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Accepted: 2003-05-27, 資料番号: SA1003326000

Propagation of Langmuir solitons in inhomogeneous plasmas is investigated numerically. Through numerical simulation solving Zakharov equations, the solitons are accelerated toward the low density side. As a consequence, isolated cavities moving at ion sound velocities are emitted. When the acceleration is further increased, solitons collapse and the cavities separate into two lumps released at ion sound velocities. The threshold is estimated by an analogy between the soliton and a particle overcoming the self-generated potential well.

As one of the tasks to find the energy source(s) of thermal electrons, which elevate(s) electron temperature higher than neutral temperature in the lower ionosphere E-region, energy distribution function of thermal electron was measured with a sounding rocket at the heights of 93–131 km by the applying second harmonic method. The energy distribution function showed a clear hump at the energy of ~0.4 eV. In order to find the reason of the hump, we conducted laboratory experiment. We studied difference of the energy distribution functions of electrons in thermal energy range, which were measured with and without EUV radiation to plasma of N2/Ar and N2/O2 gas mixture respectively. For N2/Ar gas mixture plasma, the hump is not clearly identified in the energy distribution of thermal electrons. On the other hand for N2/O2 gas mixture, which contains vibrationally excited N2, a clear hump is found when irradiated by EUV. The laboratory experiment seems to suggest that the hump is produced as a result of interaction between vibrationally excited N2 and thermal electrons, and this interaction is the most probable heating source for the electrons of thermal energy range in the lower E-region. It is also suggested that energy distribution of the electrons in high energy part may not be Maxwellian, and DC probe measures the electrons which are non Maxwellian, and therefore "electron temperature" is calculated higher.

Local electron and ion heating characteristics during merging reconnection startup on the MAST spherical tokamak have been revealed for the first time using a 130 channel YAG-TS system and a new 32 chord ion Doppler tomography diagnostic. 2D local profile measurement of $T_e$, $n_e$ and $T_i$ detect highly localized electron heating at the X point and bulk ion heating downstream. For the push merging experiment under high guide field condition, thick layer of closed flux surface formed by reconnected field sustains the heating profile for more than electron and ion energy relaxation time $��^E_{ei}\sim4-10$ms, both heating profiles finally form triple peak structure at the X point and downstream. Toroidal guide field mostly contributes the formation of peaked electron heating profile at the X point. The localized heating increases with higher guide field, while bulk downstream ion heating is unaffected by the change in the guide field under MAST conditions ($B_t>3B_{rec}$)., The article has been submitted to the journal of "Physical Review Letters" on 05/May/2015 (Code number: LE15049 (5 pages, 5 figures))

平成26年度宇宙科学に関する室内実験シンポジウム (2015年2月23日-24日. 宇宙航空研究開発機構宇宙科学研究所(JAXA)(ISAS)相模原キャンパス), 相模原市, 神奈川県, 2015 Symposium on Laboratory Experiment for Space Science (July 23-24, 2015. Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency (JAXA)(ISAS)), Sagamihara, Kanagawa Japan, 資料番号: SA6000076022

Particle and heat transport in tokamak edge is investigated by guiding center orbit following calculation. The guiding center equation is solved for both electrons and ions in the presence of magnetic perturbation. It is suggested that the remnants of the magnetic islands play a role in characterizing the radial transport. The transport coefficient is estimated which also demonstrate local structure in the vicinity of magnetic islands.

第24回大気圏シンポジウム（2010年2月18日-19日. 宇宙航空研究開発機構宇宙科学研究本部（JAXA)(ISAS)）, 相模原市, 神奈川県, 24th Atmospheric Science Symposium (February 18-19, 2010. Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency (JAXA)(ISAS)), Sagamihara, Kanagawa Japan, 資料番号: SA6000073020, レポート番号: Ⅳ-2

Physical Review Letters

[ABSTRACT]The satellites for the educational purpose are being manufactured in many Universities in the world. Their weight ranges from several kg to 20 kg. However most of the satellite seems to be engineering oriented. For the scientists, these Nano/micro satellites constellation might provide excellent chances to conduct new sciences and to increase the research opportunities. In order for the science instruments to be accommodated in the Nano/microsatellite, the following factors need to be fulfilled; 1.The small dimension/low power consumption of the instrument, and data bit rate should be very small. 2. The sensor should be easily deployed or fixed without complex mechanism and, 3.The weight of the sensor should be right so that its deployment should not disturb the attitude of the satellite. These requirements are fundamentally important for the instrument to be accommodated in tiny satellites. It goes without saying that even small instrument should have a good performance in addition to provide accurate, and reliable information. Here we developed one plasma instrument to measure both electron temperature and plasma density simultaneously. Frequency sweep circuit is added to the conventional electron temperature probe [1]. The electron temperature probe which was developed more than about 30 years ago was accommodated in 5 earth orbiting satellites as well as Mars orbitor, and about 50 sounding rockets in Japan including the sounding rocket in Antarctica. The probe was used for the sounding rocket experiment in India, Brazil[2], Canada, U.S.A, and West Germany. The probe was also accommodated in Korean, Brazil, and Russian satellites. The circular electrode (100 mm in diameter, and 1.6 mm in thickness) should be ram direction of the satellite, and it should be about 30 mm away from the satellite wall, to avoid the measurement in the satellite wake and in the sheath. The electronics consists of frequency sweep circuit (200 KHz-10 MHz), amplitude modulation circuit and conventional electron temperature probe. The total weight, and power is about 200 g and 500 mW respectively. The bit rate of 2kbits/sec allows us to calculate electron density from upper hybrid resonance. This amount of bit rate also makes it possible to calculate electron density and temperature from the output signal of the instrument in low frequency (200 KHz), which allows us to compare electron densities both from upper hybrid resonance and from the output signal of the electron temperature probe. The measurement duration is about 1 sec. The instrument can be accommodated in 10 kg satellite, that is, the instrument can be accommodated to all satellite of constellation. One of the research subjects by using satellite constellation is to study the precursor features associated with large earthquakes [3,4,5].