Numerical Life Qualification of Ion Thruster’s Ion Optics using the JIEDI Tool

Abstract

The JIEDI (JAXA's Ion Engine Development Initiative) tool has been developed to assess the ion acceleration grid erosion of an ion thruster. The sensitivity analysis of the input parameters of the JIEDI tool is conducted in this paper. We compare the simulation results of the JIEDI tool and show that it successfully reproduces the full lifetime test of the μ10 prototype model. Through sensitivity analysis, we found that the sticking factor is the most sensitive input parameter when estimating the accelerator grid erosion and electron backstreaming time. For the worst case scenario of grid erosion (without re-deposition), the uncertainty in the neutral mass flow rate through grid holes is important when estimating the accelerator grid erosion. A 30% change in the neutral mass flow rate caused by a 6% change in the propellant utilization efficiency, corresponds to about a 20% change in the accelerator grid mass loss as well as the increasing rate of minimum potential on the axis of the ion optics. In contrast to the accelerator grid erosion, the uncertainties in the discharge voltage and grid gap (that affect the trajectory of the mainstream ions), are important when estimating decelerator grid erosion. A 40% change in the discharge voltage corresponds to about a 90% change in the decelerator grid mass loss. In addition, a 30% change in the grid gap between the screen grid and the accelerator grid corresponded to about a 40% change in the decelerator grid mass loss. NomenclatureI = flux-tube current I b = total ion beam current I b,average = average ion beam current per hole m i = ion mass n m  = neutral mass flow rate N = number of beamlets n n = neutral number density T e = electron temperature T k = stay time of the k-th flux tube V element = element volume v = relative velocity between ion and neutral 1 2 v i = ion velocity Γ = flux generated by collision γ = doubly charged ion fraction ε 0 = permittivity of vacuum η u = propellant utilization efficiency ρ e = electron charge density ρ i = ion charge density σ = reaction cross section φ = potential φ 0 = plasma potential

Ion thrusters for electric propulsion: Scientific issues developing a niche technology into a game changer

“…REVIEW scitation.org/journal/rsi the programs CEX2D or CEX3D of the Jet Propulsion Laboratory, the JIEDI tool of JAXA, and others. [147][148][149] The neutral particle density within a channel, which has to be known for simulation of grid erosion, can be calculated using a number of available programs based, e.g., on the direct simulation Monte Carlo (DSMC) method (SPARTA, OpenFOAM) or others (COM-SOL). [150][151][152] Figure 7 shows an example of a particle density calculated with COMSOL.…”

Sensitivity Analysis of a Fully Kinetic Code for Physical Parameters

“…The efficiency breakdown scheme proposed by Brown 14) was used to analyze thrust generation processes influenced by the physical parameters. 9) First of all, anode efficiency t , the indicator of overall energy conversion of the thrusterhead, can be divided into energy efficiency E , propellant efficiency u , and beam efficiency a as:…”

“…The one-factorat-a-time method involves repeatedly varying one parameter value in a presumed confidence range at a time while keeping others fixed at their nominal value. Previously, Watanabe et al 9) adopted this approach to conduct a sensitivity analysis of the input parameters of a numerical tool to validate grid erosion of an ion thruster. In the following sections, the results of our sensitivity analysis are presented, and the significance of the physical parameters is discussed.…”

Erosion rate measurement in ion thrusters using Cavity Ring-Down Spectroscopy technique

“…Many studies have been performed to extend the lifetime of ion thrusters [6,7]. However, the measurement of ion thruster's lifetime is challenging due to long duration and enormous costs.…”

“…In fact, the experimental lifetime validation requires several tens of thousands of hours [3,8]. Instead of conventional experimental methods, JAXA has been developing a numerical analysis tool for this type of certifications, called "JIEDI tool" [6,7]. The details of JIEDI tool are shown in ref.…”