Development of Deuterium-loaded Targets for D-D Neutron Generator Based on High-current Gasdynamic ECR Ion Source

摘要

Development of a new generation of D-D neutron generators based on high-current gasdynamic ECR sources of deuterium ions requires engineering and creation of a neutron-generating target containing deuterium. Existing D-D neutron generators consist of deuterium ion (deuteron) source with extracted beam energy of 100-200 keV and deuterium saturated neutron production target. The deuteron beam is directed towards the target, provoking the nuclear reaction and neutron emission. However state-of-the-art D-D generators based on conventional ion sources deliver only 1-10 mA/cm~2 deuteron current density to the target and do not provide necessary neutron flux density for modern applications. Increasing the current density of deuterium ion beams bombarding the target is one of the obvious ways to amplify the neutron yield in D-D generators. A so-called high current quasi-gasdynamic ECR ion source with plasma heating by millimeter wave gyrotron radiation was suggested to be used in a scheme of D-D neutron generator. Ion source of that type was developed in the Institute of Applied Physics of Russian Academy of Sciences. It can produce deuteron ion beams with current density up to 700-800 mA/cm~2. The use of this source allows a significant increase in neutron yield, though increasing the target stress. In order to fulfill requirements of modern applications for neutron flux the target must be able to withstand a constant load of up to 1 eA of deuterium ion current with energy of 100 keV, providing efficiency of neutron generation on the level of 10~(11) neutrons per second. A lot of investigations on the proper target and wafer materials selection to be done along with target saturation technique working off for successful creation of the target. An experimental setup built for target saturation with deuterium is described in the present work. The setup consists of water-cooled vacuum chamber, set of vacuum pumps, oxygen, deuterium and air gases feeding system, programmable target and wafer heater, and load-unload system. In the frame of conducted experimental studies optimal parameters of target material annealing for its proper degassing and pumping the impurities were found. Optimal saturation process stages parameters such as time, temperature, temperature gradient and deuterium pressure have been determined for creating effective deuterium-saturated titanium targets. Experimental investigations of target quality were performed with secondary ion mass-spectrometry method (SIMS). SIMS results showed that despite oxidation of the target surface the quality of obtained samples and deuterium content are high enough for its successful use in the D-D neutron generator.