His interests extended to plasma astrophysics as well as laboratory plasmas. Factor deficient plasmas (Adsorbed Plasma & Aged Plasma, etc.) are used in mixing studies. These kinds of weakly ionized gases are also nonthermal "cold" plasmas. Neon signs and lightning are examples of partially ionized plasmas. Most of "technological" (engineered) plasmas are weakly ionized gases. This is usually not the case in fusion, space and astrophysical plasmas. Examples are charged particle beams, an electron cloud in a Penning trap and positron plasmas. Applications include simulations of plasmas, galaxies and molecules. Hydrogen plasmas can also etch silicon as well. Furthermore, fluid mechanics, where liquids, gases, plasmas and in-betweens like supercritical fluids are studied. Fluids are a phase of matter and include liquids, gases and plasmas. By varying the conditions, materials can transition between solids, liquids, gases and plasmas. Gases in this region are modeled as non-radiating plasmas. Mass spectrometers are also widely used in space missions to measure the composition of plasmas. NSTX was a "proof of principle" experiment and therefore employed deuterium plasmas only.