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An Intense Pulsed Atomic Hydrogen Beam Source

A pulsed atomic hydrogen beam source has been developed especially for studies of surface reactions. Atomic hydrogen is generated using a microwave discharge in a quartz tube and is collimated to a beam by differentially pumped stages. A hydrogen dissociation fraction of ∼70% and a beam flux of 4×1014 atoms·cm-2·s-1 with a spot size 7 mm in diameter are obtained. The beam is chopped with a mechanical disk chopper, and a pulse duration of 50 µs for a repetition rate of 100 pulses/s is obtained. The velocity distribution of the atomic hydrogen beam is fitted with a shifted Maxwell-Boltzmann distribution that gives a most probable velocity of 2410 m/s and a beam temperature of 70 K.