Investigating Beam Loss Reduction with Octupoles During Slow Extraction in the CERN SPS

Several different methods for reducing beam loss during resonant slow extraction at the CERN Super Proton Synchrotron (SPS) are being studied. One of these methods is the use of multipoles to manipulate the separatrices in order to reduce the fraction of protons hitting the thin wires of the electrostatic extraction septum (ES). In this paper the potential of using octupoles for this purpose is explored. Beam dynamics simulations using both a simplified model and full 6D tracking in MAD-X are presented. The performance reach of such a concept at the SPS is evaluated and the potential of future machine development studies using the octupoles already installed is discussed

Tracking simulations of shadowing electrostatic septum wires by means of bent crystals

The CERN Super Proton Synchrotron (SPS) slow extraction is a third integer resonant extraction and hence suffers from high losses at the electrostatic septum (ZS). This is one of the main limiting factors for the maximum number of Protons On Target (POT) deliverable from the SPS to the North Area (NA). A concept to significantly reduce the extraction losses via shadowing of the electrostatic septum wires using an upstream bent crystal has been proposed in [1], predicting a loss reduction of up to about 50% for the prototype system installed in 2018. Following the successful experimental demonstration of the concept with beam [2], detailed tracking simulations have been performed to fully understand the results obtained. Further insights, such as the effective ZS width and its alignment, could be deduced by exploiting the response of the extraction loss as a function of the two degrees of freedom of the crystal (position and angle). In this paper, the beam dynamics simulations are discussed together with the implementation of the bent crystal into the simulation framework. A comparison with measurements is presented before proposals for new configurations and parameters are discussed

The Use of a Passive Scatterer for SPS Slow Extraction Beam Loss Reduction

A significant reduction in the fraction of protons lost on the SPS electrostatic septum ES during resonant slow extraction is highly desirable for present Fixed-Target beam operation, and will become mandatory for the proposed SHiP experiment, which is now being studied in the framework of CERN's Physics Beyond Colliders program. In this paper the possible use of a passive scattering device (diffuser) is investigated. The physics processes underlying the use of a diffuser are described, and the dependence on the diffuser geometry, material and location of the potential loss reduction on the electrostatic septum (ES) wires is investigated with a semi-analytical approach. Numerical simulations to quantify the expected performance gain for the optimum configuration are presented, and the results discussed in view of the feasibility of a potential realisation in the SPS

Use of a Massless Septum to Increase Slow-Extraction Efficiency

The Super Proton Synchrotron (SPS) at CERN provides slow-extracted beam for Fixed Target experiments in the North Area. For the higher extracted beam intensities requested by future experimental proposals, beam-loss induced activation will be one of the limiting factors for the availability of such a facility. In this paper, we present and discuss the concept of using a massless septum magnet to increase the extraction efficiency and decrease losses caused by protons scattering on the electrostatic-septa wires

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

Use of a Massless Septum to Increase Slow-Extraction Efficiency

The Super Proton Synchrotron (SPS) at CERN provides slow-extracted beam for Fixed Target experiments in the North Area. For the higher extracted beam intensities requested by future experimental proposals, beam-loss induced activation will be one of the limiting factors for the availability of such a facility. In this paper, we present and discuss the concept of using a massless septum magnet to increase the extraction efficiency and decrease losses caused by protons scattering on the electrostatic-septa wires

MD#4164: Separatrix folding with octupoles during slow extraction at SPS

The powering of the SPS main octupole circuit (LOF) during third-integer slow extraction was tested to reduce the density of the beam impinging the wires of the electrostatic extraction septum (ZS). This note briefly summarises the results of the slow extraction tests carried out with 400 GeV protons, including the demonstration of a 40% reduction of the beam loss during extraction at the ZS in Long Straight Section (LSS) 2

Reduction of Resonant Slow Extraction Losses with Shadowing of Septum Wires by a Bent Crystal

A new experiment, SHiP, is being studied at CERN to investigate the existence of three Heavy Neutral Leptons in order to give experimental proof to the proposed neutrino minimal Standard Model. High-intensity slow-extraction of protons from the SPS is a pre-requisite for SHiP. The experiment requires a resonant extraction with in a 7.2 s cycle, and about 4·10¹³ protons extracted at 400 GeV in a 1 s flat-top, to achieve the needed 2·10²⁰ protons on target in five years. Although the SPS has delivered this in the past to the CNGS experiment with fast extraction, for SHiP beam losses and activation of the SPS electrostatic extraction septum (ZS) could be a serious performance limitation, since the target number of protons to resonantly extract per year is a factor of two higher than ever achieved before and a factor of four than ever reached with the third-integer slow extraction. In this paper, a novel extraction technique to significantly reduce the losses at the ZS is proposed, based on the use of a bent crystal to shadow the septum wires. Theoretical concepts are developed, the performance gain quantified and a possible layout proposed

Beam Dynamics Simulations of the Effect of Power Converter Ripple on Slow Extraction at the CERN SPS

The SPS provides slowly extracted protons at 400 GeV/c to CERN's North Area Fixed Target experiments over spills of duration from 1-10 seconds. Low frequency ripple on the current in the main magnets originating from their power converters is a common issue that degrades the slow-extracted spill quality. In order to better understand how the stability of the power converters affects losses, beam emittance and spill quality, particle tracking simulations were carried out using MAD-X and compared to measurements, with the impact of each magnet circuit investigated systematically. The implications for the performance of the SPS slow extraction are discussed