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Vertical Emittance Tuning at the Australian Synchrotron Light Source
Rohan Dowd
Presented by Eugene Tan
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
Australian Synchrotron Light Source Overview
• Storage Ring Parameters
Energy 3 GeV
Circumference 216 m
RF Frequency 499.654 MHz
Peak RF Voltage 3.0 MV
Current 200 mA
Betatron Tune (h/v) 13.3/5.2
Momentum Compaction 0.002
εx (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
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
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.
Emittance Coupling minimisation• Emittance coupling (εy/εx) 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 Coupling LOCO Measured
CouplingCalculated εy (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)
Touschek Lifetime vs RF
• By taking single bunch lifetime over extended period the Touschek component of the lifetime can be extracted.
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ICFA - Low Emittance Ring Workshop 3-5 October 2011
Touschek Lifetime vs RF
• Touschek component will also change with RF voltage.
• 2.1% energy acceptance (measured)
• Curve fit by varying εy/εx , other values fixed.
• Blue curve fit corresponds to εy = 1.24 pm
Set εy/εx (%)
Fitted εy/εx
(%)εy (pm)
0.01 0.012 ± 0.003 1.2 ± 0.3
0.06 0.043 ± 0.013 4.5 ± 1.3
0.10 0.093 ± 0.025 9.4 ± 2.6
ICFA - Low Emittance Ring Workshop 3-5 October 2011
Tune Crossing Results
LOCO Model εy (pm) ηy Component (pm) Betatron Coupling Component (pm)
Total Measured εy (pm)
Model – Measured (pm)
92.31 ± 2.77 2.24 ± 0.09 86.90 ± 2.65 89.55 ± 2.65 2.76 ± 3.83
76.30 ± 2.23 2.96 ± 0.12 76.50 ± 2.14 78.64 ± 2.14 2.34 ± 3.09
41.41 ± 1.24 1.73 ± 0.07 40.39 ± 1.84 42.23 ± 1.84 0.82 ± 2.22
22.75 ± 0.68 2.04 ± 0.08 19.69 ± 1.33 21.72 ± 1.33 1.03 ± 1.49
12.75 ± 0.38 2.14 ± 0.09 10.71± 1.02 12.85 ± 1.02 0.10 ± 1.09
7.55 ± 0.23 1.73 ± 0.07 5.41 ± 0.71 7.14 ± 0.71 0.41 ± 0.75
1.05 ± 0.03 0.73 ± 0.09 0.59 ± 0.30 1.32 ± 0.31 0.27 ± 0.31
ICFA - Low Emittance Ring Workshop 3-5 October 2011
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
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
Sextupole Offset Results
•Average offset: 70 microns
•Systematic alignment effect?
ICFA - Low Emittance Ring Workshop 3-5 October 2011
Cross Checks
Applied BPM Offset Measure Mean Beam Offset
Difference from zero
+125 234.6 ± 10.6 128.7 ± 18.8+75 167.7 ± 16.5 61.8 ± 22.6
0 105.9 ± 15.5 0-75 33.1 ± 17.8 -72.8 ± 23.6
-125 -16.1 ± 21.6 -122 ± 26.6
Magnet Original Offset (μm)
Applied Shim (μm)
New Offset (μm)
Delta offset (μm)
Sector 9 SFB -108.4 ± 44.6 150 -249.3 ± 7.2 140.9 ± 45.2Sector 11 SFB -56.7 ± 10.0 100 -120.4 ± 56.0 -63.4 ± 57.4Sector 9 SDA -14.6 ± 9.9 100 -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
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
Conclusions
• εy 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
Thank you
ICFA - Low Emittance Ring Workshop 3-5 October 2011