Plasma application

Ball lightning

 Ball lightning is an atmosphere pressure plasma and generated by discharge of high voltage on the surface of an electrolyte. Ball lightinig is a long lived plasmoid compared to the energy input period.Ball lightning plasma produces OH and O radicals and these radicals will oxidize and dispose PM2.5.These characteristics should be suitable for PM2.5 removal devices.
The physical properties of Ball lighting have not been elucidated even now. Therefore, we estimate the temperature of FB using various diagnositics(emission spectroscopy and laser diagnositics) and to demonstrate decomposing PM2.5 on a filter.

cBN field emission cathode

field emission cathode An Electro dynamic tether system is a promising system for debris removal due to the less consumption of power and no consumption of propellant. The key technology of the system is electron source, which emits electrons. There are some candidates for space electron source, filament cathode, a hollow cathode, a microwave discharge cathode and field emission cathode. Field emission cathode has a great advantage, it doesn’t consume propellant and power consumption is small. Japan Aerospace Exploration Agency (JAXA) have been developing electro dynamic tether system with carbon nanotubes field emission cathodes.
 We have been developing cubic Boron nitride (cBN) field emission cathodes. Since it will have strong tolerance against atomic oxygen, which is in low earth orbit. We got good performance, 0.55 mA/cm2 at 3.4 kV.

Cavity Ring-Down Spectroscopy (CRDS)

 CRDS is a path-enhanced laser absorption method that provides extremely high-sensitivity. The technique is seeing growing use in a range of applications including molecular spectroscopy, atmospheric monitoring, combustion diagnostics, and plasma diagnostics and has been described in several review articles [1-3]. The technique can readily measure per-pass optical absorbance of <0.1 ppm for measurement times of seconds. (The optical absorbance is the product of absorption coefficient and path length, and in the limit of small absorbance corresponds to the fractional amount of light absorbed.) As mentioned above, the technique is quantitative, self-referencing, and can measure ground states. As shown in right figure, the basic idea is to house the absorbing species within a high finesse optical cavity formed from high-reflectivity (HR) mirrors. The probe laser beam is coupled into the optical cavity where it “bounces” many times back-and-forth between the mirrors. Owing to the high reflectivity, the light within the cavity makes many passes within the cavity (e.g. ~104 passes for R~0.9999), so that the effective path length is greatly increased. A detector placed behind the cavity measures the temporal decay of optical intensity within the cavity. The difference in the temporal decay rate with and without the absorber (or with the laser tuned on/off the resonance) yields the sample concentration. The technique affords high sensitivity owing to a combination of long effective path length and insensitivity to laser energy fluctuations (since a rate is measured). CRDS can be implemented with either pulsed lasers or cw lasers . The latter method, which we use, is termed cw-CRDS and typically provides higher absorption sensitivities owing to higher sampling rates and narrower laser linewidths (allowing coupling to only a single cavity mode). In cw-CRDS setups, the light injected to the cavity must first be extinguished to generate the ring-down signal.

Laser Thomson scattering


 Laser Thomson scattering (LTS) technique is a laser based optical method for a measurement of plasma properties, such as electron number density (Ne) /electron temperature (Te). In the incoherent regime, the scattered spectrum reflects the Doppler motion of individual electrons, and the scattered intensity is proportional to Ne. This method was developed to measure plasma properties in high temperature plasma having Ne > 1019 m-3. During the last decade, its applicability has been extended to lower density plasma, with densities of less than 1016 m-3, by a signal accumulation technique.10 This technique allows us to apply LTS to the plasma in the discharge chamber of a miniature microwave ion thruster and our previous study showed that LTS technique was useful and validate tool for the measurement of plasma property.

Miniature ion sourceLFR

 We have been developing a miniature ion source for small ion etching system with the knowledge of the miniature ion thruster and Hall thruster.