Plasma, Volume 3, Issue 1 (March 2020) – 4 articles

We describe experiments and simulations of dynamical merging with two Taylor state plasmas in a Swarthmore Spheromak Experiment (SSX) device. Taylor states are formed by magnetized plasma guns at opposite ends of the device. We performed experiments with Taylor states of both senses of magnetic helicity (right-handed twist or left-handed twist). We present results of both counter-helicity merging (one side left-handed, the other right-handed) and co-helicity merging (both sides left-handed). Experiments show significant ion heating, consistent with magnetic reconnection. We suggest that the merged, warm state could be a suitable target for future magneto-inertial fusion experiments. Magnetohydrodynamic simulations of these experiments reveal the structure of the final relaxed, merged state. Full article

A model of a stationary glow-type discharge in atmospheric-pressure air operated in high-gas-temperature regimes (1000 K < T_g < 6000 K), with a focus on the role of associative ionization reactions involving N(²D,²P)-excited atoms, is developed. Thermal dissociation of vibrationally excited nitrogen molecules, as well as electronic excitation from all the vibrational levels of the nitrogen molecules, is also accounted for. The calculations show that the near-threshold associative ionization reaction, N(²D) + O(³P) → NO⁺ + e, is the major ionization mechanism in air at 2500 K < T_g < 4500 K while the ionization of NO molecules by electron impact is the dominant mechanism at lower gas temperatures and the high-threshold associative ionization reaction involving ground-state atoms dominates at higher temperatures. The exoergic associative ionization reaction, N(²P) + O(³P) → NO⁺ + e, also speeds up the ionization at the highest temperature values. The vibrational excitation of the gas significantly accelerates the production of N₂(A³∑_u⁺) molecules, which in turn increases the densities of excited N(²D,²P) atoms. Because the electron energy required for the excitation of the N₂(A³∑_u⁺) state from N₂(X¹∑_g⁺, v) molecules (e.g., 6.2 eV for v = 0) is considerably lower than the ionization energy (9.27 eV) of the NO molecules, the reduced electric field begins to noticeably fall at T_g > 2500 K. The calculated plasma parameters agree with the available experimental data. Full article

In this paper, an efficient inductively coupled medium pressure source for ultraviolet radiation (UV-source) is demonstrated. The lamp was operated with powers up to 3 kW while the radiation and the coldest point temperature were measured. In addition, different coil geometries were investigated. Here a symmetrical and asymmetrical winding density were compared. Also the operation pressures and DC to radiation efficiencies are presented. In this work, an operation pressure of one atmosphere and an UV-efficiency (200–380 nm) of 15.5% was achieved. This is comparable to conventional medium pressure Hg-lamp technology. The main advantage of the presented inductive lamp is the electrodeless operation and therefore the longer service life, since an electrode failure is eliminated. Full article