The correct and incorrect generation of a cosine distribution of scattered particles for Monte-Carlo modelling of vacuum systems

Greenwood, J. C.

doi:10.1016/s0042-207x(02)00173-2

Cited by 117 publications

(64 citation statements)

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“…We shifted the distribution in velocity space by the spacecraft velocity vector, and scaled it by velocity, i.e., f (υ) → υf (υ) such that particles are initialized according to the arrival rate at the aperture (Greenwood 2002). By contrast we subdivided the vent aperture into 20 flat sub-planes to approximate its curved surface, evaluating the number of molecules and the velocity vector distributions for each individual plane according to the portion υf (υ) within the velocity space hemisphere seen by that plane.…”

Section: Appendix F: Monte Carlo Modelingmentioning

confidence: 99%

A Revised Sensitivity Model for Cassini INMS: Results at Titan

et al. 2015

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Cassini Ion Neutral Mass Spectrometer (INMS) measurements from roughly a hundred Titan encounters over the Cassini mission yield neutral and ion densities systematically lower, by factors approximately 2 to 3, than estimates from several other spacecraft systems, including the Attitude and Articulation Control System, and Navigation system. In this paper we present a new INMS instrument sensitivity model, obtained by re-analyzing (1) the capture and transmission of neutral gas through the instrument, and (2) the detector gain reduction during pre-launch testing. By correcting for an under-estimation of gas leakage out of the instrument into space by the original calibration model, and adjusting for the gain change, the new model brings INMS densities into much closer agreement with the other Cassini systems. Accordingly, the INMS ion densities are revised upward by a constant detector sensitivity correction factor of 1.55 ± 21 %, while the neutral sensitivities have a complex instrument pointing direction dependence, due (mostly) to the effect of the INMS vent and antechamber-to-closed source tube. In the special case of on-ram pointing the neutral densities are revised upward by a constant factor of 2.2 ± 23 %. The corrected neutral and ion sensitivities given here are applicable to all previously published INMS results at Titan, Enceladus and elsewhere in the Saturn system. The new model gives reliable densities at high ram angles, in some cases above 90 degrees, thereby expanding the list of Titan flybys from which INMS densities may be extracted. We apply the model to obtain accurate densities from several off-ram Titan flybys which gave unusual neutral density vs. altitude profiles, or unreasonably high densities, with the original calibration.

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Section: Appendix F: Monte Carlo Modelingmentioning

confidence: 99%

A Revised Sensitivity Model for Cassini INMS: Results at Titan

et al. 2015

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“…Generally, the scattered atom has an energy that depends on the charge of the impinging ion, the plasma potential, the wall material, and other factors; at this moment we neglect all these effects and randomly pick the energy from a Maxwell-Boltzmann distribution with a temperature of 1 eV. The angular distribution of the neutralized particle is assumed to be given by a cosine law [13]. When the neutralized fast atom hits the wall again it loses part of its energy.…”

Section: Code Descriptionmentioning

confidence: 99%

Three-dimensional simulations of ion dynamics in the plasma of an electron cyclotron resonance ion source

Миронов

Beijers

2009

Phys. Rev. ST Accel. Beams

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The ion production in an electron cyclotron resonance ion source (ECRIS) is modeled using a particlein-cell Monte-Carlo-collision code in a three-dimensional geometry. Only the heavy particles (ions and atoms) are tracked, while the electrons are represented using a Maxwell-Boltzmann energy distribution with the electron density determined from the requirement of quasineutrality, and the electron temperature considered as a free parameter. It is found that experimentally observed features of ECRIS plasma are closely reproduced by the code, including the charge-state distributions of extracted ion beams and sputtering patterns inside the source. The isotope anomaly is observed for the mixture of 20 Ne þ 22 Ne isotopes, and a possible explanation is proposed. Finally, the wall-coating effect is treated by modeling the neutralization of ions impinging on the walls of the plasma chamber.

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“…Nevertheless, the implementation of the formula can sometimes be cumbersome and susceptible to mistakes [22]. Additionally, the cosine law is not easily includable into the finite difference method in this form, but an alternative representation of this law presented below will allow for such an integration.…”

Section: Theory For Modeling Knudsen Flowmentioning

confidence: 99%

An alternative procedure for modeling of Knudsen flow and surface diffusion

Argönül¹,

Keil²

2008

Per. Pol. Chem. Eng.

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An alternative procedure for the calculation of impingement rate distribution and simultaneously the transmission probability in pores under Knudsen diffusion conditions is introduced. It is based on a combination of the finite difference method and a projection approach. Pore entrance and exit effects, and the influence of the pore length on diffusive fluxes are investigated. Later on, it is applied for a simultaneous Knudsen and surface flow system. In the model, the equation system is built without the independent flow and adsorption-desorption equilibrium assumptions. For the conditions investigated, the results indicate that if the surface flow rate is substantial, the independent flow and adsorption equilibrium assumptions become improper estimates for the behaviour of the system. The surface and gas flow rates, the impingement rate distribution and the surface coverage behave much more complex than the characteristics found with such assumptions. KeywordsKnudsen flow · surface diffusion · equilibrium assumption · cylindrical pore · projection approach Acknowledgement One of the authors would like to thank to Mr. Erkan Aksoy and Mr. Denis Chaykin for their comments concerning mathematical calculations.

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The correct and incorrect generation of a cosine distribution of scattered particles for Monte-Carlo modelling of vacuum systems

Cited by 117 publications

References 1 publication

A Revised Sensitivity Model for Cassini INMS: Results at Titan

A Revised Sensitivity Model for Cassini INMS: Results at Titan

Three-dimensional simulations of ion dynamics in the plasma of an electron cyclotron resonance ion source

An alternative procedure for modeling of Knudsen flow and surface diffusion

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