Abstract
The CERN Proton Synchrotron Booster (PSB) has been known to suffer from horizontal instabilities since its early operation in the 1970s. These instabilities appear at specific beam energies and range of working points. The source of the instability and the reason why the instabilities appear at specific energies remained unidentified. However, in routine operation, the instabilities have not been limiting the PSB performance reach thanks to the use of a horizontal feedback system, which can suppress their onset for all beam intensities needed in the PSB. Recently, the interest in these instabilities has been revived by the ongoing LHC Injectors Upgrade (LIU) program, as well as, the Physics Beyond Colliders (PBC) study group. In fact, the PSB is being upgraded to a new energy range and higher beam intensities will be requested in future operation. To ensure that these instabilities will not limit the PSB performance in the future parameter range, a systematic characterization has been carried out through several measurements and models. At fixed energy, the dependence of the instability on the working point has been fully studied experimentally. Macroparticle simulations and analytical modeling have been applied to explain the measurements, suggesting that the main driving term behind these instabilities is the unmatched termination of the PSB extraction kickers. Analytical studies also explained for the first time why the instability appears at specific energies in the PSB cycle and showed that no other instability is expected above 1.4 GeV. Finally, the hypothesis on the main instability driving term has been verified experimentally by performing measurements with the kicker terminations temporarily matched. In this configuration, no sign of instability was observed and the extraction kicker could be unambiguously identified as the source of the instability. Some options to permanently suppress the source of the instability are proposed.
Highlights
The Proton Synchrotron Booster (PSB) is the first circular accelerator of the CERN injector complex, in operation since 1972
Thanks to the new hardware, it is expected that the transverse feedback (TFB) will be operational from the very beginning of the PSB cycle and be able to suppress the potential instability for tunes between 4.21 and 4.30
Its source remained unknown and the instability was suppressed during routine operation by the transverse feedback system
Summary
The Proton Synchrotron Booster (PSB) is the first circular accelerator of the CERN injector complex, in operation since 1972 It consists of four vertically stacked synchrotron rings that receive beams with a kinetic energy of 50 MeV from Linac and accelerate them to 1.4 GeV [1]. The extraction beam kinetic energy will be increased from 1.4 GeV to 2 GeV, with the exception of the ISOLDE facility that will not be upgraded but may require higher intensity per pulse in the framework of Physics Beyond Colliders (PBC) [10]. The instability is fully controlled in everyday operation by the TFB, interest on the subject was sparked in view of the LIU that will increase the injection and extraction energies of the PSB to 160 MeV and 2 GeV, respectively, and will provide the potential to accelerate higher intensity beams in the framework of PBC.
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