Thermal stabilities and optimal operating parameters for the Oak Ridge Spallation Neutron Source superconducting linear accelerator

The baseline Spallation Neutron Source (SNS) accelerator will provide a 1-GeV, 1.4-MW proton beam to a mercury target for the production of neutrons. The main acceleration for the H-beam is provided by 81 superconducting cavities installed in 23 cryomodules operating at 805 MHz. The design of the superconducting linac includes a 2.1-K, 2.5-kW cryogenic plant to maintain the cavities below the helium lambda point for efficient operation at high accelerating gradients. In this paper operating conditions are analyzed rather than the design ones, which still guarantees a high gradient operation without any temperature constraint. From the analysis it appears that the SNS superconducting linac can be operated at temperatures higher than 2.1 K, a fact resulting from both the pulsed nature of the superconducting cavities, the specific configuration of the existing cryogenic plant, and the operating frequency. General conditions are also given regarding the operation of pulsed superconducting cavities resonating at different frequencies.