Main progress achieved in Europe (since end 2021)
CLIC – Continued testing at Xbox test stands at CERN and initiated testing at the TEX test facility at INFN has progressed the develop the performance verification capabilities for high gradient X-band linac structures. Progress on fabrication techniques has developed, which is also an important scope of work for accelerating structure fabrication within the IFAST WP7 and for INFN EuPRAXIA linac structure prototypes.
Muon Collider – As a relatively new initiative, its primarily areas of research and development are at the early planning stage.
FCC-ee – The current design study focus does not specifcally address high-gradient issues yet, although high average power for S and C band structures operating at up to 400 Hz repetition rate is a principal challenge, the expectation for higher gradients may emerge in the future.
C^3 – Further testing at SLAC being conducted, and pulsed DC testing at Uppsala U is planned.
HALHF – As a very recent initiative, the requirements for NCRF are not yet fully defined, although linac gradient expectations are anticipated to be relatively modest at ~25 MV/m for the 31 GeV NC linac stage. The most significant new infrastructure request is for high-gradient cavity in magnetic field test stands. The test stand is driven by the Muon Collider but has strong overlap with CLIC and C^3. An ultimate test stand for the Muon Collider is for a 350 MHz RF system but a 3 GHz system could be an important first step. No resources are currently however available for such a test