Wien velocity filter

The Wien velocity filter possesses a high sensitivity and allows analysis over a mass range (using a high accelerating voltage V), but with increasing mass the mass resolution decreases.3 For his discovery Wien was honoured with the Nobel Prize in 1911. 

Figure 1.4 Schematic of a Wien velocity filter with EB configuration combination of electric ( ) and magnetic ( ) field (Wien, 1898). (C. Brunnee, Int. ). Mass. Spectrom. Ion Proc. 76, 125 (1987). Reproduced by permission of Elsevier.)...

Schnitzer and Anbar s experiments are rather similar to those of Baumann, Heinicke, Kaiser and Bethge Both employed plasma ion sources that employed by Schnitzer and Anbar was a hollow cathode duoplasmatron. Also, both used einzel lenses and momentum/charge analysis. But the different lifetimes of the doubly-charged negative ions studied dictated somewhat different analyses. Baumann, et al. used an electric deflection analysis after the magnetic sector, as already seen, whereas Schnitzer and Anbar employed a Wien velocity filter and einzel lens voltage variation prior to the magnetic sector. 

Extraction and acceleration of the negative ions from the duoplasmatron was accomplished with voltages of 5 to 15 kV. After passing through the einzel lens, the ions encounter a 30 cm Wien velocity filter. The ExB field of this filter allows analysis based only on the ion velocity according to... 

The trajectory of ions passing through the Wien velocity filter is shown in Fig. 54.3. Magnetic Analyzer... 

Wien analyzer. A velocity filter with crossed homogeneous electric and magnetic fields for transmitting only ions of a fixed velocity. 

A filter that combines both a magnetic and electric field is the so-called Wien filter (or velocity filter). In this case, charged ions pass through a region characterized by uniform magnetic and electric fields at right angles to each other and to the direction of incident ions only those particles for which the module of the Lorentz... 

In this case, the trajectory is exactly a straight line. An arrangement of crossed fields, with a pair of colinear apertures allowing only line-of-sight path, will therefore act as a filter (first demonstrated in 1898 by Wien) for ions with the velocity given above. If the exit aperture in a Wien filter is replaced with a detector array, ions will be dispersed across the array so that the device acts as a mass spectrograph. In this case, the mass resolution is... 

A single-beam technique with Wien filter velocity analysis and quad-rupole filter mass analysis of the products was used by Fink and King in experiments in the energy region from 5 to 30 eV. Details of this machine have not been published. 

As the ions collide with the gas molecules in the central stripper canal , the molecular ions (such as CH2 and CH) are broken up. The carbon atoms are stripped of three or four electrons making them into C + or C + ions, while the C ions are stripped of four electrons making them into C + ions. These are then accelerated down the second half of the tandem accelerator reaching energies of about 8 MeV. The second magnet selects ions with the momentum expected of C ions and a Wien filter checks that their velocity is also correct. 

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