  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%.
