Superconducting Radiofrequency Technology for Accelerators

7 Quest for Higher Gradients: Two-Step Baking and N-Infusion

7.1 Two-Step Baking

An enhancement of the 120 °C bake treatment developed at Fermilab shows encouraging prospects for higher gradients [289, 297]. A 4-hour bake at 75 °C is added to the customary 120 °C baking step. The treatment turns well-performing cavities into exceptional ones. Cavities treated with the 75/120 °C two-step bake exhibit some of the highest gradients with quench fields at or above 46 MV/m (Figure 7.1). More than 50 tests on single-cell cavities fabricated from material from various vendors showed gradients above 40 MV/m with a high yield (Figure 7.2) [12]. 38 tests exceeded 45 MV/m, with one cavity reaching nearly 50 MV/m (213 mT). Three cavities from the batch ...