ABSTRACT
The studies on Micro-Hollow Cathode Discharge (MHCD) have been made for the application in flat panel light source [I] [2]. The general MHCD electrode structure for flat lamp is as following; the dielectric is between the top and bottom metal electrode and then micro hole is formed at the same time in these three floors (metal/dielectric/metal) [3]. The contentment must do a restriction condition of the pD (p: pressure, D: diameter of hollow cathode) to be operated for MHCD. This restriction condition has the upper bound with the lower bound. The upper bound is related to the size ratio of the discharge to cathode hole and the lower one is related to the free path of electron for gaining electric energy to be consumed by ionization to sustain MHCD [4]. If the product of execution pressure and cathode hole diameter is not suitable, we are unable to do which we expect the hollow effect. Therefore the thing to consider a restriction condition like these in an electrode design of MHCD is in important work. To the present time the researches about pD limitation of MHCD have become the progress in the case of direct current (dc) operation. A parallel execution of each hall for the application to a plane source of light of MHCD is necessary. Karl H. Scheonbach introduced to use the ballast in each hall or to block expansion of the plasma inside hollow cathode for a parallel execution of dc MHCD [4]. And also because dc MHCD is the metal to metal discharge, there is no barrier against overflow of electron due to the thermionic emission in hollow cathode in system. Then the system ballast must be required to prevent over-current for normal operation of device. In this paper we invented the ballast free dielectric barrier microhollow cathode structure for stable parallel
operation and measured the pD upper limitation of MHCD for designing the hole dimension in pure Xe to be operated with alternative current (ac). The schematic diagram of dielectric barrier microhollow cathode is shown in Fig. 1. We applied the 30 kHz ac voltage with the downside electrode and earthed the upper hollow electrode. In this electrode structure the dielectric (A1203) barrier functions as the system ballast. Also the charge build up on the opened surface of dielectric barrier limits the each hole current up to integrand of discharge current. The Fig 2 shows the parallel operation of nine holes (250 gm) in 40 torr pure Xe. The pD upper limitation is measured by photocurrent peak and discharge image from the hollow electrode. We made the 900 gm hollow cathode to show the discharge average feature. Fig.3 and 4 show the discharge feature and photocurrent peak. From these data we can obtain the pD upper limitation. When the upper electrode is cathode, the photocurrent peak was 4 — 7 times higher than opponent half period due to the hollow cathode effect (Paschen, 1916). And also hollow hole was fully filled with glow discharge when the hollow cathode effect exists. As a result up to 10 torr the hollow cathode effect exists in our electrode system, therefore the limitation value of pD for hollow effect is about 0.9 tom in our system.
