We report the existence of enhanced heap stability as a result of the mixing of granular materials. Our setup consists of a rectangular container, filled with a binary mixture of granular matter up to some height h, that is rapidly opened at one wall to allow repose angle (θc) formation. We develop an empirical model for θc based on the Mohr–Coulomb failure criterion. The model is parameterized by an effective cohesion c and an effective coefficient of friction μ that depend on: (1) the granular proportions and (2) the c and μ for pure cases. Good agreement is achieved between the experiment and the model. We note that even the experimental fluctuations of θc as a function of granular proportions are well correlated (<2% deviation) with the computed uncertainty of the empirical model.

An E×B probe is characterized by investigating its two parameters, namely extraction voltage (Vext) and lens voltage (Vlens). The effects of Vext and Vlens on the extracted H− ion current are examined. The investigation of Vext effects is done with a constant Vlens=0 V. The results show that the optimum value for negative ion extraction is Vext=190 V. With this optimum Vext, the Vlens parameter is examined. Findings show that the optimum Vlens is 0 V. Optimized parameters give the highest ion current and narrowest full width at half maximum. With these optimum settings, the E×B probe is used to study the variation of H− ions as a function of perpendicular distance (i.e., 1 cm to 4 cm) from the center of a magnetized sheet plasma with Bave=6.59 mT.

No abstract

A simple and inexpensive 2.45 GHz microwave plasma source with a repulsive double hexapole configuration is described and characterized. In this work, the operation of the source is shown to be flexible in terms of electron density, electron temperature, and plasma uniformity even at low-pressures (approximately millitorr). It allows for easy control of the electron temperature (2-3.8 eV) and density ( approximately 10(9)-10(10) cm(-3)) by removing either of the two hexapoles or by varying the separation distance between the two hexapoles. Characterization was done via information gathered from the usual Langmuir probe measurements for electron temperature and density. The source makes a resonant surface with its repulsive double hexapole magnetic configuration providing an additional longitudinal confinement near the walls midway between the two hexapoles. Magnetic field maps are presented for varying double hexapole distances. Power delivery for various settings is also presented.

No abstract