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Abstract:

Direct space charge may be quantified, and hence the beam brightness observed, by measuring the quadrupolar beam modes in the CERN Proton Synchrotron (PS). The spectrum of the transverse beam size oscillations (i.e. the quadrupolar beam moment) contains valuable information: the betatron envelope modes and the coherent dispersive mode indicate optics mismatch, while their frequency shifts due to space charge allow a direct measurement thereof. To measure the quadrupolar beam moment we use the Base-Band Q-meter system of the PS which is based on a four electrode stripline pick-up. Past experiments with quadrupolar pick-ups often investigated coasting beams, where the coherent betatron and dispersion modes correspond to single peaks in the tune spectrum. In contrast, long bunched beams feature bands of betatron modes: the mode frequencies shift depending on the transverse space charge strength which varies with the local line charge density. By using the new transverse feedback (TFB) in the PS as a quadrupolar RF exciter, we measured the quadrupolar beam transfer function. The beam response reveals the distinct band structure of the envelope modes as well as the coherent dispersive mode.

Abstract:

The paper presents the outstanding studies performed in 2016 in preparation of the PS Booster upgrade, within the LHC Injector Upgrade project (LIU), to provide twice higher brightness and intensity to the High-Luminosity LHC. Major changes include the increase of injection and extraction energy, the implementation of a H− charge-exchange injection system, the replacement of the present Main Power Supply and the deployment of a new RF system (and related Low-Level), based on the Finemet technology. Although the major improvements will be visible only after the upgrade, the present machine can already benefit of the work done, in terms of better brightness, transmission and improved reproducibility of the present operational beams. Studies address the space-charge limitations at low energy, for which a detailed optics model is needed and for which mitigation measurements are under study, and the blow-up reduction at injection in the downstream machine, for which the beams need careful preparation and transmission. Moreover they address the requirements and the reliability of new beam instrumentation and hardware that is being installed in view of LIU.

Abstract:

At CERN we have ramped up a program to investigate space charge effects in the LHC pre-injectors with high brightness beams and long storage times. This is in view of the LIU upgrade project [1] for these accelerators. These studies require massive simulation over large number of turns. To this end we have been looking at all available codes and started collaborations on code development with several laboratories: MAD-X frozen & adaptive mode [2] and integration into the main branch of the MAD-X in-house development [3] code, PyORBIT [4] from SNS, SYNERGIA [5] from Fermilab, MICROMAP [6] from GSI . We have agreed with our collaborators to bench-mark all these codes in the framework of the GSI bench-marking suite [7], in particular the main types of frozen space charge and PIC codes are being tested. We also include a study on the subclass of purely frozen and the adaptive frozen modes both part of MAD-X in comparison with the purely frozen MICROMAP code. Last, we will report on CERN’s code development effort to understand and eventually overcome the noise issue in PIC codes.

Abstract:

The presentation will cover approaches and strategies of modeling and implementing collective effects in modern simulation codes. We will review some of the general approaches to numerically model collective beam dynamics in circular accelerators. We will then look into modern ways of implementing collective effects with a focus on plainness, modularity and flexibility, using the example of the PyHEADTAIL framework, and highlight some of the advantages and drawbacks emerging from this method. To ameliorate one of the main drawbacks, namely a potential loss of performance compared to the classical fully compiled codes, several options for speed improvements will be mentioned and discussed. Finally some examples and applications will be shown together with future plans and perspectives.