Ionization time of thyratrons

GRID-CONTROLLED vapor-filled rectifiers, or thyratrons, have not been considered in the past for use in blocking and sweep circuits for cold-cathode-type oscillographs because of their inherent ionization time. A search of the literature on the subject, and reference to manufacturers' data sheets furnished little useful information on this ionization time. A research program to determine the minimum ionization times of various tubes was thus started in 1938, and first results showed that minimum ionization times of 0.3 microsecond were obtainable with mercury-vapor thyratrons if the grid was driven sufficiently positive. These results suggested that these tubes might be successfully used in blocking circuits for high-speed oscillographs, and work on this phase of the problem is being continued. The apparatus devised for measuring ionization times made possible an extended study of the relation between ionization time and grid overvoltage as a function of anode voltage and vapor temperature (for mercury tubes) and it is the results of this extension of the original problem which will be discussed.