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Commissioning and Initial Operating Experience with the SNS Accelerator Complex

Commissioning and Initial Operating Experience with the SNS Accelerator Complex. First Beam on Target, First Neutrons and Technical Project Completion Goals Met April 28, 2006 . Beam and Neutronics Project Completion goals were met 10 13 protons delivered to the target

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Commissioning and Initial Operating Experience with the SNS Accelerator Complex

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  1. Commissioning and Initial Operating Experience with the SNS Accelerator Complex

  2. First Beam on Target, First Neutrons and Technical Project Completion Goals Met April 28, 2006 • Beam and Neutronics Project Completion goals were met • 1013 protons delivered to the target • The SNS Construction Project was formally Completed in June 2006 • We have officially started SNS Operations

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

  4. SNS High-Level Design Parameters Ring is designed for 2 MW at 1 GeV; installed for 1.3 GeV (mostly)

  5. The SNS Partnership ORNL Accelerator Systems Division responsible for integration, installation, commissioning and operation

  6. Spring 1999

  7. Now

  8. Front-End Systems • Front-End H- Injector was designed and built by LBNL • 402.5 MHz Radiofrequency quadrupole accelerates beam to 2.5 MeV • Medium Energy Beam Transport matches beam to DTL1 input parameters • Front-end delivers 38 mA peak current, chopped 1 msec beam pulse • H- Ion Source has been tested at baseline SNS parameters in several endurance runs • >40 mA, 1.2 msec, 60 Hz

  9. Accumulator Ring and Transport Lines • Designed and built by Brookhaven National Lab Collimation Accumulator Ring Extraction Injection Circum 248 m Energy 1 GeV frev 1 MHz Qx, Qy 6.23, 6.20 x, y -7.9, -6.9 Accum turns 1060 Final Intensity 1.5x1014 Peak Current 52 A RF Volts (h=1) 40 kV (h=2) 20 kV Injected p/p 0.27% Extracted p/p 0.67% RF RTBT HEBT Target

  10. Ring and Transport Lines HEBT Arc Ring Arc Injection RTBT/Target

  11. Target Region Within Core Vessel Target Module with jumpers Outer Reflector Plug Target Moderators Core Vessel water cooled shielding Proton Beam Core Vessel Multi-channel flange

  12. Normal Conducting Linac: Front-End Output Emittance and Bunch Length • MEBT inline emittance system allows routine measurement • Expect 0.3  mm mrad, rms, norm • Results ( mm mrad, rms, norm) • X = 0.29 • Y = 0.26 • Bunch length measured with mode-locked laser system RMS Bunch Length (deg) Rebuncher phase (deg)

  13. DTL and CCL RF Setpoints by Phase Scan Signature Matching J. Galambos, A. Shishlo • To tune up the linac requires finding phase and amplitude setpoints for 95 RF systems within 1%/1 deg (specification) • Model-based methods utilizing time-of-flight data have been developed • Normal conducting linac phase and amplitude setpoints determined by Phase-Scan Signature Matching • Plot shows data (lines) compared to model (pts) for two CCL2 amplitudes BPM Phase Diff (deg) CCL Module 2 RF Phase

  14. CCL Module 1 Longitudinal Bunch Shape Monitor Measurements BSM107 BSM111 • Measured values are close to the predicted bunch length • Measurements were motivated by earlier observations of a longer bunch, presumably due to longitudinal mismatch

  15. Superconducting Linac Tuneup by Phase Scan SCL phase scan for first cavity Solid = measured BPM phase diff Dot = simulated BPM phase diff Red = cosine fit • Fit varies input energy, cavity voltage and phase offset in the simulation to match measured BPM phase differences • Relies on absolute BPM phase calibration • With a short, low intensity beam, results are insensitive to detuning cavities intermediate to measurement BPMs BPM phase diff  Cavity phase

  16. Low-level RF Feedforward • Beam turn-on transient gives RF phase and amplitude variation during the pulse, beyond bandwidth of feedback • LLRF Feedforward algorithms have been commissioned (Champion, Kasemir, Ma, Crofford) Without Feed-forward With Feed-forward

  17. SCL Operations: Fault Recovery (Galambos) • We have successfully tested a cavity fault recovery algorithm in which the phase of all downsteam cavities are adjusted in response to a change in setpoint of a given cavity Turned on cavity 4a, reduced fields in 11 downstream cavities Final cavity phase found within 1 degree, output energy within 1 MeV Cavity 3a turned off

  18. Ring/RTBT/Target Commissioning Timeline January-May 2006 Jan. 12: Received approval for beam to Extraction Dump. Jan. 13: First beam to Injection Dump. Jan. 14: First beam around ring. Jan. 15: >1000 turns circulating in ring Jan. 16: First beam to Extraction Dump. Jan. 26: Reached 1.26E13 ppp to Extraction Dump. Feb. 11: ~8 uC bunched beam (5x1013 ppp) Feb. 12: ~16 uC coasting beam (1x1014 ppp) Feb. 13: End of Ring commissioning run April 3-7: Readiness Review for RTBT/Target April 27: Received approval for Beam on Target April 28: First beam on target and CD4 beam demonstration

  19. Accumulation and Extraction of 1.3x1013 protons/pulse (January 26, 2006) Ring Beam Current Monitor extraction 200 turn accumulation Extraction Dump Current Monitor

  20. Ring Orbit Correction: H,V Bumps are Due to Injection Kickers Horizontal Orbit Vertical Orbit BPM Amplitude

  21. Ring Optics Measurements: Betatron Phase Advance and Chromaticity Plots show measured betatron phase error vs. model-based fit Data indicates that the linear lattice is already very close to design

  22. High Intensity Studies (Danilov, Cousineau, Plum) Fast: electron-proton • Beam intensity records (protons/pulse): • 5x1013 in bunched beam, transported to target • 1x1014 unbunched, coasting beam • We searched for instabilities by i) delaying extraction, ii) operating with zero chromaticity, iii) storing a coasting beam • No instabilities seen thus far in “normal” conditions • See instability centered at 6 MHz, growth rate 860 us for 1014 protons in the ring, driven, as predicted by extraction kicker impedance • Zcalc22-30 kOhm/m • Zmeas 28 kOhm/m. • In coasting beam also see very fast instability at 0.2-1x1014 protons in the ring, consistent with e-p. Growth rate 20-200 turns. f 30-80 MHz depending on beam conditions. • Scaling these observations to nominal operating conditions predicts threshold > 2 MW for extraction kicker (as previously predicted) Slow: Extraction Kicker

  23. Phase Space Painting Stripping Foil Initial Closed Orbit Injected Beam Final Closed Orbit px X Wei et. al., PAC 2001, 2560 X-Y space after 1060 Turns

  24. Phase Space Painting Beam on Target View Screen Beam profiles in RTBT 65 mm 80 mm

  25. Summary of Achieved Beam Parameters

  26. Beam-Power-on-Target History Beam power administratively limited to 10 kW until November 8 Beam Power [0-65 kW] May 1, 2006 Feb 1, 2007

  27. FY 2007 Integrated Beam Power by Day and Cumulative • 6.3 MW-hrs delivered in Run 2007-1

  28. Technical Challenges: Equipment Reliability • Beam Chopper Systems • Repeated failures in Low-energy and Medium-energy Beam Transport chopper systems • New, more robust, designs will be designed and manufactured this year (FY07 Accelerator Improvement Project) • High-Voltage Converter Modulators • A number of weak components limit MTBF to 2700 Hrs • Several prototype improvements are in test in single operational units • Improvements will be deployed this year on full system of 14 modulators (FY07 Accelerator Improvement Project) • Ion Source and Low Energy Beam Transport System • Water Systems • Problems associated with clogging flow restrictors, failed gaskets, poor conductivity monitoring and control, etc. • Reliability improvements have been underway since CD-4 (also FY07 AIP) • Cryogenic Moderator System • Thermal capacity degraded in 3 week cycle prior to December 2006 • Manufacturer attempted repair in December • Capacity improved, but some sign of degradation remains • Mercury Pump • Seal failed end of November • Operating the pump now with failed seal, mitigated by installation of a cover plate to direct gas to the Mercury Off-Gas Treatment System • Replacement Mercury Pump in expected to be available for installation in September

  29. Technical Challenges: Beam Power • Beam losses must be kept below 1 Watt/m to limit residual activation • We measure higher than desired losses in the Ring Injection area • We are unable to simultaneously transport waste beams (from stripping process) to the injection dump and properly accumulate in the ring • Internal Review of Injection Dump performance was held in November and follow-up meeting in December • Short-term fixes allow >100 kW operation; mid-term fixes (April 2007) are in preparation; long-term fix requires redesign of injection dump beamline and 2 new magnets • An aggressive accelerator physics program has reduced losses and activation while allowing increased beam power • We are not operating 9 Superconducting RF cavities (out of 81) out of concern for potential failures • Recent tests indicate that 6 of these 9 cavities are operable up to 15 Hz repetition rate • Those tests also show that the behaviour of individual cavities is the same at higher repetition rates, up to the full 60 Hz • We are building infrastructure to provide cryomodule repair and maintenance capabilities on-site. We are formulating plans to restore operation of all cavities, and to procure spare cryomodules

  30. Outlook: Performance Goals FY07 FY08 FY09 • SNS Beam Power Upgrade Project will increase linac output energy to 1.3 GeV and provide 3 MW beam power

  31. E-P Feedback Experiment at the PSR • We formed a collaboration to carry out an experimental test of active damping of the e-p instability at the LANL PSR (ORNL, LBNL, IU, LANL) • We deployed a broadband transverse feedback system designed and built by ORNL/SNS and demonstrated for the first time damping of an e-p instability in a long-bunch machine • We observed a 30% increase in e-p instability threshold with feedback on.

  32. Laser-Stripping Injection Proof-of-Principle Experiment Laser Beam High-field Dipole Magnet High-field Dipole Magnet  H- H0 H0* proton Step 1: Lorentz Stripping Step 3: Lorentz Stripping Step 2: Laser Excitation H- H0 + e- H0 (n=1) +  H0* (n=3) H0* p + e- • We have observed > 90% H- to proton stripping efficiency in proof-of-principle tests at SNS H- to protons

  33. Yes, We’ve Had a Few Surprises • RFQ resonant frequency shifted by 100 kHz • Never found the cause; retuned in 2003 • Bunch length 3x design in CCL1; also had difficulty keeping DTL5 at design field • Found a charred piece of paper in DTL Tank 5 in 2004 • Large local losses and poor trajectory near SCL/HEBT transition • Found large dipole deflection with orbit response studies • Found current shunted around one quad coil • Beam is rotated about 6 degrees on target view screen • Excessive fundamental power through two SCL HOM feedthroughs; others impacted • Large local losses in injection dump line

  34. Summary • Completed 7 beam commissioning runs, amounting to more than 1 year of dedicated beam commissioning and operating time • Achieved beam and neutron project completion requirements within project schedule • SNS construction project was formally completed in June 2006 on-budget and on-schedule • We are now in the early operations stage with local users • We are beginning to ramp up the beam power of the SNS accelerator complex

  35. SNS Beam Diagnostic Systems RING 44 Position 2 Ionization Profile 70 Loss 1 Current 5 Electron Det. 12 FBLM 2 Wire 1 Beam in Gap 2 Video 1 Tune MEBT 6 Position 2 Current 5 Wires 2 Thermal Neutron 3 PMT Neutron 1 fast faraday cup 1 faraday/beam stop D-box video D-box emittance D-box beam stop D-box aperture Differential BCM Operational IDump 1 Position 1 Wire 1 Current 6 BLM Not Operating EDump 1 Current 4 Loss 1 Wire CCL 10 Position 9 Wire 8 Neutron, 3BSM, 2 Thermal 28 Loss 3 Bunch 1 Faraday Cup 1 Current RTBT 17 Position 36 Loss 4 Current 5 Wire 1 Harp 3 FBLM DTL 10 Position 5 Wire 12 Loss 5 Faraday Cup 6 Current 6 Thermal and 12 PMT Neutron SCL 32 Position 86 Loss 9 Laser Wire 24 PMT Neutron HEBT 29 Position 1 Prototype Wire-S 46 BLM, 3 FBLM 4 Current LDump 6 Loss 6 Position 1 Wire ,1 BCM CCL/SCL Transition 2 Position 1 Wire 1 Loss 1 Current

  36. Baseline SNS Ion Source Performance Our Best Run (employs new operating procedure) 3 Typical Test Runs Catastrophic antenna failure Run #9 ran for 16 days / 33 mA / 0.4 mA/day. Beam attenuation ~5 mA/day • LBNL H- ion source + ORNL antennas • Source performed well during SNS commissioning. • Successful commissioning would not be possible without use of longer-lived antennas. • 10-40 mA routinely delivered at ~0.1% duty-factor. • Availability improved: 86%  ~100% during later commissioning periods (target comm: 77 days). • Largest availability gain  redesigning LEBT insulators + Antennas: Welton et al, RSI 73 (2002) 1008 • ~10 lifetime tests performed at full 7% duty-factor and max current. • Best results shown • Outcome: Insufficient beam current, frequent antenna failures and poor beam stability with time • Vigorous R&D program to meet SNS operational requirement of 40 mA and SNS-PUP requirement of 60 mA.

  37. Recent Ion Source R&D Accomplishments Cs injection collar Ionization Cone Extractor electrode ions Air duct Cs Line Al2O3 insulator Cooling channel Cathode Ions Plasma stream Anode Elemental Cs system • 65 mA-1.2 ms, 70 mA-0.2 ms pulses achieved at 10Hz! • ~2x increase in RF power efficiency. • Multi-day runs show excellent beam stability. • Multiple cesiations show excellent reproducibility. • ~5% droop and good ~30 us rise times. • Beam emittance is expected to be similar to baseline source. Welton et al, LINAC 2006, Knoxville External Antenna & Plasma Gun • Multi-year lifetime achieved at DESY at <1% duty-factor • Plasma gun enhances H- ~50% • 51 mA – 0.2 ms pulses achieved with no Cs and no B-field confinement. • 65 mA – 0.2 ms, 50 mA – 1.2 ms pulses achieved with Cs and no confinement. Welton et al, LINAC 2006, Knoxville

  38. Energy Stability – Pulse to Pulse (J. Galambos) • RMS energy difference jitter is 0.35 MeV, extreme = + 1.3 MeV • Parameter list requirement is max jitter < +1.5 MeV 865 MeV beam ~ 1000 pulses 20 msec pulse 12 mA beam

  39. SCL Laser Profile Measurements • SCL laser profiles (H + V) were available at 7 locations • 3 at medium beta entrance, 3 at high beta entrance and 1 at the high beta end Measured horizontal profile after SCL cryomodule 4

  40. Neutrons: 4-methyl pyridine N-oxide 5 kWatt, 3 hour, ¼ detector, T = 3 K 4 meV

  41. The Spallation Neutron Source • The SNS is a short-pulse neutron source, driven by a 1.4 MW proton accelerator • SNS will be the world’s leading facility for neutron scattering research with peak neutron flux ~20–100x ILL, Grenoble • SNS construction project, a collaboration of six US DOE labs, was funded through DOE-BES at a cost of 1.4 B$ • SNS will have 8x beam power of ISIS, the world’s leading pulsed source • Stepping stone to other high power facilities

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