Dr. Olga Minayeva

Weakly ionized plasma sources are widely used in the modern industry – from the semiconductor processing and bacterial decontamination to analytical techniques and lighting. These sources include non-equilibrium (typically low-pressure) plasmas, in which the low mass electrons can gain significant energy from the electric field while the heavy particles (ions and atoms) remain at or near the room temperature. On the other end of the spectrum of weakly ionized plasmas, there are high-pressure local thermal equilibrium (LTE) plasma sources, such as short-arc Xe lamps. In these devices the heavy gas particles can reach very high temperatures (~ 10,000 K) and form a dense plasma spot in front of the cathode tip. There are two main advantages that make short-arc high-pressure Xe lamps very attractive for various cinema applications. First, the spectral output of the high-pressure Xe lamps is very similar to that of the sun in the visual wavelength range. Second, the spot attachment of the plasma leads to a very compact and bright point light source that can be efficiently focused by the optical systems. Owing to the high gas temperature in the plasma, the effectiveness of the cooling for both the cathode and the anode becomes a critical lifetime-limiting factor for these lamps. The major mechanism of the cathode cooling in short-arc high-pressure Xe lamps is electronic emission. For this reason, the tungsten cathode material is doped with the lower work function thoria (ThO₂). However, thoria is a radioactive (alpha emitter) material, and multiple attempts of replacing thoria with an alternative non-radioactive emissive dopant have been made to date. In this seminar we will discuss what makes ThO₂ so unique for short-arc high-pressure Xe lamps application. I will talk about the current state-of-the-art of Th-free cathode development, and propose a new cathode material to be used in short-arc high-pressure Xe lamps.