Abstract. The production of NO has been studied by means of arc discharges in the laboratory which simulate natural lightning in current waveform and amplitude (___ 30kA). Observations are compared to the results of a computational model that includes the dynamics of energy deposition and channel expansion, combined with the Zel'dovich equations to model the relevant chemical reactions. Results are expressed as NO produced per meter of arc length, and are measured as functions of dissipated energy and of peak current. It is found that at atmospheric pressure, the NO production per joule of dissipated energy is not constant. NO production per meter discharge length as a function of peak current appears to provide a more

As seen in Fig. 1(a), the diabatic signal does indeed increase as the value of n increases. In addition, both ionization features are evident at slew rates differing by a factor of 2 from that used to obtain the data in Fig. 1.When both lasers are polarized parallel to the direction of the electric field, then theoretically no | m x | = 2 can be produced and, in this case, we observe a dramatic decrease in the signal obtained at the diabatic threshold. In view of this test, and since the probability for diabatic passage in a given field slew rate is larger for \m l \ = 2 states than for | raj = lor |raj = 0 states, we conclude that the diabatic high-field peak is due primarily, if not wholly, to |raj = 2.The signal at electric fields between the adiabatic threshold and the diabatic threshold is attributed to a combination of adiabatic and diabatic passage through level crossings. As n increases, the ratio of this intermediate signal to the diabatic signal drops rapidly.These measurements demonstrate, for the first time, the passage of highly excited atoms from low electric fields to ionizing electric fields along predominantly diabatic paths. Clearly, it is important to account for the possibility of diabatic thresholds whenever one observes atomic states of high n using field ionization.A compact, toroidal configuration of magnetized plasma is produced by a combination of Z-and 0~pinch discharges. A paramagnetic toroidal field is produced by currents circulating in the plasma on closed flux surfaces.We report here our initial results on the formation of a plasma confinement configuration with the generic name of spheromak. 1 ' 2 This compact toroidal configuration has both toroidal (B^) and poloidal (B r ,B 2 ) magnetic field components with the toroidal field maintained by circulating plasma currents rather than by an external coil through the toroidal hole, as in a tokamak. Configurations of this type were first studied theoretically in an astrophysical context. 3 * 4 Related laboratory experiments involving plasma guns, 5 * 6 electron beams, 7 and pinches 8 have been performed. Our experiment, called paramagnetic spheromak (PS-1), makes use of Z-and 6 -pinch techniques to produce a prolate spheroid configuration. The results show, for the first time, that it is possible to establish the desired closed poloidal flux surfaces with a stabilizing paramagnetic toroidal field (i.e., with the peak magnitude of B(p near the magnetic axis). Figure 1 illustrates the formation phase. We start with a cylindrical deuterium gas column of radius 11.4 cm and a pressure of 15 mTorr. The column contains an axial bias magnetic field {-B z ) produced by I 9 currents 9 in an external, single-turn mirror coil with a mirror ratio of 1.1. The bias field is produced by a 20-kV, 18-\xY capacitor bank capable of producing fields with magnitude up to 8 kG. Typically fields of 4 kG are used. The field rises in 3 to 5 jusee (depending on the external inductance) and is clamped. Following this a Z-directed current shell is produced by disc...

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We have investigated NO production in the expansion phase of a lightning discharge using a hydrodynamic model coupled with the chemical rate equations for the two Zel'dovich reactions and oxygen dissociation. We have found that most of the NO production occurs early in the discharge, prior to shock wave formation, and that the rapid drop in density, not temperature, controls NO formation. The number of mo!eeu!es per Joule (P) depends strongly on the energy per unit 3olume in the initial heated channel: this dependence is nonlinear with a maximum value of 26 x 10 •e molecules NO/J. For a representative discharge at a pressure of I arm, the number produced is 15 x 10'6/I. Initial investigation indicates that for a constant energy density (estimated to be about 6 Ml/m •) the rate of production drops off rapidly with decreasing air density and thus altitude. Use of P appropriate for sea level pressure may !cad to a major overestimate of the rate of NO formation in atmospheric lightning, much of which occurs at high altitude. We present suggestions for new laboratory experiments to quantify global NO production by lightning.