In this paper, the cylindrical sheath around a hairpin resonator probe has been varied by applying a dc potential to the hairpin to infer different plasma parameters in an argon and oxygen discharge. As the sheath width increases due to negative bias, the resonance frequency of the hairpin correspondingly shifts toward a lower value. An analytical model based on fluid approximation has been developed to estimate the sheath width variation as a function of the applied voltage on the probe. The analytical result is then compared with the well-known capacitance model that assumes a conjugate dielectric region around the hairpin consisting of a pair of cylindrical sheaths and the plasma. Using this method, a wide range of plasma parameters, including the electron temperature T , e plasma potential V , p and electronegativity parameter a s , have been obtained in an electronegative oxygen discharge. The advantage of this method over the conventional floating hairpin resonator probe has been qualitatively discussed.

A 13.56 MHz capacitive coupled radio-frequency (RF) argon discharge under transverse magnetic field has been investigated. The discharge is operated in a push-pull mode using a 1:1 isolation transformer with its centre tap grounded to a RF generator. The power delivered to the plasma has been calculated from phase-calibrated RF current/voltage waveforms measured on the secondary side of the isolation transformer. An equivalent electrical circuit of the discharge has been described to determine the net plasma impedance. It is found that in the presence of magnetic field, the discharge impedance exhibits a series resonance as the RF power level is increased gradually. However, in the un-magnetized case, the discharge remains entirely capacitive. A qualitative discussion has been given to explain the role of external magnetic field in achieving the series resonance.

A non-invasive method of determining the collision frequency νm by measuring the net plasma impendence in a magnetized, capacitive-coupled, radio-frequency (rf) discharge circuit is developed. The collision frequency has been analytically expressed in terms of bulk plasma reactance, wherein standard sheath models have been used to estimate the reactance offered due to the capacitive rf sheaths at the discharge plates. The experimental observations suggest that in the un-magnetized case, νm remains constant over a range of rf current but steadily increases as the background pressure reduces. In the magnetized case, the collision frequency has been observed to decay with the increase in rf current while it remains unaffected by the background pressure. A qualitative discussion has been presented to explain these characteristics.

No abstract

A hybrid probe comprising of a combination of dual cylindrical and an emissive probe is developed to characterize magnetized plasma parameters in a 13.56 MHz capacitive coupled radio-frequency (RF) discharge, operated in push-pull configuration. The obtained plasma density has been verified against a standard resonance hairpin probe. It is found that under weak magnetic field, the plasma densities are in good agreement with the hairpin probe but deviate as the magnetic field increases. A brief discussion has been presented to explain this feature. The advantage of a hybrid probe circuit over the conventional triple Langmuir probe operated in RF plasma is also discussed.