LOW-POWER RF TUNING OF THE SPALLATION NEUTRON SOURCE WARM LINAC STRUCTURES

The Spallation Neutron Source (SNS) is an accelerator-based neutron source being built at Oak Ridge National Laboratory. A conventional 402.5-MHz drift- tube linac (DTL) accelerates the H − beam from 2.5 to 86 MeV, followed by a 805-MHz coupled-cavity linac (CCL) to 186 MeV. Tuning the six DTL tanks involves adjusting post-coupler lengths and slug tuners to achieve the design resonant frequency and stabilized field distribution. A 2.5-MW klystron feeds RF power into a DTL through a ridge-loaded waveguide. The CCL consists of 4 RF modules operating in the π/2 mode. Each module contains 96 accelerating cavities in 12 segments of 8 cavities each, 11 active bridge coupler cavities, and 106 nominally unexcited coupling cavities. For each RF module, power from a 5-MW klystron splits and drives bridge couplers 3 and 9. We will discuss the procedures and special tools developed for the structure tuning.