Mf Gendre

Model study of DC ignition of fluorescent tubes

Breakdown in a discharge tube is investigated by means of a fluid model. The discharge tube is similar to a compact fluorescent lamp tube, containing argon at 3 Torr and mercury at a few millitorr. It was found that the minimum breakdown voltage is decreased substantially compared with a tube containing pure argon. Penning ionization of mercury via an argon metastable state plays an important role in this effect. This is illustrated for a lamp operated on a DC voltage, where significant Penning ionization takes place in the wake of the ionization front. Furthermore, contrary to what is suggested in earlier literature, the development of the surface potential of the lamp is shown to be not only determined by surface charges, but also by volume charges.

Numerical description of high frequency ignition of fluorescent tubes

The effect of the frequency on the breakdown time in a straight discharge tube is investigated by means of a fluid model. The discharge tube is similar to a compact fluorescent lamp tube, containing argon at 3 Torr and mercury at a few Torr. The mechanism of breakdown at frequencies of the order of several 10 kHz is considered and related to breakdown at a dc voltage. During a negative potential on the powered electrode, an ionization wave traverses the tube in a way similar to that in a dc operated tube. During a positive potential on the powered electrode, the electric field in the part of the tube already traversed by the ionization wave is enhanced by negative charge on the inner wall of the tube. Although the ionized region does not extend during this phase, the ionization density increases substantially. Furthermore, we investigated the dependence of the breakdown time on the applied frequency and found that the breakdown voltage is independent of the frequency. This is shown to be consistent with experimental data.

Surface potential mapping of an argon lamp during electrical breakdown

In this paper, we present measurements related to the early stages of electrical breakdown occurring in a low-pressure argon straight discharge tube. A capacitive probe was used to retrieve the evolution of the lamp electrostatic potential over time and space. The potential and calculated electric field, displayed in space-time diagrams, show that a region of strong potential gradient propagates from the cathode toward the anode and then backward. This is followed by a homogenization of the electric field in the inter-electrode space.