1. Vertical Emittance Tuning at the Australian Synchrotron Light Source Rohan Dowd Presented by Eugene Tan

2. Overview Machine overview LOCO method and minimisation technique Minimisation results and Measurements Sextupole alignment measurements Conclusion ICFA - Low Emittance Ring Workshop 3-5 October 2011

3. Australian Synchrotron Light Source Overview Storage Ring Parameters Energy3 GeV Circumference216 m RF Frequency499.654 MHz Peak RF Voltage3.0 MV Current200 mA Betatron Tune (h/v)13.3/5.2 Momentum Compaction0.002 ε x (nominal) 10.4 nm∙rad Double bend lattice 14 fold symmetric Gradient dipoles Corrector and skew quad coils on sextupoles. Independent power supplies for all multipoles. ICFA - Low Emittance Ring Workshop 3-5 October 2011

4. LOCO method LOCO – Linear Optics from Closed Orbits. Adjusts the linear optics in the model to fit the real machine data Model response matrix – Machine response matrix = Error Minimise error by adjusting the model ‘fit parameters’ Fit Parameters normally include: –BPM/Corrector gains and coupling –Corrector gains and coupling –Quadrupole strengths –Skew Quadrupole strengths We fit skew quadrupole components in all multipole magnets in our model lattice to represent rolls and misalignments. ICFA - Low Emittance Ring Workshop 3-5 October 2011

5. LOCO Outputs Outputs: BPM Gains + Couplings Skew components Quad Strengths Corrector gains/tilts From these outputs we can calibrate the model and calculate skew corrections needed to adjust coupling Consistent BPM/corrector coupling results for differing machine coupling settings – LOCO is not attributing the machine coupling to BPM/corrector coupling Fits to varying machine coupling states (0.01- 17% coupling) Fits to identical machine coupling (10 samples) ICFA - Low Emittance Ring Workshop 3-5 October 2011 Verified from attenuation measurements for the BPM.

6. Emittance Coupling minimisation Emittance coupling (ε y /ε x ) calculated from LOCO Calibrated model. Minimisation algorithm used to adjust skew quads to desired emittance coupling. Emittance coupling can be adjusted to arbitrary amounts with this method. Set CouplingLOCO Measured Coupling Calculated ε y (pm) 0.0%0.01%1.0 0.1%0.12%12.2 0.2%0.23%23.5 0.3%0.33%33.7 0.4%0.43%43.9 0.5%0.54%55.1 0.6%0.64%65.3 0.7%0.74%75.5 0.8%0.84%85.7 0.9%0.92%93.8 1.0%1.04%106.1 Phys. Rev. ST Accel Beams, 14, 012804 (2011)

7. Touschek Lifetime vs RF By taking single bunch lifetime over extended period the Touschek component of the lifetime can be extracted. ICFA - Low Emittance Ring Workshop 3-5 October 2011

8. Touschek Lifetime vs RF Touschek component will also change with RF voltage. 2.1% energy acceptance (measured) Curve fit by varying ε y /ε x, other values fixed. Blue curve fit corresponds to ε y = 1.24 pm Set ε y /ε x (%) Fitted ε y /ε x (%) ε y (pm) 0.010.012 ± 0.0031.2 ± 0.3 0.060.043 ± 0.0134.5 ± 1.3 0.100.093 ± 0.0259.4 ± 2.6 ICFA - Low Emittance Ring Workshop 3-5 October 2011

9. Tune Crossing Results LOCO Model ε y (pm)η y Component (pm)Betatron Coupling Component (pm) Total Measured ε y (pm) Model – Measured (pm) 92.31 ± 2.772.24 ± 0.0986.90 ± 2.6589.55 ± 2.652.76 ± 3.83 76.30 ± 2.232.96 ± 0.1276.50 ± 2.1478.64 ± 2.142.34 ± 3.09 41.41 ± 1.241.73 ± 0.0740.39 ± 1.8442.23 ± 1.840.82 ± 2.22 22.75 ± 0.682.04 ± 0.0819.69 ± 1.3321.72 ± 1.331.03 ± 1.49 12.75 ± 0.382.14 ± 0.0910.71± 1.0212.85 ± 1.020.10 ± 1.09 7.55 ± 0.231.73 ± 0.075.41 ± 0.717.14 ± 0.710.41 ± 0.75 1.05 ± 0.030.73 ± 0.090.59 ± 0.301.32 ± 0.310.27 ± 0.31 ICFA - Low Emittance Ring Workshop 3-5 October 2011

10. How to improve? With current correction scheme we are stuck at 1-2 pm. Instead of correcting for misalignments, lets eliminate them. Recent ring alignments have made the coupling worse! Need to measure them independently – Beam based method ICFA - Low Emittance Ring Workshop 3-5 October 2011

11. Sextupole offsets Shunt each sextupole magnet family to different strengths and take a response matrix at each point Perform LOCO analysis and fit skew quadrupole terms to each sextupole. Gradient of skew field vs sextupole field gives vertical offset. ICFA - Low Emittance Ring Workshop 3-5 October 2011

12. Sextupole Offset Results Average offset: 70 microns Systematic alignment effect? ICFA - Low Emittance Ring Workshop 3-5 October 2011

13. Cross Checks Applied BPM OffsetMeasure Mean Beam Offset Difference from zero +125234.6 ± 10.6128.7 ± 18.8 +75167.7 ± 16.561.8 ± 22.6 0105.9 ± 15.50 -7533.1 ± 17.8-72.8 ± 23.6 -125-16.1 ± 21.6-122 ± 26.6 MagnetOriginal Offset (μm) Applied Shim (μm) New Offset (μm) Delta offset (μm) Sector 9 SFB-108.4 ± 44.6150-249.3 ± 7.2140.9 ± 45.2 Sector 11 SFB-56.7 ± 10.0100-120.4 ± 56.0-63.4 ± 57.4 Sector 9 SDA-14.6 ± 9.9100-118.3 ± 8.3-103.7 ± 14.1 Cross checks show that amplitude of offset is correct and individual magnets can be adjusted accurately. ICFA - Low Emittance Ring Workshop 3-5 October 2011

14. Sextupole Realignment – latest results Re-aligned section (girder #16-21) now has much lower offsets. Simulated minimal vertical emittance has reduced from 1pm to 0.7 pm. ICFA - Low Emittance Ring Workshop 3-5 October 2011

15. Conclusions ε y of 1.3 pm.rad achieved through LOCO based minimisation. We have developed tools to accurately measure sextupole misalignments and eliminate them. Aim to have all sextupoles realigned by end of year and expect to reach < 1 pm emittance Also working on an inexpensive way to increase available skew correctors ICFA - Low Emittance Ring Workshop 3-5 October 2011

16. Thank you ICFA - Low Emittance Ring Workshop 3-5 October 2011