Operating Experiences at SNS Ricky Campisi, Robbie Hicks, Sang-Ho Kim, and J. Mammosser

Outline: SNS Operational Reliability Overview SCL Operations SRF Activities at SNS Preparation for the Power Upgrade

SNS Accelerator Complex Accumulator Ring Collimators Front-End: Produce a 1-msec long, chopped, H- beam 1 GeV LINAC Accumulator Ring: Compress 1 msec long pulse to 700 nsec Injection Extraction RF Liquid Hg Target RTBT 2.5 MeV 87 MeV 186 MeV 387 MeV 1000 MeV Ion Source HEBT RFQ DTL CCL SRF, b=0.61 SRF, b=0.81 11-MB 12-HB Target SCL Cryomodules Chopper system makes gaps 945 ns mini-pulse Current Current 1 ms macropulse 1ms

Major Parameters achieved vs. designed Individually achieved Highest production beam Beam Energy (GeV) 1.0 1.01 0.93 Peak Beam current (mA) 38 40 Average Beam Current (mA) 26 24 Beam Pulse Length (ms) 1000 670 Repetition Rate (Hz) 60 Beam Power on Target (kW) 1440 880 Linac Beam Duty Factor (%) 6 4.0 Beam intensity on Target (protons per pulse) 1.5 x 1014 1.3 x 1014 1 x 1014 SCL Cavities in Service 81 80

Energy and power on target from October 2006 Presentation_name

NP efficiency by week, FY09

Down Time – Pareto Chart for FY09-1 & 2 HVCM + Electrical Systems MEBT Rebunchers

Unscheduled Down Time Summary Big Improvements Last year !!

Beam Study / Production Cycles Red = extended maintenance Yellow = physics Green = production ~ 1-2 weeks to recover from extended outage (coming out of a “red” period) Recovery from one 8 hour shift outage takes ~ 1 shift Moving towards a 3 week rhythm in FY2009 to reduce the number of beam-study to production transitions

SCL Maintenance and Operations highlights: Current operating parameters are providing for a very stable and reliable SCL One trip per day mainly by errant beam or control noise No cavity performance degradation has occurred to date Field emission very stable Several cryomodules were successfully repaired without disassembly Multiple beam-line repairs were successfully performed

H06 back to service Irregular dynamic detuning H01 out of service for repair Noisy FP HOMB ~35 MeV reduction in output energy; lack of available RF power ~4 MeV reduction in output energy; FPC multipacting HOMB

Linac Energy Limiting factor (I) Cavity performances Field emission (major limiting factor) Coupler heating Others

SRF R&D Underway at SNS: Two primary areas of SRF research are underway at SNS: Critical Field Limitations in Superconducting Materials Aimed at studying superconducting material limitations Fits into ORNL’s high Tc material studies as well as SRF cavity work Plasma Cleaning of Superconducting RF Structure Surfaces Addresses the field emission limited SCL performance The best way for the entire linac to gain reliability Fits nicely with ORNL’s material science resources

Plasma Cleaning of RF Structures: In September 08 we started to investigate the possibilities of applying this cleaning method to superconducting cavities Established a stable plasma in a room temperature HB cavity Then a plasma was applied to 3 of the 4 cavities in a fully populated cryomodule at 4.2K

Plasma Cleaning Investigation

Plasma Processing Development A program is underway to develop and apply plasma cleaning methods to installed accelerator RF components If successful this should significantly reduce field emission, mulitpacting and increase operating stability of RF structures Experimental Program Includes Witness samples from standard processes TM020 test cavity And full RF structures for testing and procedure development

Radiation/electron activity diagnostics in the Test Cave Cavity D Cavity C Cavity B Cavity A IC2 IC7 IC3 IC4 IC5 IC6 Phosphor Screen & Faraday Cup Phosphor Screen & Faraday Cup IC0 IC-int Ionization Chamber Internal Ionization Chamber Phosphor Screen, Camera, Faraday Cup

Radiation (before and after processing) Radiation reduced by factor of 5 to 100 Showed promising results for in-situ processing before after Eacc=10 Eacc=10

Gases coming out during partial warm-up at T1 44 During T3 28 32 28 16 16 32 14 40 12 30 4 18 2 2 18 44 20 14 4 at T2 T3 T1 T2

Test Cavity SRF cavity FPC Flange Surface analysis 3.3 GHz, TM020 mode Ep/Bp=1.12 (MV/m)/mT Ex. Ep=50 MV/m, Bp=56 mT Pdiss=36 W at 4.2 K 150 mm -Cold test w/ dual mode (CW or pulse) -Plasma processing Demountable witness plate FPC Flange Microwave Plasma processor

Multipacting at FPC MP at FPC; heating at higher beam loading 4 cavities; entered aggressive MP purely at FPC Reached limits at 21~22mA average current About 10 more FPCs may enter MP region at higher beam current DC biasing will be incorporated for those cavities

TE011 cavity surface magnetic fields Critical RF fields in SC materials TE011 cavity surface magnetic fields Purpose: determine critical RF fields in various superconducting materials to evaluate possible improvements over Niobium Method: apply 1 msec (or shorter) pulses of 100 kW to several MW at 16-18 GHz to a tunable TE011 cavity capable of holding circular samples of 1 inch diameter

Copper cavity for tests at 16-18 GHz Tuning diaphragm Transmission probe (Qext > 108) Superconducting sample Thermometer WR 62 waveguide Tuning Piston Coupling iris (Qext = 4x104) Differential thermometer 1” RF seal

Power Upgrade Activities: SRF facilities installations continue Ultra pure water system completed HPR currently being fabricated at Niowave,USA Vertical and horizontal testing facility designs completed and some fabrication has started Support refrigerator design underway Input coupler development will begin soon Currently building first spare HB cryomodule Vacuum vessel envelope was redesigned for pressure vessel compatibility Cavities are currently being qualified at Jefferson Lab

Power Upgrade Cryomodule Design Bayonets remain in original positions “Code” Bolted Flanges J-T’s repositioned

Summary: SNS is approaching the design beam power and availability currently operating at 800KW of beam power Mega watt attempt will be soon SCL operations are very stable with 99% availability Current linac energy 930 MeV + 10 reserve 80 of 81 cavities in service SRF R&D is underway Material Critical Field Limitations Plasma Processing Development