• M.T. Crofford, T.W. Hardek, S.W. Lee, M.F. Piller
  ORNL, Oak Ridge, Tennessee
• J.A. Ball, T.L. Davidson
  ORNL RAD, Oak Ridge, Tennessee

The Spallation Neutron Source (SNS) has been operating since the first neutrons were produced on April 29, 2006. During the last several years the beam energy has been methodically ramped-up and outlying issues solved to improve system reliability. During the beam studies a temperature dependence has been discovered with the Low-Level RF systems. The effect is small but readily observable as increased beam losses. The temperature dependence has been studied both in the accelerator and in the laboratory and the sensitive components identified. A prototype solution that replaces the temperature dependent components of the Low-Level RF System has been designed and is in initial testing. Preliminary results of the laboratory tests have been encouraging. Accelerator tests are planned after installation during the December 2010 maintenance cycle.

• S.W. Lee, J.A. Ball, T.L. Davidson, S.L. Jones
  ORNL RAD, Oak Ridge, Tennessee
• M.T. Crofford, T.W. Hardek
  ORNL, Oak Ridge, Tennessee

The Spallation Neutron Source (SNS) High-Power Protection Module (HPM) provided interlocks and fast shutdown for the RF system to protect the accelerating structures and high power RF (HPRF) Distribution System. The HPM has required some functionality upgrades since the start of beam operations and an upgrade to the HPM test stand was required to support these added features. The HPM test stand currently verifies functionality, RF channel calibration, and measurement of the speed of shutdown to ensure the specifications are meet. The upgraded test stand was implemented in a single FPGA to allow for future growth and flexibility. Work is currently progressing on automation of the test stand to better perform the required module calibration schedule.

• M.E. Middendorf
  ORNL RAD, Oak Ridge, Tennessee
• M.E. Clemmer, T.W. Hardek
  ORNL, Oak Ridge, Tennessee

The original SNS baseline installation included six 20kWpk vacuum tube power amplifiers (four online amplifiers and two ready spares, manually interchangeable) to drive the four rebuncher cavities that are part of the Medium Energy Beam Transport (MEBT) structure. We are in the process of replacing the six vacuum tube amplifiers with five commercially-available 25kWpk solid-state amplifiers that will connect to the rebuncher cavities through a remotely-operated 4+1 switching matrix. We report progress to date.

• Y.W. Kang, R.E. Fuja, T.W. Hardek, S.W. Lee, M.P. McCarthy, M.F. Piller, K.R. Shin, M.P. Stockli, A.V. Vassioutchenko, R.F. Welton
  ORNL, Oak Ridge, Tennessee

The Spallation Neutron Source (SNS) at Oak Ridge National Laboratory is in the process of ramping up the H^- ion beam power to 1.4 MW, its full design power for the neutron production. For robust operation of the neutron facility, work is underway for various improvements on the RF power systems of the ion source. For short and long-term higher beam power operations, an RF-driven H^- ion source employing external antenna with a water-cooled, ceramic aluminum nitride (AlN) plasma chamber has been developed*. The new ion source has been tested to deliver up to 42 mA in the SNS Front End (FE) and unanalyzed beam currents up to ~100mA (60Hz, 1ms) in the ion source test stand. In addition to the external antenna design for improved antenna lifetime, other RF developments for improvement of reliability are running 2 MHz power amplifier system is with isolation transformer, employing full solid-state 2 MHz power amplifier, more precise 2 MHz capacitive impedance matching, and upgrading 13 MHz RF plasma gun system. This paper discusses the engineering solutions with analysis and development of the above RF systems for the new ion source system.

R.F. Welton, N.J. Desai, J. Carmichael, B. Han, Y.W. Kang, S.N. Murray, T. Pennisi, M. Santana, and M.P. Stockli, "The Continued Development of the SNS External Antenna H^- Ion Source," ICIS2009