Thermal analyses and frequency shift design studies for the spallation neutron source drift tube linac

摘要

Los Alamos National Laboratory is responsible for the design of the room-temperature linac for the Spallation Neutron Source (SNS). This linac consists of a Coupled-Cavity Linac (CCL) and a Drift Tube Linac (DTL). During normal operation, about 80% of the Radio Frequency (RF) power is dissipated in the DTL cavity walls. This waste heat causes the cavities to expand, causing shifts in their RF resonant frequency. The DTL relies on the water cooling system to compensate for the frequency shift caused by RF heating. To guide the design of the cooling system and the frequency control scheme, thermal expansion and frequency shift studies for several DTL cells are performed via numerical simulations. Temperature distributions and thermal deformations resulting from RF heating are evaluated separately for the tanks and 22 drift tubes using finite element models. The frequency shift of these cells are then computed based on the calculated deformations. Size and locations of the cooling channels are designed accordingly to provide adequate cooling and minimize frequency shift. The tank finite element model used to predict the tank temperature profile is benchmarked against experiment data.