| 연구목표 |
본 연구의 목표는 자기권 내에서 흔히 발생하는 플라스마 파동의 한 종류인 magnetosonic 파동의 생성 및 전파를 이해하고, 이 파동이 방사선 대를 구성하는 고에너지 전자에 미치는 영향을 정량적으로 조사하는 것이다.
입자-파동 상호작용이 방사선 대를 구성하는 고에너지 전자의 양과 에너지를 결정한다는 것은 최근 종료된 NASA의 Van Allen Probe 미션으로 부터 확실시 되었다. 자기권 내에서 흔히 발생하는 플라스마 파동의 한 종류인 magnetosonic 파동 또한 입자-파동 상호작용으로 이들에게 영향을 끼칠 수 있다고 알려져 있다. 그러나, 다른 파동들과 다르게 magnetosonic 파동의 본질에 대해서 더 깊은 연구가 필요하며, 이를 바탕으로 이 파동이 방사선 대를 구성하는 고에너지 전자에 미치는 영향을 정량화 하는것이 필요하다.
본 연구에서는 particle-in-cell 코드를 이용하여 보다 현실적인 다차원 공간에서 이 파동을 구현하고, 이로부터 관측적 제한으로 얻기 힘든 파동의 특성을 유추하며, 구현된 파동 내에서 운동하는 고에너지 전자들의 궤적을 추적 함으로써 전자에 미치는 영향을 정량적으로 알아보고자 한다. |
| 연구내용 |
First, a new hypothesis of magnetosonic wave generation will be tested. Satellite observations have shown that the occurrence and power distributions of magnetosonic waves are narrow in latitude. These waves are thought to be generated near the equator with a wave vector quasi-perpendicular to the background magnetic field. Consequently, they will not travel far from the equatorial source region. However, there are physical and observational arguments that the equatorial-source scenario may need to be revised. The new scenario to be tested does not limit the extent of the source region, but hypothesizes that the equator naturally favors strong wave growth due to the vanishing magnetic field gradient. Two- and three-dimensional simulations will be performed to confirm, or disprove, this new hypothesis.
Second, the field-aligned structure of the magnetosonic wave field will be constructed from those simulations and a way to improve the observational uncertainty in determining the wave normal angle distribution will be sought. The wave normal angle distribution of magnetosonic spectral power is an essential input to the calculation of diffusion coefficients, but the data analysis technique of determining it yields an uncertainty to large to resolve the fine structure of the magnetosonic spectral power. The big advantage of the modeling approach is the global description of the underlying physical phenomena without any data gaps. The observational technique will be applied to the simulated waves whose characteristics are known, in order to improve the uncertainty.
Third, test particles will be traced in the simulated magnetosonic waves in order to quantify the importance of various scattering mechanisms. It has been demonstrated that radiation belt electrons can interact with magnetosonic waves through Landau resonance, transit-time scattering, and bounce resonance, but how important those mechanisms are in realistic magnetosonic waves needs to be quantified. |
| 기대효과 |
In collisionless plasmas, wave-particle interactions are the fundamental process with which dynamics can be produced. It has now been proven that the tug of war among those plasma waves are responsible for the net enhancement, net depletion, or no change at all of the outer belt.
Magnetosonic waves are suggested to be important for the dynamics of radiation belt electrons. Quantification of their effect, therefore, requires an accurate description of the waves themselves. However, the fundamental processes involving wave excitation and propagation in inherently inhomogeneous magnetospheric plasmas are still poorly understood. The expected significance of this investigation consists of providing the critically needed, improved, understanding of the generation of magnetosonic waves in the inner magnetosphere and their spectral properties that are necessary to quantify their effects on the dynamics of radiation belt electrons. |
| 키워드 |
플라스마 파동 및 불안정성,입자-파동 상호작용,수치모델링,방사선대,마그네토소닉 파동 |
