Gain Stabilization in POLAR-2 SiPMs Using Temperature Loop Corrections

Gamma-Ray Bursts (GRBs) are among the most extreme events in the universe, however much is yet to be understood about the structure of their outflows, magnetic characteristics, and kinetic energy. Knowing the polarization of light coming from GRBs is expected to help solve some of these open questions. POLAR-2 is a future space-based GRB detector which will measure the polarization of incoming photons from extragalactic sources. It will use Compton Scattering in scintillator bars that are read out by Silicon Photomultipliers (SiPMS) for these measurements. However, the characteristics of SiPMs are highly dependent on temperature, in particular their gain is inversely proportional to temperature assuming a constant bias voltage. During operation,
POLAR-2 will be subject to extreme temperature changes in space, so if a constant gain is desired the bias voltage will need to be corrected. In this study, a temperature correction loop for the bias applied to the SiPMs in a POLAR-2 module was studied and characterized. Its performance was investigated by measuring the gain of the module’s SiPMs across a range of temperatures from 20 to 34 ◦C. The results were compared against control data without a temperature correction. The correction loop was determined to be effective but not ideal, as a dependence on the order of -0.2 per ◦C was observed in the gain of many SiPM channels. An improvement to the correction loop was made, and the mean temperature dependence went from -0.07 to -0.04 per ◦C. However, a dependence on the order of -0.2 per ◦C was still observed in many SiPM channels. It was determined that the temperature loop correction is effective at reducing temperature dependence of SiPM gain, but that further optimizations may be desired.