Takaaki Iijima

Ion Acceleration by Ion-Cyclotron Resonance in Non-Uniform Magnetic Field Using the TPD-Sheet IV Linear Divertor Simulator

Ion acceleration of high density sheet plasma (ca.1018 m-3) in a non-uniform magnetic field by ion-cyclotron resonance (ICR) is investigated in a linear divertor plasma simulator, TPD-Sheet IV. The radio frequency (RF) electrodes consist of two parallel plates. The ion energy along the axis of the magnetic field or in the perpendicular direction was measured using a Faraday cup. The experiment was conducted using helium gas and a discharge current of 50 A. The ion energy in the direction perpendicular to the magnetic field line increases by with ion-cyclotron resonance. Ions are also accelerated along the axis of the magnetic field line due to the magnetic field gradient along the axis.

Study of Optimum Conditions for the V-Shaped Target of a Gas Divertor

Experimental simulation of a V-shaped target for a gas divertor via detached plasma formation is presented using a linear divertor plasma simulator, TPD-Sheet IV. Three geometries of the opposite plate on the V-shaped target were investigated with variation of the contact gas flow rate. The ionization and recombination events are discussed for each target configuration using the collisional-radiative (CR) model. The results expect that a gas divertor with a V-shaped target effectively enhances plasma recycling and detachment.

Effect of the Divertor Leg Length on the Population of Molecular Ions in the Divertor Simulator TPD-SheetIV

Abstract In TPD-SheetIV, a simulation experiment on a long leg divertor configuration has been conducted and hydrogen molecular ion formation in detached plasma was observed. Improvements to the simulation geometry used in DEGAS 2 allowed us to study the effect of leg length on neutral transport. This paper also describes a simple ion balance equation and the ion density ratios obtained with it. From these data, it is shown that a long leg divertor enhances molecular ion density in the divertor, which might enhance molecular assisted recombination.

Measurement of Hydrogen Negative Ions in Sheet Plasma

Negative ions are expected to play an essential role in particle accelerators, magnetic fusion reactor, and plasma processing. The production mechanisms of negative ions in hydrogen plasma are not easily understood because of the complex phenomena of atomic and molecular reactions. However, measurement method of negative ions using mass analyzer has not been established. We have carried out the experimental observation of negative ions in hydrogen sheet plasma [1]. The sheet plasma is suitable for the production of negative ions, because the electron temperature in the central region of the plasma as high as 10 – 15eV, whereas in the periphery of the plasma, a low temperature of a few eV of obtained. The negative and positive ions density (H , H + , H2 + , H3 + ) were detected using an “omegatron” mass analyzer, while the electron density and temperature were measured using a Langmuir probe.

Response of Hydrogen Balmer Series Spectra in Recombining Plasma with Pulse Plasma Flow

Experiments on a recombining plasma with pulse plasma flow have been performed in the linear divertor simulator TPD-SheetIV. The pulse plasma flow was generated using a switching circuit controlled by the electric potential of the adjacent floating electrode in the plasma source. The duration of the pulse was 0.3 ms at a frequency of 50 Hz. The time dependence of the electron density ne, temperature Te, and Balmer series spectra H, H, were measured using a Langmuir probe. The effective ionization and recombining coefficients calculated by using the Collisional-Radiative model, taking into account high-energy electrons.