Analysis Of Plasma Characteristics Of High-power RF Negative Ion Source Based On Plate Probe

Neutral beam injection(NBI)has become one of the main auxiliary heating and current driving means of magnetic confinement fusion because of its high heating efficiency and clear physical mechanism(which can be effectively extrapolated to large devices).Compared with the filament source,the radio frequency(RF)source has the advantages of no filament sublimation pollution and maintenance-free.In addition,the negative ion still has higher neutralization efficiency at 1 Me V,so the RF negative ion source was selected as the reference ion source by the International Thermonuclear Experimental Reactor(ITER)in 2007.At present,nuclear fusion research institutions all over the world have carried out related research on RF negative ion sources.For the RF negative ion source,in order to increase the beam density,it is necessary to increase the negative hydrogen ion density in the extraction region as much as possible,and the negative hydrogen ion density is strongly dependent on the electron temperature;in addition,the uniformity of the beam depends strongly on the uniformity of the plasma in the extraction region,and the uniformity of the plasma in the extraction region can be characterized by the distribution of the electron density in the extraction region.The electron temperature,the electron density and the distribution of the electron density can be obtained by Langmuir probe.Because the Langmuir plate probe can work under high-power and long pulse.In addition,due to the large surface area of the plate probe,it can collect a larger saturated ion current(electron current),which can effectively improve the signal-to-noise ratio.In order to realize the measurement of plasma parameters such as electron density,electron temperature,and plasma potential of the high-power RF negative ion source,the following work has been done in this paper.1.The research progress of RF negative ion source of worldwide are introduced.By understanding the research principles of probe diagnosis,microwave interference diagnosis and spectral diagnosis,the advantages and disadvantages of various plasma parameter diagnosis methods are compared.2.The basic formulas of Langmuir single and double probes for measuring plasma parameters are deduced,and the influence of factors such as probe surface temperature rise,magnetic field,probe response time and secondary electron emission on the measurement of plasma parameters are discussed.3.In order to realize the measurement of plasma parameters,a probe diagnosis system was developed,which mainly includes plate probe design,filter circuit design,and the development of data acquisition and processing system.4.In order to verify the effectiveness of the plate probe diagnosis system,a plate probe test platform was built.The I-V characteristic curve consistent with the theory is obtained on the plate probe test platform,and the test results are compared with that obtained by the microwave interferometer.The change trend of the measurement results of the probe and the microwave interferometer is consistent.In addition,the plasma parameters measured by the probe are consistent with the simulation results,which verifies the effectiveness of the probe measurement system further.5.The self-developed Langmuir plate probe was used to diagnose the plasma characteristics of the high-power RF negative ion source.The influence of power,gas pressure and bias voltage on the plasma parameters and the spatial distribution of plasma parameters in the extraction region are obtained.In this paper,a self-developed plate probe is developed by setting up a probe test platform,and the plasma characteristics of ion source are explored by using it,it lay a basis for the design and optimization of high-power RF negative ion source.