drive. A fast ion population was created by applying ion cyclotron heating at the high-field side to excite the TAEs. The odd TAEs were identified from their frequency, mode number, and timing relative to the even TAEs.