Formation of ion beams from plasma sources. i

Buckey, C.; Eckhardt, W. O.; Hyman, J.; Knechtli, R. C.

doi:10.2514/3.2655

Cited by 29 publications

(7 citation statements)

References 7 publications

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“…In some earlier simulations, the electrons were assumed to not enter the domain between the grids, and equation ( 2) was used to estimate the electron density upstream the screen grid and downstream the accelerator grid [35]. But the meniscus will become convex when plasma density is high enough [7,9], which indicates that the electron density in the domain between the grids is not necessarily zero. Considering that the difference between the potential at the edge of the upstream sheath and the saddle-point potential is high enough to prevent the electrons moving downstream, we assume that the electron density is zero in the aperture of the accelerator grid where the saddle-point potential approximately is located [24,39].…”

Section: Simulation Methods and Model Configurationmentioning

confidence: 99%

“…Besides, some concepts and models were brought to evaluate the beam divergence according to the parameters of ion optics and plasma. Hyman et al [7] introduced the concept of 'perveance-density matching' to accommodate an inhomogeneity of the ion current density available from the ion source and obtain low interception of the ion beam on the accelerator grid. Particularly, normalized perveance per hole was frequently used to describe the ion extraction performance of each grid set investigated [1,8,24], and Coupland et al [27] proposed an empirical equation for the perveance.…”

Section: Introductionmentioning

confidence: 99%

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Numerical and theoretical modeling of the sheath upstream of ion optics: sheath structure transition and its effect on the beam divergence

Li¹,

Yuan²,

Yang³

et al. 2021

Plasma Sources Sci. Technol.

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The grasp of the sheath characteristics is fundamental to evaluate the extraction capabilities of ion optics and accommodate the wide application of ion sources. A one-dimensional theoretical model is developed to investigate the sheath upstream of ion optics as well as the matching relation between the ion optics and plasma, by simplifying and decomposing the Poisson's equation at the outer surface and centerline of the grid aperture. The one-dimensional model is validated by 2D3V hybrid simulations which are also applied to visualize the sheath structure and ion beam divergence. With the increase of plasma density, it is found that the upstream sheath will transform gradually into a sheath near the plate electrode at first and then enter the screen aperture with a sheath edge approximately paralleling to the meniscus. Accordingly, the structure of the upstream sheath can be classified into four kinds which correspond to different beam divergence. The structure transition of the upstream sheath reflects the interaction between the extraction field and plasma, and the ion optics is considered to work at the matching point when the plasma is relatively balanced with the extraction field. Around the matching point, a small beam divergence angle can be achieved without the occurrence of over-perveance. Then a matching model is proposed based on the characteristics of the potential distribution at the matching point. It is verified to be effective of the model for quickly analyzing the ion beam divergence characteristics and determining an ideal operating range of the ion optics.

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Section: Simulation Methods and Model Configurationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Numerical and theoretical modeling of the sheath upstream of ion optics: sheath structure transition and its effect on the beam divergence

Li¹,

Yuan²,

Yang³

et al. 2021

Plasma Sources Sci. Technol.

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“…In the design and development of ion thruster, the grid system must be designed and optimized for individual thrusters in that the divergence angle and morphology of the ion beam are important as it directly affects the specific impulse and thrust. It is reported in the previous experimental and theoretical research that the divergent characteristics of the ion beams produced by single and multiaperture accelerator systems are affected by geometric parameters of the grid and operating conditions [8][9][10][11][12]. However, these studies have not analyzed the influence of the metal cover enclosing the engine on the divergence angle of the ion beam.…”

Section: Introductionmentioning

confidence: 99%

Evaluation of Ion Beam Behavior in 50 W Class RF Ion Thruster

Nguyen

Shin

2021

International Journal of Aerospace Engineering

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Phenomenological behavior of ion beam acceleration through the grid system in 50 W class RF ion thruster has been investigated using PIC simulation and evaluated by experimental test using Faraday probe. Beam trajectory for various grid voltages reveals that the metal engine cover of the ion thruster which is needed to seal RF coil around the discharge chamber affects the beam divergence angle. Simulation result shows that the divergence angle increases by 10.52% mainly because of the larger radial electric field in the presence of the metal engine cover. The divergence angle increases as the accelerator grid voltage increases. The current density distribution measured by the Faraday probe shows a bigger divergence angle with the engine cover installed. For the test cases with mass flow rates from 3 sccm to 4 sccm at the RF power of about 50 W, the current density distribution exhibits the 2nd peak at the radial position about 4 cm from the centerline.

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“…We assumed in the calculations, as have others [4,5], that the emitting plasma surface positions itself in such a way that j + is simultaneously emission-limited and space-charge-limited at every point on the surface. In addition, we have assumed that j + is independent of position, an assumption which may or may not be satisfied in practice.…”

mentioning

confidence: 99%

“…If insufficient nuclear fuel or the wrong kind of nuclear fuel is fed into the E-zone, the I-layer current will be reduced giving less trapping; in addition, the radiative cooling of the electrons (and also indirectly of the ions) will be in a direction to quench the nuclear fire. The importance of reaction stability [5] (negative temperature coefficient) to proper sustainment of the reaction against small fluctuations of fuel feed, T, etc., cannot be over-emphasized. Whether one can turn down the applied magnetic field must be evaluated in terms of the requirements of the system.…”

mentioning

confidence: 99%