1. SNS Operating Modes and Reliability Studies Presented at the 4 th Open Collaboration Meeting on Superconducting Linacs for High Power Proton Beams (SLHiPP-4), CERN May 15-16, 2014 Sang-ho Kim Spallation Neutron Source Research Accelerator Division, ORNL

2. 2 SLHiPP-4, May 15-16, 2014 FY14 Operation Schedule NP delivery committed: 5064 h*90%~4500 h Special in FY14 to replace target Long maintenance:2328 h Machine start up: 464 h Transition to NP: 129 h AP study: 528 h Maintenance during NP: 516 h

3. 3 SLHiPP-4, May 15-16, 2014 Till May 4, 2014 FY12 downtime includes ~150 hours target premature failure FY13 downtime includes ~1030 hours target premature failure and ~70 hours PPS SNS Operational Statistics NP hours, MWh Availability

4. 4 SLHiPP-4, May 15-16, 2014 SNS operational history Ion Source, LEBT Target CMS leak HVCM Stripper foil 1 MW beam power on target achieved in routine operation High reliability? Management decision Target premature Failure – QA/QC/Spares 1.4MW demo

5. 5 SLHiPP-4, May 15-16, 2014 Current run (93.5% availability) Optional maintenance day

6. 6 SLHiPP-4, May 15-16, 2014 Downtime by Fiscal Year (07-13) comparison

7. 7 SLHiPP-4, May 15-16, 2014 SNS SCL systems downtime statistics NP scheduled hours : 5802 : 5248 : 5436 Cavity Trip Control/BI HVCM Power dip Vacuum CHL HPRF Transmitter Others electric & water FY13 other electric: Large transformer switchgear failure FY13 HPRF: a filament power supply spare problem for klystron CHL: 2K trip due to VFD glitch, loose wire, power glitch HVCM: one or two bad actors every run FY12 NP hours includes ~150 hours target premature failure FY13 NP hours includes ~1030 hours target premature failure and ~70 hours PPS Downtime (hour) Next page

8. 8 SLHiPP-4, May 15-16, 2014 Downtime statistics from cavity/CM Coupler Temp. Errant beam or its consequence Halo at upstream or its consequence Arc detector Bad instrument/ improper setting Truncation by HPRF Conditioning period at machine startup Large reduction from errant beam/halo or their consequences in FY13 (FY14 is not as good as FY13) FY13 cavity trips due to conditioning: during preparation of full duty factor and 1.4 MW run 95 % of cavity trip due to Arc detector: during arc detector test (every mid-night to check the functionality of arc detector) FY13 bad instrument: Pressure transducer failure in CM19 Trips due to coupler temperature: flow is well- balanced or enough Downtime (hour)

9. 9 SLHiPP-4, May 15-16, 2014 Current operational strategy for 1.4 MW Beam current – Ion source current is providing the design current or higher – RFQ field is running lower than design (transmission is lower) – Added capability to run at shorter gap in LEBT chopper Pulse width – HVCM has been running at full duty factor (975us for beam) Beam energy – 940 MeV (+13 MeV energy margin) mainly due to lower operating gradients of high beta cavities – R&D, spare CMs, rework, etc.

10. 10 SLHiPP-4, May 15-16, 2014 SNS Cavity Operating Regime Time Measurements of Radiation during RF Pulse Radiation (arb. Unit) Radiation (in log, arb. Unit) Eacc FE onset Radiation onset MP Surface condition Operating setpoints: Basically running in the field emission regime. Majority of cavities

11. 11 SLHiPP-4, May 15-16, 2014 Current SCL operating gradients Average Eacc of medium and high beta cavities:12 MV/m, 13 MV/m respectively Cavity Number Eacc (MV/m) Spare CM developed in house Operation since summer 2012

12. 12 SLHiPP-4, May 15-16, 2014 Performance improvement Rework of cryomodules: only option for unrecoverable damage Spare cryomodules – High beta spare was developed and in service now – Medium beta spare is waiting for funding In-situ processing? – Investigated possible method for the SNS CMs Helium processing: did not work due to severe MP in the end group/HOM Plasma processing: just attempted. Promising result.

13. 13 SLHiPP-4, May 15-16, 2014 High beta spare cryomodule was developed by in-house SNS resources and is the first to be ASME pressure-vessel code compliant Allows removal of operating high beta cryomodule for repair – Rework is the only option for the unrecoverable damages of cavity surface/parts – Maintain same beam energy while conducting complex repairs High beta spare cryomodule serves as prototype for upgrades – Fabrication techniques were developed (the first ASME Boiler and Pressure Vessel code stamped cryomodule addressing10CFR851 requirement) – Commissioning was successfully performed at the SNS test facility Sets the baseline design for a medium beta spare cryomodule Spare has been in service since the summer of 2012 and all four cavities are operating at 16 MV/m (RF power limited)

14. 14 SLHiPP-4, May 15-16, 2014 The spare cryomodule

15. 15 SLHiPP-4, May 15-16, 2014 Motivation for in-situ processing in the tunnel Medium term – Recover from cavity performance degradations – Reach 1GeV + energy reserve (Increase high beta cavity gradients by about 2 MV/m in average) Long term – STS: 2 beam (50 Hz 33.3mA for FTS, 10 Hz 38mA for STS) – 38-mA beam loading with 2 nd target station: Need narrower performance scattering  Efficient utilization of RF power (ideally constant RF power/cavity is preferred) Develop a cost effective processing method with minimal impact on machine operation

16. 16 SLHiPP-4, May 15-16, 2014 Eacc and RF power requirement for STS For new cavities Blue Qex, ref -20 % Red Qext, ref =7e5 Green Qex, ref +20 % RF Power requirement Existing klystrons Klystrons for STS: 700kW 7 additional high beta CMs 1.3 GeV + energy margin

17. 17 SLHiPP-4, May 15-16, 2014 Cavity D 12 MV/m Camera exposure; 30 ms Cavity A 9.3MV/m Camera exposure; 30 ms Phosphor screen images before processing Processed at cold and warm up RGA analysis  some C-H-(O)-(N) Statistically optimized? Coupler damage? Solid byproduct? Need R&D

18. 18 SLHiPP-4, May 15-16, 2014 Develop in-situ plasma processing technique for superconducting RF cavities – In-situ processing means a processing in the tunnel for the cost saving with minimal impact on the machine operation – Preliminary test in 2009 gave a promising result Plasma processing aims at removing residual surface contaminants to increase cavity accelerating gradients by 10-15 % in average – This technique could be a alternative or additional cleaning method for any SRF cavities during production or in operation if successful R&D started in 2012 to develop a reliable technique for in-situ plasma processing at SNS R&D for performance improvement

19. 19 SLHiPP-4, May 15-16, 2014 SRF facilities are being developed to meet the immediate reliability goals and to provide for the long term stewardship of the accelerator Mission Statement The SCL Systems Facility will enable laboratory staff to develop and test improvement plans for the SNS SCL, advance material science for SRF, cultivate collaborations with other laboratories, and contribute to future machines and projects. With this facility in place, SNS can be responsive to customer needs! Conduct our own repairs R&D focused on improving our application Support Second Target Station (STS) with increased capability System is not intended to be production scale Reduces capital investment Ensures priorities of facility are in line with SNS objectives

20. 20 SLHiPP-4, May 15-16, 2014 SNS SRF Facilities 60 m Test cave Control room VTA CTF Kinney For CTF HTA CM development 5MW klystron & Coupler conditioning HPR CM rework String Assem. Clean room Barrel Polishing Furnace Cavity R&D

21. 21 SLHiPP-4, May 15-16, 2014 Summary The current reliability and availability of the SCL is high but there are key issues that must be addressed Cryomodule rework and development is an active program – High beta spare cryomodule commissioned and operating in LINAC – Medium beta spare cryomodule design initiated – CM6, CM20 repaired Research and development is ongoing to improve the current performance of the accelerator and prepare for the STS – Plasma R&D focused on achieving 1.4 MW – Cavity and coupler development in preparation for STS An investment in facility development is already supporting the operation and has ensured priorities are aligned with SNS goals including STS