Commissioning of the spallation neutron source accelerator systems

The Spallation Neutron Source accelerator complex consists of a 2.5 MeV H" front-end injector system, a 186 MeV normal-conducting linear accelerator, a 1 GeV superconducting linear accelerator, an accumulator ring, and associated beam transport lines. The linac was commissioned in five discrete runs, starting in 2002 and completed in 2005. The accumulator ring and associated beam transport lines were commissioned in two runs from January to April 2006. With the completed commissioning of the SNS accelerator, the facility has begun initial low-power operations. In the course of beam commissioning, most beam performance parameters and beam intensity goals have been achieved at low duty factor. A number of beam dynamics measurements have been performed, including transverse coupling in the ring, beam instability thresholds, and beam distributions on the target. The commissioning results, achieved beam performance and initial operating experience of the SNS will be discussed.

INTRODUCTION

The Spallation Neutron Source (SNS) is a short pulse neutron scattering facility located on the campus of the Oak Ridge National Laboratory in Oak Ridge, TN, USA. The construction project was a partnership of six US DOE national laboratories, each of which had responsibility for designing and manufacturing a portion of the facility. At 1.4 MW of proton beam power on target, the SNS will operate at beam powers a factor of eight beyond that which has been previously achieved [1]. The SNS baseline parameters are summarized in Table 1. Table 1: SNS Design Parameters

Beam Power on Target	1.4 MW
Beam Energy	1.0 GeV
Linac Beam Macropulse Duty Factor	6.0%
Beam Pulse Length	1.0 msec
Repetition Rate	60 Hz
Chopper Beam-On Duty Factor	68%
Peak macropulse if current	38 mA
Average Linac if current	1.6 mA
Ring accumulation time	1060 turns
Ring bunch intensity
Ring Space-Charge Tune Spread	0.15
Beam Pulse Length on Target	695 nsec
Ring betatron tune	6.23, 6.20