Nb3Sn multicell cavity coating system at Jefferson Lab

Abstract

Superconducting radio frequency niobium cavities are the building blocks of modern accelerators for scientific applications. Lower surface resistance, higher fields, and high operating temperatures advance the reach of the future accelerators for scientific discovery as well as potentially enabling cost-effective industrial solutions. We describe the design and performance of an Nb3Sn coating system that converts the inner surface of niobium cavities to an Nb3Sn film. The niobium surface, heated by radiation from the niobium retort, is exposed to Sn and SnCl2 vapor during the heat cycle, which results in about 2 μm Nb3Sn film on the niobium surface. Film composition and structure as well as radio frequency properties with 1-cell R&D cavities and 5-cell practical accelerator cavities are presented.

Properties of Nb3Sn films fabricated by magnetron sputtering from a single target

“…Samples sputtered on sapphire were deposited for 6 h, while samples sputtered on Nb were deposited for 14 h, all under the same magnetron operating current, the same Ar background pressure, and fixed target-to-substrate distance of 10 cm. The coated samples were removed from the sputter coater and then annealed for 24 h at 800, 900, and 1000 • C in a separate vacuum furnace, described in [6]. For films annealed at 1000 • C, some samples were also annealed for 1 and 12 h to study the effect of annealing time on film properties.…”

“…Nb 3 Sn thin films coated on niobium or copper are considered as potential alternative materials for SRF cavities [2,3]. A 1.3 GHz single-cell Nb 3 Sn/Nb cavity fabricated by Sn vapor diffusion at Jefferson Lab have demonstrated a Q 0 ≥ 2 × 10 10 at 4 K before quenching at a field ≥15 MV/m [4], while Nb 3 Sn/Nb CEBAF five-cell cavities had a low-field Q 0 of ~3 × 10 10 [5] and maximum accelerating gradient up to 15 MV/m at 4 K [6]. An accelerating gradient of 22.5 MV/m at 4 K was achieved at Fermilab for a 1.3 GHz single-cell cavity [7].…”

Next-Generation Superconducting RF Technology based on Advanced Thin Film Technologies and Innovative Materials for Accelerator Enhanced Performance and Energy Reach

“…Materials such as Nb 3 Sn offer order of magnitude improvements in operating efficiency, and a theoretical pathway to 100 MV/m gradient [23]. Recent R&D efforts [24][25][26][27] have demonstrated that the persistent Q-slope and gradient limitation observed in the past [28] are not fundamental but process induced and therefore amenable to improvement. Alternative deposition approaches such as sputtering, energetic condensation and atomic layer deposition (ALD) should be fully explored for enhanced properties and conformality.…”

Toward Superconducting Electron Accelerators for Various Applications

“…Recently, multicell Nb 3 Sn cavities enabled researchers at Jefferson Lab and Fermilab to achieve remarkable results. [ 30,31 ] In contrast, many fabrication techniques have been investigated, and a multicell‐coating recipe has not yet been established for MgB 2 . We proposed a plasma spraying technique to deposit MgB 2 on the inner surface of the cavity, because this technique enables the highest film growth rate.…”

“…[28] At the Temple University, a MgB 2 film with a thickness of several tens to several hundreds of nanometers was formed on the surface by supplying Mg vapor and diborane gas (B 2 H 6 ) to a single-cell Nb cavity and a superconducting transition was successfully observed at 37À40 K. [29] Recently, multicell Nb 3 Sn cavities enabled researchers at Jefferson Lab and Fermilab to achieve remarkable results. [30,31] In contrast, many fabrication techniques have been investigated, and a multicell-coating recipe has not yet been established for MgB 2 . We proposed a plasma spraying technique to deposit MgB 2 on the inner surface of the cavity, because this technique enables the highest film growth rate.…”