Thermal Stabilization and Cooling System for the TPC and ECAL Detectors of the MPD Experiment on the Collider Facility NICA

The thermal stabilization and cooling systems for the time projection chamber (TPC) and electromagnetic calorimeter (ECAL) detectors of the multi-purpose detector (MPD) experiment at the NICA (Nuclotron-based Ion Collider fAcility) are based on a leakless water-cooling concept that ensures continuous operation under subatmospheric conditions. The implementation of such a system imposes stringent constraints on the hose materials responsible for coolant delivery, especially regarding their ability to resist radiation-induced activation, their long-term chemical stability against corrosion, and minimal gas diffusion under internal water pressure conditions of approximately 0.5 bar, and sufficient mechanical robustness and flexibility to allow for seamless integration within the MPD infrastructure.

This research is dedicated to the evaluation and qualification of various types of flexible plastic hoses that are proposed to deliver distilled or deionized water to the cooling circuits of the TPC and ECAL detectors. Due to the proximity of these hoses to the TPC front-end electronics, they are expected to be exposed to neutron radiation levels approaching 10¹¹ neutrons/cm² at 1 MeV over the projected operational duration of the MPD experiment, which spans an estimated 10 years.

To emulate this cumulative neutron exposure under controlled conditions, the candidate hose materials were irradiated using neutron fluences of F₁ = 10⁹ n/cm², F₂ = 10¹⁰ n/cm², F₃ = 10¹¹ n/cm², and F₄ = 10¹² n/cm². The effects of irradiation were systematically assessed using Raman spectroscopy for molecular structural changes, mechanical tensile testing for changes in strength and elasticity, and gas permeability evaluations to measure performance degradation related to leak tightness.

These empirical results were complemented with multiphysics simulations conducted using COMSOL to analyze the thermal distribution and fluid dynamics within the selected hose materials under realistic operational conditions. Based on the collective findings from the experimental and simulation studies, reinforced polyvinyl chloride was identified as the most suitable candidate for long-term use in the MPD thermal stabilization and cooling subsystems.