Branching of negative streamers in free flight

We recently have shown that a negative streamer in a sufficiently high homogeneous field can branch spontaneously due to a Laplacian instability, rather than approach a stationary mode of propagation with fixed radius. In our previous simulations, the streamer started from a wide initial ionization seed on the cathode. We here demonstrate in improved simulations that a streamer emerging from a single electron branches in the same way. In fact, though the evolving streamer is much more narrow, it branches after an even shorter propagation distance.Comment: 4 pages, 3 figure

Stability of negative ionization fronts: regularization by electric screening?

We recently have proposed that a reduced interfacial model for streamer propagation is able to explain spontaneous branching. Such models require regularization. In the present paper we investigate how transversal Fourier modes of a planar ionization front are regularized by the electric screening length. For a fixed value of the electric field ahead of the front we calculate the dispersion relation numerically. These results guide the derivation of analytical asymptotes for arbitrary fields: for small wave-vector k, the growth rate s(k) grows linearly with k, for large k, it saturates at some positive plateau value. We give a physical interpretation of these results.Comment: 11 pages, 2 figure

Propagation and Structure of Planar Streamer Fronts

Streamers often constitute the first stage of dielectric breakdown in strong electric fields: a nonlinear ionization wave transforms a non-ionized medium into a weakly ionized nonequilibrium plasma. New understanding of this old phenomenon can be gained through modern concepts of (interfacial) pattern formation. As a first step towards an effective interface description, we determine the front width, solve the selection problem for planar fronts and calculate their properties. Our results are in good agreement with many features of recent three-dimensional numerical simulations. In the present long paper, you find the physics of the model and the interfacial approach further explained. As a first ingredient of this approach, we here analyze planar fronts, their profile and velocity. We encounter a selection problem, recall some knowledge about such problems and apply it to planar streamer fronts. We make analytical predictions on the selected front profile and velocity and confirm them numerically. (abbreviated abstract)Comment: 23 pages, revtex, 14 ps file

Combined removal of SO{sub x} and NO{sub x} from flue gas using non-thermal plasma. Quarterly report, 1 December 1994--28 February 1995

The removal of NO{sub x} from flue gas was studied during this period. About 44% of NO{sub x} in concentrations of about 400 ppm and 100% of NO{sub x} in concentrations below 80 ppm can be removed without any chemical additives. Also some pre experiments have been done on the combined removal of S0{sub 2} and NO. Indications are that the NO in the flue gas helps the removal of S0{sub 2}. Work is continuing on the combined removal at present

Combined removal of SO{sub x} and NO{sub x} from flue gas using non-thermal plasma. Technical report, March 1--May 31, 1995

A model has been developed to predict the performance of a dielectric-barrier discharge for various parameters. The model calculations have been compared with experimental results and are in close agreement for both SO{sub 2}/NO removal. The reaction scheme shows that OH is the most important radical for SO{sub 2} removal with the final product being H{sub 2}SO{sub 4}. Whereas for NO removal both oxidation by OH to form HNO{sub 3} and reduction by N to form N{sub 2} are important channels

Combined removal of SO{sub x} and NO{sub x} from flue gas using non-thermal plasma. [Quarterly] technical report, September 1--November 30, 1994

The SO{sub 2} removal efficiency was studied for concentration in the range of 333--3000 ppM (parts per million). Since the sulfur content of Illinois coal is high, the SO{sub 2} concentration in typical flue gas is in the high end of the range shown above. With high concentration of SO{sub 2} the removal efficiency decreases. However, the removal scales well with applied voltage, electrode length, and supply frequency. In this period the modeling of the process was also accomplished. The results show that a Townsend-type discharge is more efficient than a streamer type discharge in producing OH and 0 radicals. This explains why UV-irradiation helps the removal efficiency. The details are discussed in the report