A global model was developed to investigate the densities of negative ions and the other species in a low-pressure inductively coupled hydrogen plasma with a bi-Maxwellian electron energy distribution. Compared to a Maxwellian plasma, bi-Maxwellian plasmas have higher populations of low-energy electrons and highly vibrationally excited hydrogen molecules that are generated efficiently by high-energy electrons. This leads to a higher reaction rate of the dissociative electron attachment responsible for negative ion production. The model indicated that the bi-Maxwellian electron energy distribution at low pressures is favorable for the creation of negative ions. In addition, the electron temperature, electron density, and negative ion density calculated using the model were compared with the experimental data. In the low-pressure regime, the model results of the biMaxwellian electron energy distributions agreed well quantitatively with the experimental measurements, unlike those of the assumed Maxwellian electron energy distributions that had discrepancies. V C 2015 AIP Publishing LLC. [http://dx.
Recent studies have demonstrated that the two-ion-stream-instability occurs near the plasma boundary and makes the ions reach the 'modified Bohm velocity' at the sheath edge. In most low-temperature plasmas, however, the ion-neutral collisions can disturb the growth of instability to occur frequently, and the ions exit the plasma boundary with their own Bohm velocities. We report some experimental observations regarding this issue. The spatial variations of the ion drift velocities and the space potential near the sheath edge were measured in Ar/Xe mixture plasmas by increasing the total pressure in the range of 0.5-2.1 mTorr. The results show that the instability cannot occur above a certain pressure condition and that is consistent with the theoretically driven pressure criteria for the onset of the instability.
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