Repeller plate

Fig 4 is a diagram of an electron impact 1 source. The sample vapor is admitted into the ion source thru the slit in the back of the chamber and it passes thru a collimated electron beam b . On impact of electrons with the neutral molecules, positive ions (to a small extent negative ions) are produced. A small positive potential ( repeller potential ) between the back wall V of the ion source and first accelerator plate d , expels tile positive ions toward the accelerating region and at the same time attracts the negative ions which are then discharged at repeller plate c . The positive ions are accelerated by the potential difference applied to plates d and e , pass thru the exit slit T and continue toward the collector... 

To prevent withdrawal of the ions thus produced by penetration of the main accelerating field, either a small positive bias is applied to plate 6 or alternatively (31) the exit slit from the ionization chamber is covered by a transparent wire mesh. The ions are withdrawn from the ionization chamber by a voltage pulse of proper sign applied either to the repeller plate (plate 3) or to the ion withdrawal plate (plate 6). 

The ions are pushed out of the electron beam, toward the central aperture of the source electrodes by a positively charged repeller plate. They accelerate through the source by a potential gradient applied to the source electrodes, and they are then focused toward the mass analyzer. Typically a quadrupole has been used to separate the ions, although more recently time of flight has been investigated (Letarte et al.,2004). 

A small positive potential on the repeller plate of the ion source pushes ions toward the analyzer tube, and a small potential on the ion focus plates creates a focused beam. High voltage ( 1 000-10 000 V) between the ion acceleration plates imparts a high velocity to ions as they are expelled from the bottom of the ion gun. 

Fig. 9. Schematic diagram of the free jet flow reactor used by Mark Smith and co-workers for very low temperature reaction kinetic measurements [58]. The jet originates from a pulsed beam valve 1, and ions are produced by REMPI using a focussed pulsed laser. The reaction zone is bounded by a repeller plate 2 and an endplate 3 ions are propelled, by a pulsed voltage on the repeller, towards a sampling aperture in the endplate which leads to a TOF-MS 4...

Fig. 8. Images of LEI ions and electrons, obtained by taking the LEI signal from a thin rod translated across the front of the normal collecting plate at the indicated high voltages 49). The experiment apparatus is shown in the inset 1 high voltage repelling plate, 2 laser beam, 3 flame reaction zone, 4 burner head, 5 low voltage electrode plate, 6 vertically movable signal pick-off wire...

Most of the sample molecules are not ionized at all but are continuously drawn off by vacuum pumps that are connected to the ionization chamber. Some of the molecules are converted to negative ions through the absorption of electrons. The repeller plate absorbs these negative ions. A small proportion of the positive ions that are formed may have a charge greater than one (a loss of more than one electron). These are accelerated in the same way as the singly charged positive ions. 

The FC collects the ion charge for direct current measurement of the ion beam. The FC is essentially a metal bucket that collects the ion beam. Figure 17.10 shows a schematic diagram of a Faraday Cup with associated repeller plates and slits. The ion beam enters from the left and is captured in the Faraday cup on the right. The biased plate to the left of the cup has a negative voltage ( 100 V or less) to repel secondary electrons back into the cup. 

Ions are ejected from the ion source and focused into a beam by a positive potential on a repeller plate positioned at the back of the ion source and a high potential, in the order of 5-10 kV at the front of the source. The beam then enters the analyzer section of the instrument for mass separation to form the spectrum. As the molecules are essentially ionized in the vapor phase, they must be stable at the temperatures needed to vaporize them. Many molecules do not fulfill these requirements but can be stabilized and made more volatile by derivatization. However, even with derivatization and heated ion sources, the technique is only applicable to molecules with masses less than 1000. 

The pulsed technique employed by Henchman et uses an ordinary source in which a short electron pulse provides reactant ions. Another short pulse applied to a repeller plate accelerates these to a definite energy (about 1 eV). Before emerging from the exit slit of the chamber, the reactant ions may collide with un-ionized gas to give product ions. The forward velocity of both reactant and product ions is measured by applying a variably delayed gating pulse to a deflection electrode outside of the ionization chamber. A more recent version of the apparatus incorporates separate ion production and reaction chambers, as well as a stopping potential analyzer. ... 

Figure 2.21 Schematic diagram of the orthogonal acceleration ICP-TOF-MS system. RP, repeller plate ER, extraction region AR, acceleration region EG, extraction grid d, extraction region width v, beam velocity FE, flight tube entrance grid (size relations not correct)...

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