Cheong Rim Choi

AMMAP on CAS500-3, launched in November 2025 into a ∼600 km Sun-synchronous orbit, combines a Langmuir probe (LP), biased with respect to the spacecraft body, and an impedance probe (IP), which derives the density from the upper-hybrid resonance regardless of the spacecraft potential. We report the operation from December 2025 to June 2026 and initial observations on two reference days in February and June. Before the orbital noon, the sun-pointing attitude turns the solar arrays toward the direction of flight and the spacecraft charges negatively beyond the LP sweep range, so that the LP collects only ions in 50–70% of the dayside sweeps. The IP is lost mainly in the low-density winter hemisphere, where its resonance is too weak. Where both are valid, the densities agree within a factor of ∼1.7 in the median, the IP typically 20–40% lower; both lie above the IRI model, the IP by a factor of 1.4–2.1 and the LP by 2.1–3.2. Even in the ion-only sweeps, the slope of the ion current increases with the density and, calibrated against the IP for each day, gives the density with a scatter of 20–35%. Taking the IP as the reference and filling its gaps with the calibrated LP data yields a continuous profile over more than 90% of the two orbits examined.

We investigate the formation of magnetic islands and the onset of tearing instability within kinetic Alfvén solitary waves in a two-fluid space plasma. These localized structures, featuring internal magnetic shear, naturally support magnetic reconnection processes analogous to tearing modes in magnetically confined fusion plasmas. Treating the solitary wave as a quasi-static background equilibrium, we analyze the resulting topological modifications by making use of the magnetic flux function, in analogy with tokamak plasmas. We find that the spatial size of the magnetic island scales with the square root of the magnetic flux perturbation. Introducing the tearing stability index Δ ′ , we derive the growth rate of the tearing mode using a resistive magnetohydrodynamic framework. Our analysis reveals that tearing modes grow only when the mode’s wavenumber exceeds the inhomogeneity scale, becoming marginally stable when the two are comparable. The emergence of magnetic islands has significant implications for cross-field particle transport, turbulence, and acceleration. In particular, the electron diffusion across magnetic fields may be governed by the island size rather than the Larmor radius, potentially accounting for anomalous transport. Furthermore, in certain regimes, unbounded island growth may signal the collapse of the solitary wave structure, enabling a large-scale transfer of magnetic energy to particle energy. These results suggest a unifying mechanism connecting magnetic reconnection in space plasmas with tearing instabilities in laboratory fusion plasmas.

This paper presents ground calibration and orthogonality correction methods for the tri-axis fluxgate magnetometer (FGM), named as adaptive in-phase magnetometer (AIMAG), aboard the CAS500-3 satellite. The orthogonality errors of the FGM among the axes can lead to significant inaccuracies in magnetic field measurements. In this study, we employed Helmholtz coils and an autocollimator to apply controlled magnetic fields and adjust the magnetometer’s alignment. By deriving the correction matrix, we could transfer the sensor axes to the ideal orthogonal coordinate system. We validated the correction method by analyzing the sensor’s output under various magnetic field conditions. This correction method is expected to enhance the in-flight magnetic field measurements of the CAS500-3 satellite.

Ionospheric Anomaly Monitoring by Magnetometer And Plasma-probe (IAMMAP) is a suite of scientific instruments used in the Compact Advanced Satellite 500-3 (CAS 500-3), which is planned to be launched by the KSLV (Korean Space Launch Vehicle) in 2025. The main scientific objective of IAMMAP is to understand the complicated correlation between the equatorial electrojet (EEJ) and the equatorial ionization anomaly (EIA), both of which play important roles in the dynamics of ionospheric plasma in the dayside equator region. The magnetic field generated by the EEJ is tiny (~several nT) compared to the background geomagnetic field (~30,000 nT); thus, a high-resolution magnetometer with a wide dynamic range is required to investigate its correlation with the EIA. To achieve this required resolution, IAMMAP includes a set of improved fluxgate magnetometers named the AIMAG (Adaptive In-phase MAGnetometer), which was developed by adopting new technologies. Here, we report the analysis results of the manufactured AIMAG performance based on trade-off studies for optimizing the circuit and sensor configurations. The results support that the AIMAG sensor and electronic circuits with new concepts and technologies will lead to successful observations of EEJ signatures in the ionosphere.

This paper presents the derivation of a general wave dispersion relation for warm magnetized plasma under the two-fluid formalism. The discussion is quite general except for the assumption of low frequency and slow phase speed, for which the displacement current is negligible, under the implicit assumption that the plasma is sufficiently dense to satisfy the condition ωpe>ωce, where ωpe and ωce denote the plasma oscillation frequency and electron gyro frequency, respectively. The present discussion does not invoke charge neutrality associated with the fluctuations although it is implicitly satisfied. The resulting dispersion relation that includes the fluid thermal effects shows that there are three eigen modes, which include those corresponding to ideal MHD, namely, fast, slow, and kinetic Alfvén waves, as well as higher-frequency modes including the ion and electron cyclotron and lower-hybrid resonances. The fluid effects in the ideal MHD wave branches are influenced by the finite Larmor radius scales, and when the wave number in the cross field direction is comparable to these values, the fluid effects become significant. It is found that the Larmor radius should be interpreted in the sense as ion-acoustic gyro-radius instead of ion thermal gyro radius only. That is, it is found that the electrons also contribute to the non-ideal effect associated with the kinetic Alfvén wave. A comprehensive explanation of the polarization of each mode is also presented. The present findings indicate that the polarity may change its sign only for the kinetic Alfvén mode branch and that such a transition is based on the propagation angle. When such a change does take place, it is found that the kinetic Alfvén wave transits to an ion-acoustic mode. For each branch, it is also found that the electric field along the ambient magnetic field is purely transverse.

우주기술과 응용(Journal of Space Technology and Applications; J. Space Technol. Appl. 이하 JSTA )은 한국의 우주과학 및 우주 응용 분야에서 가장 권위 있는 학술단체인 한국우주과학회에서 Journal of Astronomy and Space Sciences 와 더불어 발행되고 있는 공식적인 정기 간행물이다. JSTA 는 2021년 5월 창간호를 시작으로 연 4회 분기별로 발간되고 있으며, JSTA 의 논문과 기고문 은 한국어 또는 영어로 게재 가능하며, 각 논문과 기고문에는 고유의 DOI가 부여된다. JSTA 에 게재 되는 모든 논문과 기고문은 Open Access 정책에 따라 JSTA 홈페이지(https://www.jstna.org)를 통해 누구나 전문을 무료로 열람할 수 있다.

우주기술과 응용(Journal of Space Technology and Applications; J. Space Technol. Appl. 이하 JSTA )은 한국의 우주과학 및 우주 응용 분야에서 가장 권위 있는 학술단체인 한국우주과학회에서 Journal of Astronomy and Space Sciences 와 더불어 발행되고 있는 공식적인 정기 간행물이다. JSTA 는 2021년 5월 창간호를 시작으로 연 4회 분기별로 발간되고 있으며, JSTA 의 논문과 기고문 은 한국어 또는 영어로 게재 가능하며, 각 논문과 기고문에는 고유의 DOI가 부여된다. JSTA 에 게재 되는 모든 논문과 기고문은 Open Access 정책에 따라 JSTA 홈페이지(https://www.jstna.org)를 통해 누구나 전문을 무료로 열람할 수 있다.

우주기술과 응용(Journal of Space Technology and Applications; J. Space Technol. Appl. 이하 JSTA )은 한국의 우주과학 및 우주 응용 분야에서 가장 권위 있는 학술단체인 한국우주과학회에서 Journal of Astronomy and Space Sciences 와 더불어 발행되고 있는 공식적인 정기 간행물이다. JSTA 는 2021년 5월 창간호를 시작으로 연 4회 분기별로 발간되고 있으며, JSTA 의 논문과 기고문 은 한국어 또는 영어로 게재 가능하며, 각 논문과 기고문에는 고유의 DOI가 부여된다. JSTA 에 게재 되는 모든 논문과 기고문은 Open Access 정책에 따라 JSTA 홈페이지(https://www.jstna.org)를 통해 누구나 전문을 무료로 열람할 수 있다.

The Ionospheric Anomaly Monitoring by Magnetometer And Plasma-probe (IAMMAP) is one of the scientific instruments for the Compact Advanced Satellite 500-3 (CAS 500-3) which is planned to be launched by Korean Space Launch Vehicle in 2024. The main scientific objective of IAMMAP is to understand the complicated correlation between the equatorial electro-jet (EEJ) and the equatorial ionization anomaly (EIA) which play important roles in the dynamics of the ionospheric plasma in the dayside equator region. IAMMAP consists of an impedance probe (IP) for precise plasma measurement and magnetometers for EEJ current estimation. The designated sun-synchronous orbit along the quasi-meridional plane makes the instrument suitable for studying the EIA and EEJ. The newly-devised IP is expected to obtain the electron density of the ionosphere with unprecedented precision by measuring the upper-hybrid frequency (fUHR) of the ionospheric plasma, which is not affected by the satellite geometry, the spacecraft potential, or contamination unlike conventional Langmuir probes. A set of temperaturetolerant precision fluxgate magnetometers, called Adaptive In-phase MAGnetometer, is employed also for studying the complicated current system in the ionosphere and magnetosphere, which is particularly related with the EEJ caused by the potential difference along the zonal direction.

The anomalous diffusion of resonant protons in parallel and perpendicular velocity space by kinetic Alfvén waves is discussed. The velocity diffusion coefficient is calculated by employing an autocorrelation function for proton trajectories. It is found that for protons resonant with the waves, the perpendicular diffusion coefficient decays away for a sufficiently long time, but parallel diffusion monotonically increases in time until it saturates at a certain level. This result indicates that a portion of resonant protons can undergo anomalous diffusion along the background magnetic field even if the intensity of the kinetic Alfvén wave is sufficiently low. The present findings imply that under suitable conditions, astrophysical charged-particle acceleration can take place in the parallel direction.