WP4 – Superconducting Thin Films for RF Cavities

WP4 – Superconducting Thin Films for RF Cavities

Thomas Proslier

“Our work package on superconducting thin films is important because it supports the transition of superconducting radio frequency cavity technology toward a more sustainable and resource-efficient paradigm, reducing both critical material consumption and energy demand.

A key objective is to validate Nb₃Sn thin-film-coated copper cavities in a realistic accelerator configuration, combining RF operation and cryogenic testing, and to demonstrate a quality factor above 10¹⁰ at 4.2 K.”

Oleg Malyshev

“An international collaboration is key to progress beyond existing technology, and to develop new ideas from R&D that can lead to a new advanced technology. Working with industry is important for implementing this new technology and using it in future projects.

One main result of this work package will be the new Nb₃Sn coated cavities, which will enable greener accelerating structures, consuming fewer resources and electricity in both construction and operation phases.”

The objectives of WP4 is to develop and validate a novel class of SRF cavities made using thin-film coatings, operated in a horizontal cryostat and conduction cooled by compact cryocoolers. Specific objectives:

design and fabricate high quality factor (high-Q) SRF cavities made of copper, coated with Nb₃Sn, and optimized for operation at 4.2 K;
demonstrate stable, efficient conduction cooling using commercially available cryocoolers, thus eliminating the need for liquid helium infrastructure;
integrate and test these cavities in a horizontal cryomodule suitable for industrial, medical, and scientific accelerator applications;
assist industry in equipping its manufacturing lines with a new industrial facility for cavity coating.

This WP evolves 4 Tasks:

Task1: Strategy and Industrialisation

The objectives for this task are:

Develop a long-term strategy to transition TF-SRF technology from R&D to industrial level, targeting higher TRLs and future use in accelerator applications across science, health, and industry.
Industrial partners will help identify current challenges and explore solutions for the industrialisation of TF-SRF cavity production.
The Task will organise an International TF-SRF workshop, participate in relevant conferences sessions, and support meetings to coordinate academia and industry efforts toward European TF-SRF industrialisation strategy.

Task 2: Horizontal cavity integration and RF tests

The goal of this task is to integrate the Nb₃Sn-coated cavity from Task 3 into a cryostat and test it under beam-relevant conditions. Two main challenges must be addressed: (a) replacing a liquid helium cryoplant with conduction cooling, eliminating the need for a helium tank and enabling a simpler setup than 1.8 K modules, and (b) using couplers positioned off the beam axis while maintaining adaptable input coupling. For industrial use, such as compact CW modules, conduction cooling via cryocoolers is preferred over cryoplants.

Cryostats for horizontal and vertical cavities RF tests at 4.2 K using cryocoolers.

Task 3: 1.3 GHz cavity production and coating

The main objective for this task is to provide Task 2 with single cell 1.3 GHz copper cavities integrated with power coupler and pick up ports. These cavities will be coated with Nb3Sn thin films. Superconducting TF coating will be performed at CEA, INFN and STFC to explore different coating set-ups and mitigate the risk. Zanon will equip itself with a new industrial facility for cavity coating, based on the experience gained by academic partners in IFAST.

Few example of 1.3 GHz cavities to be coated

*(b) 3D printed Cu cavity with in-wall cooling channels at CEA. (c) longitudinal split cavities at LU-UKRI*

Coating systems and set-ups will be optimized to deposit the power coupler and pickup ports doors in addition to the cell.

*PVD facilites for 1.3 GHz cavities at INFN (on the left) and UKRI (on the right).*

*Sputtering deposition systems for 1.3 GHz cavities at INFN and UKRI*

**Deposition systems at CEA: left ALD set up and right: HiPIMS apparatus for 1.3 GHz cavities.**

Task 4: Superconducting thin film development

The goal of this task is to develop cylindrical sputtering targets for Task 3, new high temperature stable substrates for Nb₃Sn deposition and continue superconducting thin films R&D on new supercondutcing alloys using state of art characterization techniques and post thermal treatments.