Total Plasma Pressure Research Articles

The Heliosheath Plasma Flow Downstream of the Solar Wind Termination Shock in a Consistent Two-Fluid View

In this article, we shall take it serious what has come out from recent theoretical studies on the plasma conditions in the heliosheath, namely downstream of the solar wind termination shock the total plasma pressure is dominated by the pressure of the electrons. We shall respect these results and try to develop the corresponding theoretical basis for an authentic multi-fluid description of the plasma flow downstream of the shock, starting with the dominant pressure action of the local electrons on the mass- and momentum flow of the multi-fluid plasma. It turns out that the usual claim made by Voyager-1 and-2 experimentalists that the bulk velocity of the upwind plasma flow is decreasing with distance from shock, would require that, in reaction to that bulkplasma momentum loss, the electron pressure even increases downstream of the shock. The alternative possibility would be that Voyager-1/-2 data up to now are misinterpreted, and that in fact solar wind bulk velocities in the upwind heliosheath downstream of the shock are increasing opposite to present understandings.

Simulation of equilibrium and transport in advanced FRCS

The advanced beam-driven FRC is a field reversed configuration (FRC) with the addition of neutral beam (NB) injection, electrode biasing, and magnetic expander divertors. The resulting configuration has novel features that make it necessary to revisit many key results in FRC theory. Three of these features include (i) a large energetic ion population, (ii) in-principle capability to adjust the electric field and rotation profiles, and (iii) a combination of magnetic and electrostatic confinement of electrons in the SOL. In some fueling scenarios the electron density profile may exhibit a significant peak outside of the separatrix. To explore these features a hybrid fluid/kinetic equilibrium model has been used to reconstruct typical experimental profiles of the C-2W experiment. Results indicate that the energetic ions provide at least 50% of the total plasma pressure. These equilibrium profiles have been used as initial conditions for global, cross-separatrix, turbulent transport simulations using the 3D electrostatic particle-in-cell code ANC. Electrostatic fluctuations were found to nonlinearly saturate at an amplitude which is an order magnitude lower than that observed previously. The tokamak turbulence code GTC code has also been extended to handle FRC physics in the new GTC-X version, which has been used to perform simulations of turbulent transport in the SOL relevant to electrode biasing. It is found that equilibrium E × B flow shear significantly decreases ion temperature gradient saturation amplitude and ion heat transport. Also in the SOL, a 1D2V continuum code has been developed and applied to parallel electron heat transport. Results show the formation of pre-sheath potential and reduction of parallel electron heat loss close to the ideal ambipolar limit, a result which has been validated by experimental diagnostics. These transport modifications caused by the three novel configuration features help to explain the remarkable plasma performance of the C-2W experiment.

Probing the thermodynamic conditions of the heliosheath plasma by shock wave propagation

Context. The pressure equilibrium between the inner heliosheath and the outer heliosheath (referred to as the local interstellar medium) is an eminent theoretical and practical problem; theoretical, because the relevant pressure carriers have to be identified, and practical, because data must be gathered in order to confirm such a pressure equilibrium. The problem is closely connected with the stability of the heliopause, that is, of the tangential discontinuity between these two counterflowing media, and is of utmost importance for understanding the stability of the whole circumsolar plasma structure. Aims. In this paper we analyze the thermodynamic conditions of the multi-fluid plasma between the solar wind termination shock and the heliopause determining the total heliosheath pressure. We look into this problem from a theoretical standpoint and revisit theoretical descriptions of the solar wind plasma after its passage over the solar wind termination shock, thereafter forming the subsonic heliosheath region. Methods. Hereby we take into account the 3D magnetohydrodynamics shock conditions and the resulting 3D temperature structure of the downstream plasma flow. We use a kind of seismological procedure to probe the heliosheath plasma by inquiring into the propagation conditions of traveling shock wave perturbations in this predetermined 3D heliosheath plasma structure. We discuss the fact that the front geometry of such a traveling shock wave most probably does not remain spherical, if it was to begin with, due to asymmetric shock propagation conditions. In contrast, the wave front is likely to become strongly deformed into an upwind bulge. Results. Concerning the plasma pressure, in addition to solar wind and pick-up proton pressures, we have to take into account the solar wind electron pressure which as a surprise turns out to be of comparable magnitude. As a consequence, the characteristic propagation speed of the traveling shock wave in the weakly magnetized heliosheath plasma is given as a mixed speed expressed by the sound speeds of the protons and the electrons. We describe local low-energy proton density signatures that can be found in Voyager-2 proton data as a consequence of traveling shock wave passages and show that the total local plasma pressure can be directly derived from them.

Cause and impact of low-frequency chirping modes in DIII-D hybrid discharges

Significant variations in MHD activity and fast-ion transport are observed in the DIII-D high-beta, steady-state hybrid discharges with a mixture of electron cyclotron (EC) waves and neutral beam injection (NBI). When electron cyclotron heating (ECH) or current drive (ECCD) is applied, Alfvén eigenmodes (AEs) are usually suppressed and replaced by low-frequency bursting modes. The analysis of a recently compiled database of hybrid discharges suggests that the change of the fast-ion pressure especially the perpendicular pressure is the main factor responsible for the instability transition although the transition in some discharges can also be explained by a slight drop of the safety factor . The lower ratio of fast-ion injection speed vinj to Alfvén speed valfven and slight drop of during ECCD also facilitate the transition. The database shows that AEs mainly occur when the fast-ion fraction is less than 0.53 and is greater than 0.50, while low-frequency bursting modes appear in the opposite regime. Here, Pf and Ptotal are the central fast-ion pressure from classical prediction and total plasma pressure, respectively. The correlation with is weaker, and is around unity in all the cases. The reason why the instability transition correlates with and is that they can significantly modify the drive of low-frequency bursting modes and AEs. The explanation is supported by the observation that low-frequency bursting modes are rarely seen in the hybrids with NBI only, with EC waves and counter-NBI, or with high plasma density. A careful check of the low-frequency bursting modes suggests that they are mainly chirping (neoclassical) tearing modes (referred to as chirping (N)TMs), i.e. the mode frequency firstly jumps up from the steady (N)TM frequency, then chirps down, and finally returns to the steady (N)TM frequency. Occasionally, the (N)TMs are fully stabilized and replaced with pure fishbones. The resonance condition calculation and ‘Kick’ model simulations suggest that (N)TMs and fishbones can interact through modification of the fast ion distribution in phase space, which influences the drive.

Extension of the operating space of high-bN fully non-inductive scenarios on TCV using neutral beam injection

The fully non-inductive sustainment of high normalized beta plasmas () is a crucial challenge for the steady-state operation of a tokamak reactor. In order to assess the difficulties facing such scenarios, steady-state regimes have been explored on the tokamak à configuration variable (TCV) using the newly available 1 MW neutral beam injection (NBI) system. The operating space is extended towards plasmas that are closer to those expected in JT-60SA and ITER, i.e. with significant NBI and electron cyclotron resonance heating and current drive (ECRH/CD), bootstrap current and fast ion (FI) fraction. values up to 1.4 and 1.7 are obtained in lower single null L-mode () and H-mode () plasmas, respectively, at zero time averaged loop voltage and . Fully non-inductive operation is not achieved with NBI alone, whose injection can even increase the loop voltage in the presence of EC waves. A strong contribution to the total plasma pressure of thermal and FIs from NBI is experimentally evidenced and confirmed by interpretative ASTRA and NUBEAM modeling, which further predicts that FI charge-exchange reactions are the main loss channel for NBH/CD efficiency. Internal transport barriers, which are expected to maximize the bootstrap current fraction, are not formed in either the electron or the ion channel in the plasmas explored to date, despite a significant increase in the toroidal rotation and FI fraction with NBI, which are known to reduce turbulence. First results on scenario development of high- fully non-inductive H-mode plasmas are also presented.

The First Direct Observational Confirmation of Kinematic Collisionless Relaxation in Very Low Mach Number Shocks Near the Earth

AbstractCollisionless shocks are ubiquitous throughout the known universe. They mainly convert the energy of the directed ion flow into heating. Upon crossing the shock front, the ion distribution becomes nongyrotropic. Relaxation to gyrotropy then occurs mainly via kinematic collisionless gyrophase mixing and interaction with waves. The theory of collisionless relaxation predicts that the downstream pressure of each ion species varies quasi‐periodically with the distance from the shock transition layer and the amplitude of the variations gradually decrease. The oscillations due to each species have their own spatial period and damping scale. Pressure balance requires that the variations in the total plasma pressure should cause anticorrelating variations in the magnetic pressure. This process should occur at all Mach numbers, but its observation is difficult at moderate‐/high‐Mach numbers. In contrast, such magnetic oscillations have been observed at low Mach number cases of the Venusian bow shock and interplanetary shocks. In this paper, simultaneous in situ magnetic field and plasma measurements from the THEMIS‐B and THEMIS‐C spacecraft are used to study, for the first time, the anticorrelated total ion and magnetic pressure spatial variations at low‐Mach number shocks. It is found that kinematic collisionless relaxation is the dominant process in the formation of the downstream ion distribution and in shaping the downstream magnetic profile of the observed shocks, confirming fundamental theoretical results. Comparison with the results from numerical models allows the role of the different ion species to be investigated and confirms the role heavy ions play in forming the downstream magnetic profile.

Electric Field and Poloidal Rotation in the Turbulent Edge Plasma of the T-10 Tokamak

The dynamics of turbulent edge plasma in the T-10 tokamak is simulated numerically by solving reduced nonlinear MHD equations of Braginskii’s two-fluid hydrodynamics. It is shown that the poloidal plasma velocity is determined by the combined effect of two forces: the turbulent Reynolds force FR and the Stringer–Winsor geodesic force FSW, which is associated with the geodesic acoustic mode of the total plasma pressure $$\left\langle {p{\text{sin}}\theta } \right\rangle $$ . It follows from the simulation results that the FR and FSW forces are directed oppositely and partially balance one another. It is shown that, as the electron temperature increases, the resulting balance of these forces changes in such a way that the amplitude of the poloidal ion flow velocity and, accordingly, the electrostatic potential $${{\phi }_{0}}(r,t)$$ decrease. As the plasma density increases, the “driving forces” of turbulence (the dn0/dr and dp0/dr gradients) also increase, while dissipation due to the longitudinal current decreases, which results in an increase in the amplitude of turbulent fluctuations and the Reynolds force FR. On one hand, the force FSW increases with increasing plasma density due to an increase in the pressure $$\left\langle {p{\text{sin}}\theta } \right\rangle $$ ; however, on the other hand, it decreases in view of the factor 1/n0. As a result, the net force driving poloidal rotation increases, which leads to the growth of the plasma potential. Both under electron-cyclotron resonance heating and in regimes with evolving plasma density, the results of numerical simulations qualitatively agree with experimental data on the electrostatic potential of the T-10 plasma.

Fixed boundary Grad-Shafranov solver using finite difference method in nonhomogeneous meshgrid

In this work we present a numerical scheme to solve the Grad-Shafranov equation which correspond to magnetohydrodynamic equilibrium equation for a two-dimensional plasma. A typical case are the toroidal plasma in magnetic confinement devices used in thermonuclear fusion well known as Tokamaks. The proposed numerical scheme is based on the finite-difference method in nonhomogeneous meshgrid, which is adjusted to the fixed plasma boundary with “D-shape”. The solution of the Grad-Shafranov equation is obtained using the successive over-relaxation method, usually applied to solve Poisson equation’s problems. The values of the total plasma current and pressure in the magnetic axis are conserved in each iteration of the convergence process. The scheme is validated by direct comparison with the analytical result obtained by Soloviev.

The Downwind Hemisphere of the Heliosphere: Eight Years of IBEX-Lo Observations

Abstract We present a comprehensive study of energetic neutral atoms (ENAs) of 10 eV to 2.5 keV from the downwind hemisphere of the heliosphere. These ENAs are believed to originate mostly from pickup protons and solar-wind protons in the inner heliosheath. This study includes all low-energy observations made with the Interstellar Boundary Explorer over the first eight years. Because the protons around 0.1 keV dominate the plasma pressure within the inner heliosheath in downwind direction, these ENA observations offer the unique opportunity to constrain the plasma properties and dimensions of the heliosheath where no in situ observations are available. We first derive energy spectra of ENA intensities averaged over time for 49 macropixels covering the entire downwind hemisphere. The results confirm previous studies regarding integral intensities and the roll-over around 0.1 keV energy. With the expanded data set, we now find that ENA intensities at 0.2 and 0.1 keV seem to anti-correlate with solar activity. We then derive the product of total plasma pressure and emission thickness of protons in the heliosheath to estimate lower limits on the thickness of the inner heliosheath. The temporally averaged ENA intensities support a rather spherical shape of the termination shock and a heliosheath thickness between 150 and 210 au for most regions of the downwind hemisphere. Around the nominal downwind direction of 76° ecliptic longitude, the heliosheath is at least 280 au thick. There, the neutral hydrogen density seems to be depleted compared to upwind directions by roughly a factor of 2.

Contribution of energetic and heavy ions to the plasma pressure: The 27 September to 3 October 2002 storm

AbstractMagnetospheric plasma sheet ions drift toward the Earth and populate the ring current. The ring current plasma pressure distorts the terrestrial internal magnetic field at the surface, and this disturbance strongly affects the strength of a magnetic storm. The contribution of energetic ions (>40 keV) and of heavy ions to the total plasma pressure in the near‐Earth plasma sheet is not always considered. In this study, we evaluate the contribution of low‐energy and energetic ions of different species to the total plasma pressure for the storm observed by the Cluster mission from 27 September until 3 October 2002. We show that the contribution of energetic ions (>40 keV) and of heavy ions to the total plasma pressure is ≃76–98.6% in the ring current and ≃14–59% in the magnetotail. The main source of oxygen ions, responsible for ≃56% of the plasma pressure of the ring current, is located at distances earthward of XGSE ≃ −13.5 RE during the main phase of the storm. The contribution of the ring current particles agrees with the observed Dst index. We model the magnetic storm using the Space Weather Modeling Framework (SWMF). We assess the plasma pressure output in the ring current for two different ion outflow models in the SWMF through comparison with observations. Both models yield reasonable results. The model which produces the most heavy ions agrees best with the observations. However, the data suggest that there is still potential for refinement in the simulations.

Formation of self-consistent pressure profiles in simulation of turbulent convection in tokamak plasmas

The formation of pressure profiles in turbulent tokamak plasmas in ohmic heating regimes and transient regimes induced by turning-on of electron-cyclotron resonance (ECR) heating is investigated. The study is based on self-consistent modeling of low-frequency turbulent plasma convection described by an adiabatically reduced set of hydrodynamic-type equations. The simulations show that, in the ohmic heating stage, turbulence forms and maintains profiles of the total plasma pressure corresponding to turbulentrelaxed states. These profiles are close to self-consistent profiles of the total plasma pressure experimentally observed on the T-10 tokamak in ohmic regimes with different values of the safety factor qL at the limiter. Simulations of nonstationary regimes induced by turning-on of on- and off-axis ECR heating show that the total plasma pressure profiles in the transient regimes remain close to those in the turbulent-relaxed state, as well as to the profiles experimentally observed on T-10.

Entropy generation at multi-fluid magnetohydrodynamic shocks with emphasis to the solar wind termination shock

In a series of earlier papers, we developed expressions for ion and electron velocity distribution functions and their velocity moments at the passage over the solar wind termination shock. As we have shown there, with the introduction of appropriate particle invariants and the use of Liouville’s theorem one can get explicit solutions for the resulting total downstream pressure by adding up from partial pressure contributions of solar wind protons, solar wind electrons and pick-up protons. These expressions are the first step toward delivering the main contributions to the total plasma pressure in the downstream plasma flow and consistently determine the shock compression ratio. Here we start from these individual fluid pressures downstream of the shock and thereafter evaluate for the first time the shock-induced entropy production of the different fluids, when they are passing over the shock to the downstream side. As shown here, the resulting ion entropy production substantially deviates from earlier calculations using a pseudo-polytropic reaction of the ions to the shock compression, with polytropies selected to describe fluid-specific reactions at the shock passage similar to those seen by the Voyagers. From these latter models, ion entropy jumps are derived that depend on the pick-up ion abundance, while our calculations deliver an abundance-independent ion entropy production that only depends on the shock compression ratio and the tilt angle between the upstream magnetic field and the normal to the shock surface. We also show here that the thermodynamically permitted upper limit in the entropy production is only reached when strongly heated electrons are included in the entropy balance.

Multifrequency constraints on the nonthermal pressure in galaxy clusters

The origin of radio halos in galaxy clusters is still unknown and is the subject of a vibrant debate both from the observational and theoretical point of view. In particular the amount and the nature of non-thermal plasma and of the magnetic field energy density in clusters hosting radio halos is still unclear. The aim of this paper is to derive an estimate of the pressure ratio X between the non-thermal and thermal plasma in radio halo clusters that have combined radio, X-ray and SZ effect observations. From the simultaneous P_{1.4}-L_X and P_{1.4}-Y_{SZ} correlations for a sample of clusters observed with Planck, we derive a correlation between Y_{SZ} and L_X that we use to derive a value for X. This is possible since the Compton parameter Y_{SZ} is proportional to the total plasma pressure in the cluster (that we characterize as the sum of the thermal and non-thermal pressure) while the X-ray luminosity L_X is proportional only to the thermal pressure of the intracluster plasma. Our results indicate that the average (best fit) value of the pressure ratio in a self-similar cluster formation model is X =0.55 \pm 0.05 in the case of an isothermal beta-model with beta=2/3 and a core radius r_c = 0.3 R_{500} holding on average for the cluster sample. We also show that the theoretical prediction for the Y_{SZ}-L_X correlation in this model has a slope that is steeper than the best fit value for the available data. The agreement with the data can be recovered if the pressure ratio X decreases with increasing X-ray luminosity as L_X^{-0.96}. We conclude that the available data on radio halo clusters indicate a substantial amount of non-thermal pressure in cluster atmospheres whose value must decrease with increasing X-ray luminosity, or increasing cluster mass (temperature). (abridged)

Solar wind‐driven plasma fluxes from the Venus ionosphere

AbstractMeasurements conducted with the ASPERA‐4 instrument and the magnetometer of the Venus Express spacecraft show that the kinetic pressure of planetary O+ ion fluxes measured in the Venus wake can be significantly larger than the local magnetic pressure, and as a result, those ions are not solely being driven by magnetic forces but also by the kinetic energy of the solar wind. Beams of planetary O+ ions with those properties have been detected in several orbits of the Venus Express through the Venus wake as the spacecraft traverses by the noon‐midnight plane along its near‐polar trajectory. The momentum flux of the O+ ions leads to superalfvenic flow conditions. It is suggested that such O+ ion beams are produced in the vicinity of the magnetic polar regions of the Venus ionosphere where the solar wind erodes the local plasma leading to plasma channels that extend downstream from those regions. The distribution of the number of cases where superalfvenic and subalfvenic conditions are measured along the Venus Express trajectory leads to dominant values when the total kinetic plasma pressure (including that of the solar wind protons) and the magnetic pressure are comparable, thus suggesting a possible equipartition of energy between the plasma and the magnetic field.

Effect of Electron Pressure on the Grad–Shafranov Reconstruction of Interplanetary Coronal Mass Ejections

We investigate the effect of electron pressure on the Grad–Shafranov (GS) reconstruction of Interplanetary Coronal Mass Ejection (ICME) structures. The GS method uses in situ magnetic field and plasma measurements to solve for a magnetohydrostatic quasi-equilibrium state of space plasmas. For some events, a magnetic flux-rope structure embedded within the ICME can be reconstructed. The electron temperature contributes directly to the calculation of the total plasma pressure, and in ICMEs its contribution often substantially exceeds that of proton temperature. We selected ICME events observed with the Wind spacecraft at 1 AU and applied the GS reconstruction method to each event for cases with and without electron temperature measurements. We sorted them according to the proton plasma β (the ratio of proton plasma pressure to magnetic pressure) and the electron-to-proton temperature ratio. We present case studies of three representative events, show the cross sections of GS reconstructed flux-rope structure, and discuss the electron pressure contribution to key quantities in the numerical reconstruction procedure. We summarize and compare the geometrical and physical parameters derived from the GS reconstruction results for cases with and without electron temperature contribution. We conclude that overall the electron pressure effect on the GS reconstruction results contributes to a 10 – 20 % discrepancy in some key physical quantities, such as the magnetic flux content of the ICME flux rope observed at 1 AU.

Phasespace transport of a quasi-neutral multi-fluid plasma over the solar wind MHD termination shock

We study the physics of a multi-ion MHD shock, i.e. an MHD shock feature that forms when a supersonic flow of mixed ion populations is forced to adapt itself to a pressure obstacle further downstream. We shall describe this situation by using a multi-fluid approach for a mixture of ion populations with different specific masses and charges per ion species. First we calculate the effective electric potential that forces the plasma bulk to decelerate to the downstream bulk flow velocity which also then defines that system into which the downstream magnetic field is frozen-in. Then we calculate the unavoidable ion-specific overshoot velocities and gain from them, requesting energy conservation, the ion-specific contributions to the downstream thermal energies and pressures. The aim thereby is to find the solution for the MHD status of the downstream flow of the plasma mixture, specifically for a proton-electron plasma. We derive an implicit equation for the effective compression ratio and explicit relations for the different, downstream ion and electron temperatures as function of the multi-fluid compression ratio s. The resulting actual multi-fluid compression ratio s eff is found by adding up all the partial downstream pressures and comparing it with the upstream ram pressure. As we can show, the electron pressure is the dominant contribution to the total downstream plasma pressure.

Investigations of high-energy electrons of the microwave discharge plasma at configuration of the “Magnetor” Bi-dipole magnetic confinement system by X-ray radiation analyses

The results of the investigations of a group of fast electrons in a microwave discharge plasma in the “Magnetor” magnetic trap are presented. The data on the presence and location of this group of electrons is important for estimating the total plasma pressure taking the previous probe measurements into account. Fast electrons are found to be localized within the magnetic separatrix in the region of confinement of the main plasma. The maximal energy of fast electrons is higher than 25 keV.

Confinement of ‘improved H-modes’ in the all-tungsten ASDEX Upgrade with nitrogen seeding

In ASDEX Upgrade the compatibility of improved H-modes with an all-W wall has been demonstrated. Under boronized conditions light impurities and the radiated power fraction in the divertor were reduced, requiring N seeding to cool the divertor plasma. The impurity seeding does not only protect the divertor tiles but also considerably improves the performance of improved H-mode discharges by up to 25%. The energy confinement increases to H98-factors up to 1.3 and thereby exceeds the best values in the carbon-dominated AUG at the same density and collisionality. This improvement is due to higher edge temperatures rather than to peaking of the electron density profile. Higher temperatures are reached at the pedestal top leading, via profile stiffness, to an increase in the total plasma pressure. There is no change to in the plasma core. The dilution at the plasma edge by nitrogen seems to play an important role since it allows higher ion temperatures at the same edge ion pressure as in the unseeded case. The dilution of the core plasma remains moderate.

Boundary conditions at the limiter surface obtained in the modelling of plasma wall interaction with a penalization technique

Isoardi et al. [1] recently proposed a penalization technique to model solid plasma facing components that treats a solid obstacle as a sink region corresponding to the strong plasma recombination in the solid state material. A major advantage of this approach is that it produces a system that can be solved in an obstacle free domain, thus allowing the use of powerful numerical algorithms. Such a technique implemented in a minimal transport model for ionic density and parallel momentum appeared to exhibit a Mach-1 transition at the boundary layer between the plasma presheath and the limiter region. In this paper, we reconsider this result by analysing the physics of detached plasmas that are governed both by strong recombination and plasma pressure decrease, as imposed by the penalization technique within the limiter region. The analysis provides a unique control parameter A=Γcsmi/Π (Γ being the parallel particles flux, cs the sound speed, mi the ionic mass and Π the total plasma pressure) that allows one to understand the results of the penalization technique for the Mach-1 transition.

Contribution of the Large Helical Device Plasmas to Alfvén Eigenmode Physics in Toroidal Plasmas

In the large helical device (LHD) having three dimensional configuration, Alfvén eigenmodes (AEs) destabilized by energetic ions are widely investigated using neutral beam heated plasmas with monotonic and non-monotonic rotational transform (ι/2π) profiles. In a plasma with monotonic ι/2π-profile, core-localized toroidicity-induced Alfvén eigenmode (TAE) as well as global one are often observed. With the increase in the averaged toroidal beta value, defined as the ratio of total plasma pressure to toroidal magnetic pressure, core-localized TAE with low toroidal mode number becomes global. In a relatively high beta plasma with monotonic ι/2π-profile, two TAEs with different toroidal mode number often interact nonlinearly and generate another modes through three wave coupling. In a plasma with non-monotonic ι/2π-profile generated by intense counter neutral beam current drive, reversed shear Alfvén eigenmode (RSAE) and geodesic acoustic mode (GAM) excited by energetic ions were observed for the first time in a helical plasma. Nonlinear coupling was also observed between RSAE and GAM.