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FCC-ee tuning meeting
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FCC-ee tuning meeting
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Forced 3D measurements in PETRA III, Lukas Malina
Lukas has found a solution to avoid the use of MAFF filters for the turn-by-turn (TbT) data acquisition with Libera BPM system. This is a remarkable achievement as the need of these filters made TbT data not practical for optics corrections in light sources, opening the door for very fast optics mesaurements. First measurements show beta functions with few % uncertainty. This should be easy to improve by improving the model (e.g. orbit bumps at sextupoles) and optimizing excitation amplitude and beam current. A limitation on how much the forced frequency could be approached to the natural tune was observed since the excitation was kept for minutes and tunes likely vary by 0.002 over minute time scale (no feedback system on).
For the future: Comparisons to LOCO measurements, scan in driven frequency and chromaticities.
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AC dipole experience in ESRF, Andrea Franchi
Optics measurements from orbit and from AC dipole showed good agreement for low chromaticity. However increasing chromaticity introduced large systematic errors, also seen in simulations. Mitigation is to increase the driven-to-natural tune separation. The role of synchrotron radiation in the distortion has not been isolated in current simulations and it could play some role in distorting the optics measurement. Surely, the chromaticity plays a key role in distorting optics measurements.
Driven tune separation in ESRF was explored up to 0.04, that introduces a large lambda of ~0.3. The factor (1-lambda^2) introduced by Ryoichi can be removed from formulas without affecting quality of measurement.
For the future: Understand role of radiation in simulations (key for FCC-ee!) and explore measurements in ESRF (Simon confirms experiments could be possible in ESRF, instrumentation to be checked).
Lukas asked if the oscillation amplitudes were comparable when doing the scan versus tune separation as it is known that oscillation amplitude also distorts optics measurements due to non-linear elements in the lattice (mostly sextupoles). Andrea answered that this is to be checked, to try to disentangle the two sources of distortions. After the meeting Andrea replied that the oscillation amplitude was indeed the same for different tune separations, so distortion from sextupoles is excluded.
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AC dipole measurements in SuperKEKB, Jacqueline Keintzel
In SuperKEKB these measurements are limited by actual strength of the excitation. This requires to excite very close to the tune which generates modulation in the oscillation amplitude, likely due to tune drifts during measurement. Yet comparisons between horizontal beta-beating from COD and AC dipole yield agreement within error bars. The vertical measurement is less reliable. Lukas suggested to increase beam intensity by increasing the number bunches. Jacqueline commented that it will not be easy to have more measurements as machine time is very scarce. Comparisons to single kick measurements might also be explored when machine time is available for further experiments.
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