Measurement of the Ion Blocking by the Passive Bipolar Grid

The ion backflow (IBF) is the main limiting factor for operating time projection chambers (TPCs) at high event rates. A significant effort is invested by many experimental groups to solve this problem. This article explores a solution based on operating a passive bipolar wire grid. In the presence of the magnetic field, the grid more effectively attenuates the ion current than the electron current going through it. Transparencies of the grid to electrons and ions are measured for different gas mixtures and magnitudes of the magnetic field. The results suggest that in a sufficiently strong magnetic field, the bipolar wire grid can be used as an effective and independent device to suppress the IBF in TPCs.