An anomalous phenomenon was observed in the retarding potential analyzer （RPA） measurements of the energy of the ion beam from an 8 cm argon ion source. The current-voltage （Ⅰ- Ⅴ） curve, which should theoretical...An anomalous phenomenon was observed in the retarding potential analyzer （RPA） measurements of the energy of the ion beam from an 8 cm argon ion source. The current-voltage （Ⅰ- Ⅴ） curve, which should theoretically descend, went up as the ion retarding potential was increased. Various explanations, such as the Townsend discharge theory and secondary electron emission etc. were proposed but denied by the theory application condition or the experiment results. An angle of about -10° was found between the axes of the ion beam and the RPA according to the contours of the ion beam density and direction. The particle simulation and experiment of the sum of the collector and wall current were conducted at different incident ion angles. The trends of the Ⅰ- Ⅴ curve in simulation results conformed with the experimental results in most cases. The ion trajectories were simulated at different retarding potentials with an incident angle of -10°. According ：to these results, the reason for the anomalous phenomenon is that when there is a specific angle between the axes of the ion beam and the RPA, more ions are repelled from the vicinity of the ion retarding grid to avoid striking on the grid as the ion retarding potential increases. These redundant ions reach the plate and thus lead to the formation of an ascending Ⅰ- Ⅴ curve.展开更多
An ionic liquid ion source(ILIS)is a kind of high brightness ion source capable of providing high-speed positive or negative ion beams.This paper presents a miniaturized ILIS based on an array of porous metal strips.T...An ionic liquid ion source(ILIS)is a kind of high brightness ion source capable of providing high-speed positive or negative ion beams.This paper presents a miniaturized ILIS based on an array of porous metal strips.The porous emitter array,integrated with seven 10 mm long strips,is fabricated using wire electrical discharge machining(WEDM)combined with electrochemical etching.The assembled ILIS is 30 mm×30 mm×17.5 mm in size and weighs less than 25 g.A series of experiments,including anⅠ-Ⅴcharacteristic test,a retarding potential analyzer(RPA)test,and a spatial plume distribution test,have been conducted in vacuo to characterize the performance of the ILIS.Results show that the emitted current is up to about 800μA and ion transparency is as high as 94%.Besides,RPA curves reveal that the total fragmentation rate of the emitted particles accounts for 48.8%in positive mode and 59.8%in negative mode.Further,with the increase in applied acceleration voltage,the voltage loss rises while the energy efficiency decreases.It is also found that the plume perpendicular to the strips has a higher divergence than the one parallel to the strips.A numerical simulation by COMSOL reveals that the electric field distribution between the two electrodes results in such a spatial plume profile.展开更多
基金supported by National Natural Science Foundation of China(No.10805004)the Fundamental Research Funds for the Central Universities of China(No.YWF-13-D2-HT-12)
文摘An anomalous phenomenon was observed in the retarding potential analyzer （RPA） measurements of the energy of the ion beam from an 8 cm argon ion source. The current-voltage （Ⅰ- Ⅴ） curve, which should theoretically descend, went up as the ion retarding potential was increased. Various explanations, such as the Townsend discharge theory and secondary electron emission etc. were proposed but denied by the theory application condition or the experiment results. An angle of about -10° was found between the axes of the ion beam and the RPA according to the contours of the ion beam density and direction. The particle simulation and experiment of the sum of the collector and wall current were conducted at different incident ion angles. The trends of the Ⅰ- Ⅴ curve in simulation results conformed with the experimental results in most cases. The ion trajectories were simulated at different retarding potentials with an incident angle of -10°. According ：to these results, the reason for the anomalous phenomenon is that when there is a specific angle between the axes of the ion beam and the RPA, more ions are repelled from the vicinity of the ion retarding grid to avoid striking on the grid as the ion retarding potential increases. These redundant ions reach the plate and thus lead to the formation of an ascending Ⅰ- Ⅴ curve.
基金supported by National Natural Science Foundation of China(No.52075334)。
文摘An ionic liquid ion source(ILIS)is a kind of high brightness ion source capable of providing high-speed positive or negative ion beams.This paper presents a miniaturized ILIS based on an array of porous metal strips.The porous emitter array,integrated with seven 10 mm long strips,is fabricated using wire electrical discharge machining(WEDM)combined with electrochemical etching.The assembled ILIS is 30 mm×30 mm×17.5 mm in size and weighs less than 25 g.A series of experiments,including anⅠ-Ⅴcharacteristic test,a retarding potential analyzer(RPA)test,and a spatial plume distribution test,have been conducted in vacuo to characterize the performance of the ILIS.Results show that the emitted current is up to about 800μA and ion transparency is as high as 94%.Besides,RPA curves reveal that the total fragmentation rate of the emitted particles accounts for 48.8%in positive mode and 59.8%in negative mode.Further,with the increase in applied acceleration voltage,the voltage loss rises while the energy efficiency decreases.It is also found that the plume perpendicular to the strips has a higher divergence than the one parallel to the strips.A numerical simulation by COMSOL reveals that the electric field distribution between the two electrodes results in such a spatial plume profile.
