Hot-cathode thyratrons: practical studies of characteristics

Abstract

The paper surveys the main features which determine the characteristics and life of thyratrons in the light of direct experiment and of field experience. These include electron emission from the cathode, ionization and current build-up, grid control, the current-carrying capacity of the valve, the decay of ionization at the end of conduction, and the provision of suitable operating conditions.Emphasis is laid on factors which, while not immediately affecting electrical performance, may determine valve life; one example is positive-ion bombardment, which may cause damage to the cathode.The control characteristics of different types of grid are discussed; particular reference is made to the pentode design, a recent development enabling heavy currents to be controlled from high-impedance grid circuits.The arc voltage drop varies considerably with filling pressure and with current value, abrupt changes being associated with modifications in the form of the discharge. If the current-carrying capacity of the arc path is exceeded, the arc, if it cannot transfer to an alternative path, may suddenly go out, giving rise to generally undesirable high-voltage surges.A method of studying de-ionization time is described, and results are given showing this time as a function of the gas and its pressure. The characteristics of various gas and vapour fillings are discussed. A non-uniform pressure distribution in mercury-vapour valves assists rapid starting.