Progress with the SNS front-end systems

LBNL-47317 PROGRESS WITH THE SNS FRONT-END SYSTEMS* R. Keller,** W. Abraham, J.J. Ayers, D.W. Cheng, P. Cull, R. DiGennaro, L. Doolittle,** R.A. Gough,** J.B. Greer,** M.D. Hoff,** K.N. Leung, S. Lewis, C. Lionberger, R. MacGill, Y. Minamihara, M. Monroy, D. Oshatz,** J. Pruyn, A. Ratti,** J. Reijonen, T. Schenkel,** J.W. Staples,** D. Syversrud, R. Thomae, S. Virostek,** and R. Yourd** Ernest Orlando Lawrence Berkeley National Laboratory, Berkeley, CA Abstract The Front-End Systems (FES) of the Spallation Neutron Source (SNS) project have been described in detail else- where [1]. They comprise an rf-driven H - ion source, electrostatic LEBT, four-vane RFQ, and an elaborate MEBT. These systems are planned to be delivered to the SNS facility in Oak Ridge in June 2002. This paper dis- cusses the latest design features, the status of development work, component fabrication and procurements, and ex- perimental results with the first commissioned beamline elements. the present paper emphasizes design changes and progress with construction. Some basic features, however, are pre- sented here as well, to facilitate easier understanding and address recent changes in main SNS parameter values as they relate to the front end. A 3-dimensional CAD layout of the front-end beamline is shown in Figure 1, omitting all ancillary systems. The SNS accelerator systems aim at delivering intense proton-beam pulses of less than 1-µs duration to the spal- lation target at 60-Hz repetition frequency and with an average beam power of 1.44 MW. The 1-ms long H - mac- ro pulses that are accelerated in the linac to 1-GeV energy have to be chopped into ‘mini pulses’ of 645-ns duration, with 300-ns pauses. Chopping is performed in the front end by two separate chopper systems located in LEBT and MEBT, respectiv- ely. The LEBT chopper removes most of the beam power during the mini-pulse gaps, and the MEBT chopper re- duces the rise and fall time of the transported beam. The main requirements for the SNS Front-End Systems are listed in Table 1. The front end is being assembled and commissioned at the Integrated Testing Facility at LBNL before being shipped to ORNL in the summer of 2002. 1 INTRODUCTION The Spallation Neutron Source (SNS) project [2] is presently in the third year of its construction phase. LBNL is building the front end (linac injector) with its main sub- systems consisting of ion source, low-energy beam- transport section (LEBT), RFQ accelerator, and medium- energy beam-transport section (MEBT). Some parts of the front end, i.e. the rf power system for the RFQ and the MEBT chopper structures with their power supplies, will be supplied by LANL; some diagnostic elements by BNL. The SNS Front-End project has been described in detail elsewhere with an ample collection of references [1], and Ion Source/LEBT Create 50-mA beam RFQ Accelerate beam to 2.5 MeV LEBT/MEBT Chop beam into mini-pulses MEBT Match 40-mA beam into DTL Figure 1. Layout of the SNS front-end beamline. *Work supported by the Director, Office of Science, Office of Basic En- ergy Sciences, of the US Department of Energy under Contract No. DE- AC03-76SF00098. **Author/co-author of other contributions submitted to this conference.