Abstract
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.
Highlights
T HE time projection chambers (TPCs) are introduced by Nygren [1] and have been successfully used in different particle physics experiments [2]–[8]
Analogous effects would be present in a real detector in which Et coupled to the TPC amplification plane below the bipolar gating grid (BPG) would extract ions into the drift volume of the detector
When the BPG is at V = 0 for all values of the magnetic field Teg ≈ 0.95 and Tig ≈ 0.67, which is defined by the choice of Ed/Et
Summary
T HE time projection chambers (TPCs) are introduced by Nygren [1] and have been successfully used in different particle physics experiments [2]–[8]. TPCs have a number of features that make them an attractive technological choice for detectors in high-energy and nuclear physics experiments Due to their excellent capability to reconstruct 3-D topology of charged particles produced in interactions, TPCs are widely used in experiments where the measurement of a multiparticle final state is required. All TPCs built by the large-particle experiments till date used the BPG in a synchronous mode, passive mode was considered for the detectors in the magnetic fields above 1 T [7], [8]. The principle of the BPG operation in a passive mode is based on the effect that in the presence of the magnetic and electric fields, the direction of the electron drift has a component along the vector product of the two fields. TPCs operated in a strong magnetic field, for example, in the sPHENIX TPC [27], [28]
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