Numerical observation of preferred directionality in ion ejection from stretched rectilinear ion traps

Krishnaveni, A and Verma, Neeraj Kumar and Menon, AG and Mohanty, Atanu K (2008) Numerical observation of preferred directionality in ion ejection from stretched rectilinear ion traps. In: International Journal of Mass Spectrometry, 275 (1-3). pp. 11-20.

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Abstract

We report on numerical investigations of directionality of ion ejection in stretched rectilinear ion traps (RIT). Three 4-electrode trap geometries have been investigated. In all cases, one pair of electrodes has slits at their center and the other pair has no slits. The studied traps include the RIT-S, in which the mass analyzer electrodes are symmetrically positioned around the central axis; the RIT-X, in which the mass analyzer has a stretch in the direction of the electrodes which have slits (labeled as x-direction); and the RIT-Y, in which the mass analyzer has a stretch in the direction of the electrodes which have no slits (labeled as y-direction). Our analysis has been carried out on two-dimensional (2D) fields at the centre of an infinitely long mass analyzer. The boundary element method (BEM) has been used for field computations. The trajectory of ion motion has been generated using Runge Kutta fourth order integration. Three sets of simulations have been carried out on each of the RIT-S, the RIT-X and the RIT-Y to check for directionality of ion ejection. In the first, we numerically obtain the stability region on the potential $(U_{dc}-V_{rf})$ axes. In the second we generate an escape velocity plot with $U_{dc} = 0$ for different values of $V_{rf}$. In the third, we simulate the mass selective boundary ejection experiment on a single ion. In the symmetric RIT-S, as expected, all three simulations show that there is an equal probability of ion reaching the trap boundary in either of the x- or y-directions. For the stretched traps, however, the results are dramatically different. For the RIT-X, all three simulations suggest that ion destabilization at the stability boundary occurs in the x-direction. Similarly, for the RIT-Y, ions preferentially get destabilized in the y-direction. That is, ions reaching the trap boundary overwhelmingly prefer the stretch direction.

Item Type:	Journal Article
Publication:	International Journal of Mass Spectrometry
Publisher:	Elsevier
Additional Information:	Copyright of this article belongs to Elsevier.
Keywords:	Rectilinear ion trap;Nonlinear ion trap;Stretched geometry;Directionality of ion ejection;Boundary element method (BEM).
Department/Centre:	Division of Physical & Mathematical Sciences > Instrumentation Appiled Physics Division of Interdisciplinary Sciences > Supercomputer Education & Research Centre
Date Deposited:	13 Oct 2008 09:45
Last Modified:	19 Sep 2010 04:50
URI:	http://eprints.iisc.ac.in/id/eprint/15993

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