Frequency dependence of the pulsed high-pressure sodium arc spectrum

Abstract

Spectral energy distributions are calculated and measured for a wall-stabilized high-pressure Na-Hg-Xe arc in pulsed operation. These and other quantities are studied as a function of the pulsing frequency over the range 500–5000 Hz, and as a function of duty cycle over the range 25%–100% for a fixed power input of 150 W. The arc is contained in a 5.5-mm-diam channel with an electrode separation of 39 mm containing a gas mixture of 100-Torr Na, 470-Torr Hg, and 190-Torr Xe. The fully time-dependent energy balance model assumes local thermodynamic equilibrium and one-dimensional cylindrical symmetry. The radiation transport calculation includes the effects of 28 Na lines in the visible and infrared, 20 of which are treated as optically thick. The amount of nonresonance Na radiation in the spectrum is found to be maximum at the lowest frequency and duty cycle. Under these conditions the model shows the arc center temperature to be lowest prior to the pulse, but to reach the highest peak values well before the end of the power pulse.