Hiroki Watanabe
(Tokyo Metropolitan University, Japan)

In order to liberate electric propulsion from the limits of hollow cathode without thrust performance degradation, inductively coupled plasma (ICP) is employed for electron sources in this study, because ICP achieves sufficiently high electron number density without an oxide insert and magnetic fields. The ICP cathode (ICP/C) has been developed and demonstrated its steady operation and self-ignition successfully. Through the experimental evaluation, it was obtained that the ICP/C is properly operated as a main cathode of DC cusped ion thruster and a neutralizer of RF ion thruster. In addition, a negative bias power supply is not necessary while it works as a neutralizer. However, the power consumption of the cathode is not acceptable for actual applications on electric propulsion. Therefore, in order to improve the cathode performance, its ignition and electron emission characteristics are investigated as functions of RF antenna configuration and cathode dimension. Moreover, plasma parameters and cathode inner pressure are measured to clarify the electron emission mechanism of ICP/C. The detailed experimental results will be described in the presented paper.

Yasuyoshi Hisamoto
(The Graduate University for Advanced Studies, Japan)

There is an increasing need for super low Earth orbiting satellites to observe the terrestrial environment from an altitude of 150km to 250km. These satellites have to cancel the air drag to stay in such an orbit for several years. A completely new concept, the Air Breathing Ion Engine (ABIE), has been proposed for spacecraft drag compensation. The ABIE takes in and uses the low-density atmosphere surrounding the satellite as a propellant. A laboratory environment which imitates the orbital conditions on such a super low earth orbit is essential to study ABIE on ground. This project attempts to synthesize the environment in super low Earth orbit using a 6cm ECR plasma source. An atomic oxygen beam with 5eV was realized by reflecting plasma off a metallic surface. We achieved a flux of 1E15 atom/cm2/sec, which corresponds to the orbital conditions at an altitude of 250km. We are directly determinating the atomic oxygen speed using the Doppler shift measurement. The next step is retrofitting the laboratory equipment to use as an intake feed for the air breathing ion engine. We will report the results of the environment simulated by the 6cm ECR plasma source.

Naoji Yamamoto
(Kyushu University, Japan)

In order to improve the thrust performance of a miniature microwave discharge ion thruster, plasma properties were measured by means of laser Thomson scattering for understanding the physics in the discharge chamber in the thruster and designing a grid system. A photon counting method and a triple grating spectrometer were used against a small Thomson scattering signal and a strong stray laser light. Electron number density and temperature in the vicinity of the screen grid at mass flow rate of 0.15 sccm and incident microwave power of 4 W are 2.7times 10^17 m-3 and 5.1 eV, respectively. Estimated ion saturation current is 3.4 mA, which is good agreement in the extracted ion beam current of 3.1 mA at beam voltage of 1200 V and acceleration grid potential of -200 V.

Ryudo Tsukizaki
(The University of Tokyo, Japan)

The world 1st ECR ion thruster mu 10 was improved 25 % in the point of thrust force by adding new propellant inlets in the discharge chamber. In order to reveal a mechanism of increase in thrust force of mu 10, laser absorption spectroscopy has been applied to inside of mu 10 using an optical fiber. In this study, an absorption line of neutral xenon at 823. 388 nm (in vacuum) was measured with an external cavity diode laser and a rigid optical fiber. Compared with Langmuir probe, the optical fiber made of dielectric material has little disturbance against the electromagnetic field of microwaves. By inserting the optical fiber into mu 10, the length of laser path changes, which enables the in situ measurement of a particle density along with the displacement of the fiber. Avoiding a saturation of the absorption in the ion engine mu 10 caused by a high intensity laser, the absorption line was properly obtained and it has a unique broad line for Zeeman effect. It is measured that the averaged neutral density between a waveguide of mu 10 to its grids is 1.86 * 10^17 m-3.

Fakhuradzi Baharudin
(Gifu University, Japan)

With a increase of mission of an ion engine due to its high specific impulse, an evaluation of its lifetime by an experiment becomes difficult. Therefore, numerical evaluations of the lifetime are required. Because fluid models are not appropriate for the ion engine analysis, a calculation time becomes long, and some models including a flux tube model are proposed. In this study, to evaluate a validity of an application of an electron density model using a Boltzmann relation into the ion engine analysis were done. In the study, the analyses by the full PIC(Particle in cell) code and the hybrid PIC code employing the electron density model were carried out and the effects of the electron models were investigated. The results show that the electron density model effects the positive electric potential distribution in the vicinity of the grid hole axis just downstream of the accel grid. However, the ion beam profile and the grid current are little affected by the difference of the potential. These results suggests that the Boltzmann relation can be applied to the simulation codes for the electron density evaluations.