The effect of active antennas on the hot-restrike of high intensity discharge lamps

Hoebing, T.; Bergner, Andreas; Koch, Benjamin; Manders, F Freddy; Ruhrmann, C; Mentel, J.; Awakowicz, Peter

doi:10.1088/0022-3727/47/20/205501

Cited by 5 publications

(2 citation statements)

References 9 publications

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“…[11] The formation of arc spots on cold tungsten electrodes of HID lamps plays especially a role when the lamps are ignited. [12][13][14][15] It starts the heating up of the electrodes ending in a diffuse, spot-or emitter spot mode of cathodic arc attachment. [16][17][18][19][20][21][22] Tungsten sticks out by reason of its high melting temperature of 3695 K and boiling temperature of 6203 K. The boiling temperature is much higher than the boiling temperature of the tungsten oxides WO 2 and WO 3 amounting to 2003 and 2110 K. [23,24] The order of the boiling temperatures of tungsten and tungsten oxides is reversed compared to the other metal electrodes.…”

Section: Introductionmentioning

confidence: 99%

Investigation of the interaction of dense noble gas plasmas with cold cathodes:III—Arc spot ignition on pure and doped W cathodes

Frohnert

Mentel

2022

Contributions to Plasma Physics

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The study of the commutation of atmospheric pressure noble gas arcs on cold cathodes made of Al, Cu, Ti, graphite, Au, Pd, and Pt is extended to W cathodes. Rods with a diameter of 2 mm are inserted in a UHV tight stainless steel vessel filled with Ar 5.6 or Kr 4.8. The negatively biased electrodes are brought into interaction with arc plasma by a magnetic blast field. Their end faces are mostly polished with diamond grinding powder; some are electrolytic polished, others additionally covered with a thick oxide layer or pasted with W powder. Moreover, electrodes are investigated being doped with Al, K, and Si or doped with ThO2. The arc commutation is observed by short time photography, streak camera records, and temporally highly resolved optical spectroscopy for a lower and higher voltage applied between the arc plasma and the commutation electrode (CE). Varying the electrode properties revealed that basically ionized vapour of electrode material and less distinctly lowering of the work function by doping accelerate the arc commutation. It is initiated by plasma ions, which initially generate secondary electrons across the whole end face of the electrode. Since the electron emission varies locally, the multiplication of ions within the plasma layer by emitted electrons varies too. The positive feedback between both provokes a constriction of the commutation current and the power input into an arc spot. The electrode vapour promotes at first the development of an arc spot but finally quenches it by cooling the plasma layer in front of it.

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Section: Introductionmentioning

confidence: 99%

Investigation of the interaction of dense noble gas plasmas with cold cathodes:III—Arc spot ignition on pure and doped W cathodes

Frohnert

Mentel

2022

Contributions to Plasma Physics

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“…[ 5,6 ] Another example is the ignition phase in high‐intensity discharge lamps during which the cold electrodes are heated up onto their stationary operation temperature. [ 7–10 ] Current densities of the order of 10 8 A/m 2 are locally observed within arc roots on cold cathodes initiating the spot, emitter spot—but also the diffuse mode of cathodic arc attachment. [ 11–17 ] Quite recently, in a special issue on thermal‐plasma‐material interactions further examples of the role and preconditions of arc spot ignition were given.…”

Section: Introductionmentioning

confidence: 99%

Investigation of the interaction of dense noble gas plasmas with cold cathodes: I—Experimental setup and application to Al, Cu, Ti, and graphite cathodes

Frohnert

Mentel

2022

Contributions to Plasma Physics

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The formation of arc spots on cold cathodes, called arcing, is an interference factor in all kinds of plasma technical devices. It is investigated by igniting an arc in a clean atmospheric pressure Ar or Kr filling of a stainless steel vessel. It is brought into interaction by a magnetic blast field with a negatively biased commutation electrode (CE), formed by a rod with a diameter of 2 mm consisting of pure Al, Cu, Ti, or graphite; its end face is polished with diamond grinding powder. The arc commutation is observed by short‐time photography, streak camera records, and temporally highly resolved optical spectroscopy for different applied voltages. The emission of ion lines of the filling gas and of vaporized electrode material by the plasma in front of the cathode is indicating the formation of a positive space charge layer in front of its surface. It provides the ions, which induce secondary electron emission of the cathode surface and with it, the arc commutation. The commutation time tc elapsing between a signal generated by the arc plasma in front of the CE and the beginning of a current flow through the electrode increases for low voltages with increasing permittivity of a surface layer formed by electrically insulating metal oxide and decreases with increasing electrical conductivity of the layer. It is lowest for graphite without an oxide layer. On scanning electron microscope pictures, taken of the end face of the electrode after arc commutation, craters with diameters of less than 1 μm are visible.

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Antenna induced hot restrike of a ceramic metal halide lamp recorded by high-speed photography

Hermanns

Hoebing

Bergner

et al. 2016

Journal of Applied Physics

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The hot restrike is one of the biggest challenges in operating ceramic metal halide lamps with mercury as buffer gas. Compared to a cold lamp, the pressure within a ceramic burner is two orders of magnitude higher during steady state operation due to the high temperature of the ceramic tube and the resulting high mercury vapour pressure. Room temperature conditions are achieved after 300 s of cooling down in a commercial burner, enclosed in an evacuated outer bulb. At the beginning of the cooling down, ignition voltage rises up to more than 14 kV. A significant reduction of the hot-restrike voltage can be achieved by using a so called active antenna. It is realized by a conductive sleeve surrounding the burner at the capillary of the upper electrode. The antenna is connected to the lower electrode of the lamp, so that its potential is extended to the vicinity of the upper electrode. An increased electric field in front of the upper electrode is induced, when an ignition pulse is applied to the lamp electrodes. A symmetrically shaped ignition pulse is applied with an amplitude, which is just sufficient to re-ignite the hot lamp. The re-ignition, 60 s after switching off the lamp, when the mercury pressure starts to be saturated, is recorded for both polarities of the ignition pulse with a high-speed camera, which records four pictures within the symmetrically shaped ignition pulse with exposure times of 100 ns and throws of 100 ns. The pictures show that the high electric field and its temporal variation establish a local dielectric barrier discharge in front of the upper electrode inside the burner, which covers the inner wall of the burner with a surface charge. It forms a starting point of streamers, which may induce the lamp ignition predominantly within the second half cycle of the ignition pulse. It is found out that an active antenna is more effective when the starting point of the surface streamer in front of the sleeve is a negative surface charge on the inner tube wall. The high-speed photos show that the ignition process is very similar in lamps with Hg or Xe as buffer gas.

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The effect of active antennas on the hot-restrike of high intensity discharge lamps

Cited by 5 publications

References 9 publications

Investigation of the interaction of dense noble gas plasmas with cold cathodes:III—Arc spot ignition on pure and doped W cathodes

Investigation of the interaction of dense noble gas plasmas with cold cathodes:III—Arc spot ignition on pure and doped W cathodes

Investigation of the interaction of dense noble gas plasmas with cold cathodes: I—Experimental setup and application to Al, Cu, Ti, and graphite cathodes

Antenna induced hot restrike of a ceramic metal halide lamp recorded by high-speed photography

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