  The performance of superconducting radio-frequency (SRF) cavities depends on
the niobium surface condition. Recently, various heat-treatment methods have
been investigated to achieve unprecedented high quality factor (Q) and high
accelerating field (E). We report the influence of a new baking process called
furnace baking on the Q-E behavior of 1.3 GHz SRF cavities. Furnace baking is
performed as the final step of the cavity surface treatment; the cavities are
heated in a vacuum furnace for 3 h, followed by high-pressure rinsing and
radio-frequency measurement. This method is simpler and potentially more
reliable than previously reported heat-treatment methods, and it is therefore,
easier to apply to the SRF cavities. We find that the quality factor is
increased after furnace baking at temperatures ranging from 300C to 400C, while
strong decreasing the quality factor at high accelerating field is observed
after furnace baking at temperatures ranging from 600C to 800C. We find
significant differences in the surface resistance for various processing
temperatures.
