Superconducting Radio-Frequency Technology R&D for Future Accelerator Applications

Abstract

Superconducting rf technology (SRF) is evolving rapidly as are its applications. While there is active exploitation of what one may term the current state-of-the-practice, there is also rapid progress expanding in several dimensions the accessible and useful parameter space. While state-of-the-art performance sometimes outpaces thorough understanding, the improving scientific understanding from active SRF research is clarifying routes to obtain optimum performance from present materials and opening avenues beyond the standard bulk niobium. The improving technical basis understanding is enabling process engineering to both improve performance confidence and reliability and also unit implementation costs. Increasing confidence in the technology enables the engineering of new creative application designs. We attempt to survey this landscape to highlight the potential for future accelerator applications.

Evaluation of niobium as candidate electrode material for dc high voltage photoelectron guns

“…Niobium can provide very high rf accelerating gradient, >40 MV=m, with surface fields in excess of 100 MV=m [21]. Niobium has a work function comparable to stainless steel and with similar hardness.…”

Laser polishing for topography management of accelerator cavity surfaces

“…Moving forward has required a technology transition from room‐temperature copper accelerating cavities to superconducting radio‐frequency (“SRF”) niobium cavities operating at about 2 K. The journey of this technology community has been chronicled ; the current state and future path have been recently reviewed .…”

The International Linear Collider (Report to Snowmass 2021)

“…4.27(c) [145]) for the same cavity. However, the best multi-cell cavities of the new shapes have only reached 42 MV/m [146], mostly due to the dominance of field emission. A 5-cell cavity of the LSF shape recently tested at JLAB showed 50 MV/m gradient in three of the five cells [147] by exciting several modes of the fundamental pass-band.…”