# Studies on ion back-flow of Time Projection Chamber based on GEM and anode wire grid

## TL;DR

This study explores a hybrid TPC design combining GEM foils and anode wires to reduce ion back-flow while maintaining stable gain, using simulations and experimental validation.

## Contribution

It introduces a novel hybrid chamber design that integrates GEM foils with anode wires, optimizing IBF suppression and gain stability.

## Key findings

- IBF ratio reduced to ~0.58% with the hybrid setup
- Effective gain around 2500 achieved with low-voltage GEMs
- Energy resolution approximately 10%

## Abstract

Gated wires are widely used in Time Projection Chamber (TPC) to avoid ion back-flow (IBF) in the drift volume. The anode wires can provide stable gain at high voltage with a long lifetime. However, switching on and off the gated grid (GG) leads to a dead time and also limit the readout efficiency of the TPC. Gas Electron Multiplier (GEM) foil provides a possibility of continuous readout for TPC, which can suppress IBF efficiently while keeping stable gain. A prototype chamber including two layers of GEM foils and anode wires has been built to combine both advantages from GEM and anode wire. Using Garfield++ and the finite element analysis (FEA) method, simulations of the transmission processes of electrons and ions are performed and results on absorption ratio of ions, gain and IBF ratio are obtained. The optimized parameters from simulation are then applied to the prototype chamber to test the IBF and other performances. Both GEM foils are run at low voltage (255V), while most of the gain is provided by the anode wire. The measurement shows that the IBF ratio can be suppressed to ~0.58% with double-layer GEM foils (staggered) at an effective gain about 2500 with an energy resolution about 10%.