Purpose Purpose

Purpose

• Purpose

• Provide almost-free neutron target to improve our understanding of neutron structure.

Measure slow protons

• Measure slow protons

• Identify spectator protons to tag e-d events in which the neutron was struck.

Time Projection Chamber (TPC)

• Time Projection Chamber (TPC)

• Just a box of gas
• Readout elements only on the surfaces.
• Windows can be made thin.

To make mechanical structure even lighter, use no wires --> no wire tension to support.

• To make mechanical structure even lighter, use no wires --> no wire tension to support.

• Eliminating wires also eliminates local artifacts in the data.

• Use GEMs instead of wires:

• Gas Electron Multiplier
• A sheet of material providing gas gain.
• Sauli, ~1998

Needs

• Needs

• Signals are typical of any TPC.
• Channel Count: 3200 4mm x 5mm pads.
• Space only for simple preamp on-board, to drive ~6m cable to crate.
• Drift time ~5 microseconds (3cm).
• 100ns time bins gives 50 samples/track.