Why use water vapor and chlorine in the Papp gas mix? It may all come down to negative ion formation.
The process of plasmoid formation starts out during the formation of the spark discharge. In turn, spark discharge starts with corona formation. A corona is a process by which a current flows from an electrode with a high potential into a neutral fluid, usually air, by ionizing that fluid so as to create a region of plasma around the electrode. The ions generated eventually pass charge to nearby areas of lower potential, or recombine to form neutral gas molecules. In the case of the Papp reaction, the corona is negative because Papp uses electronegative gases in his gas envelope. Papp also uses sharply pointed electrodes. Ideally, to produce a negative corona, the cathode should be sharply pointed and the anode should be blunt. A negative corona is a non-uniform corona, varying according to the topology of the curved conductor. It often starts out on the sharpest edge of the cathode, the sharpness of the cathode determines the strength of the ionizing field. The form of negative coronas is a result of its source of secondary avalanche electrons (see below). It appears a little larger than the corresponding positive corona, as electrons drift out of the ionizing region, and so the plasma continues some distance beyond it. The total number of electrons, and electron density is much greater than in the corresponding positive corona. However, they are of a predominantly lower energy, owing to being in a region of lower potential-gradient. The increased electron density will increase the reaction rate, the lower energy of the electrons will mean that reactions which require a higher electron energy may take place at a lower rate. A further feature of the structure of negative coronas is that as the electrons drift outwards, they encounter neutral molecules and, with electronegative molecules (such as oxygen and water vapor), combine to produce negative ions. These negative ions are then attracted to the positive uncurbed electrode, completing the 'circuit'. A negative corona can be divided into three radial areas, around the sharp electrode. In the inner area, high-energy electrons inelastically collide with neutral atoms and cause avalanches, while outer electrons (usually of a lower energy) combine with neutral atoms to produce negative ions The Papp gases are all highly electronegative. Electronegative molecules (such as oxygen(3.44) and water vapor, hydrogen(2.20), Kripton(3.00),Xenon(2.60), Fluorine (3.98), and Cloriene(3.16)) will add in the formation of the spark discharge. See Electro negativity of the elements in http://en.wikipedia.org/wiki/Electronegativity On the most basic level, electronegativity is determined by factors like the nuclear charge (the more protons an atom has, the more "pull" it will have on negative electrons) and the number/location of other electrons present in the atomic shells (the more electrons an atom has, the farther from the nucleus the valence electrons will be, and as a result the less positive charge they will experience—both because of their increased distance from the nucleus, and because the other electrons in the lower energy core orbitals will act to shield the valence electrons from the positively charged nucleus). The opposite of electronegativity is electropositivity: a measure of an element's ability to donate electrons. As the spark formation process begins, the electric potential difference increases sharply between the electrodes, the electronegative gas molecules will be drawn to the cathode and repelled from the anode. In a negative corona that forms just before the spark discharged is triggered, the electrons drift outwards from the sharply pointed cathode toward the anode; these electrons encounter a dense concentration of neutral electronegative gas molecules and, with electronegative molecules, combine to produce negative ions. In other words, these positively charge molecules will gorge themselves on electrons and become negative ions. As the spark formation process advances, these negative ions are then attracted to the positive uncurbed anode, completing the ‘plasma circuit'. This negative corona is divided into three radial areas, around the sharp electrode. In the inner area, high-energy electrons inelastically collide with electronegative neutral atoms and cause electron avalanches, while outer electrons (usually of a lower energy) combine with neutral atoms to produce negative ions. In the intermediate region, electrons combine to form negative ions, but typically have insufficient energy to cause avalanche ionization. Papp could have used water vapor and chlorine as a way to ionize the spark gap during pre-spark discharge preparation. Because many of these electronegative elements are corrosive, he may have decided that his cylinder would last longer if he confined his design to noble gases. However, a non-corrosive cylinder design made of plastic, nickel, and noble metal electrodes may be able to fully utilize the complete set of electronegative gases. When the spark discharge produces the plasmoid, it will be comprised of heavy concentrations of negative gas ions and electrons in circulation around its outer surface. The positively biased dielectric gas outside the boundary of the plasmoid will accelerate the plasmoid through electrostatic attraction and zero-point energy in am over unity chain reaction as explained in my previous posts. Cheers: Axil