# Design and Diagnostics of High-Precision Accelerator Neutrino Beams
## 3 Extraction and Monitoring of Primary Protons
Similar pulses with a length of a few microseconds are obtained also for the neutrino beams at J-PARC [26, 36] and Fermilab [29, 30]. The nominal slow extraction of the SPS [37, 38] is based on a third-integer resonance, and produces typically a few second long spill, which is delivered on multiple targets to produce the secondary particle beams serving the North Area (NA) fixed-target experiments. In this context, two narrow-band secondary hadron beamlines have been recently built and commissioned for the ProtoDUNE detectors hosted at the NA Neutrino Platform [39, 40, 41, 42]. The low particle rate provided by the SPS slow extraction allows precise monitoring of the beam parameters, as, for instance, particle by particle momentum measurement and beam composition (Section 7). Before 1998, a different implementation of the SPS slow extraction was used to extract the beam in a few hundred \(\upmu\)s up to a few ms long spills, serving the West Area (WA) neutrino facility [43, 44, 45, 46], decommissioned in 2004. This type of extraction, referred to as \"fast-resonant\" or \"fast-slow\" [47], was based on a half-integer resonance and fast-discharge quadrupoles. Recent slow extraction studies have been carried out at the SPS in the context of the ENUBET project [48], aimed at delivering the technology of monitored neutrino beams. In ENUBET, the pile-up at the instrumented decay volume poses stringent limits on the particle rate, making the use of a \(\mathcal{O}\)(s)-long slow extraction the preferred option. However, to retain the possibility of using a magnetic horn or reduce the cosmic background at the neutrino detector, a new pulsed slow extraction scheme has been developed and tested. It consists in the extraction of 2-to-10 ms proton pulses, repeated at 10 Hz for the full extraction time [49]. An example of this new scheme, the _burst-mode slow extraction_, can be seen in Figure 3.  
The experimental results of the study have shown that this extraction method can be readily implemented and optimized at the SPS, based on the nominal slow extraction settings. During the machine development studies performed before the CERN Long Shutdown 2 (LS2, 2019-2021), the minimum observed temporal length of the pulses was 10 ms. Dedicated simulation studies performed later on showed the possibility to span a 2-10 ms range, and they will be validated after LS2. Unlike fast extractions, the slow extraction is an intrinsically lossy scheme: as the unstable particles gradually spiral out of the ring through the electrostatic septum, a small fraction of them will hit the septum blade. In the SPS, another fraction of the beam is lost on the downstream septa used to split the beam among the different transfer lines. As a consequence, the maximum number of integrated protons-on-target (POT) is limited by the activation of the accelerator equipment and the radiation hazard due to dose exposure of the workers. The number of POT extracted at the SPS in 2018 of about \(1.2\times 10^{19}\), which represents a record since the WA times, is still far from the typical yearly POT of a fast-extracted neutrino beam. Even if significantly higher yearly rates are within the machine capabilities, important reductions of the extraction and splitting losses will be required to reach them. A dedicated campaign is ongoing at the SPS to reach this goal [50, 51, 52]. For instance, local shadowing techniques as the insertion of a passive diffuser or a silicon bent crystal in front of the electrostatic septum have shown, during machine tests, loss reductions of about 10-15% and 20-40%, respectively [53, 54, 55]. Other techniques based on machine optics have also been investigated. In particular, first tests of octupole-based separatrix folding have shown a loss reduction of \(\sim\)40% at the electrostatic septum [56]. Long-standing efforts of reduction of the slow extraction losses are being undertaken at a global scale (e.g., [57, 58]), calling for exciting developments in the future years.