Biased hairpin probe in magnetized plasma column

Hairpin probe is a microwave resonant structure which used to determine the frequency dependent permittivity of the surrounding medium. In the recent years hairpin probe is used to determine the electron density accurately in low-pressure plasmas. In presence of magnetic field the equilibrium condition of plasma is greatly modified. In case of magnetized electrons, the dielectric constant of plasma becomes anisotropic. The orientation of hairpin about the external magnetic field direction has a minimal effect in its resonance frequency. A biased hairpin in a magnetized plasma can measure the corrected sheath thickness around it for a range of electron density. In this paper the effect of probe orientation about the external magnetic field direction in resonance frequency in presence of magnetized plasma of biased hairpin probe is studied. The resonance frequency of hairpin in magnetized plasma is measured for different biasing voltages with respect to plasma potential and magnetic field strengths. It is observed that by varying the biasing from highly negative value to plasma potential, the resonance frequency of hairpin moves from vacuum resonance frequency to higher value. It is also observed that for a fixed biasing the resonance frequency varies with magnetic field variation. The plasma density is measured by considering electron cyclotron frequency and the experimentally measured resonance frequencies of hairpin and this density is verified by Langmuir probe measured density. The sheath thickness around the biased cylindrical hairpin probe is experimentally verified for different magnetic field range. A theoretical model has been proposed by using hydrodynamic model to verify the experimentally measured sheath thickness around the biased cylindrical hairpin probe. (author)