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Ion Motion Through an RFQ Varying the q-value Varying the Buffer Gas Pressure The q-value We define the q-value for an ion inside an RFQ device to be:. Where: e = the charge on the ion V pp = the peak-to-peak voltage applied to the RFQ m = the mass of the ion - PowerPoint PPT Presentation
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Ion Motion Through an RFQVarying the q-valueVarying the Buffer Gas Pressure The q-valueWe define the q-value for an ion inside an RFQ device to be:
220
2
mr
eVq pp
Where:e = the charge on the ionVpp = the peak-to-peak voltage applied to the RFQm = the mass of the ionr0 = the radius of the RFQΩ = the angular frequency of the applied RF-fieldThe q-value governs the stability of the ions paths in the RFQ. In an RFQ the ion motion is stable for q ≤ 0.908. For q-values higher than 0.908 the ion motion is unstable and hence the ions are not trapped.
The Effect of Varying the q-value
q=0.1
q=0.3
q=0.5
q=0.7
q=1
Buffer Gas Cooling
An ion beam can be cooled via collisions with an inert buffer gas however such collisions cause the beam to diverge. The RFQ provides a force that pushes the ions onto its Z-axis hence an ion beam can be cooled inside an RFQ via collisions with a buffer gas without the beam diverging. By varying the buffer gas pressure one can control the time it takes for cooling to take place.
The Effect of Varying the Buffer Gas Pressure
q=0.4_p=1^-2
q=0.4_p=1^-3
q=0.4_p=2.5^-2
q=0.4_p=5^-2
q=0.4_p=5^-3
