High precision gaseous detectors such as Time Projection Chambers (TPC) are widely used in high energy physics for many years. Recent progress in electronics allows operating TPC readout in a continues mode, significantly increasing TPC readout capability. Further increase in the TPC data taking rates is impeded by the space charge formed in the sensitive volume of the TPC which distorts the electric field uniformity. The main contribution to the space charge is generated by the TPC amplification elements emitting gas ions back into the detector volume. To resolve this problem, a significant effort is undertaken by several large collaborations, utilizing the amplification devices themselves as ion filters.

A new opportunity opens up for the sPHENIX experiment operating TPC in the magnetic field of 1.4 T. A combination of a strong magnetic field and electric fields makes it possible to construct a static grid with different transparencies to primary electrons and back-flowing positive ions. This well-known effect is described in the detector text-book published back in ‘90 [1], however, it has not been implemented in any real detector. In this talk, I will present results showing that the bi-polar grid operated at a constant voltage can have a practical effect on reducing the space-charge problem of a real TPC. Results will be presented for several gas mixtures and compared to the Monte Carlo simulations.

[1] Walter Blum, Werner Riegler, and Luigi Rolandi. “Particle detection with drift chambers”; 2nd ed. Berlin: Springer, 2008. doi: 10.1007/978-3-540-76684-1. url: https://cds.cern.ch/record/681105920