Detectors for High Energy and Nuclear Physics Experiments

Time Projection Chambers (TPC) with Gas Electron Multipliers (GEM)

New instruments using recent advances in technology and gas physics are being studied for proposed upgrades of PHENIX and STAR experiments. The encouraging results from research and development that have been performed with GEM have led to its choice as the electron multiplication stage in micro-TPCs under development for two separate projects, one with the RHIC upgrade effort, and one with the LEGS experiment at NSLS.

The LEGS TPC is expected to be completed in 2004. It is likely to be the first GEM based TPC for an experiment. The key specifications are:

• Designed for low rate, low multiplicity environment: single sample per channel per trigger
• TPC Active Volume: Inner diameter ~9cm; Outer diameter ~35cm; Drift Length: 50cm
• Double GEM amplification, gas gain <1000
• Drift field ~ 600V/cm (-30kV high voltage), total drift time ~ 5µs.
• Interpolating zigzag anode pad plane, 200µm position resolution for stiff tracks
• Readout channel count ~8000 
• Customized ASICs, 32 channels per chip, 1mW per channel
• Electronic noise <250e, 500ns peaking time, single peak time and amplitude measurement, timing resolution ~ 20ns
• 8 sets of ADCs digitize the sparsified and serialized data streams, worst case event processing time <0.5ms
  

The schematic view of the LEGS TPC is shown below: