The Effect of Current and Pressure on the Impedance of Cold Cathode Glow Discharge Tubes†

An optical study of pulse, dc, and ac (50–400 kHz) ignition of metal halide lamps has been performed by investigating intensified CCD camera images of the discharges. The ceramic lamp burners were filled with xenon gas at pressures of 300 and 700 mbar. In comparison with dc and pulse ignition, igniting with an ac voltage decreases the ignition voltage by up to 56% and the breakdown time scales get much longer (∼10−3 s compared with ∼10−7 s for pulse ignition). Increasing the ac frequency decreases the ignition voltages and changes the ionization channel shapes. External irradiation of UV light can have either an increasing or a decreasing effect on ignition voltages.

Section: Influence Of Irradiating Uv Light On the Pulse And DC Igniti...mentioning

confidence: 99%

Pulse, dc and ac breakdown in high pressure gas discharge lamps

Beckers¹,

Manders²,

Aben³

et al. 2008

“…Due to the low work function of this emitter mixture, normal operation of a fluorescent lamp electrode is 3 Present address: Philips Automotive and Special Lighting, Philipsstrasse 8, D-52068 Aachen, Germany. 4 Present address: Philips Turnhout, Steenweg op Gierle 417, Turnhout B-2300, Belgium. possible at a temperature of around 1200-1300 K. In order to reduce the amount of power necessary to keep the active parts of the electrodes at these temperatures, fluorescent lamp electrodes are usually made of coiled-coil electrodes (see figure 1).…”

Section: Introductionmentioning

confidence: 99%

High-frequency cold ignition of fluorescent lamps

Haverlag

Kraus

Sormani

et al. 2002

Experimental and theoretical investigations have been performed on the ignition process of low-pressure mercury-noble gas fluorescent lamps operating on a 50 kHz electronic driver circuit. In case the electrodes of the lamp are not heated prior to the ignition process, the ignition process can, under certain conditions, lead to premature fracture of the coiled-coil electrode, which means that the lamp ceases to operate before the emitter is consumed completely. Experimental studies of this process have shown that the erosion process responsible for this premature end-of-life consists of localized sputtering of the tungsten electrode by energetic ions from the glow discharge that is present during the ignition process. In order to understand the basic process that leads to localized sputtering of the electrodes in a glow discharge, a simple glow-discharge fluid model, in combination with a finite-element model of the heat transport in the electrode, has been built. The model shows that thermionic emission can supply a significant fraction of the electrons already at temperatures far below the normal operating temperature in fluorescent lamps. This thermionic emission is responsible for a contraction process. After the beginning of the discharge contraction it takes typically a few milliseconds before the glow-to-arc transition is observed in the lamp voltage and the normal electrode operating temperature is reached. During this time localized sputtering takes place, which eventually leads to coil fracture.

“…As a consequence all unipolar square pulses of positive polarity are preceded by a 2 µs negative pulse of 120 to 140 V amplitude (see figure 4) that serves the purpose of pre-ionizing the active electrode surroundings with thermallyemitted electrons from this temporary cathode. This pre-ionization pulse is kept at the lowest level possible enabling some ionization while the associated priming current level is too low to influence the overall breakdown conditions [30]. Yet, this measure ensures the repeatability of positive-polarity ignitions down to the 10 ns time scale.…”

Section: Lamp Voltage Waveformsmentioning

confidence: 99%

“…The expression of the wave front velocity as a function of n e0 is thus obtained by combining (20) with (30), giving:…”

Section: Modelling Of the Pre-breakdown Wavementioning

confidence: 99%

Optical and electrostatic potential investigations of electrical breakdown phenomena in a low-pressure gas discharge lamp

Gendre¹,

Haverlag²,

Kroesen³

2010

The ignition phase is a critical stage in the operation of gas discharge lamps where the neutral gas enclosed between the electrodes undergoes a transformation from the dielectric state to a conducting phase, eventually enabling the production of light. The phenomena occurring during this phase transition are not fully understood and the related experimental studies are often limited to local optical measurements in environments prone to influencing these transient phenomena. In this work unipolar ignition phenomena at sub-kilovolt levels are investigated in a 3 Torr argon discharge tube. The lamp is placed in a highly controlled environment so as to prevent any bias on the measurements. A fast intensified CCD camera and a specially-designed novel electrostatic probe are used simultaneously so as to provide with a broad array of measured and computed parameters which are displayed in space-time diagrams for cross comparisons. Experiments show that three distinct phases exist during successful ignitions: Upon the application of voltage a first ionization wave starts from the active electrode and propagates in the neutral gas toward the opposite electrode. A local front of high axial E field strength is associated with this process and causes a local ionisation to occur, leading to the electrostatic charging of the lamp. Next, a second wave propagates from the ground electrode back toward the active electrode with a higher velocity, and in this process leads to a partial discharging of the lamp. This return stroke draws a homogeneous plasma column which eventually bridges both electrodes at the end of the wave propagation. At this point both electrode sheaths are formed and the common features of a glow discharge are observed. The third phase is an increase of the light intensity of the plasma column until the lamp reaches a steady state operation. Failed ignitions present only the first phase where the first wave starts its propagation but extinguishes in the lamp, leading to a charge memory effect. It is found that the full propagation of this first wave is a requirement for a successful lamp ignition. Differences in the properties of the waves were observed depending on the voltage polarity, and it was estimated that a photoelectric effect at the wall is the most likely source of electron for the ionisation wave of positive polarity. Finally a simple model of the first ionization wave is developed and used to analyse the fundamental differences between processes occurring at negative and at positive polarity. From this study three conditions are developed for the successful unipolar ignition of lamps and the relations between them are derived.