Dependence of optimal spacing on applied field in ungated field emitter arrays

In ungated field emitter arrays, the field enhancement factor β of each emitter tip is reduced below the value it would have in isolation due to the presence of adjacent emitters, an effect known as shielding or screening. Reducing the distance b between emitters increases the density of emission sites, but also reduces the emission per site, leading to the existence of an optimal spacing that maximizes the array current. Most researchers have identified that this optimal spacing is comparable to the emitter height h, although there is disagreement about the exact optimization. Here, we develop a procedure to determine the dependence of this optimal spacing on the applied electric field. It is shown that the nature of this dependence is governed by the shape of the β(b) curve, and that for typical curves, the optimal value of the emitter spacing b decreases as the applied field increases

The manufacturing of wet-laid hydroentangled glass hybrid composites: preliminary results

The potential for manufacturing a nonwoven preform for composites using blends of glass and low melt polyester or bicomponent sheath/core (polyester/polyethylene) fibers is demonstrated. Wet-lay webs were hydroentangled to form strong, flexible preforms that could be easily manipulated for the production of compression molded composites. An appropriate white water recipe for dispersing glass and binder fibers was critical to the formation of good quality webs. Optimal dispersion times were determined experimentally by examining the total number of defects present in hand sheet samples. To achieve the required web density, several wet-laid sheets were stacked and hydroentangled into a single sheet. This final sheet structure was subsequently heat pressed in a mold to achieve the final form. Forming temperatures producing binder fiber melting and a rigid uniform composite were selected. Mechanical properties of these composites were evaluated. Composite strength increased with increasing glass fiber content (up to 30-40%)

Explosively-driven magnetohydrodynamic (MHD) generator studies

Plasma jet generators have been designed and tested which used an explosive driver and shocktube with a rectangular cross section that optimize the flow velocity and electrical conductivity. The latest in a series of designs has been tested using a reactive load to diagnose the electrical properties of the MHD generator/electromagnet combination. The results of these tests indicate that the plasma jet/MHD generator design does generate a flow velocity greater than 25 km/s and produces several gigawatts of pulsed power in a very small package size. A larger, new generator design is also presented