Speaker
Description
Harsh Patel1, *, Maulik Panchal1, Aroh Shrivastava1, 2, Paritosh Chaudhuri1, 2
1Institute for Plasma Research, Bhat, Gandhinagar – 382428, India
2Homi Bhabha National Institute, Anushaktinagar, Mumbai – 400094, India
An experimental setup was developed to measure the coefficient of thermal expansion (CTE) of lithium ceramic pebble beds within the typical operating temperature range of fusion reactor blankets. The setup enables accurate characterization of the thermal expansion behaviour of granular ceramic materials, which is critical for understanding the thermo-mechanical performance of breeder zones in fusion blankets.
The pebble bed is formed by filling lithium metatitanate (Li2TiO3) pebbles into a cylindrical container, compacted slightly and confined by a cylindrical block placed on top. Axial expansion of the bed is captured using a Linear Variable Differential Transformer (LVDT), which is mechanically connected to the container and the top block via two precision quartz rods. These rods act as displacement transmitters, allowing accurate transfer of bed expansion to the LVDT while thermally isolating it from the high-temperature zone. To provide uniform heating across the bed height, a three-zone split-tube radiation furnace surrounds the assembly. The heating rate is kept sufficiently low to ensure that the entire pebble bed attains thermal equilibrium during each measurement interval, thus avoiding transient temperature gradients within the bed that could affect measurement accuracy.
Correction mechanisms were implemented to isolate the thermal expansion of the pebble bed from that of the setup components. Two separate correction curves were developed. The first correction was obtained experimentally by replacing the pebble bed with a solid cylindrical quartz block of the same height and measuring the system’s axial expansion using the same method. The intrinsic expansion of the quartz block, measured using a calibrated dilatometer, was then added to this axial expansion to generate an accurate correction curve. The second correction accounted for the radial expansion of the container, which could alter the contact and packing conditions of the pebbles. This was addressed analytically and through Finite Element Method (FEM) simulations, allowing the derivation of a precise radial expansion compensation factor.
The setup was validated by measuring the thermal expansion of reference materials using cylindrical blocks of the same height as the pebble beds, and the results were found to be in good agreement with standard values. The experimental setup, calibration methodology, and representative results will be presented and discussed in detail.
