Measurement of velocity distribution functions of neutral particles in ion source plasma

The velocity distribution function of the gas effusing from a 5.5-cm-diam, 5-cm-long small ion source was measured by the mass separated time-of-flight method. The measured distribution function could be fitted to a Maxwellian distribution before the commencement of a discharge, when the deuterium pressure in the ion source was below 0.6 Pa. The effect of discharge upon the distribution function of neutral deuterium below this operating pressure was investigated by changing the arc power. The deuterium gas temperature determined by fitting the measured distribution function to a Maxwellian showed a maximum gas temperature of 800 K at discharge power density of 6 W/cm3. Effects of discharge upon argon and helium gas temperature were also measured, which showed a monotonic increase against the discharge power.