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

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