Ion beam trajectories

The mass dispersion coefficient (D ) of a single focusing magnetic sector is proportional to the radius of curvature (r j ) of the ion beam trajectory in the magnetic field. The spatial separation (y) of two similar masses with mean mass (m) and mass difference (Am) is related to the mass dispersion coefficient by ... 

Figure Bl.23.2. (a) Shadow cone of a stationary Pt atom in a 4 keV Ne ion beam, appearing with the overlapping of ion trajectories as a fiinction of the impact parameter. The initial position of the target atom that recoils in the collision is indicated by a solid circle, (b) Plot of the nonnalized ion flux distribution density across the shadow cone in (a). The flux density changes from 0 inside the shadow cone, to much greater than l in the focusing region, converging to 1 away from the shadow cone edge, (c) Blocking cones...

Deflection in a magnetic field of an ion beam consisting of increasing mass-to-chaige ratios, m/z,. .,, m,/z, and split into different trajectories (1-5), respectively. 

Collision of an ion with an inert gas molecule leads to some deflection in the ion trajectory. After several collisions, the ion could have been deflected so much that it no longer reaches the detector. This effect attenuates the ion beam as it passes through the gas cell, leading to loss of instrumental sensitivity. An attenuation of 50 to 70% is acceptable and is not unusual in practice. 

The TOF analyzer provides the full mass spectrum of all the ions in the main ion beam at the time the pulse of electric potential was applied, m/z values being derived from the flight times of the ions along their trajectory in the TOF analyzer. 

The other very important function of the ion optics is to shape the ion beam. Voltages on the various lenses should be set to avoid chromatic aherration, which causes energy-dependent transmission of ions in the instrument, and as a result erroneous lEDs [161, 163]. The correct lens settings have been found by simulations of ion trajectories in the EQP using the simulation program SIMION [329], In addition, an experimental method to find the correct settings has been presented [161, 163]. 

Linear quadmpole Q Continuous ion beam in linear radio frequency quad-rapole field separation due to stability of trajectories... 

The quadrupole analyzer uses oscillating electrical fields to separate ions based on their stable trajectories. The analyzer consists of four parallel poles placed between the ion source and the detector in such a manner that the path of the ion beam travels through the middle. The rods have DC voltages applied to opposite rods to carry the same charge, yielding one set of positive rods and one set of negative rods. All four rods have an oscillating radio frequency (RP) applied to them (Honour, 2003). If the ion mass is too... 

Figure 11. Effect of a 500 gauss cross magnetic field on the trajectories of an ion beam as a function of mass.

The effect of the ion beam current on model predicted ion trajectories [105] is shown in Fig. 3.11. Important inputs for the model are the location and distance over which charge separation occurs to produce a positive ion beam. A charge separation function was assumed (Fig. 3.11a) for the simulation. When space charge effects are not included, a large fraction of the ions pass from the skimmer... 

Figure 11 Simulated Sc+ ion trajectories (a) Ion optic geometry and voltages. Plot shows assumed charge separation function, (b) No space-charge effect included, (c) Total beam current through skimmer of 1 xA (d) Total beam current through skimmer of 1500 xA. (Note that darker trajectories correspond to 1% of the ion beam 99% of the ion beam is lost as indicated by the lighter trajectories.) (From Ref. 105.)...

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