Enhancement of cathodic electronic emission by slow positive ions in high-pressure arcs

Abstract

Some recent results indicate that the electronic current emitted by the cathode of a high-pressure electric arc may be enhanced by very close positive ions. This problem is addressed here by means of a 2D treatment of the Schrödinger equation, based on a finite element method. In addition, a diagonalization method has been implemented to study the specific role played by processes of electronic resonance. This approach is applied to the test case of an ionized hydrogen plasma in front of a copper cathode. By comparison with a previous 1D study, the present predictions show that a full 2D treatment is required in most cases.

Arc/Cathode Interaction Model

“…Theoretical papers [33] and [34] deal with the influence of external parameters on this emission phenomenon. Moreover, experimental results can be found concerning the secondary electron emission coefficient [35].…”

“…The experimental value of the secondary electron emission coefficient given by Phelps and Petrović [35] in these conditions is equal to 0.1 and has been incorporated in our model. In other configurations, it would be necessary, due to the lack of experimental results, to use the theoretical works proposed by authors such as [33], [34]. The density of Ar + at the sheath/presheath interface n Ar + was determined using the theory presented next.…”

“…Nevertheless, problems are still encountered in plasma applications, such as the motion and behavior of the arc root and the damage that thermal plasma causes to materials particularly to the electrodes. Studies are therefore underway to improve our knowledge of arc behavior in the vicinity of the electrodes [1]- [34].…”

Near-cathode phenomena in HID lamps

“…Parameters have been within the domain of Schottky-amplified thermionic emission [27] in all the calculations performed until now, therefore the present version of the model uses the Richardson-Schottky equation. Note that in [28]- [30] the enhancement of electron emission due to individual electric fields of ions moving to the cathode was studied. According to these works, the effect is likely to play a role if the electric field at the cathode surface is of the order of 10 V/m or higher while the ion density in front of the cathode is of the order of 10 m or higher.…”