The inset shows the most important stability region where x and y stability bounds overlap, resulting in a small triangular stability region in a and q space. In the absence of quadrupolar DC, which is used in quadrupolar mass filters (QMFs) but not used in linear ion traps, a is always equal to 0; thus, ion stability is explained only by q. Here, ions are stable if their q is between 0 and 0.908. Within this region (0 ≤ q ≤ 0.908) ions will be contained within the trap without colliding with electrodes or escaping.