Upper Hybrid Research Articles

Utilizing parametric instabilities to diagnose edge density fluctuations in TCV

Abstract Two-plasmon decay instabilities (TPDIs) are a class of parametric instabilities where a gyrotron beam, polarized in X-mode, decays nonlinearly into two upper hybrid waves at approximately half frequency. Here, we present the design of a simple radiometer that was installed at Tokamak á configuration variable to diagnose TPDIs as well as a novel technique that was used to calibrate the radiometer using thermal electron cyclotron emissions. We show examples of measured radiation from TPDIs that occur when the gyrotron beam intersects blob filaments in the scrape-off layer and demonstrate that the frequency separation of the TPDI daughter waves can be used to assess the densities of the blob filaments. This technique could be utilized to diagnose density fluctuations due to both blobs, ELMs, and rotating magnetic islands.

Heating characteristic of electron Bernstein wave using high-field side X-mode injection in QUEST

Abstract A comparative investigation was conducted to assess the impact of high-field side (HFS) extraordinary (X) mode (HFS X) injection and low-field side (LFS) ordinary (O) mode (LFS O) injection of 8.2 GHz radio frequency (RF) power in the Q-shu University experimental steady-state spherical tokamak. In the case of the HFS X injection, the ratio of electron plasma frequency and RF frequency f pe / f RF was 1.3, indicating an overdense plasma, whereas in the LFS O injection, this ratio was 0.9. Distinctive features emerged in the electron temperature and density profiles between the two injection scenarios. In the HFS X injection, the profiles peaked between the fundamental electron cyclotron resonance (ECR) layer and the upper hybrid resonance layer. Conversely, in the LFS O injection, the peaks were situated near the 1st ECR layer. This implies effective excitation of the electron Bernstein wave (EBW) in the case of the HFS X injection, with the wave power being absorbed through the doppler-shifted ECR of the EBW. Density and temperature oscillations were observed only in the start-up phase of the HFS X injection, which may correlate with the presence of the left-hand cutoff of the X-mode. These findings will be contributed to understand the distinctive characteristics associated with plasma heating through EBW excitation in the HFS X injection.

Analyte-dependent Rabi splitting in solid-state plexcitonic sensors based on plasmonic nanoislands strongly coupled to J-aggregates

A key challenge in the field of plexcitonic quantum devices is the fabrication of solid-state, device-friendly plexcitonic nanostructures using inexpensive and scalable techniques. Lithography-free, bottom-up nanofabrication methods have remained relatively unexplored within the context of plexcitonic coupling. In this work, a plexcitonic system consisting of thermally dewetted plasmonic gold nanoislands (AuNI) coated with a thin film of J-aggregates was investigated. Control over nanoisland size and morphology allowed for a range of plasmon resonances with variable detuning from the exciton. The extinction spectra of the hybrid AuNI/J-aggregate films display clear splitting into upper and lower hybrid resonances, while the dispersion curve shows anti-crossing behavior with an estimated Rabi splitting of 180 eV at zero detuning. As a proof of concept for quantum sensing, the AuNI/J-aggregate hybrid was demonstrated to behave as a plexcitonic sensor for hydrochloric acid vapor analyte. This work highlights the possibility of using thermally dewetted nanoparticles as a platform for high-quality, tunable, cost-effective, and scalable plexcitonic nanostructures for sensing devices and beyond.

Effect of spin quantum force on lower and upper hybrid waves’ instability under the influence of an electron beam in a magnetized semiconductor plasma

Effect of spin quantum force on lower and upper hybrid waves’ instability under the influence of an electron beam in a magnetized semiconductor plasma

Demonstration of metaplectic geometrical optics for reduced modeling of plasma waves.

The Wentzel, Kramers, and Brillouin (WKB) approximation of geometrical optics is widely used in plasma physics, quantum mechanics, and reduced wave modeling, in general. However, it is well-known that the approximation breaks down at focal and turning points. In this paper, we present an unsupervised numerical implementation of the recently developed metaplectic geometrical optics framework, which extends the applicability of geometrical optics beyond the limitations of WKB, such that the wave field remains finite at caustics. The implementation is in 1D and uses a combination of Gauss-Freud quadrature and barycentric rational function inter- and extrapolation to perform an inverse metaplectic transform numerically. The capabilities of the numerical implementation are demonstrated on Airy's and Weber's equations, which both have exact solutions to compare with. Finally, the implementation is applied to the plasma physics problem of linear conversion of X mode to electron Bernstein waves at the upper hybrid layer and a comparison is made with results from fully kinetic particle-in-cell simulations. In all three applications, we find good agreement between the exact results and a reduced wave modeling paradigm of metaplectic geometrical optics.

On the Effect of Two-Dimensional Plasma Inhomogeneity in a Magnetic Island on the Parametric Excitation Threshold of Trapped Upper Hybrid Waves and the Level of Anomalous Absorption in ECRH Experiments

The effect of two-dimensional localization of an upper hybrid (UH) wave in a magnetic island is found. The influence of this effect on the threshold and saturation level of the absolute parametric decay instability of an extraordinary wave, which results in the excitation of two two-dimensional localized UH waves, is investigated.

Io's Near‐Field Alfvén Wings and Local Electron Beams Inferred From Juno/Waves

AbstractJuno conducted two close Io flybys on 30 December 2023 and 03 February 2024, both at a minimum altitude of 1,500 km. Filamentary structures in the electric and magnetic field spectra indicate Juno crossed the Alfvén wing, the magnetic structure connecting Io to Jupiter's polar ionosphere. We show that the first pass took Juno diametrically through the northern Alfvén wing, while the second pass had Juno graze the southern Alfvén wing boundary, enabling extended measurements of the transition region between Io's vicinity and the Jovian magnetosphere. Of note, evidence of local electron beams is inferred from whistler‐mode emissions. We demonstrate that their energies are sub‐keV, are sourced from Io's ionosphere or local torus, and are part of a distributed current system connecting Io to Jupiter. Finally, upper hybrid resonances indicate electron densities are significantly elevated in Io's polar region (∼28,000 cm−3) compared to the local Io torus (∼2,000 cm−3).

On possibility of anomalous microwave power absorption and gyrotron frequency sub-harmonics emission in X2-mode ECRH experiments at the TCV tokamak

In this paper, we analyze theoretically the low-threshold parametric decay instability (PDI) that can be excited at the tokamak à configuration variable (TCV tokamak, Lausanne, Switzerland) during X2 electron cyclotron resonance heating experiments producing a two-dimensionally localized upper hybrid (UH) wave and a daughter extraordinary wave running from the decay layer outward to the plasma edge. The primary instability is then saturated due to the cascade of secondary decays into two-dimensionally localized UH and ion Bernstein waves. The level of plasma microwave emission in the frequency range substantially below half the pump wave frequency and of anomalous power losses of the pump are predicted.

Cold Electron Temperature in the Inner Magnetosphere Estimated Through the Dispersion Relation of ECH Waves From the Arase Satellite Observations

AbstractWe have analyzed Electrostatic Electron Cyclotron Harmonic (ECH) waves observed using interferometry observation mode performed by the Arase satellite to estimate low‐energy electron temperatures. Interferometry can be used to calculate velocities, but the Arase satellite can only perform interferometry observations in a one‐dimensional direction. We proposed a method to estimate the wave vector of the observed ECH waves from the observed electric fields and calculated the phase velocity for each frequency. We determined the particle parameters from the particle detector and the upper hybrid resonance and estimated the unknown low‐energy electron temperature from the agreement between the observed ECH dispersion relation and the theoretical dispersion curves. We performed our analysis for six events and found that the low‐energy electron temperature in the observed region is on the order of 1 eV.

On the Coefficient of Nonlinear Coupling of Two Electromagnetic Waves with Ordinary Polarization and a Longitudinal Upper Hybrid Wave in a High-Temperature Plasma

On the Coefficient of Nonlinear Coupling of Two Electromagnetic Waves with Ordinary Polarization and a Longitudinal Upper Hybrid Wave in a High-Temperature Plasma

Effect of mutual interaction of two cosh-Gaussian laser beams on upper hybrid wave excitation and subsequent electron acceleration

This paper presents the excitation of an upper hybrid wave by resonant excitation of two intense cosh-Gaussian laser beams of frequencies ω 1 and ω 2 in a collisionless plasma. The excited upper hybrid wave is used for electron acceleration which accelerates the electrons towards higher energy. The acceleration of electrons through an excited upper hybrid wave has also been studied. This study has been analysed using the Wentzel Kramers Brillouin (WKB) and paraxial-ray approximation, where relativistic and ponderomotive nonlinearities are employed together. Analytical expressions for the beam width/intensity of the cosh-Gaussian laser beams, the electric field/power of the excited upper hybrid wave and the electron acceleration have been derived, which have been solved numerically for an established set of laser and plasma parameters. The results are also compared to relativistic nonlinearity. It has been observed that the mutual interaction of two cosh-Gaussian laser beams at a difference frequency significantly affects the self-focusing of each beam, leading to an increase in the amplitude/power of the upper hybrid wave as well as energy gain by the electrons. The effect of the magnetic field (ωc) and decentered parameter (b) on the power of the excited upper hybrid wave and the energy gain by the electrons are also explored. The results show that the power of upper hybrid wave and the energy gain by the electrons increase at higher values ​​of b and ω c.

Hybrid electrostatic waves in linearized gravity

Linearized gravity around a rotating black hole or compact object introduces the concept of a gravitomagnetic field, which originates from the matter–current in the rotating object. Plasma in proximity to this object is subsequently subjected to motion guided by this gravitomagnetic term (where mass serves as the effective charge) in addition to the conventional magnetic field. Such an interplay of fields complicates the accessible plasma waves of the system and thus merits exploration to delineate this interplay, to identify any observable signatures of the gravitomagnetic field in weakly magnetized systems, and to motivate future numerical work in a fully relativistic setting where the effects may be stronger. In this work we analyse the dispersion of the upper and lower hybrid electrostatic waves in a plasma immersed in both magnetic and gravitomagnetic fields. In particular, we discuss the effective augmentation or cancellation of the two fields under the right conditions for the upper hybrid wave. In contrast, the lower hybrid wave experiences a frequency up-shift from the gravitomagnetic field regardless of whether it is parallel or antiparallel to the magnetic field for the studied field strengths.

Ray‐Tracing Analysis for the Propagation of Saturn Narrowband Emission Within the Saturnian Magnetosphere

AbstractThis study investigates the propagation characteristics of Saturn's Narrowband (NB) emissions using a 3D ray‐tracing code incorporating Saturn's magnetic field and electron density parameters. The potential source regions and propagation zones of the L‐O mode, Z mode and whistler mode NB emissions are distinguished. The L‐O mode NB emissions, generated along local electron plasma frequency surfaces through mode conversion, exhibit straight‐line propagation but undergo reflections between the ionosphere, the plasma torus, and the magnetosheath. The slot region, characterized by a lower electron density distributed around the plasma torus boundary, significantly influences emission propagation, potentially leading to trapping and depolarization. The 5 kHz Z mode NB emissions propagate and fill the trapping region delineated by lower cut‐off and upper hybrid resonance frequencies. In contrast, the 20 kHz Z mode NB emissions are primarily confined near source regions at the north and south edges of the plasma torus, with the possibility of escaping under variable plasma conditions.

The Hunt for Perpendicular Magnetic Field Measurements in Plasma

The one consistent technique for remotely estimating the magnetic field in plasma has been Faraday rotation. It is only sensitive to the portion of the vector parallel to the propagation path. We show how to remotely detect the portion of the vector that is perpendicular using a modified measurement. Isolating this electromagnetic propagation wave mode to measure the magnetic field enables us to (i) study more about the magnetic field vector in plasma, (ii) reduce error in total electron content measurements, and (iii) discover new magnetic field information from archived data sets. The Appleton–Hartree equation is used to verify a new approach to calculating the phase change to an electromagnetic wave propagating through a plasma at frequencies larger than the gyrofrequency, the cyclotron frequency, and the upper hybrid frequency. Focusing on the perpendicular propagation modes, the simplified equation for the integrated path effect from a perpendicular magnetic field is calculated. The direction of the perpendicular component is unknown, because the magnetic field is squared. Isolating the magnetic term in the equation with dual frequency waves is shown. We also show how to eliminate the magnetic field contribution to total electron content measurements with a similar approach. In combination with Faraday rotation, the degeneracy of the magnetic field vector direction is reduced to a cone configuration.

Electron Density Specification in the Inner Magnetosphere From the Narrow Band Receiver Onboard DSX

AbstractElectron density plays an important role in the study of wave propagation and is known to be associated with the index of refraction and radiation belt diffusion coefficients. The primary objective of our investigation is to explore the possibility of implementing an onboard signal processing algorithm to automatically obtain electron densities from the upper hybrid resonance traces of wave spectrograms for future missions. U‐Net, developed for biomedical image segmentation, has been adapted as our deep learning architecture with results being compared with those extracted from a more traditional semi‐automated method. As a product, electron densities and cyclotron frequencies for the entire DSX mission between 2019 and 2021 are acquired for further analysis and applications. Due to limited space measurements, a synthetic image generator based on data statistics and randomization is proposed as an initial step toward the development of a generative adversarial network in hopes of providing unlimited realistic data sources for advanced machine learning.

Influence of upper hybrid wave on electron acceleration by Laguerre–Gaussian pulse in relativistic-ponderomotive plasma

Influence of upper hybrid wave on electron acceleration by Laguerre–Gaussian pulse in relativistic-ponderomotive plasma

Nonlinear Landau damping of electron Bernstein waves in MAST-U

The Mega-Amp Spherical Tokamak Upgrade (MAST-U) is preparing to investigate microwave based current drive using an advanced wave coupling scheme known as O-X-B at high power. The main goal is to assert if this is an efficient method for current drive in the future fusion demonstration power plant STEP. A model for the nonlinear wave-particle interaction nonlinear Landau damping (NLD) is presented. A relativistic, kinetic and electrostatic description is used. For MAST-U, NLD could lead to heating and current drive at the upper hybrid (UH) layer or at the electron cyclotron (EC) resonance of a substantially downshifted daughter wave produced by the wave-particle interactions. It is found that the typical treatment used for nonlinear waveinteractions fails at two critical points in the vicinity of the UH layer.

Two-plasmon decay of microwaves in low temperature magnetized laboratory plasmas

Observations from magnetically confined fusion experiments have in the past decades revealed instances of two-plasmon decay instabilities (TPDIs) between injected 2nd harmonic X-mode waves and trapped upper hybrid (UH) waves near half frequency of the injected wave. We present and compare growth rates of TPDIs computed from reduced analytical models and particle-in-cell (PIC) simulations in low-temperature plasmas, emulating conditions found in more accessible controllable laboratory devices. The growth rates obtained from simulations agree with our modeling, confirming that we can model TPDIs using both analytical models and PIC simulations in low-temperature plasmas. Furthermore, the growth rates are on the order of 0.01 ns−1 to 0.1 ns−1 for injected waves with intensity of 103 W/cm2, which indicates that we can expect to see signals of TPDIs in controllable laboratory plasma devices.

Effect of Two-Dimensional Plasma Inhomogeneity in Magnetic Island on Threshold of Parametric Excitation of Trapped Upper Hybrid Waves and Level of Anomalous Absorption in ECRH Experiments

Effect of Two-Dimensional Plasma Inhomogeneity in Magnetic Island on Threshold of Parametric Excitation of Trapped Upper Hybrid Waves and Level of Anomalous Absorption in ECRH Experiments

Study of a high-precision complex 3D geological modelling method based on a fine KNN and kriging coupling algorithm: a case study for Jiangsu, China

A high-precision, complex, three-dimensional (3D) geological model can directly express the attributes of stratum thickness, geological structure, lithology and spatial form, which can provide a reliable basis for the development and utilization of underground space and planning decisions. However, it is difficult to perform accurate modelling due to the lack of basic data. As such, this paper proposes coupling a machine learning algorithm (K-nearest neighbour (KNN)) with the kriging algorithm to construct the topological relationship between the Delaunay triangle and the Thiessen polygon in order to perform the simulation and prediction of virtual drilling. Based on KNN, support vector machine (SVM) and neural network algorithms as well as the virtual borehole encryption data, data standardization processing and analysis are carried out. Through model verification, algorithm optimization is realized, and the optimal modelling method is explored. The results show that the fine KNN algorithm improved by Bayesian optimization can effectively improve the modelling accuracy through 0.1-m encryption, standardization processing and 5-fold cross-validation. Stratum modelling combined with the fine KNN and kriging algorithms can obtain a more accurate modelling without adding virtual boreholes. The improved levels of upper and lower hybrid modelling with an appropriate number of profile boreholes can also effectively optimize model accuracy. Both modelling accuracy and efficiency can be significantly improved by using Delaunay triangles and Thiessen polygons with virtual boreholes. Stratum modelling can effectively express the geological pinch-out in areas with adequate degrees of stratification, and hybrid modelling performs well in irregular geological bodies such as karsts and lenses.