Spektroskopische Messung des zeitlichen Verlaufs der radialen Dichte- und Temperaturverteilung in einem Wasserstoffunken

Abstract

The temporal variation of the radial distribution of electron density and temperature in an oscillating spark in H₂ at p₀=460 Torr, initiated by the streamer process, was investigated in order to obtain an insight into the the dynamic behaviour of the spark plasma channel. At the beginning of the channel expansion the electron densities measured from the STARK effect broadening of H_β amount to ∼ 10¹⁸ cm^-3, and after the end of expansion ∼ 10¹⁷ cm^-3. The measurements gave a maximum axial temperature of 52 000°K at the maximum in current of the first halb period (i_max=1800 A). The pressure increase in the plasma channel at the beginning of its expansion was calculated from the measured density and temperature values to be p/p₀ ∼ 20. By the end of the first half period in current this pressure ratio has already sunk to p/p₀ ∼3. The spark channel achieves a maximum specific conductivity of η= 520 (Ω cm) ^–1 at the maximum in current of the first half period and reaches its maximum conductance of G=6 Ω^-1 after the end of the third half period of current. The energy supplied to the spark is expended in approximately equal proportions for the ionisation, heating and expansion of the spark plasma. The temporal and radial variation of the total density within the heated plasma channel and in the surrounding shock disturbed region is given and an interpretation of the so-called “envelope” of the channel is put forward.