Detector R&D

Previous generation TPC’s typically employed wires to amplify the electron signals but today most TPC projects plan to use MPGD’s that include MICROMEGAS (MICROMEsh GASeous detectors) and GEMs (Gas Electron Mulitiplier).  Their are several advantages to MPGD’s such as good timing properties (fast response and good resolution), good spatial resolution, and less susceptibility to electronic discharge or “sparking” at high counting rates.  These detectors are also more robust, and can be produced in a variety of shapes and sizes ranging from as little as a few millimeters and can be made to cover large surface areas of up to 1 meter.

Figure 1 - Prototype MICROMEGAS detector at GANIL with a pad pitch of 2 mm x 2 mm and 576 total channels.

In a MICROMEGAS detector, the size of the amplification gap can be specified according the particular application but it is typically a hundred microns (The detector shown in Figure 1 is 128 um).  A thin (30 micron) stainless steel micromesh is polarized at a few hundred volts to generate a sufficient electric field in the amplification gap of several tens of kV/cm.  For example, at 1 atmosphere of gas pressure a typical operating voltage is about 400 V.

Micromegas detector tests are being performed using prototype detectors with 576 square pads with 2 mm pitch  to determine the optimal ranges of gases, pressures, and voltages for nuclear physics applications.  Good angular resolution as well as an accurate reconstruction of the Bragg peak are necessary to properly reconstruct the kinematics of physics events inside the TPC.