Spallation Neutron Source Superconducting Linac Commissioning Algorithms

We describe the techniques which will be employed for establishing RF setpoints in the SNS Superconducting linac. The longitudinal tuneup will be accomplished using phase-scan methods, as well as a technique that makes use of the beam induced field in the unpowered cavity [1].

INTRODUCTION

The SpallationNeutron Source Linac will accelerate a 26 mA average current pulse to 1 GeV at 60 Hz. The SNS linac consists of a 38 mA peak current H^– injector, a six-tank Drift Tube Linac to accelerate the beam to 87 MeV, a four-module Coupled Cavity Linac to accelerate the beam to 187 MeV, and a Superconducting Linac to accelerate the beam to 1 GeV. The SCL consists of two types of cavities, one with geometric beta equal to 0.61 (the “medium-beta” cavity) and another with geometric beta of 0.81 (the “high-beta” cavity) [2]. The medium-beta linac consists of 11 cryomodules with three cavities per cryomodule, while the high-beta linac consists of 12 cryomodules with four cavities per cryomodule, for a total of 81 superconducting cavities. Each cavity is powered by a single 550 kW klystron providing individual cavity phase and amplitude control. The inter-cryomodule segments are maintained at room temperature, and consist of a quadrupole doublet, dipole correctors and beam diagnostics.