Design and Simulation of Double-Helix Ion Funnel

The ion guide system, functioning as a pivotal component in mass spectrometers, governs ion regulation and transmission along the ion transfer route, and serves as an important part influencing the performance of mass spectrometry instruments. In this work, a novel double-helix ion funnel (DH-IF) was designed for ion transmission in the rough vacuum region, which combined the advantages of multipole electrodes in symmetry and continuity and stacked-ring ion guides in ion capturing. The electric field properties of DH-IF were investigated using COMSOL Multiphysics 6.0. The results showed that the steep radial pseudopotential distribution of DH-IF is effective in reducing the divergence of ion clouds in rough vacuum region. In addition, the DH-IF improves the axial electric field distributions compared with the conventional stacked-ring ion funnels (IF) benefiting from the continuous symmetric electrode, and sufferes little from the potential traps. Then, the model of ion trajectory simulation in rough vacuum was constructed in SIMION8.1 to assess the impacts of structural parameters (electrode spacing), operational conditions (operating pressure), and radiofrequency (RF) parameters (frequency and amplitude) on ion transmission efficiency. The results showed that DH-IF maintains high transmission efficiency across a broad operating pressure range (200-1 200 Pa) for low-to-medium mass-to-charge ratio (m/z) ions. Under typical operating pressure for rough vacuum ion guides (266.6 Pa), optimal ion transmission efficiency was achieved with a distance between RF⁺ and RF⁻ electrodes of 0.5 mm and RF frequency of 1.5 MHz. Additionally, the influence of RF amplitude on the transmission efficiency of ions ranging from m/z 68 to m/z 1 755 was studied. The results showed that the transmission efficiency of all ions increases rapidly with the increase of the RF voltage amplitude and remains stable after reaching the peak value. It was worth noting that DH-IF improves the efficiency of the simultaneous transferring of low and medium m/z ions compared with IF, which is attributed to its improved electric field distribution. The structure design and transmission performance of DH-IF were elaborated and simulated, hoping to provide some theoretical support for the practical application. This study of DH-IF provides a new idea for the design of ion guides used in rough vacuum region, and the DH-IF is expected to be widely used as an ion import device in MS instruments, which is due to its improved performance and advantages in, e.g., integration and power supply design.