The anodic emitter effect and its inversion demonstrated by temperature measurements at doped and undoped tungsten electrodes

Hoebing, T.; Bergner, Andreas; Hermanns, Patrick; Mentel, J.; Awakowicz, Peter

doi:10.1088/0022-3727/49/15/155504

Cited by 7 publications

(16 citation statements)

References 28 publications

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“…By reason of the field inversion in front of cold anodes there may be some similarities between cathode and anode. [24,41,42] An improved understanding of arc commutation may help to implement measures by which arcing in plasma devices can be prevented.…”

Section: Open Questions and Further Approachmentioning

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: Open Questions and Further Approachmentioning

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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“…For the experimental investigations of the gas phase emitter effect in front of doped tungsten electrodes, the so-called Bochum model lamp is utilized [4,15,16]. The concept of the model lamp, and many technical details, are published in [1,6,42].…”

Section: The Bochum Model Lampmentioning

confidence: 99%

“…The control voltage is supplied by a signal generator (Agilent 33120A). In some recent investigations [15,16], the model lamp was operated with a current controlled power supply (Heinzinger 200-75) providing a maximum current of 75 A, and a maximum voltage of 200 V.…”

Section: The Bochum Model Lampmentioning

confidence: 99%

“…The Ba-compound is dissociated at elevated temperature supplying Ba atoms, which diffuse along the surface to the electrode tip [11,13]. A recent development is the introduction, not only in high intensity discharge lamps but also in arc welding, of tungsten electrodes which are doped with La 2 O 3 ; tungsten electrodes doped with Ce 2 O 3 have also been tested [14][15][16]. These electrodes show, principally, a behavior quite similar to thoriated electrodes.…”

Section: Introductionmentioning

confidence: 99%

“…To date, it has been assumed that the vaporization of emitter material during lamp operation from the tip of doped tungsten electrodes is substituted by its diffusion from the interior of the electrode [8][9][10][11]. But recent investigations of doped tungsten electrodes, especially in the Bochum model lamp [1] but also in the Hannover model lamp [31], have shown that vaporized emitter material is at least in parts ionized in front of the cathode, and also in front of a cold anode, and repatriated as an ion current onto the electrode tip [4,15,16,32]. This version of the cataphoretic emitter effect is also reviewed here.…”

Section: Introductionmentioning

confidence: 99%

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The cataphoretic emitter effect exhibited in high intensity discharge lamp electrodes

Mentel¹

2018

J. Phys. D: Appl. Phys.

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A mono-layer of atoms, electropositive with respect to the substrate atoms, forms a dipole layer, reducing its work function. Such a layer is generated by diffusion of emitter material from the interior of the substrate, by vapour deposition or by deposition of emitter material onto arc electrodes by cataphoresis. This cataphoretic emitter effect is investigated within metal halide lamps with transparent YAG ceramic burners, and within model lamps. Within the YAG lamps, arcs are operated with switched-dc current between rod shaped tungsten electrodes in high pressure Hg vapour seeded with metal iodides. Within the model lamps, dc arcs are operated between rod-shaped tungsten electrodes—one doped—in atmospheric pressure Ar. Electrode temperatures are determined by -pyrometry, combined with simulation of the electrode heat balance. Plasma temperatures, atom and ion densities of emitter material are determined by emission and absorption spectroscopy. Phase resolved measurements in YAG lamps seeded with CeI3, CsI, DyI3, TmI3 and LaI3 show, within the cathodic half period, a reduction of the electrode temperature and an enhanced metal ion density in front of the electrode, and an opposite behavior after phase reversal. With increasing operating frequency, the state of the cathode overlaps onto the anodic phase—except for Cs, being low in adsorption energy. Generally, the phase averaged electrode tip temperature is reduced by seeding a lamp with emitter material; its height depends on admixtures. Measurements at tungsten electrodes doped with ThO2, La2O3 and Ce2O3 within the model lamp show that evaporated emitter material is redeposited by an emitter ion current onto the electrode surface. It reduces the work function of tungsten cathodes above the evaporation temperature of the emitter material, too; and also of cold anodes, indicating a field reversal in front of them. The formation of an emitter spot at low cathode temperature and high emitter material density is traced back to a locally reduced work function generated by a locally enhanced emitter ion current density.

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A Survey of Chemical Nonequilibrium in Argon Arc Plasma

Baeva

2016

Plasma Chem Plasma Process

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The anodic emitter effect and its inversion demonstrated by temperature measurements at doped and undoped tungsten electrodes

Cited by 7 publications

References 28 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

The cataphoretic emitter effect exhibited in high intensity discharge lamp electrodes

A Survey of Chemical Nonequilibrium in Argon Arc Plasma

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