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

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

3. 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

4. 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

5. Energy and power on target from October 2006
Presentation_name

6. NP efficiency by week, FY09

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

8. Unscheduled Down Time Summary
Big
Improvements
Last year !!

9. 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

10. 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

11. 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

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

13. 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

14. 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

15. Plasma Cleaning Investigation

16. 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

18. 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

19. 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

20. 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

21. 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

22. 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

23. 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 GHz to a tunable TE011 cavity capable of holding circular samples of 1 inch diameter

24. 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

25. 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

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

27. 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