Chromaticity during injection
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CERN, FiDeL meeting, 15 th February 2011. Chromaticity during injection. Nicholas Aquilina TE-MSC-MDA Acknowledgements : E. Todesco, W. Venturini, EIC and operators. Contents. Measurements of chromaticity during injection

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Chromaticity during injection

CERN, FiDeL meeting, 15th February 2011

Chromaticity during injection

Nicholas Aquilina



E. Todesco, W. Venturini, EIC and operators


  • Measurements of chromaticity during injection

  • Post-processing of data in order to get the bare chromaticity of the machine removing the chromaticity trims

  • Fitting of the data with FiDeLparametrization

  • Proposal for the average correction

Measurements and trims
Measurements and trims

  • The value of the chromaticity is obtained from the logbook (as done by [W. Venturini])

  • Unfortunately there is no chromaticity measurement during injection in TIMBER

  • The trims can be obtained:

    • from the logbook

    • from TIMBER; currents in MCSF/MCSD

Chromaticity decay
Chromaticity decay

  • Chromaticity decay as obtained by W. Venturini

  • Note the two different families of decay

  • In this case the trims were being obtained from the logbook

Horizontal chromaticity versus time at injection, beam1 (blue), beam2 (red) [W. VenturiniDelsolaro]

Chromaticity decay1
Chromaticity decay

  • The chromaticity measurement was taken from the logbook without taking note of the trims

  • Instead the trims were obtained from TIMBER

  • The bare chromaticity of the machine was then obtained by adding the trims to the measurements

  • Note how the data converged to one plot

Fitting of the data
Fitting of the data

  • A double exponential1 of this form was used to model this decay

  • This model fits very well the chromaticity decay

1 N. Sammut, L. Bottura, and J. Micallef. Phys. Rev. ST Accel. Beams 9, 012402 (2006)

Fitting of the data1
Fitting of the data

where Q’h* and Q’v* are the starting bare chromaticity values as dictated by the machine optics

Average correction
Average correction

  • Based on the fits shown in the previous slide the following corrections are suggested:

suggested values

  • 1 taking 1 unit of b3 = 40 units of Q’

  • 2 N. Sammut, L. Bottura, and J. Micallef. Phys. Rev. ST Accel. Beams 10, 082802 (2007) for a 50A/s ramp rate and IFT = 12kA

  • 3 parameters in FiDeL database since 2008, for a 10A/s ramp rate and IFT = 12kA, in fact c = 0.5 was used instead (since IFT = 6kA)


  • Chromaticity measurements during injection can be used to understand better the b3 decay behaviour

  • From this analysis it can be seen that the b3 decay is a factor of 5 slower than the expected value from the measurements done at SM18, however the decay amplitude is in line with these measurements

  • Injecting the beam as soon as possible once at injection will help to get a better model of the chromaticity during the first moments of the decay

  • Having more measurements of the chromaticity both during injection and ramping logged in TIMBER will be very helpful for further analysis