Status and performance of the spallation neutron source superconducting linac

The Superconducting Linac at SNS has been operating with beam for almost two years. As the first operational pulsed superconducting linac, many of the aspects of its performance were unknown and unpredictable. A lot of experience has been gathered during the commissioning of its components, during the beam turn on and during operation at increasingly higher beam power. Some cryomodules have been cold for well over two years and have been extensively tested. The operation has been consistently conducted at 4.4 K and 10 and 15 pulses per second, with some cryomodules tested at 30 and 60 Hz and some tests performed at 2 K. Careful balance between safe operational limits and the study of conditions, parameters and components that create physical limits has been achieved.

Introduction

The Spallation Neutron Source at the Oak Ridge National Laboratory is designed to provide a 1 GeV, 1.4 MW proton beam to a mercury target for neutron production. Approximately 81% of the beam energy is achieved in the superconducting part of the linac, where H- ions are accelerated in two different sections with 33 and 48 superconducting RF 6-cell cavities operated at 805 MHz (Table 1). Table 1: Major Design Parameters of the SNS SCL

Cryomodule Parameter	Medium Beta Section	High Beta Section
Output Energy (MeV)	379	1000
No. of Cryomodules	11	12
No. of cavities per cryomodule	3	4
Cavity Parameter	Medium Beta Cavity	High Beta Cavity
Geometric beta	0.61	0.81
EoT (MV/m)	10.1 at	15.9 at
Epeak (MV/m)	27.5	35.0
Hpeak (kA/m)	46.2 (580 Oe)	59.7 (750 Oe)
	176	228
r/Q at design beta	279	483
Equivalent Cavity Length (cm)	68.2	90.6