Properties of Arc Cathode Spots

Abstract

Arc cathode spots operating by formation of surface-microplasmas are reviewed for discharges in vacuum and in gases. New experimental studies using advanced optical methods (image converter cameras and laser absorption techniques) reveal that the spot is composed of fragments with a size below 10 pm. In vacuum these are highly mobile, for copper on a rime scale < 50 ns. The motion and the rapid sequences of extinctions and re-ignitions determine the behavior of the whole spot. Cu-spots in vacuum exhibit displacements in times < 100 ns. A tentative explanation of the spot movement is given on the base of the fragment dynamics. In gases the fragments are more separated than in vacuum. The ignition of fragments is discussed in the framework of recent studies on the glow-toarc transition in high pressure discharges. Finally, new mechanisms for enhanced field electron emission are mentioned.

Near-cathode phenomena in HID lamps

“…During the last decade, experimental evidence has been collected confirming the existence of fragments (microspots) in discharges on cold cathodes and, thus, supporting the second point of view insofar as cold cathodes are concerned; see, e.g., [18] and references therein. No unambiguous evidence of such type has been obtained for hot cathodes.…”

“…Reviews of early works in which such an approach was used can be found in [8]- [13]; models specifically designed for cathodes of HID lamps are presented in [14] and [15] (see also [16], in which the model of [14] is reconstructed). Second, there are works in which plasma-cathode interaction is considered as a sequence of individual events (termed by different authors as microexplosions, or microspots, or fragments) occurring on extremely small length and time scales of the orders of micrometers and nanoseconds, respectively; see, e.g., the reviews of [17] and [18]. While models considered in the framework of the first approach are stationary or quasi-stationary, models considered in the framework of the second approach are essentially nonstationary.…”

Near Plume Modeling of a Micro Cathode Arc Thruster

“…Hence, ̇ ⁄ . We next assume that this mass is expelled by the thruster in the form of doubly-ionized Titanium ions [8]. The corresponding current is thus…”

Эрозия Катода В Газовом Дуговом Разряде В Области Пороговых Токов

“…В воздухе поверхность электродов покрыта оксидами [15]. В [16] были обнаружены пленки азота толщиной 10 nm при давлении 670 Pa и толщиной два раза большей при давлении 1300 Pa. В [15,17,18] изучали влияние слоев загрязнения на типы пятен и их движение. Было обнаружено, что при увеличении давления газа начинают преобладать пятна первого типа, т. е. поверхностные загрязнения способствуют зажиганию новых КП на больших расстояниях от существующего.…”