David Walter Branston

PSEUDOSPARK SWITCH DEVELOPMENT AT SIEMENS - COMPACT HIGH POWER SWITCHES FOR GAS DISCHARGE LASERS AND

The development of high average power, high peak power pseudospark switches for use in TE gas discharge lasers and applications requiring similar ratings is reported. The results achieved as of today in metaceramic sealed-off experimental tubes of conventional pseudospark geometry are: hold-off voltage 32 kV; peak current 15 kA; pulse duration 300 ns; current rate of rise > 300 Wp; pulse repetition rate > 250 pps; tum-on delay 200 ns; temporal jitter < 10 ns. These are all simultaneous ratings, with limitations mainly imposed by the power supply and the pulse forming network, respectively. An attractive alternative to spark gaps, with their lifetime being limited to the order of 40 kC, also is the pseudospark switch, which incorporates the advantages of both thyratron and spark gap high dI/dt, high reverse current capability, high charge transfer capability, long lifetime, low jitter, cold-cathode operation without having the correspondmg disadvantages. At SIEMENS, a pseudospark switch the CAVATRON has been developed in order to replace a commercial spark gap in the SIEMENS LITHOSTAR kidneystone hsintegrator. Typical operating parameters (simultaneous ratings) are: hold-off voltage 22 kV; current rate of rise > 10 kA/p; peak current 10 kA; peak reverse current 5 kA; pulse duration 3.5 ps; pulse repetition rate 5 5 pps. The total lifetime amounts to 1.5*105 A*s of transfered charge, as compared to 4*1

The tempestuous life of the arc

As for comparable spark gaps. At a repetition rate of 2 pps and dc charging conditions, the prefiring rate of the three-electrode CAVATRON is around

Electro-Hydrodynamic Control of Premixed Turbulent Methane Flames at Pressures Above 1 ATM

Most people are familiar with the flicker of the lights which often occurs during a thunderstorm; what is not always realised, however, is that this is an indication of a circuit-breaker somewhere within the power distribution network doing its job properly. It is usually the result of a fault (e.g. a short circuit) having been detected, a circuit-breaker opening to clear the fault and then reclosing to allow the normal current flow to resume, all within a fraction of a second.

Evaporation of zirconia in an inductively coupled plasma

Electric field control of combustion offers the potential of stabilizing flames and reducing emissions with comparatively little effort. Previous investigations of the effects of electric fields on flames were restricted to atmospheric pressure and the question whether field effects persist at higher pressures remained open. In the present work effects of electric fields on flame behavior are established for pressures up to 10 bar without any indication that this should be an upper limit. Voltage-current measurements and optical emission spectroscopy gave clear evidence that at all experimental conditions under investigation electric field induced ionization and dissociation reactions were negligible with regard to the combustion process. Thus it is concluded that all observed effects are due to electro-hydrodynamic distortions of the gas flow caused by electrostatic forces acting on the ions generated in the reaction zones of the flames. The concentration of pollutants such as CO, NO and NO2 in the presence of an electric field depends on the ratio U/p of electrode voltage U and pressure p which implies that the electric field strength required to obtain a given effect increases linearly with pressure. In an electric field directed towards the burner CO emissions could be reduced by about 90%, irrespective of pressure. The decrease of CO was accompanied by an increase of NOx by about 20%. The electric power required for a CO reduction of 90% amounted to 0.1% of the thermal power. The improvement of the lean blow-off limit upon application of an electric field observed so far ranges from 1 to 3% and increases with pressure.Copyright

Method and device for influencing combution processes of fuels

Abstract A 30 kW inductively coupled argon–hydrogen plasma was investigated to assess the feasibility of plasma flash evaporation of zirconia. The evaporation time of zirconia was estimated to be 130 and 560 μs for spherical particles with radii of 6 and 12.5 μm, respectively. The plasma temperature in excess of 7000 K as inferred from spectroscopic measurements allows for the existence of zirconia vapour. Mie scattering of laser light yielded evidence that zirconia particles with a maximum diameter of 12 μm could be completely vaporised at a rate of 200 mg min −1 , if the hydrogen content of the argon–hydrogen plasma was sufficiently high.