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

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

Design and Diagnostics of High-Precision Accelerator Neutrino Beams

Neutrino oscillation physics has entered a new precision era, which poses major challenges to the level of control and diagnostics of the neutrino beams. In this paper, we review the design of high-precision beams, their current limitations, and the latest techniques envisaged to overcome such limits. We put emphasis on “monitored neutrino beams” and advanced diagnostics to determine the flux and flavor of the neutrinos produced at the source at the per-cent level. We also discuss ab-initio measurements of the neutrino energy–i.e., measurements performed without relying on the event reconstruction at the ν detector–to remove any flux induced bias in the determination of the cross sections

Model and measurements of CERN-SPS slow extraction spill re-shaping - the burst mode slow extraction

The ENUBET (Enhanced NeUtrino BEams from kaon Tagging) Project aims at reaching a new level of precision of the short-baseline neutrino cross section measurement by using an instrumented decay tunnel. The North Area (NA) experimental facility of the CERN Super Proton Synchrotron (SPS) offers the required infrastructure for the experiment. A new slow extraction type, consisting of bursts of many consecutive millisecond spills within one macro spill, has been modeled and tested for the ENUBET Project. The burst-mode slow extraction has been tested for the first time at CERN-SPS, and MADX simulations of the process have been developed. In this paper the experimental results obtained during the test campaign are presented along with the results of the quality of the produced spill and comparing it with predictions from simulations

The ENUBET Multi Momentum Secondary Beamline Design

The aim of neutrino physics for the next decades is to detect effects due to CP violation, mass hierarchy, and search for effects beyond the Standard Model predictions. Future experiments need precise measurements of the neutrino interaction cross-sections at the ~GeV/c regime, currently limited by the exact knowledge of the initial neutrino flux on a ~10-20% uncertainty level. The ENUBET project is proposing a novel facility, capable of constraining the neutrino flux normalization through the precise monitoring of the Ke3 (K±>e+pi0nu) decay products in an instrumented decay tunnel. ENUBET can also monitor muons from the two body kaon and pion decays (nu flux) and measure the neutrino energy with a 10% precision without relying on the event reconstruction at the neutrino detector. We present here a novel design based on a broad (4-8.5 GeV/c) momentum range secondary beamline, that widen the cross-section energy range that can be explored by ENUBET. In this poster, we discuss the target optimization studies and we show the early results on the new line’s optics and the layout design. We discuss the expected performance of this line and the forthcoming activities

Demonstration of slow extraction loss reduction with the application of octupoles at the CERN Super Proton Synchrotron

The powering of octupoles during third-integer resonant slow extraction has been studied and recently tested with the beam at the CERN Super Proton Synchrotron (SPS) in order to increase the extraction efficiency and reduce the induced radioactivity along the extraction straight. The octupoles distort the particle trajectories in phase space in such a way that the extracted separatrix is folded, which decreases the particle density impinging the wires of the extraction septum at the expense of increasing the extracted beam emittance. During experimental SPS machine studies a reduction of over 40% in the specific (per extracted proton) beam loss measured at the extraction septum was achieved. In this paper, the prerequisite studies needed to safely deploy the new extraction scheme in a limited time-frame are described, the experimental results are presented and an outlook given toward the next steps to bring slow extraction with octupoles into routine operation

Observations of SPS Slow-Extracted Spill Quality Degradation and Possible Improvements

The SPS delivers slow extracted proton and heavy ion spills of several seconds to the North Area fixed target experiments with a very high duty factor. Reduced machine reproducibility due to magnetic history and power supply ripples on the main circuits lead however to frequent degradation of the spill duty factor. In this paper, the measured effect of the SPS magnetic history on spill quality and principal machine parameters is presented. Another detailed measurement campaign was aimed at characterising the frequency content and response of the spill to noise on the main power supplies ripples. The main findings of this study will also be reported. Finally, simulations of possible improvements based on the data acquired are discussed, as well as an extrapolation to the possible spill quality after the implementation of the improvements

Septum shadowing by means of a bent crystal to reduce slow extraction beam loss

The flux of high-energy protons slow-extracted from the CERN Super Proton Synchrotron (SPS) is limited by the induced radioactivity caused by the beam loss intrinsic to the extraction process. Methods to substantially increase the efficiency of the extraction process are of great interest to fulfill requests for an increasing flux of 400 GeV protons to the present experiments, located in the North Area of the SPS, and also for potential future experiments with very high demanded protons on target. A crystal shadowing technique to significantly reduce the beam scattered and lost on the electrostatic extraction septum during the third-integer resonant slow extraction process has been developed and a prototype system tested with beam. The technique is based on the use of a thin, bent silicon crystal to coherently channel or volume reflect the portion of beam that would otherwise impinge the wire array of the electrostatic septum and instead eject it into the transfer line toward the production targets of the experiments. In this paper, the concept is described and applied to the SPS machine in order to specify the requirements of the prototype crystal shadowing system. Beam dynamics simulations of the prototype system are compared and benchmarked to the results obtained through beam tests, before being exploited to understand the characteristics of the present system and the potential performance reach of an optimized, future operational configuration. The remaining challenges faced to bring the system into operation, the optimization possibilities and other potential applications are discussed

Improvements to the SPS Slow Extraction for High Intensity Operation

Slow extraction using the third-integer resonance and thin electrostatic septa as used in the SPS to serve the North Area is a process with inherent beam loss. For high-flux 400 GeV protons, the beam losses result in high machine activation, reduced component lifetime and severe limitations on personnel access and maintenance. The instantaneous and integrated loss levels are strong limitations on the annual attainable POT for present operation and for the much higher fluxes requested by SHiP at the proposed BDF facility. In this report the present constraints and potential improvements to the slow extraction system in the SPS are described along with the recent theoretical studies and practical implementation of prospective operational improvements. Machine results of testing of new extraction loss reduction techniques and hardware are presented in the context of SHiP POT requests, SPS BDF and the PBC project and the potential extraction loss reduction factor is evaluated with an outlook to future high intensity operation. The prospects of deployment on the present operational beams and the resulting improvement factors are discussed