Circular 117

The annual flower trials were planted from 30 May through 4 June, 1999 in the Perennial Landscape and All America Selections Display Garden of the Georgeson Botanical Garden (64°51N, 147°52W). Fairbanks silt loam soil was fertilized with 1 0 -2 0 -2 0 S (4 lbs per 100 sq feet, 195 g per sq meter) on 28 May. With the exception of dahlias, all flowers were grown as seedling transplants and were hardened off outdoors for one week prior to transplanting. Tuberous roots of dahlias were planted in containers five weeks prior to transplanting and were hardened off

Diagnostic techniques for atmospheric streamer discharges

Fast electrical and optical diagnostics are required for the analysis of atmospheric streamer discharges. This is illustrated for the case of positive streamer corona produced along wire electrodes by high voltage pulses with rise times of tens of nanoseconds. Electrical measurements with a high time resolution reveal the energy input in two discharge phases (primary and secondary streamer). The discharge structure is visualised using a gated image intensifier. The number of streamers per unit length of anode wire and the streamer diameter are determined. The streamer velocity is measured with a time-of-flight method using two optical fibres. Time-resolved spectroscopic measurements of the intensity ratio of N2+ and N 2 emission lines reveal that the average electron energy in the primary streamer phase is significantly higher than in the subsequent secondary streamer. The neutral gas temperature in the discharge is determined from the rotational structure of an N2 emission line and is only slightly above the background gas temperature. Schlieren photographs visualise the heat dissipated in residual streamer channel

Gas phase hydrogen peroxide production in atmospheric pressure glow discharges operating in He - H2O

The gas phase production of hydrogen peroxide (H2O2) in a RF atmospheric pressure glow discharge with helium and water vapour has been investigated as a function of the gas flow. It is shown that the production of H2O2 is through the recombination of two OH radicals in a three body collision and the main destruction is through radical reactions involving OH or surface losses at the electrodes. Balancing these production and losses of H2O2 allows estimating OH densities which correspond with reported densities in literature for this type of discharge. 1. Introductio

Modeling of the reactivity of vibrationally excited molecules in a corona plasma for catalytic reactions

A model is developed to describe the transfer of vibrational energy from excited gas molecules to a heterogeneous surface or to heating of the gas. Diffusion of excited species is included in the model. The model is used to compute the maximum possible energy efficiency of a plasma-induced catalytic reaction, which is driven by vibrationally excited molecules. The computational results of the model are correlated to experimental data on quenching rates and the relevant parameters of the self-sustained discharge. It is con cluded that the mechanism of plasma-induced catalysis with vibrationally excited molecules is highly unlikely

Branching of positive discharge streamers in air at varying pressures

The formation of positive streamers in a 17 mm gap in air is studied at pressures varying in the range from 1010 mbar to 100 mbar. An intensified charge coupled device camera is used to image the discharge. At high pressures, the discharge shows many branches, while at low pressure fewer branches arise. The structure is not simply determined by the ratio of voltage over pressur

Laboratory experiments on the interaction of streamers

Pictures show that streamer or sprite discharge channels emerging from the same electrode or position sometimes seem to reconnect or merge even though their heads carry electric charge of the same polarity; one might therefore suspect that reconnections are an artifact of the two-dimensional projection in the pictures. We have used stereo-photography of laboratory scale streamer discharges to investigate the full three-dimensional structure of such events. We analyze reconnection, possibly an electrostatic effect in which a late thin streamer reconnects to an earlier thick streamer channel, and merging, a suggested photo-ionization effect in which two simultaneously propagating streamer heads merge into one new streamer. We also investigate the branching lengths and angles in the 3D streamer tree structures