• T.W. Hardek, M.T. Crofford, Y.W. Kang, S.W. Lee, M.P. McCarthy, M.F. Piller, A.V. Vassioutchenko
  ORNL, Oak Ridge, Tennessee
• M.E. Middendorf
  ORNL RAD, Oak Ridge, Tennessee

Funding: SNS is managed by UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U.S. Department of Energy.

The SNS has been operational and delivering beam to the target for 3 years. Over this time period we have increased the beam power delivered to the target to 700 kW, 50% of the design goal. The RF Group has acquired a fair amount of experience in the operation and maintenance of our RF systems during the power ramp up process. This paper reviews the design and layout of the various SNS RF systems, documents the present state and performance of the systems and covers, in a broad sense, issues raised during operation and improvements we have undertaken as well as future RF system requirements.

• S.-H. Kim, D.E. Anderson, I.E. Campisi, F. Casagrande, M.T. Crofford, R.I. Cutler, G.W. Dodson, J. Galambos, T.W. Hardek, S. Henderson, R. Hicks, M.P. Howell, D. Jeon, Y.W. Kang, K.-U. Kasemir, S.W. Lee, J. Mammosser, M.P. McCarthy, Y. Zhang
  ORNL, Oak Ridge, Tennessee

Funding: SNS is managed by UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U.S. Department of Energy

The Spallation Neutron Source (SNS) is a second generation pulsed-neutron source and designed to provide a 1-GeV, 1.44-MW proton beam to a mercury target for neutron production. Since the initial commissioning of accelerator complex in 2006, the SNS has begun neutron production operation and beam power ramp-up has been in progress toward the design goal. Since the design beam power is almost an order of magnitude higher compared to existing neutron facilities, all subsystems of the SNS were designed and developed for substantial improvements compared to existing accelerators and some subsystems are first of a kind. Many performance and reliability aspects were unknown and unpredictable, for which it takes time to understand the systems as a whole and/or needs additional performance improvements. A power ramp-up plan has been revised based on the operation experiences and understandings of limits and limiting conditions through extensive studies with an emphasis on machine availability. In this paper the operational experiences of SNS Superconducting Linac (SCL), the power ramp-up status and plans will be presented including related subsystem issues.

• M.T. Crofford, T.W. Hardek, K.-U. Kasemir, M.F. Piller
  ORNL, Oak Ridge, Tennessee

The Spallation Neutron Source (SNS) has recently installed a prototype low level radio frequency (LLRF) control system for initial testing. This system is designed to replace the original fixed frequency, two harmonic Accumulator Ring LLRF system used to maintain a gap in the proton beam for extraction to the target. This prototype system is based on the hardware for the Linac LLRF system that has been modified to operate at the low frequencies required for the ring. The goal of the final system is to leverage the mature hardware and software of the Linac systems with the added flexibility needed to support the heavy beam loading requirements of the Accumulator Ring.

• M.F. Piller, M.T. Crofford, T.W. Hardek
  ORNL, Oak Ridge, Tennessee

Funding: SNS is managed by UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U.S. Department of Energy.

Four ferrite loaded resonant radio frequency (RF) cavity structures and one resistive wall current monitor (WCM) located in the South leg of the Spallation Neutron Source (SNS) accumulator ring provide a 250 ns beam extraction gap. Three ring RF cavities operate at the fundamental accumulator ring revolution frequency (~ 1.05 MHz) to bunch the beam while the fourth cavity operates at the second harmonic (~ 2.10 MHz) to suppress the peak beam current. The SNS ring low-level RF (LLRF) control system utilizes dynamic cavity tuning and proportional, integral, and derivative (PID) feedback control to regulate the amplitude and phase of the fields in the ring RF cavities. In April 2009 the SNS accelerator delivered 835 kW of beam power (928 MeV, 60 Hz, 15 uC/pulse) to the target during a neutron production run. This paper discusses operation and performance of the SNS ring LLRF system with high intensity beam loading.