Progress In NEXT Ion Optics Modeling

Emhoff, Jerold; Boyd, Iain D.

doi:10.2514/6.2004-3786

Cited by 9 publications

(4 citation statements)

References 6 publications

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“…The nature of plasma flow in ion optics renders particle-in-cell (PIC) [1] based models, which simulate a collisionless plasma by solving plasma particle trajectories, space charge, and the electric field self-consistently as the most appropriate approach for ion optics modeling. Numerous PIC-based ion optics simulation codes have been developed (see, for example, [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] and references therein). Whereas earlier studies have focused on the physics of a single beamlet, recent studies have also begun to use ion optics models to predict the behavior of entire ion optics.…”

mentioning

confidence: 99%

Whole Ion Optics Gridlet Simulations Using a Hybrid-Grid Immersed-Finite-Element Particle-in-Cell Code

Kafafy

Wang

2007

Journal of Propulsion and Power

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A new model is developed for three-dimensional global simulations of plasma flow in an entire subscale ion optics. This model explicitly includes apertures located near the edge of the grid surface and fully accounts for the effects of multiple ion beamlets and geometric asymmetry. This model is based on a new algorithm, the streamline hybrid-grid immersed-finite-element particle-in-cell. This algorithm is capable of achieving the same accuracy as an unstructured body-fit mesh-based particle-in-cell with a faster computational speed. Simulation results are presented to understand the plasma sheath upstream of the screen grid, direct impingement of beam ions, the crossover limit, the perveance limit, and the electron backstreaming onset. Nomenclature e = electron charge F = force vector I = current k = Boltzmann constant m = mass q = charge T = temperature t = time v = velocity vector x = position vector = IFE mesh stretching parameter 0 = electric permittivity of vacuum D = Debye length = charge density = electrostatic potential Subscripts a = accelerator grid b= beamlet cc = center-to-center e = electron g = gap between ion optics grids i = ion, or impingement s = screen grid w = grid wall 0 = upstream plasma condition 1 = downstream plasma condition

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mentioning

confidence: 99%

Whole Ion Optics Gridlet Simulations Using a Hybrid-Grid Immersed-Finite-Element Particle-in-Cell Code

Kafafy

Wang

2007

Journal of Propulsion and Power

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“…The model presented in this work is an axisymmetric simulation of a single ion optics aperture. This model has been under development for several years, 9 and has previously been applied to both the NSTAR 10 and NEXT [11][12][13] ion engines. The simulation is applied to NEXT in this work, with the goal of comparing simulated performance and erosion to the experimentally measured data.…”

Section: Introductionmentioning

confidence: 99%

NEXT Ion Optics Modeling of Total Thruster Performance

Emhoff¹,

Boyd²

2005

41st AIAA/ASME/SAE/ASEE Joint Propulsion Conference &Amp;amp; Exhibit

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An axisymmetric ion optics model is applied to the NEXT ion engine. The model is used to simulate the performance of the entire thruster by modeling several apertures at varying radii on the thruster face and integrating the results. The integrated results are compared to experimentally measured data for the NEXT thruster, showing good agreement in most areas. The primary area of discrepancy is in the accelerator grid current, although erosion results suggest that the measured current is unaccountably high. The model is also used to estimate the life of the thruster before the onset of electron backstreaming. Three separate methods are applied, and each predicts thruster failure after approximately 40,000 hours of operation, or 845 kg of xenon throughput.

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“…Previously, cyclic life testing was performed on the neutralizer heater design for the International Space Station (ISS) Plasma Contactor hollow cathode assembly. 39,40 These heaters were validated to have a B 10 life of approximately 6700 cycles (this corresponds to the cycles at which 10 % of the population of heaters would fail). The NSTAR heaters were the same design and from the same manufacturer as the tested hollow cathode assembly heaters, so cyclic testing was not needed to demonstrate that they met the NSTAR requirements.…”

Section: Swaged Heater Cyclic Lifementioning

confidence: 99%

“…Several different computer software models, such as CEX3D 44 , CEX2D 44 , ffx 11 , erode 10 , and MICHELLE 45 , have been used to examine NEXT accelerator grid erosion. Table 3 shows the pit and groove penetration of the NEXT accelerator grid based on predictions from the codes and an extrapolation of the NEXT LDT and 2000 hour wear test results.…”

Section: Previous Computer Modelsmentioning

confidence: 99%

Lifetime Assessment of the NEXT Ion Thruster

VanNoord

2007

43rd AIAA/ASME/SAE/ASEE Joint Propulsion Conference &Amp;amp; Exhibit

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Ion thrusters are low thrust, high specific impulse devices with required operational lifetimes on the order of 10,000-100,000 hours. The NEXT ion thruster is the latest generation of ion thrusters under development. The NEXT ion thruster currently has a qualification level propellant throughput requirement of 450 kg of xenon, which corresponds to roughly 22,000 hours of operation at the highest throttling point. Currently, a NEXT engineering model ion thruster with prototype model ion optics is undergoing a long duration test to determine wear characteristics and establish propellant throughput capability. The NEXT thruster includes many improvements over previous generations of ion thrusters, but two of its component improvements have a larger effect on thruster lifetime. These include the ion optics with tighter tolerances, a masked region and better gap control, and the discharge cathode keeper material change to graphite. Data from the NEXT 2000 hour wear test, the NEXT long duration test, and further analysis is used to determine the expected lifetime of the NEXT ion thruster. This paper will review the predictions for all of the anticipated failure mechanisms. The mechanisms will include wear of the ion optics and cathode's orifice plate and keeper from the plasma, depletion of low work function material in each cathode's insert, and spalling of material in the discharge chamber leading to arcing. Based on the analysis of the NEXT ion thruster, the first failure mode for operation above a specific impulse of 2000 s is expected to be the structural failure of the ion optics at 750 kg of propellant throughput, 1.7 times the qualification requirement. An assessment based on mission analyses for operation below a specific impulse of 2000 s indicates that the NEXT thruster is capable of double the propellant throughput required by these missions.

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Progress In NEXT Ion Optics Modeling

Cited by 9 publications

References 6 publications

Whole Ion Optics Gridlet Simulations Using a Hybrid-Grid Immersed-Finite-Element Particle-in-Cell Code

Whole Ion Optics Gridlet Simulations Using a Hybrid-Grid Immersed-Finite-Element Particle-in-Cell Code

NEXT Ion Optics Modeling of Total Thruster Performance

Lifetime Assessment of the NEXT Ion Thruster

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