Transport of nonequilibrium charge carriers in irradiated silicon detectors at super fluid helium temperature

The system for the monitoring of the radiation field near electromagnets of the Large Hadron Collider (LHC) consists of detectors registering protons that leave the acceleration trajectories. In accordance with the purpose, this system was called Beam Loss Monitors (BLM). Currently the ionization chambers located on the bodies of the LHC magnets are using as BLM sensors. However, according to the plans to increase the proton beam luminosity in the accelerator, it was proposed to also improve the BLM system. The key point of the improving is to place the BLM sensors as close as possible to the superconducting elements inside the cryostat. That leads to the requirements of the devices' compactness and their predictable operation in a wide range of radiation doses at a temperature of superfluid helium. Taking into account specific requirements, it was proposed to use compact semiconductor radiation detectors capable of operating under such conditions. Scenario for sensor operation at a temperature of superfluid helium cannot be constructed by extrapolation of the experimental data obtained at a temperature close to room temperature and requires targeted studies. The detector signal is determined by the characteristics of the nonequilibrium charge carriers (NCC) transport. Therefore, the purpose of this work is to characterize the NCC transport process in silicon detectors operating at a temperature of superfluid helium and irradiated by relativistic protons. This work is devoted to the development of methods for studying the semiconductor detectors in their operation at the temperature of superfluid helium and to the analysis of the experimental results of in situ radiation tests of silicon detectors carried out at a temperature of 1.9 K. In this work, the algorithm for processing of the experimental current responses of semiconductor detectors is constructed. This made it possible to reconstruct the electric field distribution and analyze the transport parameters of NCC in the sensors. Complete ionization of phosphorus atoms in the space charge region of the p-n junction of a silicon detector at a temperature of 6 K is experimentally shown; the extrapolation of the results to a range of lower temperatures showed the possibility of ionization of phosphorus atoms in the electric field at 1.9 K. The results obtained in this work made it possible to quantitatively characterize the transport of NCC in silicon detectors. In conditions typical for monitoring the radiation field near the superconducting coils of LHC magnets the multistage process of charge collection in silicon detectors was observed. Anomalously high introduction rate of electrically active defects into the sensitive region of sensors was obtained at a temperature of superfluid helium.