Thermohydraulic Simulation Of The ITER Magnet System


The main aims of the ITER CSMC testing were to validate all CSMC specifications, to determine the operational limits and to verify the design criteria for the superconducting magnets applied in fusion. About 350 experimental runs were carried out during these tests and more than 400 sensors used to acquire data allowed us to store a considerable amount of information during this test campaign.

A detailed VINCENTA model has been developed to simulate the thermo-hydraulic behaviour of CSMC at pulsed operation with high heat pulses generated in the conducting components of the ITER magnets.

The CSMC mathematical model is a combination of three partial numerical models:

1. The 1D model used to simulate the transient behaviour of helium flows in different tubes, including the cooling channels of the superconducting cables of inner and outer modules, the Central Solenoid Coil Insert (CSCI), two supercritical helium heat exchangers, the upper and lower support structures, the base, auxiliary cryogenic systems etc. The total number of channels modelled in the 1-D approximation was above 160. Each of 36 superconducting cables-in-conduit conductors (CICC) was modelled separately. In each CICC, two thermodynamically non-equilibrium helium flows were considered: one flowing in the cable space between strands and another within spiral core. Transverse heat and mass transfer between these flows occurred through the gaps between spiral convolution.

2. The 2D difference model used to simulate transient heat exchange conditions over the CSMC cross-section in the cylindrical coordinate system. Thermal inter-turn interaction takes place between turns including the upper and lower support structures. The 2D calculation mesh for 5 cross- sections has over 450,000 nodes. The 2D heat transfer model is combined with the 1D thermo-hydraulic model via consistent boundary conditions for a 2D wetted boundary and the heat load for the 1D flow model.

3. The 2D model used to simulate the alternating current (AC) losses in the CSMC and CSCI conductors based on field maps for different time points of the experiment scenario.


The comparison between numerical simulations and the CSMC experiment has shown that the VINCENTA model ensures good accuracy for the integral and local transient cooling parameters (helium pressure, flow rate and temperature) under a series of current pulses despite different magnitudes of the current at the flat top. The proper evolution (time-history) of transient cooling parameters could be found for each current pulse (30, 40, 43 and 46kA) even if the initial cooling parameters and AC losses were verified for only one current pulse with a flat top current of 46kA.

These results allow us to qualify the VINCENTA code as a reliable tool for modelling the magnet systems operating at high pulsed heat loads non-uniformly distributed over a winding pack.

The VINCENTA code can be recommended for modelling the active cooling control of the ITER magnet system that operates at high pulsed heat deposition due to variable electromagnetic losses and nuclear heat load. When using the active cooling control, the VINCENTA models facilitate careful monitoring of the local temperature of each conductor and checking whether its temperature is within the design limits.



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