The Precision Trap

Precision Trap

The second trap is a precision Penning trap used as a mass spectrometer. The ion motion is driven by an azimuthal rf-field of frequency omegarf . If omegarf = omegac = q/m * B, an increase of the amplitude of the cyclotron motion of the stored ions is achieved. This change in the ion motion is accompanied by an increase in radial kinetic energy in the radial plane, as well as of the magnetic moment of the ion orbit. The increase in energy at resonance is detected by a time-of-flight technique. After excitation, the ions are ejected from the trap and allowed to drift through the inhomogeneous fringe field of the magnet to an ion detector. The inhomogeneous magnetic field gives rise to an axial force due to the orbital magnetic moment, resulting in an increase in the axial momentum of the ion. Ions in resonance with the rf-field therefore reach the detector faster than those off resonance. Hence, the determination of the time of flight as a function of the frequency omegarf of the rf-field leads to a resonance, as shown in the figure on the right for the example of 134Nd.

The precision trap. 
(Visible is the vessel for the liquid nitrogen and helium cooling the magnet coils, the channel plate mounting on top of the setup, the electrical switchox...) 

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The precision trap with scale. 
(Visible are the copper electrodes, the isolating marcor elements...)