ORNL is managed by UT-Battelle for the US Department of Energy Low Level RF Status and Development Activities at the Spallation Neutron Source Mark Crofford RF Systems Manager LLRF 2015 Workshop, Shanghai, China

2 LLRF2015 Workshop LLRF Overview Original LLRF systems installed in 2005 continue to support reliable operation –Accelerator availability is >4500 –LLRF system failures account for <1% of accelerator downtime Majority of LLRF downtime is attributed to cable and connector failures Incremental improvements only –Improved EPICS screens for Operations –Cavity conditioning screens –Diagnostics tools (MatLab and user scripts) Investigation to add predictive beam loading compensation –Provides an initial compensation starting point to limit beam losses Operation above 1.3 MW is routine –Limited by spare target availability

3 LLRF2015 Workshop Typical High-Availability Operation

Energy and power on target from October 2006

5 LLRF2015 Workshop Projects and Developmental Work The LLRF Team provides engineering support for the SNS project –Diagnostic systems Linac & Ring Beam Position Monitor (BPM) Analog Front End (AFE) Beam Loss Monitor (BLM) amplifier –Electrical and Magnet systems Low Energy Beam Transport (LEBT) Chopper Pulser Extraction-Kicker Pulse Monitor –Ion Source RF –LLRF Development Linac LLRF Ring LLRF

6 LLRF2015 Workshop Diagnostics Systems New systems must be drop-in replacements for existing systems Use commercial-off-the-shelf solutions where possible Linac BPM AFE based on LLRF AFE redesign –805 MHz –402.5 MHz –Ring version is currently under development BLM AFE designed for both low and high gain applications to support all 362 detectors *IBIC’15, MOBLA02, - “SNS Beam Diagnostics: Ten Years After Commissioning” Linac BPM AFE Linac BPM System BLM AFE

7 LLRF2015 Workshop LEBT Chopper Pulser Logic Board Digital timing adjustments for setting chopper pulse parameters Fiber Optic isolation On – Off command signal generation Digital delay devices –Digitally select pulse width –Digitally select phase shift –Digital over temp detector *PPC2015, Peplov, V. - “New Pulsed Power Supply for the Spallation Neutron Source Linac LEBT Chopper System”

8 LLRF2015 Workshop Extraction Kicker Pulse Monitor 4 channel – gated window comparator Magnet current Pulse Forming Network (PFN) current High Voltage Power Supply (HVPS) voltage PFN voltage *Courtesy of Robert Saethre E-Kicker Pulse Monitor Board

9 LLRF2015 Workshop Vertical Test Area (VTA) Control System Combination of commercial-off-the-shelf equipment and custom hardware –Self-excited loop NI PXIe based control/data acquisition Successfully commissioned –4 & 2K operation –CW & pulsed VTA Main Screen – 2K pulsedVTA RF Control System *SRF2015, TUPB093, - “Initial Commissioning Experience with the Spallation Neutron Source Vertical Test Area RF System”

10 LLRF2015 Workshop Ion Source RF SNS RF Ion Source generates pulsed 50+ mA H- beam Production SNS RF Ion Source plus three additional RF Ion Source test stands Pulsed and CW RF systems (2 MHz – MHz, up to 120 kW) HV environment: –-65 kV source potential provides initial H- beam acceleration –RF isolation transformer development Issues with source plasma density variations during high intensity RF pulse –Addressed using feed-forward amplitude and frequency shifting

11 LLRF2015 Workshop High-power Protection Module (HPM) Development LLRF system is one of the major troubleshooting tools for the accelerator Original HPM design is adequate for operations but improved diagnostics are desired –More and deeper history buffers –Improved time resolution –Additional hardware inputs –Improved triggering functions SNS VXI interface redesigned & tested ADCs selected and prototype tested –14 bit versus original 10 bit ADC Test Board HPM Development Board

12 LLRF2015 Workshop Field Control Module (FCM) Development Current FCM has been very reliable but many of the key parts are now obsolete –Additional ADC input would be beneficial for beam loading compensation Investigating COTS solution for sections of the design Prototyping with the VME64 SVEC Janztec board from the Open Hardware Repository –Supports dual FMC mezzanine cards Testing both commercial FMC and custom cards –Front panel space can be an issue Limitation of VME bus needs to be addressed 4DSP FMC-150 SVEC FMC Carrier Card

13 LLRF2015 Workshop What Platform to Choose? All platforms have pros & cons… –How to stay compatible with the currently installed systems? –Is the current VXI bus adequate for the data rates desired? –Should the Linac and Ring LLRF be identical? These are questions we are working to answer now. MicroTCA VME/VXI PXIe Pizza Box

14 LLRF2015 Workshop Summary The accelerator is a mature facility that has been in operation since –Continues to meet the power, availability and reliability goals of 4500 >90% availability. –Routine operation >1.3 MW The LLRF systems meet all requirements and continue to support incremental improvements. –Operator convenience improvements –Investigating better beam loading compensation Considerable time and effort is used to support designs outside of the normal LLRF roles. We are actively working on the next generation control system but are still in the early stages of development. –Looking forward to the discussion on platforms!

15 LLRF2015 Workshop Acknowledgement Thanks to the SNS LLRF Team for their dedication and hard work. None of this would be possible without the help of everyone involved. *This presentation has been authored by UT-Battelle, LLC under Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (