Measurements on the Vapor Stream from the Cathode of a Vacuum Arc

The velocity of the vapor stream issuing from the cathode region of a vacuum arc between copper electrodes is calculated from (1) the energy received by a vane 3 cm in front of the cathode, as measured by the rate of rise of temperature; (2) the momentum imparted to the vane, as determined by the deflection of the vane. The mass used in the calculations is that of the copper deposited on the vane. The average velocity of the vapor, computed from data obtained by either method, is about 2×${10}^6$ cm per second, confirming Tanberg's momentum measurements. There is some evidence that the vapor is ionized to a considerable degree. Radiation from the arc, or energy of recombination on the vane, can account for only a small part of the total energy received by the vane.