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Frozen vs PIC Codes in Coherent Effects: Implementing Time-Varying Fields

This comparison explores the relevance of frozen space charge and PIC codes in simulating effects of strong space charge and time-varying fields, particularly in scenarios like double RF injection in PTC-ORBIT. While frozen space charge codes excel in long time scales, coherent phenomena like the half-integer resonance in the PSB necessitate a deeper study. The efficiency of frozen codes, as seen in simulations of debuncher operations, makes them favorable for many aspects. Notably, recent versions of MAD-X offer frozen space charge capabilities, enhancing their usefulness in handling complex physics scenarios with time-varying fields. Overall, this analysis provides insights into selecting the most appropriate simulation approach for various accelerator studies.

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Frozen vs PIC Codes in Coherent Effects: Implementing Time-Varying Fields

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  1. PIC versus Frozen? • PIC codes are definitely needed when coherent effects are relevant. • In our case in presence of strong space charge, time varying fields, double RF at the beginning of injection using PTC-ORBIT makes a lot of sense! • However, one of the main SC-13 outcomes is the fact that probably the most relevant issues are of incoherent nature ➔ Frozen space charge approach might be sufficient for many aspects of our studies. • Frozen space charge codes are 10-100 faster ➔ Long time scales • Clearly for the simulations of 1.2s of the PSonly frozen space charge codes can do the job! • It has been argued that the half integer resonance in the PSBis a good candidate for coherent phenomena. However, a half integer resonance compensation improves losses a lot ➔ needs studies. • MAD-X in the newest version has the frozen space charge implemented and by the way with time varying fields. • Example for the FermilabDebunchershows quite similar results. Outcome of SC-13 1

  2. Slow extraction in Debuncher using Orbit • 3-order resonance with variable tune Qx and sext. str. K2 • First “strange” results for extraction: “intensity drop” intensity vs turns • “Intensity drop” was resolved simply at the beginning: Valery advised to make mesh refinements • PIC: “Total Beam size increases at slow extraction => mesh number should be increased to keep the cell size”

  3. Simulations with ORBIT by V. Nagaslaev Ramps are given in tables; Npart in bunch ~ 2.5e12 SC-13

  4. N_macro_surv vs Turn Number for the Debuncher • Timing on CERN computer • Macro version ~20-24h • MADX-SC • ~2-4h MAD-X V3 with Macros MADX-SC V5 SC-13

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