High-Velocity Vapor Stream in the Vacuum Arc

The discovery and importance of a high-velocity vapor stream issuing from the cathode region of a vacuum arc led to a summary of the experiments showing the existence of a vapor stream and a review of the theories proposed to account for it. The velocities were determined from: (1) force on the cathode and loss weight by the cathode; (2) force on a vane in front of the cathode, and mass of cathode material deposited on the vane; and (3) energy imparted to vane, and mass of material deposited. Methods (1), (2) and (3) on the copper arc gave vapor velocities from 1 to 2.5 ?? 10⁶ cm/sec, while method (1) on a mercury arc gave an average of 2.24 ?? 10⁶ cm/sec. Sources of error would not change the above values greatly. Several proposed theories are shown to be inadequate; the one possible theory (Risch and L??di) is based upon the presence of multiply-charged ions which leave the cathode after neutralization with a high velocity.