Exploration of beam fault scenarios for the Spallation Neutron Source target

The Spallation Neutron Source (SNS) accelerator systems will provide a 1 GeV, 1.44 MW proton beam to a liquid mercury target for neutron production. In order to ensure adequate lifetime of the target system components, requirements on several beam parameters must be maintained. A series of error studies was performed to explore credible fault scenarios which can potentially violate the various beam-on-target parameters. The response of the beam-on-target parameters to errors associated with the phase-space painting process in the ring and field setpoint errors in all the ring-to-target beam transport line elements were explored and will be presented. The plan for ensuring beam-on-target parameters will also be described.

INTRODUCTION

The Spallation Neutron Source (SNS) accelerator consists of a 2.5 MeV H- Injector, a 1 GeV Linear Accelerator, an Accumulator Ring and associated transport lines [1]. The linac provides an average macropulse current of 26 mA which is accumulated over 1060 turns by charge-exchange injection in the accumulator ring. The ring intensity reaches protons at which point the current is extracted in a single turn and transported to the target via the Ring-to-Target Beam Transport (RTBT) line [2]. With a repetition rate of 60 Hz, the SNS provides 1.44 MW average beam power to the liquid mercury target [3] for spallation neutron production. The baseline SNS beam parameters are summarized in Table 1. Table 1: Baseline SNS Parameters

Parameter	Baseline Value
Beam Power on Target	1.44 MW
Accumulated Protons
Accumulated Turns	1060
Repetition Rate	60 Hz
Beam Energy	1 GeV
Target Cross-section	404mm × 104 mm
Beam spot width x	200mm × 70 mm