Hisayoshi Kurokawa

Fundamental Research on Mercuryless Fluorescent Lamps II – External Electrode Operation with Pulsed Dielectric Barrier Discharge –

The characteristics of electrodeless xenon discharge fluorescent lamps using dielectric barrier discharge are described in this paper. All lamps were operated with pulsed discharge. The luminance of phosphor increases as the pressure of xenon increases. As the pressure of xenon increases, the second peak of phosphor emission increases. These increases seem to be caused by the VUV light of xenon excimers. Therefore, in order to obtain high luminance, xenon should be filled at high pressure. In the case of the lamp operated by inner electrodes, if only xenon is contained in the lamp, the cathode is bombarded and is damaged by the large mass of a xenon ion. On the other hand, the external electrode type is never damaged by the ions or electrons. Moreover, the efficacy of the external electrode type is as great as the inner electrode type, and it can be improved by increasing the distance between electrodes.

Fundamental Research on Mercuryless Fluorescent Lamps I – Inner Electrode Operation with Pulsed Discharge –

The characteristics of xenon-neon discharge fluorescent lamps with inner electrodes are described in this paper. All lamps were operated by pulsed discharge. When the partial pressure of neon is high, the ignition voltage and operation voltage are low because of the Penning effect. Thus, a higher mixing ratio of neon is desirable for lower ignition and operation voltages. However, the luminance of phosphor increases as the mixing ratio of xenon increases. As the pressure of xenon increases, the second peak of phosphor emission in afterglow increases. These increases seem to be caused by the VUV light of xenon excimers. Therefore, though there is the problem of ion bombardment of the cathode under a high operation voltage, the pulsed discharge of the xenon-neon mixture at a high xenon mixing ratio is desirable in mercuryless fluorescent lamps because a strong radiation of xenon excimer is obtained.

Comparative Inactivation of Bacillus subtilis Spores Using a DBD-Driven Xenon Iodide Excilamp and a Conventional Mercury Lamp

In this paper, we compared the inactivation of Bacillus subtilis spores in water by means of a dielectric-barrier-discharge (DBD)-driven XeI* excilamp and a low-pressure mercury lamp. The main part ( ~ 76%) of the excilamp output was due to the B → X transition of XeI* exciplex at 253 nm. It is shown for the first time that a better sterilization action is achieved with the DBD-driven XeI* excilamp compared with the monochromatic mercury lamp at the same UV dose. The contribution of an atomic iodine emission in the range of 178-207 nm has been confirmed. Germ-reduction experiments with the XeI* excilamp have been carried out in a steady-state mode and in a water-flow reactor.

The afterglow characteristics of xenon pulsed plasma for mercury-free fluorescent lamps

In this study, the spectroscopic characteristics of radiations from xenon pulsed plasma are measured experimentally as a study on a mercury-free fluorescent lamp. Each radiation waveform has two peaks and they vary according to the inner diameter of lamp and the pressure of xenon as follows: (a) As the inner diameter of lamps increases, the afterglow radiation, that is the second peak, decays faster. (b) As the xenon pressure increases the first peak of radiation just after the start of discharge decreases and the afterglow increases. The characteristics of afterglow are explained by the rate equation of metastable xenon atoms Xem, and its coefficients are determined through the experimental results. This equation shows that in order to obtain intense phosphor afterglow, i.e. strong radiation of xenon excimer, high pressure of xenon and large lamp diameter are desirable. Moreover, high pressure of xenon brings fast decay of afterglow. Then the afterglow radiation has no overlap on the first peak of next discharge at a high frequency. Consequently, higher pressure of xenon and large lamp diameter are desirable for high intensity and high efficacy for xenon fluorescent lamps.

Water sterilization using a DBD-driven xenon iodide excilamp

Summary form only given. Conventional technology for disinfection by UV irradiation is based on mercury lamps. The development of a new mercury-free UV lamp is very important due to the environmentally unfriendly nature of mercury. In present study we compared the inactivation of Bacillus subtilis spores in water by means of a developed dielectric barrier discharge-driven Xel* excilamp and a conventional low- pressure mercury lamp. Experiments have been carried out with the air-cooled sealed off lamp, filled with a Xe/L = 13.3/0.04 kPa mixture, which has been determined as optimum from the viewpoint of maximal UV output. The main part (-76%) of the excilamp output was due to the BrarrX transition of Xel* exciplex at 253 nm. The excilamp was excited using a custom built power supply, providing bipolar pulses with peak-to-peak voltage U = 0-4.4 kV, rising and falling times of 0.9 and 0.6 mus, f= 21.5-115 kHz. A more detail description of the design and output characteristics of a developed Xel* excilamp has been presente. It has been shown for the first time that better sterilization action is achieved with the developed DBD-driven Xel* excilamp compared to a conventional monochromatic mercury lamp at the same UV fluence. A reduction by more than 6 orders of magnitude of B. subtilis spores concentration (CFU/ml) has been reached and the D-value was about 5-9.5 mJ/cm2. A reduction by four orders of magnitude (99.99% inactivated microorganisms) was achieved at 22-25 mJ/cm2 for the Xel* excilamp and at 40 mJ/cm2 for the mercury lamp. An additional effect of the I* radiation at 206 nm and in the VUV range (178-188 nm) has been confirmed. It has been tested that the DBD-driven Xel* excilamp can be used for the inactivation of the microorganisms in a steady state mode or in the movable systems (drinking water treatment or food package sterilization).

Fundamental research on mercuryless rare gas fluorescent lamps at pulsed discharge

The characteristics of xenon-neon discharge fluorescent lamps with inner electrodes, and xenon discharge lamps with external electrodes are described in this paper. All these lamps were operated at pulsed discharge. In the case of inner electrode type, when the partial pressure of neon is high, the ignition voltage is low because of the Penning effect. Then, the high mixing ratio of neon is desirable for the lower ignition voltage. However, the luminance of phosphor increases as the mixing ratio of xenon increases. Therefore, in order to obtain high luminance, xenon should be filled at high mixing ratio. If only xenon is filled in the lamp of inner electrode type, the cathode is bombed and damaged by the large mass xenon ions. Consequently, the most suitable mixing ratio of xenon and neon or some buffer gas should be found experimentally for inner electrode type. On the other hand, when the lamp filled only with xenon is operated by external electrodes, as the pressure of xenon increases, the afterglow peak of phosphor emission increases. These increases seem to be caused by the UV light of xenon excimers. However, the starting voltage becomes high at high xenon pressure. So, the optimization of some conditions such as electrodes, pulse frequency, etc. is required for external electrode type.