This article discusses improvements in the efficiency, output power, and operational flexibility of MEDEA II, a double-pulse electron beam accelerator at McDonnell Douglas Research Laboratories. A modified charging circuit, based on the triple-resonance pulse transformer concept, was implemented on both of MEDEA U's two stages. The output switches were modified to increase maximum output voltages, and a new, second output switch with asymmetric breakdown characteristics was developed. To avoid degradation of the secondpulse output waveform at the diode, a keep-alive circuit was installed. The effects of diode closure on double-pulse operation are also discussed.

A rotary-valve gas pulser that produces a pulse-modulated seedant gas for mixing with a steady flow carrier is described.

Spectral measurements and analysis of beamgas emissions J. Appl. Phys. 55, 611 (1984); 10.1063/1.333113 Kinetics of metastable excited state products in a beam-gas chemiluminescent reactionA beam-gas collision experiment to measure excitation cross sections for translation-to-vibration (T-V) energy-transfer collision processes that produce short-wavelength infrared radiation (SWIR) has been assembled and used to obtain the (0,0 0 ,0 ----+ 0,0 0 ,1) excitation cross section for CO 2 by collision with Ar. A unique modulation technique used in this system involves pulsemodulating one of the reactants, injecting the pulses into a flowing plasma carrier, supersonically expanding the pulse and carrier, and extracting a beam from the expansion while preserving the modulation of the reactant. Enhanced radiation due to thermalization of excited CO 2 at sphere pressures greater than single collision conditions, has been measured and a correction factor for this effect obtained. Measurements of the argon velocity and flux in a helium beam, CO 2 number density in an integrating sphere, and infrared radiation at 4.25 Jlm were made to determine the excitation cross section at a collision velocity of 2.3 km s -I. The average of three sets of measurements yields a value of