Electrode contamination effects of retarding potential analyzer

Study and design of a lens-type retarding field energy analyzer without a grid electrode

A retarding field energy analyzer (RFEA) for measuring the energy distribution of charged particles offers the advantages of a simple structure and suitability for simultaneous observations of beam patterns in two dimensions. In this study, lens-based RFEAs without a grid electrode were theoretically investigated with regard to the geometry and lens condition to achieve high performance. The simulation results show that the proposed RFEA can achieve a resolution of 2.6 meV at an energy level of 500 eV. In addition, performance, which is the ratio of the resolution to the beam energy, reached 5.2×10^-6. These results indicate that the RFEA designed in this study is capable of high-performance outcomes. The findings here demonstrate that the most important factors when attempting to realize a high-resolution RFEA design are to reduce the sagging effect of the electron beam through the focusing lens and ensure that V″(z) in the retarding electrode is close to zero. The design of the lens-based RFEAs is described in detail.

A retarding potential analyzer design for keV-level ion thruster beams

We present a new Retarding Potential Analyzer (RPA) design that is capable of measuring keV-level energy, high-density plasma beams. This instrument overcomes the limitations of existing RPAs and can operate in plasmas with densities in excess of 1 × 10¹⁵ m^-3 and ion energies up to 1200 eV. The RPA design parameters were determined by analyzing the electron density and temperature, the sheath thickness, and the ion density in the beam based on the Faraday probe and Langmuir probe measurements. A previously unobserved grid spacing arcing phenomenon was observed in experiments. This arcing phenomenon was also investigated and a grid spacing criterion was proposed to eliminate the arcing. We present measurement results on the plasma beam emitted from the 20 cm Xenon ion thruster used on the Chinese SJ-9A satellite.

Including sheath effects in the interpretation of planar retarding potential analyzer's low-energy ion data

The interpretation of planar retarding potential analyzers (RPA) during ionospheric sounding rocket missions requires modeling the thick 3D plasma sheath. This paper overviews the theory of RPAs with an emphasis placed on the impact of the sheath on current-voltage (I-V) curves. It then describes the Petite Ion Probe (PIP) which has been designed to function in this difficult regime. The data analysis procedure for this instrument is discussed in detail. Data analysis begins by modeling the sheath with the Spacecraft Plasma Interaction System (SPIS), a particle-in-cell code. Test particles are traced through the sheath and detector to determine the detector's response. A training set is constructed from these simulated curves for a support vector regression analysis which relates the properties of the I-V curve to the properties of the plasma. The first in situ use of the PIPs occurred during the MICA sounding rocket mission which launched from Poker Flat, Alaska in February of 2012. These data are presented as a case study, providing valuable cross-instrument comparisons. A heritage top-hat thermal ion electrostatic analyzer, called the HT, and a multi-needle Langmuir probe have been used to validate both the PIPs and the data analysis method. Compared to the HT, the PIP ion temperature measurements agree with a root-mean-square error of 0.023 eV. These two instruments agree on the parallel-to-B plasma flow velocity with a root-mean-square error of 130 m/s. The PIP with its field of view aligned perpendicular-to-B provided a density measurement with an 11% error compared to the multi-needle Langmuir Probe. Higher error in the other PIP's density measurement is likely due to simplifications in the SPIS model geometry.