lariat itself is a cylindrical cryostat with convex ends, capable of holding 550l of liquid argon. the cryostat is heavily insulated thermally, in part by a region of vacuum surrounding it. inside the cryostat is the time projection chamber, in which the argon atoms are ionized by beam particles. an electric field is applied across the chamber perpendicular to the beam direction, causing the ionization electrons to move towards the side, where they are detected by two wire planes oriented at ±30° to the vertical. these wire planes are made up of 240 parallel wires with a separation of 4mm. a third wire plane of 225 wires, aligned along the vertical axis, is placed in front of the other two planes in order to prevent the electric field from interfering with the instrumentation.