PIP-II: Nitrogen doping and electropolishing

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The surface treatment of niobium cavities has been shown to significantly influence the efficiency of high power, superconducting particle accelerators. Heat treatment and surface preparation processes that deposit nitrogen in the near-surface region of cavities can greatly improve machine efficiency and hence drive down the cost of performing research.An international research consortium is advancing the science of surface preparation for niobium cavities. The United Kingdom's academic institutes and businesses are not currently active in this forum. Knowledge sharing on developments in particle accelerator efficiency is therefore not guaranteed.As part of a project to support the US-led Proton Improvement Plan - Phase 2 (PIP-II), the UK is developing a supply chain for superconducting cavities. The scope of supply does not extend to the surface treatment of these cavities. The organisations involved are Daresbury Laboratory (within STFC-UKRI) and an industrial consortium led by The Welding Institute (TWI).The Proton Improvement Plan is part of a larger project to create Long Baseline Neutrino Facility (LBNF) in support of the Deep Underground Neutrino Experiment (DUNE). Benefits to science and industry of the UK's involvement in this broad initiative are captured in the outline business case for LBNF-DUNE.This proposal seeks to augment the scientific and economic benefits introduced in the LNBF-DUNE business case by developing processing techniques in the UK for superconducting accelerating cavities. Specifically, this proposal requests investment in two lines of scientific development:1. nitrogen doping; and 2. chemical polishing to improve cavity efficiency. Within the work to develop chemical polishing techniques, will be the investigation of alternative polishing methods to reduce hazards associated with the current chemical procedures.