SLS Beam Dynamics Group

History of SLS Commissioning

Storage Ring

Jan. 2001 - July 2001

The SLS storage ring is a 12 TBA (8°-14°-8°) lattice of 288 m circumference with 6 straights of 4 m length, 3 of 7 m and 3 of 11 m. Four 500 MHz cavities of 600 kV peak voltage occupy two short straight, injection is done in one of the long straights. The lattice is designed to provide an emittance of 5 nm rad at 2.4 GeV with dispersionfree straight sections and approx. 4 nm rad when allowing some dispersion. 174 quadrupoles with independent power supplies grouped into 22 soft families allow large flexibility, 120 sextupoles in 9 families are carefully balanced to provide large dynamic apertures (see NIM A 404 (1998) 237-247). A Touschek dominated beam life time of 3.5 hrs is expected for the design current of 400 mA in the presence of undulators with 4 mm full gap size, and will be raised to 8 hrs in a later upgrade by means of a 3rd harmonic cavity. User operation of SLS is scheduled to start at August 1, 2001.

Commissioning Milestones:

  • Dec. 13: First turn

  • Dec. 15: Stored Beam! 2.7 mAmp, 8.5 min lifetime (1/e)

  • Dec. 19: 8 hours lifetime with relaxed optics (1.6 mA). Low emittance optics runs immediately from upload with theoretical settings, 45 minutes lifetime. First response matrix measurements indicate very good agreement between model and reality.
    Shutdown until Jan.15,2001.

  • Jan. 19: 18 mA stored beam with relaxed optics.
    Breakdown of booster extraction septum requires extensive repair and upgrade: no operation for approx 3 weeks.

  • Feb 20: 50 mA stored beam with relaxed optics at pressure of 1E-7 mbar.

  • Feb.28: 100 mA stored beam. All relevant lattice modes operating (low emittance mode with and without dispersion in straights, and relaxed mode). Injection efficiency booster to ring approx. 40%.

  • Mar 15: up to 225 mA stored beam after cavity HOM tuning. Injection efficiency booster to ring up to 100%. Best working point around 20.40/8.15. One week shut down.

  • Mar 28: Control of filling pattern after upgrade of timing system. "Laundry" shift at 200 mA level. - Vacuum leak due to local overheating caused by too large beam current at insufficiently corrected orbit. Reason for bad orbit: shortcuts in connectors of sextupole coils. One sector chamber removed, baked out and reinstalled (one week shutdown)

  • Apr 8: first single bunch operation: 2 hours of lifetime with 1 mA, reducing to approx. 40 minutes at 6 mA, but increase to 14 hours at 10 mA correlated with vertical beam blow up.

  • Apr 23-26: Restart after shutdown for installation of U24 in-vacuum undulator in 6S straight and 12 mm gap vacuum chamber (for later wiggler installation) in 4S straight. Successful correction of gradient errors. Breakdown of linac modulator.

  • May 4: Orbit correction down to rms values of 7 micro meters in the horizontal and 1 micro meter in the vertical plane.

  • May 10: 325 mA stored beam with 8 hours of lifetime after careful treatment of cavity higher order modes.

  • May 17: Gap of in vacuum undulator U24 closed to 6.5 mm with 70 mA of beam.

  • June 5, 20:45: SLS reaches the design current of 400 mA!

  • June 23: Top up injection.

  • July 10: Photon beam focussed (approx. 25 micron x 38 micron) in protein crystallography beamline 6S.

  • July 11/12: Start of user operation: Diffraction pattern of protein crystal measured at SLS!
    Data collection over 12 hours at 200 mA with top up injection at U24 10 mm gap

  • July 19: Slow (1 Hz) orbit feedback operational.

  • Aug 9: First operation of transverse multibunch feedback system (TMBF).

  • Aug 9: Materials Science beamline 4S gets monochromatic beam from high field wiggler W61 focussed into the experimental chamber.

  • Aug 10: Surfaces Interfaces Spectroscopy beamline 9L gets monochromatic beam from elliptic undulator UE212 focussed into the experimental chamber.

  • Nov 21: Surfaces Interfaces Microscopy beamline 11M measures first spectrum from Apple-undulator UE56.

  • Dec 18: Direct beam energy measurement by means of spin depolarization.

  • End 2001 status: SLS operates to 70% for users with four active beamlines. Currents up to 300mA and topping up are routinely used. 400 mA operation requires special care in HOM optimization. The lattice optics is well understood and calibrated. Beam lifetime agrees with the model. Booster operates with sextupoles now, required to suppress head-tail instability in single bunch mode.
    Remaining tasks for 2002 machine shifts: Full understanding of multibunch instability: seems to be partially due to resistive wall and to ion trapping, can be suppressed by increased chromaticity. Routine operation of transverse multibunch feedback system. Understanding of pin hole measured beam size. Beam based BPM calibration and dynamic girder alignment. Recommissioning of injection (still waiting for replacement of bad linac prebuncher).



July 2000 - Sept. 2000

The SLS booster synchrotron is mounted onto the inner wall of the storage ring tunnel. The circumference is 270 m, 93 small gradient bends in 3 achromatic arcs will provide a low emittance of 10 nm at 2.4 GeV. 3 quadrupole families in 3 straight sections allow variation of the tunes. The diameters of the elliptical vacuum chamber are 30 mm in the horizontal and 20 mm in the vertical. Ramping is done from 0.1 to 2.4 GeV in a 3 Hz cycle powered by a digital power supply (no white circuit). The digital BPM system provides turn by turn data from 54 BPMs.
For more info view our EPAC-98 report (PDF).

Commissioning Milestones:

  • July 11: First turn, even with correctors off

  • July 18: 40% of first turn particles survive until next injection (320 msec).

  • July 26: Acceleration from 0.1 to 1.5 GeV, limited by RF ramp not yet implemented.

  • Aug. 8: Acceleration of small charge (8 pC) to 2.4 GeV.

  • Aug. 17: > 80% of injected beam (400 pC) accelerated to 2.4 GeV (however one shot only, continuous operation with higher losses due to vacuum with beam still bad). Tune measured and set to design value. Measured betas agree to 10% with design. 

  • Aug. 23: Booster accepted: 1.1 nC before septum, 0.9 nC captured, 0.8 nC extracted at 2.4 GeV. These are values for first shot after a break of few minutes, extracted charge in steady state is approx. 0.16 nC. Residual gas mainly CO, pressure 5.10-7 mbar. Cleaning by beam during the next weeks.

  • Sep. 12: After two weeks of cleaning by beam, the extracted charge at 2.4 GeV in the steady state has increased to 0.3 nC (for an injected charge of 0.9 nC).

  • Sep. 21: The booster has reached its design performance of extracting 1 nC at 2.4 GeV in steady state (1.5 nC before injection septum). Since the beam suffers most from gas scattering at low energy, injection is done on the ramp at 14 msec delay in order to raise the energy faster. Next three weeks are devoted to further laundry (vaccum still in the 3E-7 mbar range with beam) and to operator training.


Feb. 2000 - May 2000

 For a summary of results please view our EPAC-00 contribution (PDF, 640K).

Old time schedules

Commissioning/Operations time schedules 2001

Operations time schedule Jan.-June 2002 (GIF/Postscript), July-Dec. 2002 (GIF/Postscript)

24.3.2003 A.Streun