Experimental investigation of magnetoconvective oscillations and impulsive disturbances in liquid-metal flows for cooling systems of thermonuclear reactors


Аuthors

Balabaev N. E.1, Rakhimov R. F.1, Listratov Y. I.1, Belyaev I. A.2

1. ,
2. Joint Institute for High Temperatures of the Russian Academy of Sciences, 13, Izhorskaya str., Moscow, 125412, Russia

Abstract

This paper presents a comprehensive experimental program aimed at studying fundamental magnetohydrodynamic (MHD) processes in liquid metals under strong steady and pulsed magnetic fields, with an applied focus on ensuring the reliability and safety of thermal protection systems (blankets) in fusion reactors. The relevance of the study is driven by the fact that liquid-metal blankets, des-pite their high technological potential for heat removal and tritium breeding, face a number of instabilities caused by the interaction of the electrically conducting coolant with the strong magnetic field used for plasma confinement.
Within this work, experiments are carried out on the RK-3 (HELMEF) test facility, located at the Joint Institute for High Temperatures of the Russian Academy of Sciences (JIHT RAS), using mercury as a model coolant and magnetic fields with induction up to 2,7 T.
The investigation covers two key directions. The first is the study of magnetoconvective fluctuations (MCF): low-frequency, large-scale fluctuations in temperature and velocity arising during mixed convection in vertical channels under a transverse magnetic field. It has been shown that, although the magnetic field suppresses small-scale turbulence, it promotes flow self-organization into “elevator modes,” leading to localized detachment of overheated fluid and sharp temperature spikes. Such fluctua-tions generate cyclic thermomechanical loads, threatening the fatigue strength of structural materials. Experimentally, an MCF regime map has been constructed in the coordinates of the Richardson and Stuart numbers; its correlation with theoretical stability boundaries obtained in numerical studies has been confirmed. It has been established that the use of passive vortex generators (rods oriented along the field) allows complete suppression of MCF, while simultaneously compensating for the heat transfer level compared to the non-magnetic case.
The second direction concerns the study of unsteady pulsed disturbances simulating accident scenarios in tokamaks, specifically, electrical breakdowns and abrupt changes in the magnetic field (e.g., during plasma thermal quench). For these tasks, a modified experimental model has been developed: a square Plexiglas cavity (40×40×250 mm), filled with mercury, placed in a constant transverse magnetic field up to 1,65 T, with the possibility of superimposing either a longitudinal pulsed magnetic field (up to 0,8 T, duration 50–100 ms) or a pulsed electric current (up to 1,5 kA). This configuration allows visualization of the liquid surface and the use of micro-thermocouples as passive tracers.

Keywords:

magnetohydrodynamics, liquid-metal coolant, magnetoconvective fluctuations (MCF), pulsed electromagnetic effects, fusion blanket, experimental modeling

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