Experimental Investigation On High Voltage Electrical Breakdown Characteristics Of Ceramic Envelope Of Sealed Neutron Tubes

Sealed neutron tube is a kind of portable and small accelerator neutron source,with high neutron yield,good monochromatic spectrum,no gamma background and other excellent features.While the neutron tube is working,a high voltage of 2kV is applied on the ion source,and a high voltage of-100kV or more is applied to the target.The mixed gas of deuterium and tritium is supplied from the hydrogen-absorbing filament,mixed gas pressure is in the range of 10^-310^-1Pa.The huge voltage difference in the neutron tube and the gas environment lead to the phenomenon of surface flashover of the ceramic envelope,and the surface flashover phenomenon will seriously affect the stability and service life of neutron tube.Therefore,the research on the high voltage breakdown behavior of the sealed neutron tube is very important for the design and application of neutron tube.In this paper,by using a set of high-voltage experimental device,deuterium pressure provided by the hydrogen-absorbing filament,and the DC high-voltage generator and pulse high-voltage generator,with self-designed gas spark switch to achieve the supply of DC high voltage,pulse high voltage and the supply of deuterium pressure.At the same time,for a better simulation of the actual working conditions of the neutron tube,this paper did a series of experiments of hydrogen-absorbing filament by using the gas path of the high-voltage experimental device.Experiments on hydrogen-absorbing filament show that when the current of hydrogen-absorbing filament is below 250mA,the amount of deflation is very small;when the current of filament is more than 250mA,the amount of deflation is very large;for an initial gas pressure of several Pa,the hydrogen-absorbing filament takes about 15 seconds to reduce the pressure to 10^-3Pa;when the hydrogen-absorbing filament is operated in a pulsed manner,300 to 400 mA current is applied to the filament,it takes about 8 minutes to reach a stable pressure value;the deflation performance of the hydrogen-absorbing filament will gradually decay after the absorbing is completed,and the maximum vacuum becomes stable after about 10 times of using.Experiments on 95%alumina ceramic envelope show that when the deuterium gas pressure is in the range of 10^-4Pa to 1Pa,the surface flashover voltage is independent of the deuterium pressure;the surface flashover voltage of DC high voltage is about 2.0kV/mm,and the surface flashover voltage of pulsed high voltage is slightly higher,about 2.2kV/mm;as the deuterium gas pressure rising,the surface flashover voltage decreases rapidly with the increase of gas pressure,and it follows the law of Paschen.