Simulation study of the harmonic structure of lower hybrid waves driven by energetic ions

Kotani, Tsubasa; Toida, Mieko; Moritaka, Toseo; Taguchi, Satoshi

doi:10.1103/physreve.108.035208

Phys. Rev. E

2023

DOI: 10.1103/physreve.108.035208

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Simulation study of the harmonic structure of lower hybrid waves driven by energetic ions

Tsubasa Kotani,

Mieko Toida,

Toseo Moritaka

et al.

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2024

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Cited by 4 publications

References 40 publications

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Parametric Study of the Harmonic Structure of Lower Hybrid Waves Driven by Energetic Ions

Kotani,

Toida,

Moritaka

et al. 2024

JGR Space Physics

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The harmonic structure of lower hybrid waves (LHWs) driven by energetic ions can be generated through non‐linear wave‐wave coupling. We investigate the parameter dependence of the excitation and time evolution of this structure, using one‐dimensional electromagnetic particle‐in‐cell (PIC) simulations. Focusing on two parameters, (ratio of the electron plasma to electron gyro frequencies) and (ratio of energetic‐ion to Alfvén velocities), we analyze the fluctuation spectra in the wavenumber‐frequency plane and demonstrate that the harmonic structure can be excited across wide parameter ranges of and , indicating a weak parameter dependence. However, the excitation region and time evolution of the harmonic structure can be significantly affected by these parameters. We find that conditions of low and intermediate are preferable for the excitation and survival of the harmonic structure. Previous observations have reported the harmonic structure of LHWs in the polar region at 4,000 km altitude and in the plasma sheet at XGSM 17 . Nevertheless, this study predicts that the harmonic structure can also be excited in other regions of the magnetosphere where energetic ions are present.

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Parametric Study of the Harmonic Structure of Lower Hybrid Waves Driven by Energetic Ions

Kotani,

Toida,

Moritaka

et al. 2024

JGR Space Physics

View full text Add to dashboard Cite

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Simulation study of energetic-ion mass dependence on nonlinear development of lower hybrid wave instabilities

Toida,

Kotani

2024

Physics of Plasmas

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In both space and fusion plasmas, energetic ions with a ring-like velocity distribution are present in various ion species with different masses. We study how the nonlinear development of lower hybrid wave (LHW) instabilities, driven by the ring-like energetic ions, depends on the mass of the energetic ions, by using the electromagnetic particle-in-cell simulation with a model where the energetic ions are continuously injected into a plasma. As expected from linear theory, the initial growth of the LHWs slows down as the energetic-ion mass (M) increases. However, long-time simulations have revealed that as M increases, the LHWs eventually grow to larger amplitudes. This is because the velocity distribution of the energetic ions, influenced by spreading due to wave development and reformation due to injection, can maintain a steep gradient when M is large. As a result, in a large M plasma, a greater part of the injected energy is converted to the energies of the electric field and background ions. In addition, it has been found that a larger value of M leads to an increase in the amplitudes of the second and third harmonics of the LHWs because of enhanced nonlinear wave-wave coupling.

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The consequences of tritium mix for simulated ion cyclotron emission spectra from deuterium-tritium plasmas

Slade-Harajda,

Chapman,

Dendy

2024

Nucl. Fusion

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Measurements of ion cyclotron emission (ICE) are obtained from most large magnetically confined fusion (MCF) plasma experiments, and may be used in future to quantify properties of the fusion-born alpha-particle population in deuterium-tritium (DT) plasmas in ITER. ICE is driven by spatially localised, strongly non-Maxwellian, minority energetic ion populations which relax collectively under the magnetoacoustic cyclotron instability (MCI). ICE spectral peaks are typically observed at, near, or separated by, integer harmonics of the energetic ion cyclotron frequency. Here, for the first time, we study how simulated ICE spectra from DT plasmas vary with tritium concentration and compare with an observed JET DT ICE spectrum. We incorporate a population of thermal tritons, in addition to thermal deuterons and an energetic minority population of fusion-born alpha-particles, in simulations with the kinetic particle-in-cell (PIC) code EPOCH. This code has previously been used extensively for interpretation of ICE observations in terms of the self-consistent gyro-resolved collective Maxwell-Lorentz dynamics of tens of millions of simulation particles. Our simulation parameters are relevant to the ICE-generative outer midplane edge region of JET DT plasma 26148, which included 11% tritium. Quantifying the variation of simulated ICE power spectra with tritium concentration reveals that our simulation with 11% tritium concentration most accurately represents the observed ICE spectrum from this plasma. This outcome is encouraging for the diagnostic application of ICE to fusion plasmas containing two thermal ion species, including future DT plasmas.

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Simulation study of the harmonic structure of lower hybrid waves driven by energetic ions

Cited by 4 publications

References 40 publications

Parametric Study of the Harmonic Structure of Lower Hybrid Waves Driven by Energetic Ions

Parametric Study of the Harmonic Structure of Lower Hybrid Waves Driven by Energetic Ions

Simulation study of energetic-ion mass dependence on nonlinear development of lower hybrid wave instabilities

The consequences of tritium mix for simulated ion cyclotron emission spectra from deuterium-tritium plasmas

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