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Injectors and Normal Form in MAD-NG
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Injectors and Normal Form in MAD-NG
27/05/2021 Injectors and Normal Form in MAD-NG
This meeting coincides with the IPAC'21 week https://www.ipac21.org (virtually) attended by several of us.
While it is certainly regrettable that people can not meet in person, it was also felt that there are some advantageous in the virtual format : poster contributions can be watched as video, in preparation of discussions with the presenter in virtual chatrooms.
Rogelio says there will be a BE retreat next week. Among the subjects discussed is manpower planning and he hopes to reinforce our section.
Discussion on Normal Forms in MAD-NG, Laurent Deniau, slides
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This work is based on several publications related to the subject, and in particular on two books by Etienne Forest.
Laurent illustrates the main principles of normal form analysis and FPP ( Fully Polymorphic Package).
For the implementation in MAD-NG he finds it important to be able to reproduce examples given in the FPP book.
He already reproduced the pendulum example in a MAD-NG script and is now extending to more dimensions using the ALS (Argonne Light Source) lattice as an example to fully validate his implementation with the ALS map example as described in the FPP book.
An important ingredient is the creation of the one turn map presentation, starting from a linear map, with extension by adding higher orders, involving Lie algebra and perturbation approach techniques.
Rogelio and Riccardo are worried that a general implementation and ALS validation may take a long time and propose to start with a simple well known FODO cell lattice structure with a single thin multipole element and compare with MAD-X/PTC and analytical predictions. This task seems feasible in one or two months. We will aim for another presentation in LNO after this period.
PS recent issues, Alex Huschauer
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The PS restart progresses well. One issue has been a significant electron cloud induced pressure rise observed for the 25ns beams required for the LHC.
To improve this, it was decided to perform a scrubbing run in the PS. This in fact allowed to decrease the dynamic pressure rise by an order of magnitude.
Running with high intensities as required for scrubbing however also resulted in losses and local activation of some regions in the PS.
The main loss peaks were meanwhile identified (removing a sponge at end of cavity, steering to avoid aperture bottle necks and resonance compensation of 3Qy). Actually the source of the stronger 3Qy resonance was identified as the field from a new BGI introduced in LS2. Field measurements have been requested to MSC together with possibilities to decrease the skew sextupolar component.
It was also observed that the alignment of the PS during the shutdown generally helped to reduce losses, and that various hardware changes done during the shutdown like changing power supplies required a re-optimization of operational parameters.
Progress with turn by turn measurements in the PS and PSB, Ewen Maclean, slides
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Ewen reported from turn by turn measurements in the booster (PSB) and PS, to verify TWISS parameters and minimize the phase advance beat.
Oscillations are excited using AC dipoles or tune kickers. After adjustments of individually powered quads, a fairly good agreement with the expected phases was observed.
The shot by shot tune stability in the PSB was measured and found to be not so great, resulting in changes of the oscillations induced by the AC dipole and complicating the data acquisition and analysis. The reasons are currently not well understood. Optimized degauss cycles can be expected to help to reduce the fluctuations within supercycles.
Afer some initial problems and bug fixes, the PS turn by turn data is looking good, and allows to verify that the beta-beating and coupling remain within tolerances. At injection in the PS at peak of 15% beta-beating is observed coming from the new injection bumps. Alex proposed to see if the beta-beating is compatible with these elements.
The observation in the PSB where the oscillation induced by a single kick strongly depends on the tune has been confirmed again and it is highly puzzling. Further studies are needed.
Next meetings:
The next LNO meeting is planned in two weeks.
A more dedicated meeting on the medium term planning for MAD-X features is planned, probably around 20 June.
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