Operating of electrode less, indium iodide based high intensity discharge lamps within the use of plasma guided microwaves

Abstract

The increase of the efficacy as well as the lifetime of high intensity discharge lamps (HID lamps) is the object of the present research. One of the main limits is the thermal loss due to the lamps electrodes. This reduces the lamps efficacy. Furthermore, corrosion of the electrodes is the main failure criteria and limits the lifetime of the lamp. One possible solution for this is the plasma stimulation by plasma guided microwaves. In this way both of the effects can be prevented by heating the discharge without electrodes.Guided microwaves can be launched at plasma surfaces within the use of an E-mode surfatron. In comparison to previous approaches, in this setup no surface waves will be launched at the plasma glass interface. Instead the electrical field of the microwave will be guided along the plasma. Within the use of this, high intensity discharge columns can be launched and the radiation of microwaves from this system can be suppressed without external shielding.The geometric limits as well as the benefits of this method will be shown using indium iodide based discharges with argon as auxiliary gas. Different indium iodide based discharge configurations were under investigation, using electromagnetic finite element simulations with the plasmas dielectric configuration as input parameters. Furthermore, the configurations were studied experimentally. The spectral distributed radiant flux of the lamps was estimated for different configurations and driving powers. Furthermore, the dependence of the luminous efficacy on the indium iodide and Argon concentration inside the plasma columns was under investigation.A high influence of the skin effect on the behavior of the high intensity discharges could be shown. The guidance of the microwaves over the plasma surface increases with the increase of the plasma temperature. This can be explained by the dependence of the skin effect on the plasmas dielectric properties. No dependence of the luminous efficacy on the auxiliary gas partial pressure could be detected, within the use of practically limited pressures. A strong dependence of the luminous efficacy on the indium iodide concentration inside the lamp was shown.