We utilize an interleaved reference method to achieve extreme control over system drift. This is possible due to the use of our novel “flat trap” geometry in conjunction with a pair of linear Paul traps. Reference and unknown ions are separately accumulated in linear Paul traps on either side of the flat trap. Reference ions are transferred to the flat trap, cooled, and ejected orthogonally to enter the MRTOF. While the reference ions are being analzed in the MRTOF, the unknown ions are transferred to the flat trap for cooling; they are ejected from the flat trap and enter the MRTOF soon after the analysis of the reference ions has been completed.
Flat Trap
The “flat trap” is a linear Paul trap with a special geometry to provide maximum flexibility. The trap is built from a pair of printed circuit boards. Each board has three segmented stripes as seen in the image at left. By applying a radio-frequency signal between the inner stripe and the outer stripe, ions can be radially confined. Applying proper DC voltages to each segment of the inner strip provides axial confinement. Additionally, a buffer gas of helium at ~10-3 mbar causes the ions to lose energy via collisions, eventually coalescing in the center — a process we refer to as “cooling". The central electrodes of each board have a small hole, ~0.8 mm diameter, above which the cooled ions will accumulate.
In a traditional linear Paul trap, after cooling the ions the DC voltages used for axial confinement would be quickly changed to axially extract the ions. While this can be done with the flat trap, as well, it produces ion pulses typically with microsecond pulse duration and large initial optical abberations. The advantage of the flat trap geometry is that it allows orthogonal extraction of the ions. By leaving the DC voltages largely unaltered and changing only the voltages of the top and bottom central electrode, a dipole field can be produced at the center. The ions then exit through the tiny hole as nanosecond pulses with minimal optical abberations.