The lead-copper option for heavy ion accelerating cavities: history, status, and future prospects

Superconducting radio-frequency (SRF) cavities have been used to accelerate heavy ion beams for the last quarter century. Over this period devices based on pure lead or a lead-tin alloy electrodeposited on to a copper structure have been a viable alternative to solid niobium cavities, with many comparative advantages such as lower unit cost, ease of re-coating and better thermal stability. We review the historical development, current status and future prospects of the lead-based SRF technology in the context of recent advances in solid and thin-film niobium