Azimuthal velocity measurement in the ion beam of a gridded ion thruster using laser-induced fluorescence spectroscopy

Self Cite

We report the experimental and simulated azimuthal ion velocities of a gridded ion thruster, which generates a roll torque around the thrust axis. Laser-induced fluorescence spectroscopy was applied to two microwave ion thrusters with opposite magnetic polarities. A comparison of the measured results revealed a net misalignment of the grid optics and showed that the ions are continuously accelerated from inside the discharge chamber towards a direction downstream of the grid optics. To investigate the effect of the electromagnetic field, the authors conducted a two-dimensional particle-in-cell Monte Carlo collision (2D-PIC-MCC) numerical simulation. The numerical simulation agrees with the measurements and reveals that the ions are azimuthally accelerated by a gradient B drift, curvature drift, E×B drift and the Lorentz force. The reproduced roll torque is 3.1±2.3 μNm and arises due to the mechanical tolerance of the grid optics. The roll torque shows good agreement with the result observed in the space operation.Therefore, the roll torque can be predicted by using our experiment and simulation.

Section: Introductionsupporting

confidence: 76%

“…The plasma is generated by electron cyclotron resonance (ECR). More information about the ionization process in the ion thruster μ10 can be found in [1].…”

Section: Microwave Ion Thruster μ10mentioning

confidence: 99%

See 1 more Smart Citation

Azimuthal ion drift of a gridded ion thruster

Yamashita¹,

Yamamoto²,

Koda³

et al. 2018

Self Cite

“…However, the grid system will deviate from the optimal perveance, when the grid holes shift which may occur due to manufacturing tolerances or thermal expansion. In ion thrusters, the misalignment of grid aperture and the resulting deflection of beam may cause an unexpected roll torque about the thruster axis and even reduce the lifetime of the thruster [37,38]. Okawa et al performed an experimental investigation of the ion beam deflection caused by the grid translation [39].…”

Section: Introductionmentioning

confidence: 99%

Three-dimensional analysis of RF-biased ion optics with misalignments of apertures

Wang

Liu

et al. 2023

The accelerator grid holes shift is a critical reason for erosion failure of optic systems in ion thrusters, which may also cause an unexpected roll torque about the ion beam axis. A three-dimensional model of ion optics is developed based on particle-in-cell Monte Carlo collision (PIC-MCC) method to investigate the plasma dynamics and performance of the radio frequency (RF) grid systems with misalignments of apertures, which are compared with those in the direct current (DC) grid system. For benchmark case, the three-dimensional model gives a better agreement with the experiments in the ion energy distribution function (IEDF) compared with the two-dimensional model from a previous publication, with 36.4% and 47.9% relative error reduction of the peak position and full width at half maximum (FWHM) respectively, indicating the effectiveness of the developed three-dimensional model. Simulations show that in the RF grid system the ion beamlet is deflected in the direction opposite to the shift of the accelerator grid hole, while electrons move first in the holes shift direction, and then deflect in the opposite direction. The average ion beamlet deflection angle calculated is consistent with the predictions by the linear optical theory in both the RF and DC grid system. The amplitude of beamlet deflection angle fluctuation with time decreases with the increase of RF frequency. When the grid holes shift, the ion beamlet will deflect with the divergence angle almost unchanged in the DC grid system, while the beamlet divergence angle increases in the RF grid system. When RF frequency is low, the big vortex-like structure in electron velocity phase diagram breaks into small vortices, showing a reduced oscillation intensity. The holes shift also causes high-frequency oscillation in the shift direction. In terms of performance, RF grid system is more sensitive to grid holes shift than DC grid system.

“…Gridded ion sources are widely applied in fields such as film deposition, etching, surface modification, and electric propulsion [1][2][3][4][5][6]. When ions are extracted from gridded ion sources, crossover and direct impingements occur in low and high plasma density regimes [7], respectively.…”

Section: Introductionmentioning

confidence: 99%

Effects of secondary γ-electrons from accelerator grid under ion impingement in gridded ion sources

Fu¹,

Tian²,

Ding³

2022

Thus far, effects of secondary γ-electrons emitted from accelerator grids of gridded ion sources on ionization in discharge chambers have not been studied. The presence and induced processes of such secondary electrons in a microwave electron cyclotron resonance gridded ion source are confirmed by the consistent explanations of: (1) the observed jump of ion beam current (Ib) in case of a low-density plasma appearing at the chamber’s radial center due to the microwave skin effect; (2) the evolution of glow images recorded from the end-view of the ion source during the jump of Ib; (3) the over-large jump step of Ib with the increasing microwave power; (4) the pattern appearing on the temperature sticker exposed to the discharge operated in the regime where the arrayed energetic-electron beamlets are injected into the discharge chamber; (5) the measured step-increment in the voltage drop across the screen grid sheath. A positive feedback loop composed of involved processes are established to elucidate the underlying mechanism. Energetic γ-electrons from the accelerator grid and warm δ-electrons from the opposite antenna do not produce direct excitation and ionization, but they enhance the electrical confinement of cold electrons by elevating the voltage drop across the sheaths at the antenna and screen grid, thus leading to the jump of Ib. The energetic γ-electrons-based model can be also modified to explain abnormal results observed in the other gridded ion sources. Energetic γ-electrons from accelerator grids should be taken into account in understanding gridded ion sources.