Structural materials for HFM magnets
Inventory of structural materials, based on 11 T and MQXF magnet design, is finished and the list of their thermal-mechanical properties is now nearly completed.
A first version of material data will be released in couple of weeks. Further investigation of the data to dress a list of reference values for simulation studies is ongoing.
Materials inventory for the 11 T magnets:
Material Table and Literature for the Ti6Al4V:
Irradiation damage of polymers for superconducting magnets studied under relevant irradiation conditions
Superconducting magnets of future particle accelerators will be exposed to high radiation doses, and polymers are the magnet constituent materials most sensitive to irradiation effects. The integrity of polymer dielectric insulation and coil impregnation systems must be guaranteed for the entire magnet live time.
In the context of the HFM study the CERN Polymer Laboratory is performing an irradiation damage study with candidate materials for superconducting coil impregnation and insulation. Since in superconducting magnets irradiation occurs at cryogenic temperatures in the absence of oxygen, the effect of ionising radiation on functional properties is studied not only in ambient air, but also in inert atmosphere, and with the samples being irradiated in liquid helium at 4.2 K.
The results of the first stage of the irradiation study have been reported in two recent publications [1],[2], identifying the most radiation resistant epoxy resin systems, and confirming the strong effect of the irradiation temperature on degradation rates.
For the second stage of the irradiation study the CERN Polymer Laboratory prepares to irradiate entire superconducting magnet insulation systems in cryogenic environment to doses beyond 30 MGy to determine the irradiation induced changes of mechanical, thermal and dielectric properties under relevant irradiation conditions.
Quench detection, protection and diagnostic methods for Nb3Sn and HTS high-field magnets
Quench protection of future high-field accelerator magnets becomes increasingly challenging as the magnet’s stored energy and energy density increase due to a rise in the magnetic field. Established quench protection techniques may not have Nb3 sufficient effectiveness. One of these new concepts is based on a set of very small coils strategically positioned in proximity to the main magnet. They are powered with AC and, as a result, induce AC loss that locally heats up the magnet conductor and transitions it to a normal state. This method can be regarded as an inductive quench heater and is called E-CLIQ (External coil Coupled Loss Induced Quench.
At the start of 2024, the latest iteration of E-CLIQ coils was successfully tested in CERN’s cryogenic laboratory in collaboration with TE-CRG-CL. The coils were mounted on a sample of Nb3Sn Rutherford cable that was placed in gaseous helium at a temperature of 4.5 K, and a background magnetic field of up to 5 T was applied. Activation of the E-CLIQ coils demonstrated a significant rise in the Nb3Sn cable sample’s temperature, which is an important milestone and a good starting point for further E-CLIQ development.
Cryogenic and thermal management studies for HFM magnets
Enhanced-range thermal conductivity test stand (pictured below):
An enhanced-range cryocooler-based system for thermal conductivity measurements is starting its commissioning phase!
The standard cryocooler set-up can be used for measurements of thermal conductivity and diffusivity at temperatures > 4 K; for measurements between 4 K and 1.8 K, a closed-loop He II circuit provides the cooling power instead.
A gas-gap heat switch (GGHS) between the cryocooler cold head and the He pot can be switched OFF (low conductance mode) or ON (high conductance mode) to decouple the He circuit from the warmer cryocooler after cooldown.
Thermal properties of magnet components at cryogenic temperatures:
Measurements of thermal contraction of resins and insulating materials of interest continues; thermal conductivity/diffusivity measurements will resume as the commissioning of the test stand is completed.
Authors: C. Marques, C. Garion, C. Scheuerlein, M. Wozniak, P. Tavares Coutinho Borges De Sousa.