Equilibrium ion distribution modeling in RF ion traps and guides with regard to Coulomb effects

Grinfeld, Dmitry; Kopaev, I A; Makarov, Alexander; Monastyrskiy, Mikhail

doi:10.1016/j.nima.2010.12.168

Cited by 16 publications

(15 citation statements)

References 7 publications

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“…it is estimated as 80 million ions for this setup [7][8][9][10]. As expected, we observed very small deviation in the limits, the average radius at 600 μs in the simulation with 100,000 ions and that of 5000 ions obtained by the explicit method from our previous study.…”

Section: Simulation #2: Quadrupole Ion Storage Devicesupporting

confidence: 82%

Application of Parallel Hybrid Algorithm in Massively Parallel GPGPU—The Improved Effective and Efficient Method for Calculating Coulombic Interactions in Simulations of Many Ions with SIMION

Saito

Koizumi

2012

J. Am. Soc. Mass Spectrom.

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In our previous study, we introduced a new hybrid approach to effectively approximate the total force on each ion during a trajectory calculation in mass spectrometry device simulations, and the algorithm worked successfully with SIMION. We took one step further and applied the method in massively parallel general-purpose computing with GPU (GPGPU) to test its performance in simulations with thousands to over a million ions. We took extra care to minimize the barrier synchronization and data transfer between the host (CPU) and the device (GPU) memory, and took full advantage of the latency hiding. Parallel codes were written in CUDA C++ and implemented to SIMION via the user-defined Lua program. In this study, we tested the parallel hybrid algorithm with a couple of basic models and analyzed the performance by comparing it to that of the original, fully-explicit method written in serial code. The Coulomb explosion simulation with 128,000 ions was completed in 309 s, over 700 times faster than the 63 h taken by the original explicit method in which we evaluated two-body Coulomb interactions explicitly on one ion with each of all the other ions. The simulation of 1,024,000 ions was completed in 2650 s. In another example, we applied the hybrid method on a simulation of ions in a simple quadrupole ion storage model with 100,000 ions, and it only took less than 10 d. Based on our estimate, the same simulation is expected to take 5-7 y by the explicit method in serial code.

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Section: Simulation #2: Quadrupole Ion Storage Devicesupporting

confidence: 82%

Application of Parallel Hybrid Algorithm in Massively Parallel GPGPU—The Improved Effective and Efficient Method for Calculating Coulombic Interactions in Simulations of Many Ions with SIMION

Saito

Koizumi

2012

J. Am. Soc. Mass Spectrom.

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“…The rest of the trapped ions would form an ion cloud with an ion spatial distribution in both x-and y-directions following the Boltzmann distribution under thermal equilibrium [9,16,41,42]. Therefore, excited ions would penetrate through the ion cloud many times before ejection, and the Coulombic force (or relative distance) between the ion cloud and an excited ion changes with time or the momentary position of the excited ion [10,17,19].…”

Section: Resultsmentioning

confidence: 99%

Reducing Space Charge Effects in a Linear Ion Trap by Rhombic Ion Excitation and Ejection

Zhang¹,

Wang²,

Hu³

et al. 2016

J. Am. Soc. Mass Spectrom.

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Abstract. Space charge effects play important roles in ion trap operations, which typically limit the ion trapping capacity, dynamic range, mass accuracy, and resolving power of a quadrupole ion trap. In this study, a rhombic ion excitation and ejection method was proposed to minimize space charge effects in a linear ion trap. Instead of applying a single dipolar AC excitation signal, two dipolar AC excitation signals with the same frequency and amplitude but 90°phase difference were applied in the xand y-directions of the linear ion trap, respectively. As a result, mass selective excited ions would circle around the ion cloud located at the center of the ion trap, rather than go through the ion cloud. In this work, excited ions were then axially ejected and detected, but this rhombic ion excitation method could also be applied to linear ion traps with ion radial ejection capabilities. Experiments show that space charge induced mass resolution degradation and mass shift could be alleviated with this method. For the experimental conditions in this work, space charge induced mass shift could be decreased by~50%, and the mass resolving power could be improved by~2 times at the same time.

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“…The low‐density cases contrast with the situation at much higher ion densities (ca. 4 × 10 8 cm –3 ) where the effective potential is almost completely counteracted by the space charge field, to give a constant charge density with ions of a single m/z value or rings of ions of different m/z values with a mixture of ions …”

Section: Methodsmentioning

confidence: 99%

“…If large numbers of ions are trapped, ca. 10 8 cm –3 , so that the trapping potential is completely countered by space charge, it is necessary to consider (i) boundary conditions for the potential at the electrodes, (ii) image charges of the cloud in the electrodes, (iii) ion‐neutral collisions in the trap, and (iv) a self‐consistent space charge formulation . However, in this work, we consider the case where mass shifts are small (ca.…”

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confidence: 99%

Trajectory calculations of space‐charge‐induced mass shifts in a linear quadrupole ion trap

Douglas

Konenkov

2012

Rapid Comm Mass Spectrometry

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RATIONALE:If too many ions are stored in a linear quadrupole ion trap, space charge causes the oscillation frequencies to decrease. Ions therefore appear at higher apparent mass-to-charge ratios in a mass spectrum. To further understand this process, we have used trajectory calculations of ions to determine mass shifts. METHODS: Two models of the ion cloud are used. The first assumes that the acceptance of the quadrupole is uniformly filled with ions. The second assumes that the ions have a thermal distribution trapped in the effective potential. Both give analytical descriptions of the field from space charge. Ion trajectories are calculated with and without space charge. Oscillation frequencies are determined with a Fourier transform. Shifts in oscillation frequency with space charge are then used to calculate mass shifts. RESULTS: Both ion cloud models give similar results. More diffuse ion clouds or ion clouds that have higher temperatures produce lower electric fields near the center of the trap and hence lower mass shifts. Space charge produces a nonlinear field. As a result, the discrete resonant frequencies of ions in a pure quadrupole field become distributions of frequencies.Comparisons with experiments show agreement for reasonable values of the parameters of the two ion cloud models. CONCLUSIONS: This relatively simple method for calculating the effects of space charge shows (i) that the spread of oscillation frequencies reduces mass resolution with axial ejection and (ii) that mass shifts are reduced with ion clouds with greater spatial extents or higher ion temperatures. Copyright © 2012 John Wiley & Sons, Ltd.Linear quadrupole ion traps are finding increasing applications in mass spectrometry, either combined with other mass spectrometers such as 3D trap, time-of-flight, or ion cyclotron resonance (ICR) mass analyzers to improve duty cycle, [1] or used as stand-alone mass analyzers. [2,3] In a linear quadrupole ion trap ions are confined radially by a potential given by:where x and y are Cartesian coordinates, r 0 , the field radius, is the distance from the center of the trap to an electrode, U and V rf are the amplitudes of the dc and radio-frequency (rf) voltages, respectively, applied between an electrode and ground, and Ω = 2pf is the angular frequency of the rf voltage. Ions are confined axially by stopping potentials applied to electrodes at the ends of the quadrupole. The motion of an ion is described in terms of the Mathieu parameters:where z is the number of charges on an ion, e is the magnitude of the electron charge, and m is the ion mass. If ions are confined at q ≤ 0.4, ion motion can be described approximately as motion in the effective potential V eff given by:where the well depth D is given by:Ions oscillate in the quadrupole potential with angular frequencies given by:where n = 0, AE1, AE2. . .. and b is a function of the parameters a and q. For mass analysis, ions are excited with an auxiliary dipole voltage at an oscillation frequency corresponding to a high q value. The trappi...

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Equilibrium ion distribution modeling in RF ion traps and guides with regard to Coulomb effects

Cited by 16 publications

References 7 publications

Application of Parallel Hybrid Algorithm in Massively Parallel GPGPU—The Improved Effective and Efficient Method for Calculating Coulombic Interactions in Simulations of Many Ions with SIMION

Application of Parallel Hybrid Algorithm in Massively Parallel GPGPU—The Improved Effective and Efficient Method for Calculating Coulombic Interactions in Simulations of Many Ions with SIMION

Reducing Space Charge Effects in a Linear Ion Trap by Rhombic Ion Excitation and Ejection

Trajectory calculations of space‐charge‐induced mass shifts in a linear quadrupole ion trap

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