Study and development of SPS slow extraction schemes and focusing of secondary particles for the ENUBET monitored neutrino beam

The Enhanced NeUtrino BEams from Kaon Tagging (ENUBET) project aims at developing a first "monitored" neutrino beam, in which the neutrino flux could be measured with a ~1% precision. To do so, the secondary particles decay tunnel will be fully instrumented with compact segmented calorimeters, with the goal of tagging each Ke3 decay of kaons. As a consequence of this, a high precision measurement of the electron neutrino cross-section could be performed, since the uncertainty on the neutrino flux represents the current main limitation. A full instrumentation of the decay tunnel significantly influences the requirements on the extraction of the primary protons. The pile-up in the detectors rules out the fast-extraction scheme, and calls for the use of the slow resonant extraction, in which continuous spills of the length of several seconds are extracted from the accelerator. Such a long spill would require the use of static focusing devices on the beamline. However, given the low number of produced electron neutrinos, speeding up the cross-section measurement by resorting to a magnetic horn for improved focusing represents an appealing idea. This would require to modify the slow extraction scheme in order to produce a new "pulsed" version of it, with pulse lengths of the order of some millisecond. In the present work, such a pulsed slow extraction scheme is designed, implemented, and tested at CERN-SPS, with the goal of proving its feasibility according to the requirements of ENUBET. The obtained experimental results are validated with simulations and future possible improvements are investigated. In connection to this, a dedicated study on the frequency response to magnet ripples of the slow extraction process is undertaken: this problem is strictly connected with the performance of the pulsed slow extraction, and can also significantly contribute to improve the standard continuous-spill operation of the experiment (and any other fixed target facility). Both measurements and simulations are used to characterize the process and propose meaningful improvements. Finally, a framework for the simulation and optimization of the ENUBET magnetic horn is developed. This is used to start the investigation of the potential flux gain which could come from the use of the magnetic horn in the ENUBET beamline, coupled with the pulsed slow extraction.