Ions in the helium film

The existence of a small negative ion current flow in a saturated helium film has been inferred from the current collected at electrodes situated in the vapor above a surface of liquid helium in diode and triode cells. Currents to a disk collector in the vapor and a ring collector in the helium film on the walls were measured as a function of temperature between 0.9 and 4.2 K and of applied field up to 200 V cm^–1. A current of 10^–13 A attributed to an ion flow in the film was detected in a temperature range 1.2–1.6 K and at low fields <70 V cm^–1 under conditions where the current to the collector in the vapor was much smaller than the current to the collector in the film. A positive current which appeared to reach the collector in the vapor was attributed to a negative current of photoelectrons emitted from the collector into the vapor.