Development Of An ECR Ion Source And Pre-analysis System For D-D/D-T Intense Neutron Generator

The intense DD/DT neutron generator is an important accelerator-based neutron source,which can be used in neutron photography,nuclear data measurement,neutron detector calibration,radiation resistance reinforcement and material irradiation,etc.It has a wide range of applications in the fields of scientific research,production and military.An intense accelerator-based D-D/D-T neutron generator called ZF400 is being built at Lanzhou University in China,with the aim of generating neutron yields of 6×10¹⁰ n/s by the D-D reaction and 6×10¹² n/s by the D-T reaction.It is composed of an ECR ion source,a pre-analysis system,an acceleration tube,and a rotating target.When the neutron generator operates,the mixed deuterium ion beam（consisting of D₁⁺,D₂⁺,and D₃⁺）extracted from the 2.45 GHz ECR ion source is purified by the pre-analysis system.The pure D₁⁺beam is then accelerated using the electrostatic acceleration tube to above 400 ke V and the rotating target is bombarded.The pre-analysis system separates polyatomic ions from the mixed ion beam to reduce the current loading of the acceleration tube,and increases the life of the target and the neutron yield.It is also applied as a low-energy beam transport（LEBT）line to transport and match the ion beam from the exit of the ECR ion source to the entrance of the acceleration tube.The ECR ion source and pre-analysis system are designed to provide and transport 35 m A and 50 ke V CW D₁⁺beams for neutron production,and 50 m A and 50 ke V CW proton beams for commissioning.This thesis focuses on the development requirements of the 6×10¹² n/s DD/DT intense neutron generator,and completed the development of the ECR ion source and the pre-analysis system.The main content and results are as follows:The designing and commissioning of the ECR ion source was completed.When the plasma electrode aperture is 6 mm in diameter and the extraction voltage is 50 k V,the total extraction current is greater than 80 m A.The ion source can work in a larger range of H₂ gas flow Q and microwave power P;the microwave window material and thickness have a significant impact on the beam extraction,a higherandcan be obtained with a 2 mm Al N used for the microwave window;theandwill fluctuate greatly by adjusting the three-stub tuner to change the impedance matching between microwave and plasma.When there are ECR surfaces around the microwave window,and the magnetic field near the microwave is greater than that in the extraction area,it is more conducive to the extraction of intense ion beams.In order to study the damage mechanism of microwave window,the finite element software was used to calculate the temperature and stress distributions of Al₂O₃ ceramic microwave window under the effect of the microwave,plasma and backstreaming electrons.The calculation result shows that the maximum Von Mises stress is at the edge of the microwave window under the effect of microwave and plasma,while under the effect of the electron beam,the largest stress is at the center of the microwave window.Enhanced water-cooling performance can reduce the influence of microwave and plasma on microwave window,and an increased thickness of BN can protect the window from electron beam more effective.The combination of these two methods is feasible and effective in practice to extend the service life of the ECR ion source.In order to solve the ignition problem of the ECR ion source,the pressure distribution in the extraction area was calculated.By optimizing the shape of the electrode,the vacuum in the extraction area was improved and the ignition probability was reduced.The design of the pre-analysis system was completed.The pre-analysis system can transmit 80 m A/50 ke V hydrogen ion beam or 60 m A/50 ke V deuterium ion beam,which can completely separate the polyatomic ions in the beam and match the acceleration tube injection requirements.The pre-analysis system is composed of a solenoid,a correction magnet,an analysis magnet,a triple quadrupole lens and a vacuum system.The beam transmission envelope of the pre-analysis system and the magnetic field distribution of each magnet are calculated.The commissioning of the ECR ion source and the pre-analysis system was completed.When the total current extracted by the ion source was more than 70 m A,the proton beam at the end of the pre-analysis system yielded a proton beam greater than 50 m A,and the beam radius is less than 20 mm,which can meet the beam intensity requirements of the high current neutron generator.