Kazunori Takahashi 교수

Abstract Development of electrodeless radiofrequency plasma thrusters, e.g., a helicon thruster, has been one the of challenging topics for future high-power and long-lived electric propulsion systems. The concept simply has a radiofrequency plasma production/heating source and a magnetic nozzle, while it seems to include many aspects of physics and engineering issues. The plasma produced inside the source is transported along the magnetic field lines and expands in the magnetic nozzle, where th

The axial force imparted from a magnetically expanding current-free plasma is directly measured for three different experimental configurations and compared with a two-dimensional fluid theory. The force component solely resulting from the expanding field is directly measured and identified as an axial force produced by the azimuthal current due to an electron diamagnetic drift and the radial component of the magnetic field. The experimentally measured forces are well described by the theory.

Direct thrust measurements of a permanent magnet helicon double layer thruster have been made using a pendulum thrust balance and a high sensitivity laser displacement sensor. At the low pressures used (0.08 Pa) an ion beam is detected downstream of the thruster exit, and a maximum thrust force of about 3 mN is measured for argon with an rf input power of about 700 W. The measured thrust is proportional to the upstream plasma density and is in good agreement with the theoretical thrust based on

Cross-field diffusion and plasma expansion in a rapidly diverging magnetic nozzle are controlled while maintaining constant plasma production in a contiguously attached radio frequency plasma source. It is demonstrated that the measured electron-diamagnetic-induced axial momentum increases with increasing magnetic field strength to approach the theoretical limit derived using an ideal nozzle approximation. The measured axial momentum exerted onto the axial and radial plasma source boundaries val

Electrostatic comb-drive micro actuator with submicron comb fingers was connected to silicon microring resonator to consist a wavelength-selective add-drop switch at 1.5 microm wavelength with variable coupling mechanism. A 500 nm wide 260 nm thick 63.4 microm long silicon microring waveguide was suspended in air with low-loss suspension arms. The air gap between the microring and the input/output waveguides was adjusted by the voltage applied to the comb actuator to vary the coupling efficiency

In the high potential plasma, upstream of the double layer, the measured electron energy distribution function (EEDF) shows a very clear change in slope at energies (εbreak) corresponding to the double layer potential drop. Electrons with lower energy are Maxwellian with a temperature of 8eV, whereas those with higher energy have a temperature of 5eV. The EEDF in the downstream plasma has a temperature of 5eV. Over the range of pressures wherein the double layer and accelerated ion beam are dete

Studying cell functions for cellomics studies often requires the use of purified individual cells from mixtures of various kinds of cells. We have developed a new non-destructive on-chip cell sorting system for single cell based cultivation, by exploiting the advantage of microfluidics and electrostatic force. The system consists of the following two parts: a cell sorting chip made of poly-dimethylsiloxane (PDMS) on a 0.2-mm-thick glass slide, and an image analysis system with a phase-contrast/f

Peripheral magnetic field lines extending from the plasma source into the diffusion chamber are found to separate two regions of Maxwellian electron energy probability functions: the central, ion-beam containing region with an electron temperature of 5 eV, and region near the chamber walls with electrons at 3 eV. Along the peripheral field lines a bi-Maxwellian population with a hot tail at 9 eV is shown to both originate from electrons in the source traveling downstream across the double layer

Development of a magnetic nozzle radiofrequency (rf) plasma thruster has been one of challenging topics in space electric propulsion technologies. The thruster typically consists of an rf plasma source and a magnetic nozzle, where the plasma produced inside the source is transported along the magnetic field and expands in the magnetic nozzle. An imparted thrust is significantly affected by the rf power coupling for the plasma production, the plasma transport, the plasma loss to the wall, and the

The azimuthal plasma current in a magnetic nozzle of a radiofrequency plasma thruster is experimentally identified by measuring the plasma-induced magnetic field. The axial plasma momentum increases over about 20 cm downstream of the thruster exit due to the Lorentz force arising from the azimuthal current. The measured current shows that the azimuthal current is given by the sum of the electron diamagnetic drift and drift currents, where the latter component decreases with an increase in the ma

Two dimensional profiles of electron temperature are measured inside and downstream of a radiofrequency plasma thruster source having a magnetic nozzle and being immersed in vacuum. The temperature is estimated from the slope of the fully swept I-V characteristics of a Langmuir probe acquired at each spatial position and with the assumption of a Maxwellian distribution. The results show that the peripheral high temperature electrons in the magnetic nozzle originate from the upstream antenna loca

Electron energy distributions upstream of a current-free double layer (CFDL) contained in a low-collisional plasma are modeled and compared with experimental results. The experimentally observed electron energy probability functions (EEPFs) with a depleted tail above the energy corresponding to the potential drop of the CFDL can be well approximated by a Druyvesteyn distribution function. Theoretical effective electron temperatures for the Druyvesteyn distribution are in good agreement with the

The performance of a permanent magnet helicon plasma thruster (PM-HPT) is improved by modifying the magnetic field configuration and increasing the magnetic field strength for operating source conditions of 13.56 MHz radiofrequency power up to 2 kW and 24

Space debris removal from Earth orbit by using a satellite is an emergent technological challenge for sustainable human activities in space. In order to de-orbit debris it is necessary to impart a force to decelerate it, resulting in its atmospheric re-entry. A satellite using an energetic plasma beam directed at the debris will need to eject plasma in the opposite direction in a controlled manner in order to maintain a constant distance between it and the debris during the deorbiting mission. B

Ion acceleration is achieved in a low-pressure solenoid-free plasma expanded by permanent magnet arrays. Although a permanent magnet normally forms cusp magnetic fields which prevents plasma diffusion and double layer formation, by employing double concentric arrays of permanent magnets, a constant field area, and a diverging magnetic field can be generated near the outlet of the plasma source. In the source, a rapid potential drop with 4cm thickness from 50V to 20V is generated at the diverging