Numerical Investigation of Ion Transport in Under-Expanded Jet Flows

et al. 2004

The transport of free ions through highly under-expanded jet flows of neutral gases and in the presence of applied electric fields is investigated by continuum-based numerical simulations. In particular, numerical results are described that are relevant to ion flows occurring in the interface region of mass spectrometer systems. A five-moment mathematical model and parallel multi-block numerical solution procedure are developed for predicting the ion transport. The model incorporates the effects of ion-neutral collision processes and is used in conjunction with a Navier-Stokes model and flow solver for the neutral gas to examine the key features of the ion motion. The influences of the neutral gas flow, electric field, and flow field geometry on ion mobility are all carefully assessed. Several ions of varying mass and charge are considered, and the relative importance of competing effects (i.e. electric field and ion-neutral collision effects) is discussed. The capability of controlling the charged particle motions through a combination of directed neutral flow and applied electric field is demonstrated for high-speed, hypersonic jet flows.

Section: Axisymmetric Free-jet Flowsupporting

confidence: 62%

“…Equation ( 12) is used here to model the high-speed flow of the neutral gas. The validity of the preceding equations for describing the high-speed neutral jet flows of interest here has been clearly demonstrated in recent studies by the authors [17,18].…”

Section: Navier-stokes Equations For Neutral Gas Flowmentioning

confidence: 52%

Numerical investigation of interface region flows in mass spectrometers: ion transport

Jugroot

Groth

et al. 2004

“…Companion numerical studies of ion transport in the interface regions of mass spectrometer systems have also been carried out recently by the authors. The non-equilibrium transport of ions through the background neutral gas under the influence of a prescribed electric field and subject to ionneutral collision processes have been studied using an extended fluid model [7,8]. As is the case for other technological devices [9,10], the neutral gas is shown to play an important role in dictating the ion dynamics and cannot be neglected.…”

Section: Introductionmentioning

confidence: 99%

Numerical investigation of interface region flows in mass spectrometers: neutral gas transport

Jugroot

Groth

et al. 2004

The supersonic jet flows of neutral gas from atmospheric to near-vacuum conditions in the interface region of mass-spectrometer systems is investigated by continuum-based (fluid) numerical simulations. An enhanced understanding of the neutral gas transport is of paramount importance to fully understand flows in the interface region of mass spectrometers, for it is the neutral dynamics that governs and drives the ions from the high pressure ion source through the interface orifice towards the ion optics and detector subsystems. The key features and structure of the complex neutral gas flow are examined and the influence of large pressure differences imposed across the interface region, orifice geometry, and gas skimmer configuration used for flow control are assessed. The flow structure is shown to be that of a classical under-expanded free jet for 'skimmer-absent' cases and very good agreement between the numerical predictions and empirical and experimental values is demonstrated. For the 'skimmer-present' cases, the shock structure downstream of the orifice and skimmer is identified and fully described and its influences on the flow skimming and focusing processes are discussed.

“…The five-moment model has been used successfully in previous studies of ion transport in MS systems by Jugroot et al [12,13]. It provides 'one-way' coupling between the ion and neutral flows by incorporating the effects of ion-neutral collision processes.…”

Section: Introductionmentioning

confidence: 99%

Coupled gas and ion transport in quadrupole interfaces

Jugroot¹,

Groth²,

et al. 2008

The transport of free ions through highly under-expanded jet flows of neutral gases and in the presence of applied electric fields is investigated by continuum-based (fluid) numerical simulations. In particular, numerical results are described which are relevant to ion flows occurring in quadrupole interfaces of mass spectrometer systems. A five-moment mathematical model and parallel multi-block numerical solution procedure are developed for predicting the ion transport. The model incorporates the effects of ion-neutral collision processes and is used in conjunction with a Navier-Stokes model and flow solver for the neutral gas to examine the key influences controlling the ion motion. The effects of the neutral gas flow, electric fields (both dc and rf) and flow field geometry on ion mobility are carefully assessed. The capability of controlling the charged particle motions through a combination of directed neutral flow and applied electric field is demonstrated for these high-speed, hypersonic, jet flows. The neutral dynamics is shown to have a strong influence on the ion transport whereas the electric field imparts a more gradual effect. The combined effect of the applied (dc and rf) electric field and neutral collision processes with the dilute neutral gas results in a strong tendency for ion focusing towards the axis of symmetry, with the overall efficiency governed by the mass-to-charge ratio.