Horia-Eugen Porteanu

Low-Power Microwave Plasma Conductivity

Plasma conductivity is of general interest for both fundamental research and specific applications. For this purpose, plasma equivalent impedance and complex conductivity are measured at 2.2 GHz, at pressures between 1 and 103 mbar, as a function of microwave power in a slot-type resonator, predominantly capacitively coupled to plasma. The plasma impedance is self-adjusting, maintaining a quasi-constant microwave amplitude. The sign of the imaginary part of the impedance (or conductivity) depends on pressure and, consequently, on electron density. The reactive part becomes significant if the Debye length is comparable with the size of the resonator and the plasma frequency is close to the microwave driving frequency.

Global models for the microwave driven double icp plasma jet

Summary form only given. For many technical applications, microwave driven plasma jets are possible alternatives to conventional RF plasma sources. They are of uncomplicated construction, and have the advantages of small size and large electrical efficiency.

Langmuir-type of investigations of atmospheric pressure plasma jets

The new generation of microplasma sources, generating plasma jets of few millimeter size at atmospheric pressure, requires specific methods of characterization.

Microwave excitation of metal halide plasma lamps

High pressure metal halide plasma (HID) lamps as compact light sources are characterized by high efficiency, excellent color rendering and long lifetime. Usually the lifetime is mainly influenced by electrode erosion leading to wall blackening and a reduction of the luminous flux. Therefore it is of actual research interest to have an electrodeless power input into HID lamps. More then ten years ago there was a high power electrodeless sulfur lamp with a microwave excitation commercially available1. New trends with lower power HID units below 50 W including research on electrodeless HID lamps could expand the field of application and break into new markets. This work discusses the high frequency power input and the plasma behavior in high pressure lamps2,3. Therefore several lamp geometries and lamp fillings were tested. The lamps were made of quartz and ceramics containing Ar as an ignition gas and several metal halides as light emitting substances. The lamps were ignited by an external high voltage pulse and operated in a special resonator configuration at frequencies around 2.45 GHz. The main energy input by inductive coupling was varied between 5 and 30 W. The power supply was built on a semiconductor basis. Input power, spectral distribution in the visible spectral range and vessel temperature were observed by a vector network analyzer, a fiber spectrometer and an infrared camera respectively. To enhance the vapor pressure of the additives, the lamps were also operated in a vacuum chamber. Variations in the filling, the input power and the wall temperature lead to changes in the spectral output, color temperature, color rendering and to changes in the coupling with the circuit. Further experiments are planed to study the influence of other resonator configurations and lamp shapes.

Low power microwave conductivity of atmospheric pressure plasma

Air, He, and Ar plasmas are analyzed at different pressures between 102-105 Pa. COMSOL simulation is used to approximate the value of plasma conductivity. Electron density is calculated for a scattering time tau of about 10-11 s, which is very close to the critical density, for which plasma frequency equals the microwave frequency. This might explain the sign change of the imaginary part of conductivity.