Design and performance of a UV source as pre-ionizer of gas puff PRS loads

Summary form only given. A UV source was designed to pre-ionize a 7-cm diameter argon gas puff to be employed on the DM2 generator at Primer Physics International Company. The source is a 19-cm diameter cylinder consisting of two flashboards bent into semi-circles. The flashboard plasma is directed toward the axis of the cylinder which is co-linear with the axis of the gas nozzle. The plane of the flashboard is located 18 cm from the nozzle exit so that the ionizing UV is emitted at 60-80/spl deg/ angles and promptly illuminates the gas while the flashboard plasma arrives at the PRS load region about 4 /spl mu/s later. The pre-ionization is measured absolutely using a high-sensitivity interferometer with which we can discriminate between phase shifts due to neutral argon and those due to free electrons as a function of space and time. Pre-ionization levels in the 1-10% range were measured near the outer edge of the DM2 nozzle rendering this outer layer sufficiently conductive to carry the DM2 current.