| 摘要 |
PURPOSE:To suppress initial property fluctuation by having a construction wherein an electrode stem is projected from electrode coils while making the electrode stem tip part thinner than the central part. CONSTITUTION:A sodium metal together with a metal for buffer gas are sealed into a transmissive luminous tube provided with electrodes 1 on both ends while lighting it under the operating condition where average potential inclination in the luminous tube may become more than 20V/cm. An electrode which performs duties of cathode during operation consists of an electrode stem 2, electrode coils provided so as to surround the electrode stem and an electron radiating material provided in an air gap formed by the electrode stem and electrode coils 3, 4 and 5, so as not to be exposed to a discharge space of the luminous tube 12. In this case, it is so constructed that the electrode stem is projected from the electrode coils while the tip part of the electrode stem is made to be thinner than the central part.
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