A Scaling Law of the Life Estimation of the Three-Grid Optics for an Ion Engine.

Abstract

A scaling law on the wear of three-grid optics is proposed for the lifetime estimation of ion engines. The charge exchange ions erode the accel grid holes; therefore, the reduced retarding potential results in electron backstreaming, which is the end of life of the three-grid optics. The arithmetic formulas are induced by use of the space-charge-limited current density law and a newly introduced parameter called the modified effective acceleration length. The model is based on the following scenario of grid life: (1) Charge exchange ion erosion enlarges the accel grid hole diameter, (2) which shortens the modified effective acceleration length between the screen and accel grids and (3) reduces the retarding potential to keep the beam current constant under the space-charge limited flow. The characteristic of the proposed formulas is that the lifetime of the three-grid optics strongly depends on the beam current and the accel grid voltage. The correlation between the arithmetic formulas and the numerical simulations showed good qualitative agreement with one another in all regions of the normalized perveance per hole and achieved quantitative consistency in its high value.

Ion Thruster Operation with Carbon Nanotube Field Emission Cathode

“…A 30 W class microwave discharge ion thruster [22] was used for the ion source. Three flat grids were used to extract the ion beam, the screen grid, acceleration grid, and deceleration grid, with grid parameters optimized using a numerical analysis code developed by Nakano et al [23]. The grid parameters are shown in Table 1.…”

Measurement of xenon plasma properties in an ion thruster using laser Thomson scattering technique

“…These results show that a flux tube model can be used to simulate the ion beam trajectory for the ion engine grid erosion evaluation code, and the calculation cost is much lower than that of the Full Particle in Cell (PIC) model. 24 Miyasaka et al 25 show that there is no difference between the numerical results using the full-Particle In Cell (PIC) model and those using the flux tube model, 26,27 if the EEDF in the vicinity of the screen grid is Maxwellian. From this spectrum and the Rayleigh scattering calibration using nitrogen gas, N e and T e were calculated to be (6.2 ± 0.4) × 10 17 m −3 and 2.2 ± 0.4 eV, respectively.…”

Thomson Scattering Diagnostics in the Plasma of an Ion Thruster

“…The geometric parameters are shown in Table 1. This geometry was designed using a numerical analysis code developed by Arakawa et al 7) . The grid is made of pyrolytic carbon and ceramic insulators are used as an isolator between the three grids.…”