Ion Cyclotron Frequency Research Articles

Generation of O-Mode in the Presence of Ion-Cyclotron Drift Wave Turbulence in a Nonuniform Plasma

This study aims to investigate the effect of ion-cyclotron drift wave turbulence on the generation of ordinary mode (O-mode) in the presence of density and temperature gradients. For this, a Vlasov plasma is considered where a resonant, and non-resonant modes are considered to be present in the system. Here, the non-resonant mode is a perturbation caused by O-mode in a quasi-steady state of plasma, which is characterised by the presence of low frequency ion-cyclotron resonant mode waves. The interaction between these waves is studied by the Vlasov-Maxwell set of equations and a modified Maxwellian-type distribution function for particles that includes the external force field and associated density and temperature gradient parameters . The study analyses the growth rate of electromagnetic O-mode at the expense of ion-cyclotron drift wave energy and the associated impact of the density and temperature gradient. This model uses the linear response theory on weakly turbulent plasma, evaluates the responses due to turbulent and perturbed fields, and obtains the nonlinear dispersion relation for O-mode.

The role of electron current in high-β plasma equilibria

This paper is aimed at investigating the role of electrons in creation of currents in plasma equilibria with high plasma pressure (β≈1). Despite the long history of studies of these equilibria, there is still no consensus on what kind of particle species is responsible for the creation of the diamagnetic current and what characteristic size the current layer should have. For example, simulations of isothermal plasma injection into a multi-cusp magnetic trap [J. Park et al., Front. Astron. Space Sci. 6, 74 (2019)] demonstrate the formation of a transition layer with a thickness comparable to the electron Larmor radius, where the equilibrium current is carried by electrons. At the same time, studies of a diamagnetic bubble created by a hot-ion plasma in a mirror trap [I. Kotelnikov, Plasma Phys. Control Fusion 62, 075002 (2020)] assume ion dominance and completely ignore electron currents. In this paper, we show that the equilibrium initially governed by the ion diamagnetic current is unstable against perturbations at the ion-cyclotron frequency harmonics, and this instability forces the plasma to come to a new equilibrium state in which the current is mainly created by the E×B-drift of electrons. The same type of equilibrium is also found to form in a more realistic problem setup when plasma is continuously injected into the uniform vacuum magnetic field.

DO THE DISPERSION PROPERTIES OF ELECTROMAGNETIC SURFACE WAVES AT THE SHARP BOUNDARY PLASMA-METAL IN SLAB VOIGT GEOMETRY REPRESENT THE LIMITING CASE OF THOSE FOR THE INTERFACE OF TWO PLASMAS?

Electromagnetic surface waves in Voigt geometry are considered to resolve the contradiction between two classical studies. One investigated the waves at the boundary of two plasmas. These waves were reported not to propagate with frequencies below the ion cyclotron frequency. The other approach studied the waves at the metal-plasma interface. Dispersion properties of the waves with frequencies below the ion cyclotron frequency were investigated.

Dynamic Formation of a Transient Jet from Arched Magnetized Laboratory Plasma

A laboratory plasma experiment was built to explore the eruptive behavior of arched magnetized plasmas with dimensionless parameters relevant to the Sun’s photosphere (β ≈ 10−3, Lundquist number ≈104, plasma radius/ion gyroradius ≈20, ion–neutral collision frequency ≫ion cyclotron frequency). Dynamic formation of a transient plasma jet was observed in the presence of the strapping magnetic field. The eruption leading to the jet is unintuitive because the arched plasma is both kink- and torus-stable. The jet structure erupts within a few Alfvén transit times from the formation of the arched plasma. Extensive measurements of plasma temperature, density, magnetic field, and flows are presented. In its early stages, the jet plasma flows away from the arch with supersonic speeds (Mach 1.5). This high-speed flow persists up to the resistive diffusion time in the arched plasma and is driven by large gradients in the magnetic and thermal pressures near the birthplace of jets. There are two distinct electric current channels within the jet, one consisting of outgoing electrons and another composed of electrons returning to the anode footpoint. Significant current density around the jet is a consequence of the diamagnetic current produced by a large thermal pressure gradient in the jet. Ion–neutral charge-exchange collisions provide an efficient mechanism to produce the cross-field current and control the dynamics of the complex current channels of the jet.

On equations for ion cyclotron modes in ‘warm’ bounded plasmas

An equation describing eigenmodes in the ion cyclotron frequency range in ‘warm’ bounded plasmas, i.e. eigenmodes which are absent in the two-fluid model but exist in kinetic theory due to finite Larmor radius of the ions, is derived for the first time. It is valid for electrostatic modes but the developed approach is generic. Calculations are carried out for two cases: first, for a homogeneous magnetic field; second, taking into account the effects of toroidicity in tokamaks. It is found that, in general, equations for eigenmodes in warm plasmas do not reduce to second-order differential equations (in contrast to those which are usually used to describe the radial structure of eigenmodes in fusion devices). The study of modes in warm plasmas is of interest, in particular, in connection with the recent observations of superthermal ion cyclotron emission in the NSTX-U spherical torus and DIII-D tokamak, which can be hardly explained by conventional theories employing fast magnetoacoustic modes.

A novel Doppler backscattering (DBS) system to simultaneously measure radio frequency plasma fluctuations and low frequency turbulence.

A novel quadrature Doppler Backscattering (DBS) system has been developed and optimized for the E-band (60-90GHz) frequency range using either O-mode or X-mode polarization in DIII-D plasmas. In general, DBS measures the amplitude of density fluctuations and their velocity in the lab frame. The system can simultaneously monitor both low-frequency turbulence (f < 10MHz) and radiofrequency plasma density fluctuations over a selectable frequency range (20-500MHz). Detection of high-frequency fluctuations has been demonstrated for low harmonics of the ion cyclotron frequency (e.g., 2fci ∼ 23MHz) and externally driven high-frequency helicon waves (f = 476MHz) using an adjustable frequency down conversion system. Importantly, this extends the application of DBS to a high-frequency spectral domain while maintaining important turbulence and flow measurement capabilities. This unique system has low phase noise, good temporal resolution (sub-millisecond), and excellent wavenumber coverage (kθ ∼ 1-20cm-1 and kr ≲ 30cm-1). As a demonstration, localized internal DIII-D plasma measurements are presented from turbulence (f ≤ 5MHz), Alfvenic waves (f ∼ 6.5MHz), ion cyclotron waves (f ≥ 20MHz), as well as fluctuations around 476MHz driven by an external high-power 476MHz helicon wave antenna. In the future, helicon measurements will be used to validate GENRAY and AORSA modeling tools for prediction of helicon wave propagation, absorption, and current drive location for the newly installed helicon current drive system on DIII-D.

Centrifugal instability in a weakly magnetized rotating plasma column

A two-fluid model is developed to study the stability of weakly magnetized rotating plasma columns. Previous works have shown that rotating plasma columns are prone to centrifugal flute modes. Most of these models are based on the low-frequency assumption which is valid when the instability frequency and the plasma azimuthal frequency are small compared with the ion cyclotron frequency. This assumption is challenged in many laboratory plasma devices, including weakly magnetized plasma columns. A radially global dispersion relation relaxing the low-frequency approximation and applicable in these devices is derived. The validity domain of the low-frequency approximation is discussed. In addition, the impact of the radial boundary on the linear stability is investigated and comparison with results obtained in the radially local approximation are performed.

Observation of ion-cyclotron-range-of-frequency wave emission in electron-cyclotron-resonance-heated tokamak plasma

Emissions of ion-cyclotron-range-of-frequency (ICRF) waves have been observed in a solely electron-cyclotron-resonance-heated plasma, namely no fast-ion plasma, on the JT-60U tokamak for the first time. The mode frequencies are around the ion cyclotron frequency at the low-field-side plasma edge. The waves are considered to be electromagnetic and standing waves from poloidal and toroidal phase differences measured with ICRF antennas. Wave characteristics of the ICRF emissions such as frequency, polarization and propagation are similar to those of edge-ion cyclotron emissions (ICEs) driven by neutral-beam-injected fast ions although driving sources are completely different. From analysis of the resonance conditions, this ICRF wave emission is considered to be driven by the electron-cyclotron-resonance-heated fast electrons via the Cherenkov resonance condition. When ICE is used for fast ion diagnostics, such fast-electron-driven ICRF wave emission may complicate its interpretation during electron cyclotron resonance heating.

Estimation of Turbulent Proton and Electron Heating Rates via Landau Damping Constrained by Parker Solar Probe Observations

The heating of ions and electrons due to turbulent dissipation plays a crucial role in the thermodynamics of the solar wind and other plasma environments. Using magnetic field and thermal plasma observations from the first two perihelia of the Parker Solar Probe, we model the relative heating rates as a function of the radial distance, magnetic spectra, and plasma conditions, enabling us to better characterize the thermodynamics of the inner heliosphere. We employ the Howes et al. steady-state cascade model, which considers the behavior of turbulent, low-frequency, wavevector-anisotropic, critically balanced Alfvénic fluctuations that dissipate via Landau damping to determine proton-to-electron heating rates Q p /Q e . We distinguish ion cyclotron frequency circularly polarized waves from low-frequency turbulence and constrain the cascade model using spectra constructed from the latter. We find that the model accurately describes the observed energy spectrum from over 39.4% of the intervals from Encounters 1 and 2, indicating the possibility for Landau damping to heat the young solar wind. The ability of the model to describe the observed turbulent spectra increases with the ratio of thermal-to-magnetic pressure, β p , indicating that the model contains the necessary physics at higher β p . We estimate high magnitudes for the Kolmogorov constant which is inversely proportional to the nonlinear energy cascade rate. We verify the expected strong dependency of Q p /Q e on β p and the consistency of the critical balance assumption.

Examination of High-Density Plasma Heating on the GAMMA 10/PDX Central Cell with 3D Wave Analysis Code

In GAMMA 10/PDX, ion heating is achieved using slow wave in the ion cyclotron frequency absorbed near the resonance layer. However, in high-density plasma, the slow wave is less likely to be excited due to the shielding effect. To overcome this challenge, researchers have investigated difference frequency (DF) waves excited by the nonlinear interaction of fast waves have been investigated. The fast waves can propagate to the core plasma even in high-density plasma making DF-waves an efficient option for ion heating. This study has suggested that a DF-wave with left-handed polarization, which is excited as a slow wave, is effective for ion heating in high-density plasma. The characteristics of the DF-wave were analyzed using a three-dimensional (3D) wave analysis code, TASK/WF3D, to investigate the ion resonance absorption of DF-wave heating. The results showed that when the antenna is positioned inside the core plasma to simulate DF-wave heating, ion resonance absorption is higher in high-density plasma than in low-density plasma. These results indicate that DF-wave heating is effective in high-density plasmas.

Effects of ion temperature on detached plasma formation using a linear divertor simulator TPDsheet-U

The effect of ion cyclotron resonance heating (ICRH) on the detached plasma formation process was investigated using a linear divertor simulator, TPDsheet-U. We measured the stored energy (ion temperature), electron temperature, electron density, and Balmer series emission intensity ratio of the plasma while increasing the ICRH RF power from 0 to 400 W. It was observed for the first time that the electron temperature of detached plasma increased and the Balmer series emission intensity ratio became smaller when the ion temperature was increased by applying a resonance frequency ωRF, which is about 1.2 times the ion cyclotron frequency ωci of hydrogen ions. This suggests that increasing the ion temperature causes a transition from a detached plasma to an attached plasma.

An axisymmetric mirror device for studying confinement and instability.

We describe a magnetic mirror device, namely, the Keda Mirror with AXisymmetricity (KMAX), which aims to study new approaches to confine and stabilize the mirror plasma as well as basic plasma research. KMAX consists of one central cell, two side cells, and two end chambers at two ends of the device. For the central cell, the mirror-to-mirror distance is 5.2m, while the central cylinder is 2.5m in length and 1.2m in diameter. The plasmas are generated by two washer guns located in the end chambers, which subsequently flow into the central cell and merge there. The density in the central cell is usually adjusted by changing the magnetic field strength inside the side cell, and it ranges from 1017 to 1019m-3, depending on the experimental requirement. Ion cyclotron frequency heating with two 100 kW transmitters is routinely used to heat up the ions. Plasma controls mainly rely on configuring the magnetic geometry and rotating magnetic fields to improve the confinement and suppress instability. Routine diagnostics, such as probes, interferometers, spectrometers, diamagnetic loops, and bolometers, are also reported in this paper.

Analysis of high frequency Alfvén eigenmodes observed in ASDEX Upgrade plasmas in the presence of RF-accelerated NBI ions

High frequency Alfvén eigenmodes in the ion cyclotron frequency range are actively researched on the ASDEX Upgrade tokamak (AUG). The general properties of this particular mode type are: (a) the mode is beam-driven and, if excited, can persist for the entire duration of the beam-on time window; (b) the mode is sub-cyclotron with the frequency ω ∼0.5ω ci, where ωci corresponds to the on-axis cyclotron frequency of the beam ions; (c) the mode propagates in the counter-current/counter-injection direction; and (d) the field-aligned (∼toroidal) mode number is large: |n //| ∼50. It has been observed on AUG that radio frequency- (RF)-acceleration of beam-injected ions at the 3rd cyclotron harmonic significantly expands the number of excited modes. In this work we demonstrate how this observation is consistent with the global Alfvén eigenmode (GAE) behavior. The RF-driven fast ion population is modeled using a combination of an orbit-following Monte Carlo code (ASCOT-RFOF) and an electro-magnetic wave code (TORIC). The application of this code combination is a first to model beam-ion RF-acceleration at the 3rd cyclotron harmonic. The RF-accelerated fast ion distributions are then used to analytically calculate anisotropy-driven mode growth rates. We see that the region of positive (unstable) growth rates is expanded by RF-accelerated fast ions in both the frequency and the mode number directions for the GAEs, consistent with the measurements. Although the compressional Alfvén eigenmode growth rates are also positive for our particular fast ion distributions, the growth rate values are ∼3 orders of magnitude lower. The plasma conditions on AUG are more destabilizing to the GAEs. Overall, our results are consistent with the observation of similar modes on other conventional tokamaks, namely JT-60U and DIII-D.

Electrostatic Ion Cyclotron Waves Observed by CSES in the Equatorial Plasma Bubble

AbstractBroadband ELF electrostatic emissions have been observed by the China Seismo‐Electromagnetic Satellite (CSES) inside the equatorial plasma bubbles (EPBs). Analyses reveal that the electric field fluctuates nearly perpendicular to the ambient magnetic field, with the transverse component gyrotropically distributed around the magnetic field line. The observed emissions, Doppler shifted and broadened, are found to be close to the local oxygen ion (O+) cyclotron frequency in the plasma reference frame. Accompanying ion heating and deceleration are consistent with the consequences of the ion cyclotron resonance. All these results indicate that the electrostatic emissions pervading a major part of the EPB are the O+ electrostatic ion cyclotron (EIC) waves. The inhomogeneous‐energy‐density‐driven instability triggered by the non‐uniform electric field and density gradient across the EPBs could be the source of the EIC waves. The CSES observation provides new evidence for the shear driven EIC wave in the equatorial ionosphere.

Kinetic theory of parametric decay instabilities near the upper hybrid resonance in plasmas

Parametric decay instabilities (PDIs) near the upper hybrid resonance layer are studied with a 1D framework. In a uniform plasma, the kinetic nonlinear dispersion relation of PDI is numerically calculated for parameters corresponding to electron cyclotron heating experiments at the ASDEX-U tokamak, in which O-mode radiation was converted to X-mode radiation by reflection from the high-field sidewall. The forward scattering processes driven by X-mode and linearly converted electron Bernstein waves (EBWs) are investigated and found to lead to a primary PDI where the pump waves decay into lower hybrid waves and sideband EBWs. A frequency shift of 930 MHz is obtained for the sideband EBWs in the primary PDIs. Subsequently, the sideband EBWs can decay into a low-frequency ion Bernstein quasi-mode (IBQM) and a secondary EBW, where the dominant forward scattering channel is the first-order IBQM with a frequency close to twice the ion cyclotron frequency. The decay channels obtained by numerical calculation can explain the characteristics of the signal observed in ASDEX-U experiments. The threshold of the pump electric field strength required to excite the primary PDI in the presence of plasma inhomogeneity is also estimated.

Spatiotemporal dynamics of high-wavenumber turbulence in a basic laboratory plasma

High-spatial resolution observation of high-wavenumber broadband turbulence is achieved by controlling the magnetic field to be relatively low and measuring with a azimuthally arranged multi-channel Langmuir array in a basic laboratory plasma. The observed turbulence consists of narrowband low-frequency fluctuations and broadband high-frequency turbulent fluctuations. The low-frequency fluctuations have a frequency of about 0.7 times the ion cyclotron frequency and a spatial scale of 1/10 of the ion inertial scale. In comparison, high-frequency fluctuations have a higher frequency than the ion cyclotron frequency and spatial scales of 1/10–1/40 of the ion inertial scale. Two-dimensional correlation analysis evaluates the spatial and temporal correlation lengths and reveals that the high-wavenumber broadband fluctuations have turbulent characteristics. The measurements give us further understanding of small scale turbulence in space and fusion plasmas.

Wave-driven electron inward transport in a magnetic nozzle

Plasma flows in divergent magnetic fields resembling a magnetic nozzle can be found over wide scales ranging from astrophysical objects to terrestrial plasma devices. Plasma detachment from a magnetic nozzle is a frequent occurrence in natural plasmas, e.g., plasma ejection from the Sun and release from the Sun’s magnetic field, forming the solar wind. Plasma detachment has also been a challenging problem relating to space propulsion devices utilizing a magnetic nozzle, especially the detachment of the magnetized electrons having a gyro-radius smaller than the system’s scale is required to maintain zero net current exhausted from the system. Here we experimentally demonstrate that a cross-field transport of the electrons toward the main nozzle axis, which contributes to neutralizing the ions detached from the nozzle, is induced by the spontaneously excited magnetosonic wave having the frequency considerably higher than the ion cyclotron frequency and close to the lower hybrid frequency, driving an E × B drift that only effects the electrons. Wave-induced transport and loss have been one of many important issues in plasma physics over the past several decades. Conversely, the presently observed electron inward transport has a beneficial effect on the detachment by reducing the divergence of the expanding plasma beam; this finding will open a new perspective for the role of waves and instabilities in plasmas.

СРАВНЕНИЕ СПЕКТРАЛЬНЫХ ХАРАКТЕРИСТИК УЗКОПОЛОСНОГО ИСКУССТВЕННОГО РАДИОИЗЛУЧЕНИЯ ИОНОСФЕРЫ ПРИ Х-НАГРЕВЕ ВЫСОКОШИРОТНОЙ F-ОБЛАСТИ ИОНОСФЕРЫ НА ЧАСТОТАХ НИЖЕ И ВЫШЕ КРИТИЧЕСКОЙ ЧАСТОТЫ Х-КОМПОНЕНТА СЛОЯ F2

The paper presents the results of investigating generation conditions and features of the narrowband stimulated electromagnetic emission (NSEE) induced by an extraordinary (X-mode) HF pumping into the high-latitude ionosphere F region. It was shown that NSEE spectral features were recorded at a distance of more than 1100 km from the heating facility. Distinctive features of NSEE discrete spectral lines at the pump frequencies fH below and above the F2 layer X-component critical frequency (fH &lt; fXF2 and fH і fXF2) were analyzed. It was found that the NSEE spectrum contains the strongly pronounced discrete lines ordered by the electrostatic ion cyclotron frequency for the atomic oxygen ions (O+). When fH &lt; fXF2, the multiple downshifted and upshifted spectral components (Stokes and anti-Stokes modes, respectively) were excited in the NSEE spectra. When fH і fXF2, the Stokes modes were only generated. The plausible mechanisms for the NSEE excitation by an X-mode HF pump waves are discussed.

A Parametric Study of Oxygen Ion Cyclotron Harmonic Wave Excitation and Polarization by an Oxygen Ring Distribution

AbstractOxygen ion cyclotron harmonic (OCH) waves are electromagnetic emissions with frequencies near the harmonics of the oxygen ion cyclotron frequency. These waves can be excited by an energetic O+ ring distribution. Here, we perform a parametric study of OCH waves by an O+ ring distribution. We investigate the effects of ring concentration (ηho), velocity (vr), temperature (Tr), total O+ concentration (ηo), and wave normal angles (WNAs) on the wave growth rate and polarization. We find that four‐wave modes are related to OCH waves. The growth rates and frequency range increase with ηho and ηo and decrease with Tr. The peak growth rate roughly follows the first peak of (square of the Bessel function corresponding to the O+ ring) or cold plasma wave modes, which can be used to explain the vr and WNA dependences. OCH waves shift from the transverse mode to the compressional mode as vr increases.

Effects of Ion Cyclotron Frequencies on Human Resistance and Reactance in 31 Healthy Subjects

In order to test the theory of Brizhik et al. about the dynamic allocation of acupuncture meridians on human body and their role as hydric paths for solitons, we tested the effect of both acupuncture and exposure to extremely low frequencies (ELF) tuned with suitable ion cyclotron frequencies. The similarity of the effects, inducing variations of body impedance measured in well-known acupuncture points, up to the interchangeability and the synergy of the two treatments, the mechanic and the electromagnetic ones, turns to be evidence of the validity of the theory. Resistance and reactance variations have been detected in a group of 31 healthy volunteers before and after stimulation with a standard sequence of cyclotron frequencies, emitted from an innovative electromagnetic therapy (EMT) device. These variations were then compared with the variations produced by the well-known percutaneous stimuli of mechanical and piezoelectric nature, and, in particular in this work, acupuncture. Our results show that the observed variations can be considered as significant in both groups: cyclotron and acupuncture. The greater variations brought about by the cyclotron treatment stand out clearly.