Simulation of Properties of COMPASS Drift-Chamber Prototypes Ran Bi University of Illinois at Urbana-Champaign DNP 2013 24 Oct 2013

Overview New drift chamber (DC5) will be designed and built for COMPASS-II Goal: attain 200 µm position resolution Two prototypes (PTA & PTB) have been built at UIUC Requirements for the charge threshold needed for the DC5 FEE were simulated with GARFIELD and confirmed experimentally with test beam measurements using PTA at DESY.

Steps in GARFIELD Simulations Gas composition High voltage Arrival time distributions Induced signals Position resolution

High Voltage/Gas Mixture Cathode planes: 0 V Field wires: −300 V Sense wires: +1700 V Gas composition: 45% Ar, 50% C2H6, 5% CF4 Equipotential lines Electron drift velocity vs. Electric field

Arrival Time Distribution For each electron from a fixed track Arrival time distribution Sense wire

Position Resolution Use RMS of the arrival time distribution of the nth electron multiplied with vDrift to estimate the position resolution. Need to detect the 5th electron or earlier to reach 200 µm

Induced Signals vs Charge Sensitivity of FEE Induced signal is integrated till the arrival time of the 5th electron 4 fC threshold is required to achieve 200 µm position resolution

Test of PTA with CMAD-based FEM in test beam at DESY

Garfield vs DESY Test Beam Results with DC Prototype A: R-T Relation DD R – T relation from Garfield PTA: scatter plot Garfield: solid line

DESY Test Beam Results: Position Resolution vs Position in Drift Cell Position resolution vs. location of electron beam track between sense and field wires 200 µm Drift Time [ns]

Summary Position resolution of 200 µm can be achieved with a FEE that has a 4 fC threshold Results from DESY test beam agree with GARFIELD simulations