Synchrotron Light Source Rohan Dowd Presented by Eugene Tan - - PowerPoint PPT Presentation

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 Coupling Calculated 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 ,
• ther 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 ± 22.6 105.9 ± 15.5

• 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 ± 45.2 Sector 11 SFB

• 56.7 ± 10.0

100

• 120.4 ± 56.0
• 63.4 ± 57.4

Sector 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