Effect of electrode temperature on the evolution of photoplasma under electric field

A photoplasma is produced by two-step resonant photoionization scheme by shining pulsed lasers on an atomic beam of barium (Ba). There is an interest in ion collection from photoplasma by electrostatic field when ion collection assembly is maintained at high temperature. A double furnace system consisting of two resistively heated furnaces has been developed. One furnace is placed on the top of the other in high vacuum chamber. The lower furnace is used to generate a wedge shaped barium atomic beam while the upper one heats the ion collection assembly. The photoplasma evolves in an external electric field produced by two parallel plate electrodes. The motion of electrons and ions in electric field generates currents that are recorded across series resistors connected to the electrodes. It is observed that a large dc current flows in the circuit when electrodes are kept at high temperature (similar to 800 K). The large current is probably due to thermionic emission from Ba coated electrodes, electron impact ionization of vapor between electrodes, thermal ionization of vapor and leakage through insulator that holds the electrodes etc. When electrodes are at room temperature, the photoplasma is embedded in the atomic beam, where as it is produced in a vapor cell when electrodes are at high temperature. The photo-ion pulse is superimposed on the dc background current and its amplitude as well as time duration increase compared to that when electrodes are at room temperature.