Matthias Walker

How to Ignite an Atmospheric Pressure Microwave Plasma Torch without Any Additional Igniters.

This movie shows how an atmospheric pressure plasma torch can be ignited by microwave power with no additional igniters. After ignition of the plasma, a stable and continuous operation of the plasma is possible and the plasma torch can be used for many different applications. On one hand, the hot (3,600 K gas temperature) plasma can be used for chemical processes and on the other hand the cold afterglow (temperatures down to almost RT) can be applied for surface processes. For example chemical syntheses are interesting volume processes. Here the microwave plasma torch can be used for the decomposition of waste gases which are harmful and contribute to the global warming but are needed as etching gases in growing industry sectors like the semiconductor branch. Another application is the dissociation of CO2. Surplus electrical energy from renewable energy sources can be used to dissociate CO2 to CO and O2. The CO can be further processed to gaseous or liquid higher hydrocarbons thereby providing chemical storage of the energy, synthetic fuels or platform chemicals for the chemical industry. Applications of the afterglow of the plasma torch are the treatment of surfaces to increase the adhesion of lacquer, glue or paint, and the sterilization or decontamination of different kind of surfaces. The movie will explain how to ignite the plasma solely by microwave power without any additional igniters, e.g., electric sparks. The microwave plasma torch is based on a combination of two resonators - a coaxial one which provides the ignition of the plasma and a cylindrical one which guarantees a continuous and stable operation of the plasma after ignition. The plasma can be operated in a long microwave transparent tube for volume processes or shaped by orifices for surface treatment purposes.

Development and spectroscopic investigation of a microwave plasma source at atmospheric pressure

Summary form only given.Microwave plasma sources at atmospheric pressure have a variety of different applications. On the one hand they can be used for the treatment of surfaces, for example the activation or cleaning, and on the other hand they can be applied for the conversion of gases, such as the abatement of waste gases or other chemical synthesis. The presented atmospheric plasma source is based on an axially cylindric resonator which is powered by 2.45 GHz microwaves. The plasma is confined in a quartz tube and the gas is supplied via a metallic nozzle. For a successful application in industrial processes an easy ignition as well as stable plasma operation are indispensable. To gurantee ignition of the plasma without any additional igniters, detailed information about the electric field is necessary. Simulations of the electric field distribution of different configuration with the commercial simulation software COMSOL Multiphysics™ were performed for this purpose. The simulation results could be verified by measurements with a network analyser and led to a configuration which provides an ignition of the plasma without any additional igniters as well as stable and efficient plasma operation.The characterisation of the plasma was carried out by means of optical emission spectroscopy. Overview spectra of a humid air plasma exhibit NO- and OH-bands in the UV range as well as atomic oxygen lines in the IR range. The OH-bands were used to obtain the gas rotational temperature Trot, which provides a good estimate of the gas temperature Tg. The electron temperature Te was estimated by the excitation temperature Tex, which was determined from a Boltzmann plot of the atomic oxygen lines. Maximum values of Trot of 3600 K and about 2200 K higher excitation temperatures of 5800 K were measured. Parametric studies of Trot and Tex in dependences of the gas flow and the supplied microwave power showed that the maximum temperatures are independent of these parameters in the regarded range of an air flow of 10 sl/min to 70 sl/min and a supplied microwave power of 1 kW to 3 kW. However, the plasma volume depends on these parameters and increases with an increase of the microwave power and decreases when the gas flow is increased.