At the thermal center, the temperature gradient in the yoke longitudinal cooling channels is zero. Positions where temperatures are calculated are specified in the magnet cross- section inset.
https://www.researchgate.net/figure/Temperature-profile-of-t...

In building design, thermal mass is a property of the mass of a building which enables it to store heat, providing "inertia" against temperature fluctuations. It is sometimes known as the thermal flywheel effect.[1] For example, when outside temperatures are fluctuating throughout the day, a large thermal mass within the insulated portion of a house can serve to "flatten out" the daily temperature fluctuations, since the thermal mass will absorb thermal energy when the surroundings are higher in temperature than the mass, and give thermal energy back when the surroundings are cooler, without reaching thermal equilibrium. This is distinct from a material's insulative value, which reduces a building's thermal conductivity, allowing it to be heated or cooled relatively separate from the outside, or even just retain the occupants' thermal energy longer.
https://en.wikipedia.org/wiki/Thermal_mass

The thermal center is a concept used in applied mechanics and engineering. When a solid body is exposed to a thermal variation, an expansion will occur, changing the dimensions and potentially the shape of the body and the position of its points. Under certain circumstances it may happen that one point belonging to the space associated to the body has no displacement at all: this point is called the thermal center (TC).
https://en.wikipedia.org/wiki/Thermal_center

As an optical component such as a mirror, grwos with the temperature, there is a spot in the component that can be designed to remain stationary called the "thermal center".
Figure 19: Proper constraints for a stationary thermal center [Giesen, 2003]
https://www.google.de/url?sa=t&rct=j&q=&esrc=s&source=web&cd...

As shown with the gridiron pendulum, a design principle is to use materials with different coefficients of thermal expansion to compensate the thermal expansion to (almost) zero. Another commonly applied design principle is the so-called 'thermal centre'. When a system is constrained in a statically determined manner, it is possible to define a centre: a point which does not displace under homogeneous thermal expansion. This is illustrated in figure 4, where a body is connected to a base frame with three contact points. A spring applies a force to ensure that the body is in contact with the three contact points. When the body or the base frame expands homogeneously, the thermal centre remains at the same location [Koster, 2008].
https://www.dspe.nl/knowledge-base/thermomechanics/chapter-3...