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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

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

Sns accelerator complex
SNS Accelerator Complex Completion Goals Met April 28, 2006

Accumulator Ring



Produce a 1-msec long, chopped, H- beam

Accumulator Ring: Compress 1 msec long pulse to 700 nsec





Liquid Hg Target


2.5 MeV

87 MeV

186 MeV

387 MeV

1000 MeV

Ion Source








Chopper system makes gaps

945 ns




1 ms macropulse


Sns high level design parameters
SNS High-Level Design Parameters Completion Goals Met April 28, 2006

Ring is designed for 2 MW at 1 GeV; installed for 1.3 GeV (mostly)

The sns partnership
The SNS Partnership Completion Goals Met April 28, 2006

ORNL Accelerator Systems Division responsible for integration, installation, commissioning and operation

Commissioning and initial operating experience with the sns accelerator complex

Spring 1999 Completion Goals Met April 28, 2006

Commissioning and initial operating experience with the sns accelerator complex
Now Completion Goals Met April 28, 2006

Front end systems
Front-End Systems Completion Goals Met April 28, 2006

  • 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

Accumulator ring and transport lines
Accumulator Ring and Transport Lines Completion Goals Met April 28, 2006

  • Designed and built by Brookhaven National Lab


Accumulator Ring



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%





Ring and transport lines
Ring and Transport Lines Completion Goals Met April 28, 2006


Ring Arc



Target region within core vessel
Target Region Within Core Vessel Completion Goals Met April 28, 2006

Target Module with jumpers

Outer Reflector Plug



Core Vessel water cooled shielding

Proton Beam

Core Vessel Multi-channel flange

Normal conducting linac front end output emittance and bunch length
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)

Dtl and ccl rf setpoints by phase scan signature matching
DTL and CCL RF Setpoints by Phase Scan Signature Matching Bunch Length

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

Ccl module 1 longitudinal bunch shape monitor measurements
CCL Module 1 Longitudinal Bunch Shape Monitor Measurements Bunch Length



  • Measured values are close to the predicted bunch length

  • Measurements were motivated by earlier observations of a longer bunch, presumably due to longitudinal mismatch

Superconducting linac tuneup by phase scan
Superconducting Linac Tuneup by Phase Scan Bunch Length

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

Low level rf feedforward
Low-level RF Feedforward Bunch Length

  • 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

Scl operations fault recovery galambos
SCL Operations: Fault Recovery Bunch Length(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

Ring rtbt target commissioning timeline january may 2006
Ring/RTBT/Target Commissioning Timeline January-May 2006 Bunch Length

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

Accumulation and extraction of 1 3x10 13 protons pulse january 26 2006
Accumulation and Extraction of 1.3x10 Bunch Length13 protons/pulse (January 26, 2006)

Ring Beam Current Monitor


200 turn accumulation

Extraction Dump Current Monitor

Ring orbit correction h v bumps are due to injection kickers
Ring Orbit Correction: H,V Bumps are Due to Injection Kickers

Horizontal Orbit

Vertical Orbit

BPM Amplitude

Ring optics measurements betatron phase advance and chromaticity
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

High intensity studies danilov cousineau plum
High Intensity Studies Chromaticity(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

Phase space painting
Phase Space Painting Chromaticity

Stripping Foil

Initial Closed Orbit

Injected Beam

Final Closed Orbit



Wei et. al., PAC 2001, 2560

X-Y space after 1060 Turns

Phase space painting1
Phase Space Painting Chromaticity

Beam on Target View Screen

Beam profiles in RTBT

65 mm

80 mm

Beam power on target history
Beam-Power-on-Target History Chromaticity

Beam power administratively limited to 10 kW until November 8

Beam Power [0-65 kW]

May 1, 2006

Feb 1, 2007

Fy 2007 integrated beam power by day and cumulative
FY 2007 Integrated Beam Power by Day and Cumulative Chromaticity

  • 6.3 MW-hrs delivered in Run 2007-1

Technical challenges equipment reliability
Technical Challenges: Equipment Reliability Chromaticity

  • 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

Technical challenges beam power
Technical Challenges: Beam Power Chromaticity

  • 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

Outlook performance goals
Outlook: Performance Goals Chromaticity




  • SNS Beam Power Upgrade Project will increase linac output energy to 1.3 GeV and provide 3 MW beam power

E p feedback experiment at the psr
E-P Feedback Experiment at the PSR Chromaticity

  • 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.

Commissioning and initial operating experience with the sns accelerator complex

Laser-Stripping Injection Proof-of-Principle Experiment Chromaticity

Laser Beam

High-field Dipole Magnet

High-field Dipole Magnet





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

Yes we ve had a few surprises
Yes, We’ve Had a Few Surprises Chromaticity

  • 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

Summary Chromaticity

  • 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

Commissioning and initial operating experience with the sns accelerator complex

SNS Beam Diagnostic Systems Chromaticity


44 Position 2 Ionization Profile

70 Loss 1 Current 5 Electron Det. 12 FBLM

2 Wire 1 Beam in Gap

2 Video 1 Tune


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



1 Position

1 Wire 1 Current


Not Operating


1 Current 4 Loss 1 Wire


10 Position 9 Wire

8 Neutron, 3BSM,

2 Thermal

28 Loss 3 Bunch

1 Faraday Cup 1 Current


17 Position

36 Loss

4 Current

5 Wire

1 Harp



10 Position 5 Wire 12 Loss

5 Faraday Cup 6 Current

6 Thermal and 12 PMT Neutron


32 Position 86 Loss

9 Laser Wire

24 PMT Neutron


29 Position

1 Prototype Wire-S

46 BLM, 3 FBLM

4 Current


6 Loss

6 Position

1 Wire ,1 BCM

CCL/SCL Transition

2 Position 1 Wire

1 Loss 1 Current

Baseline sns ion source performance
Baseline SNS Ion Source Performance Chromaticity

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.

Recent ion source r d accomplishments
Recent Ion Source R&D Accomplishments Chromaticity

Cs injection collar

Ionization Cone

Extractor electrode


Air duct

Cs Line

Al2O3 insulator

Cooling channel



Plasma stream


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

Energy stability pulse to pulse j galambos
Energy Stability – Pulse to Pulse Chromaticity(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

Scl laser profile measurements
SCL Laser Profile Measurements Chromaticity

  • 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

The spallation neutron source
The Spallation Neutron Source detector, T = 3 K

  • 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