Beam Loss Reduction by Barrier Buckets in the CERN Accelerator Complex

For a future intensity increase of the fixed-target beam in the accelerator complex at CERN, new techniques to reduce beam loss are required. A major fraction of the losses during extraction of the coasting beam from the PS towards the SPS originate from poorly kicked particles during the Multi-Turn Extraction. A line density depletion, synchronised with the extraction kickers, decreases these losses significantly when successfully combined with the present extraction scheme involving the transverse splitting of the beam. The Finemet® wide-band cavity recently installed in the PS as a longitudinal feedback kicker was used to generate a so-called barrier bucket, which is utilised to deplete the line density and reduce the losses. The drive to generate the barrier bucket waveform synchronously with the beam was developed and installed by the radiofrequency cavity as part of these studies. The effectiveness of the combination of the Multi-Turn Extraction and the barrier bucket was evaluated with beam. This manipulation was performed for the first time in a particle accelerator. The measured data with beam in the CERN PS shows a substantial, up to an order of magnitude beam loss reduction at extraction, even well beyond the standard operational beam intensity. This means that the combination of the Multi-Turn Extraction with the barrier buckets achieves a practically loss-less extraction for the fixed target beam from the PS. Based on the results of the measurements and simulations with beam, a concept for the synchronisation between the CERN PS and SPS accelerators is also presented to realise the beam loss reduction in future operation

Implementation of synchronised PS-SPS transfer with barrier buckets

For the future intensity increase of the fixed-target beams in the CERN accelerator complex, a barrier-bucket scheme has been developed to reduce the beam loss during the 5-turn extraction from the PS towards the SPS, the so-called Multi-Turn Extraction. The low-level RF system must synchronise the barrier phase with the PS extraction and SPS injection kickers to minimise the number of particles lost during the rise times of their fields. As the RF voltage of the wide-band cavity generating the barrier bucket would be too low for a conventional synchronisation, a combination of a feedforward cogging manipulation and the real-time control of the barrier phase has been developed and tested. A deterministic frequency bump has been added to compensate for the imperfect circumference ratio between PS and SPS. This contribution presents the concept and implementation of the synchronised barrier-bucket transfer. Measurements with high-intensity beam demonstrate the feasibility of the proposed transfer scheme.Comment: Talk presented at LLRF Workshop 2022 (LLRF2022, arXiv:2208.13680

‘1-8 interferon inducible gene family': putative colon carcinoma-associated antigens

Db−/−xβ2 microglobulin (β2m) null mice transgenic for a chimeric HLA-A2.1/Db-β2m single chain (HHD mice) are an effective biological tool to evaluate the antitumour cytotoxic T-lymphocyte response of known major histocompatibility-restricted peptide tumour-associated antigens, and to screen for putative unknown novel peptides. We utilised HHD lymphocytes to identify immunodominant epitopes of colon carcinoma overexpressed genes. We screened with HHD-derived lymphocytes over 500 HLA-A2.1-restricted peptides derived from colon carcinoma overexpressed genes. This procedure culminated in the identification of seven immunogenic peptides, three of these were derived from the ‘human 1-8D gene from interferon inducible gene' (1-8D). The 1-8D gene was shown to be overexpressed in fresh tumour samples. The three 1-8D peptides were both antigenic and immunogenic in the HHD mice. The peptides induce cytotoxic T lymphocytes that were able to kill a colon carcinoma cell line HCT/HHD, in vitro and retard its growth in vivo. One of the peptides shared by all the 1-8 gene family primed efficiently normal human cytotoxic T lymphocyte precursors. These results highlight the 1-8D gene and its homologues as putative immunodominant tumour-associated antigens of colon carcinoma

Barrier bucket gymnastics and transversely split proton beams: Performance at the CERN Proton and Super Proton Synchrotrons

During the 2018 proton run, a new radio-frequency beam manipulation has been studied and successfully implemented at the CERN Proton Synchrotron (PS) for the first time. This technique is used to deplete a well-defined fraction of a continuous longitudinal beam distribution by creating a so-called barrier bucket. We propose a new application of the barrier bucket gymnastics in the multiturn extraction scheme used at CERN. These two exotic techniques are combined into a highly sophisticated procedure that dramatically reduces the beam losses at PS extraction, thus paving the way to high-intensity proton beams for future fixed-target experiments at the CERN Super Proton Synchrotron (SPS). In this paper, the expected performance of the PS and SPS is analyzed in detail to define a road map for making this novel extraction scheme operational

Barrier bucket and transversely split beams for loss-free multi-turn extraction in synchrotrons

A special radio-frequency manipulation has been studied and successfully implemented at the CERN Proton Synchrotron for the first time. This technique aims at depleting a well-defined fraction of a continuous longitudinal beam distribution by creating a so-called barrier bucket. In addition to the intrinsic interest for its originality, this approach has an immediate application at CERN in combination with the Multi-Turn Extraction scheme. The combination of these two exotic techniques into a single, highly sophisticated process allows to dramatically reduce the beam loss at PS extraction, thus opening the door to the production of high-intensity proton beams for future fixed-target experiments at the CERN Super Proton Synchrotron