Study On Electrostatic Analyzer With A Variable Geometric Factor System

As the fourth state of matter,plasma is the most abundant material in the universe and more than 99% of all known matter exists in the plasma state.Space plasma has been one of the important detection targets since artificial earth satellites were sent into space.In-situ detection is the most commonly used means for space-borne plasma detection.With the deepening of space exploration missions,interaction between solar wind and magnetosphere has become a new research hotspot,and more precise technical requirements have been proposed for the space plasma detection.It is difficult for conventional plasma detectors to meet the detection requirements due to their limitations of detectable flux dynamic range,field of view(FOV)and resolution.There is an urgent need to design high-resolution,wide-FOV hot plasma detectors with variable geometric factors.Solar wind Magnetosphere Ionosphere Link Explorer(SMILE)is a joint space science mission proposed by European Space Agency and Chinese Academy of Sciences.The in-situ plasma analyzer for SMILE will determine the basic moments of the solar wind distributions,such as number density,bulk velocity,temperature tensor,and heat flux vector under different solar wind conditions.To achieve this,three-dimensional velocity distribution functions of the solar wind ions will be measured with a wide FOV Light Ion Analyzer(LIA)on a three-axis stabilized satellite platform,providing background data for soft X-ray and extreme UV imaging.Based on the scientific needs of SMILE satellite,this paper focuses on the design and simulation technology of LIA,and introduces the measurement error of LIA on plasma moments.Three instruments schemes with different performance parameters applied to different detection targets were designed.To fulfill the requirements of solar wind detection,the symmetric FOV electrostatic analyzer with a variable geometric factor system is designed based on the top cap hemispherical electrostatic analyzer.The FOV of the sensor is ±45°×360°(~2.8? sr).The top cap voltage is used to realize the variable geometric factor in order to realize the detection requirements in a large-dynamic flux range.For the coverage of 4? FOV in magnetosheath ions detection,based on sensor prototype of a 45° asymmetric FOV,higher resolution and better ions counts response uniformity within the 2? FOV are obtained by redesigning and simulating the ion optics system.The sensor structure of the 30° asymmetric FOV is first proposed internationally and used as the final design of SMILE/LIA instrument.The baseline design of the 30° asymmetric FOV design is a top-cap spherical electrostatic analyzer with deflectors of spherical prototype to accept incident ions at the continuous elevation range from 0° to 90°,single LIA achieving a 2? hemispherical FOV.The 30° asymmetric structure substantially improves the azimuth resolutions in the elevation angle,nearly doubling the resolution compared to that of the 45° asymmetric structure.In the meantime,geometric factor response uniformity within the 2? FOV is ensured.Two LIAs will be used in SMILE satellite to cover the 4? FOV detection for ions in magnetosheath and solar wind.For the targets of a large-dynamic flux range detection from magnetosheath to solar wind,the geometric factor function is applied to the design of the asymmetric FOV electrostatic analyzer for the first time internationally.Compared to traditional symmetric FOV prototypes,the geometric factor function is improved greatly and continuous adjustment of geometric factors in two orders of magnitude is achieved with much lower voltages to fulfill the detection requirements for magnetosheath ions and solar wind with a large-dynamic flux range and high resolutions.Based on the design of the asymmetric FOV electrostatic analyzer,the research on moments calculation and measurements error analysis for the plasma instrument with a 2? hemispherical FOV is carried out for the first time both home and abroad.Taking the space hot plasma obeying Maxwellian distribution as input,the moments are obtained by integrating the distribution function with different orders at the velocity phase space.Measurement uncertainties are figured out by comparing the input and output values.Taking the CLUSTER/CIS measurement data as input,and current LIA design as the simulation model,the LIA simulation and the measurement results have good consistency in the main operating region of SMILE,which shows that LIA can fulfill the requirements of large-dynamic flux range,high precision and high resolution at 4? FOV,with measurement errors controlled in a reasonable range both in solar wind and magnetosheath.