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Optimizing LHC Pre-Accelerators: Understanding Harmonics and Space Charge Limitations

The LIU project focuses on enhancing the performance of LHC pre-accelerators—PSB, PS, and SPS—in preparation for the HL-LHC upgrade. The aim is to achieve brighter beams with higher intensity while maintaining or reducing emittance, constrained by the space charge limits. Current efforts involve developing codes to address the interplay between space charge and nonlinearities, alongside machine experiments for validating simulations. This work includes measuring harmonics of dipole magnets and utilizing advanced measurement techniques to refine acceleration processes.

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Optimizing LHC Pre-Accelerators: Understanding Harmonics and Space Charge Limitations

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  1. Harmonics for the LHC Pre-Accelerators PSB, PS, SPS • The goal of LIU is to optimize the performance of the LHC pre-accelerators in view of the HLHC upgrade. • This requires to get brighter beams, i.e. more intensity with equal or smaller emittances. • An essential limitation is the space charge limit. • On the other hand the interplay between space charge and the nonlinearities seems to be the limiting process. • We are presently developing codes to treat both effects simultaneously. • Equally relevant are machine experiments to benchmark the simulations, directly measure and eventually correct resonances. • Ideally we would need good knowledge of the harmonics. • Can the magnet experts and help in the framework of Fidel? Fidel 03.07.2012

  2. The machines – PSB (Christian) • Reference magnets without vacuum chambers  change of fields • Spares are available Quad/Dipoles • Little is known about the harmonics other than b1 & b2. (A b4 component expected in the dipoles???) • There is a rather sizable skew sextupole (a3) component. This has been successfully measured and corrected with a driving term analysis.  Peter Urschűtz thesis • During LS1 3 close-by H&V pickups will be prepared for 1000 Turn measurements and the damper kicker will be used as a AC-dipole for continuous excitations. • Intense space charge measurements in progress. Fidel 03.07.2012

  3. The machines – PS (Simone) • An effort has been done to understand the harmonics of the dipole magnets (including pole windings). I understand that harmonics have been modeled till b4 (I would have liked b5 to understand Q’’’!). The expert is with you now. • There are reference magnets recently upgraded with fixed coils (b4/b5 can be measured) • There are a few spares for measurements. • Automated (local!) driving term measurements are being prepared with 1000T BPM system and kickers available. • Systematic space charge measurements in conjunction with linear and nonlinear resonances under way in collaboration with GSI experts. Fidel 03.07.2012

  4. The machines – SPS (Hannes) • 2 reference magnets (MBA & MBB) and spares available. • Problems with vacuum grounding and eddy currents. • b3/b5 in body and the edges, fringe fields? • NL chromaticity (Q’, (Q’’), Q’’’)  effective model of b5 in MBA, MBB. • Supercycle dependent and year-by-year changes (grounding, aging, hysteresis???) • Both driving-term and space charge measurements in progress. • Modeling possible for the dipoles, in particular b5? • Quads (small b4) model as well. • Q20 is more sensitive to multipoles (Q’/Q’’’ larger for same b3/b5). Fidel 03.07.2012

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