Velocity of neutral atoms emanating from the cathode of a steady‐state low‐pressure mercury arc

The velocity of the neutral atoms emanating from the cathode of a steady‐state low‐pressure mercury‐arc discharge has been studied by a gravimetric‐calorimetric method. The results can be interpreted in a consistent way by attributing a superthermal rms velocity of (7.5±0.6)×103 m sec−1 to a first neutral flux component arising from cathode‐spot action (and having a particle flux proportional to the arc current), and a thermal rms velocity of (2–10)×102 m sec−1 to a second neutral flux component comprising particles evaporated from the spot‐free mercury surface. A model is proposed and discussed which explains the origin of the fast neutrals: It is suggested that the primary particles emerging in connection with the cathode spots are essentially all ions which have gained superthermal velocities in the vicinity of the cathode spots, and that a fraction of these ions subsequently becomes neutralized retaining most or all of its energy while, on the other hand, the primary particles evaporated from the spot...

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