A very high performance stabilization system for macro-calorimeter arrays experiments

Abstract

Large array of macro-calorimeter detectors, operated at very low cryogenics temperatures, plays a crucial role for the search of rare events, such as Neutrinoless Double Beta Decay and Dark Matter. In experiments of this type the stability of the system is mandatory over many years of data taking, often in conflict with the intrinsic instabilities of the cryogenic setups. A solution to accomplish this requirement is to inject a voltage pulse across a heating resistor glued on each calorimeter absorber to develop a known calibrated heating power. For this purpose we designed a custom system able to generate a small and short voltage pulse across the heaters. This system is composed by different custom PCB each of them having multi-channel outputs. Each output can be completely remotely programmable from the acquisition system, in pulse width and amplitude, through an on-board Cortex-M3 microcontroller. Pulse amplitudes must be selectable, in order to handle each detector on its full dynamic range. Outputs can be connected to the heater in single-ended or differential configuration and the resolution of the output voltage is 12 bits over 5 V range (10 V in differential configuration). An additional 2 steps programmable voltage attenuator is added at each output. By using a 12-bit ADC and a 24-bit ADC is possible to perform on-board diagnostic, monitoring and self-check routines. The pulse amplitude thermal drift are compensated using a calibrated 8-bit, four channel trimmer. Each board is remotely controlled through an optically coupled CAN bus. In this contribution we present the solution adopted in the realization of a this very stable system.