In this paper, we present the physics performance of the ESSnuSB experiment in the standard three flavor scenario using the updated neutrino flux calculated specifically for the ESSnuSB configuration and updated migration matrices for the far detector. Taking conservative systematic uncertainties corresponding to a normalization error of $$5\%$$ 5 % for signal and $$10\%$$ 10 % for background, we find that there is $$10\sigma $$ 10 σ $$(13\sigma )$$ ( 13 σ ) CP violation discovery sensitivity for the baseline option of 540 km (360 km) at $$\delta _\mathrm{CP} = \pm 90^\circ $$ δ CP = ± 90 ∘ . The corresponding fraction of $$\delta _\mathrm{CP}$$ δ CP for which CP violation can be discovered at more than $$5 \sigma $$ 5 σ is $$70\%$$ 70 % . Regarding CP precision measurements, the $$1\sigma $$ 1 σ error associated with $$\delta _\mathrm{CP} = 0^\circ $$ δ CP = 0 ∘ is around $$5^\circ $$ 5 ∘ and with $$\delta _\mathrm{CP} = -90^\circ $$ δ CP = - 90 ∘ is around $$14^\circ $$ 14 ∘ $$(7^\circ )$$ ( 7 ∘ ) for the baseline option of 540 km (360 km). For hierarchy sensitivity, one can have $$3\sigma $$ 3 σ sensitivity for 540 km baseline except $$\delta _\mathrm{CP} = \pm 90^\circ $$ δ CP = ± 90 ∘ and $$5\sigma $$ 5 σ sensitivity for 360 km baseline for all values of $$\delta _\mathrm{CP}$$ δ CP . The octant of $$\theta _{23}$$ θ 23 can be determined at $$3 \sigma $$ 3 σ for the values of: $$\theta _{23} > 51^\circ $$ θ 23 > 51 ∘ ($$\theta _{23} < 42^\circ $$ θ 23 < 42 ∘ and $$\theta _{23} > 49^\circ $$ θ 23 > 49 ∘ ) for baseline of 540 km (360 km). Regarding measurement precision of the atmospheric mixing parameters, the allowed values at $$3 \sigma $$ 3 σ are: $$40^\circ< \theta _{23} < 52^\circ $$ 40 ∘ < θ 23 < 52 ∘ ($$42^\circ< \theta _{23} < 51.5^\circ $$ 42 ∘ < θ 23 < 51 . 5 ∘ ) and $$2.485 \times 10^{-3}$$ 2.485 × 10 - 3 eV$$^2< \varDelta m^2_{31} < 2.545 \times 10^{-3}$$ 2 < Δ m 31 2 < 2.545 × 10 - 3 eV$$^2$$ 2 ($$2.49 \times 10^{-3}$$ 2.49 × 10 - 3 eV$$^2< \varDelta m^2_{31} < 2.54 \times 10^{-3}$$ 2 < Δ m 31 2 < 2.54 × 10 - 3 eV$$^2$$ 2 ) for the baseline of 540 km (360 km).

The 2.0 GeV, 5 MW proton linac for the European Spallation Source, ESS, will have the capacity to accelerate additional pulses, interleaved with the proton pulses for neutron production, and send them to a neutrino target, providing an excellent opportunity to produce an unprecedented highperformance neutrino beam, the ESS neutrino Super Beam (ESSnuSB), to measure, with precision, the CP violating phase at the 2 nd oscillation maximum. In order to comply with the acceptance of the target and horn systems that will form the neutrino super beam, the long pulses from the linac must be compressed by about three orders of magnitude with minimal particle loss, something that will be achieved in an accumulator ring. This ring will accommodate about 10 15 protons, which means that several design challenges are encountered. Strong space charge forces, low-loss injection, efficient collimation, and e-p instabilities are some of the aspects central to the design work. Different pulse structures and injection painting schemes have been studied, with the goal of mitigating space charge effects and of minimizing the heating of the stripping foil despite the very high beam intensity. This paper presents the status of the accumulator ring design, with multi-particle simulations of the injection procedure.

A design study, named $${\text {ESS}}\nu {\text {SB}}$$ ESS ν SB for European Spallation Source neutrino Super Beam, has been carried out during the years 2018–2022 of how the 5 MW proton linear accelerator of the European Spallation Source under construction in Lund, Sweden, can be used to produce the world’s most intense long-baseline neutrino beam. The high beam intensity will allow for measuring the neutrino oscillations near the second oscillation maximum at which the CP violation signal is close to three times higher than at the first maximum, where other experiments measure. This will enable CP violation discovery in the leptonic sector for a wider range of values of the CP violating phase $$\delta _{{\mathrm{CP}}}$$ δ CP and, in particular, a higher precision measurement of $$\delta _{{\mathrm{CP}}}$$ δ CP . The present Conceptual Design Report describes the results of the design study of the required upgrade of the ESS linac, of the accumulator ring used to compress the linac pulses from 2.86 ms to 1.2 μs, and of the target station, where the 5 MW proton beam is used to produce the intense neutrino beam. It also presents the design of the near detector, which is used to monitor the neutrino beam as well as to measure neutrino cross sections, and of the large underground far detector located 360 km from ESS, where the magnitude of the oscillation appearance of $$\nu _{e }$$ ν e from $$\nu _{\mu }$$ ν μ is measured. The physics performance of the $${\text {ESS}}\nu {\text {SB}}$$ ESS ν SB research facility has been evaluated demonstrating that after 10 years of data-taking, leptonic CP violation can be detected with more than 5 standard deviation significance over 70% of the range of values that the CP violation phase angle $$\delta _{{\mathrm{CP}}}$$ δ CP can take and that $$\delta _{{\mathrm{CP}}}$$ δ CP can be measured with a standard error less than 8° irrespective of the measured value of $$\delta _{{\mathrm{CP}}}$$ δ CP . These results demonstrate the uniquely high physics performance of the proposed $${\text {ESS}}\nu {\text {SB}}$$ ESS ν SB research facility.

In order to handle extremely-high stored energy in future proton-proton colliders, an extremely high-efficiency collimation system is required for safe operation. At LHC, the major limiting locations in terms of particle losses on superconducting (SC) magnets are the dispersion suppressors (DS) downstream of the transverse collimation insertion. These losses are due to the protons experiencing single diffractive interactions in the primary collimators. How to solve this problem is very important for future proton-proton colliders, such as the FCC-hh and SPPC. In this article, a novel method is proposed, which arranges both the transverse and momentum collimation in the same long straight section. In this way, the momentum collimation system can clean those particles related to the single diffractive effect. The effectiveness of the method has been confirmed by multi-particle simulations. In addition, SC quadrupoles with special designs such as enlarged aperture and good shielding are adopted to enhance the phase advance in the transverse collimation section, so that tertiary collimators can be arranged to clean off the tertiary halo which emerges from the secondary collimators and improve the collimation efficiency. With one more collimation stage in the transverse collimation, the beam losses in both the momentum collimation section and the experimental regions can be largely reduced. Multi-particle simulation results with the MERLIN code confirm the effectiveness of the collimation method. At last, we provide a protection scheme of the SC magnets in the collimation section. The FLUKA simulations show that by adding some special protective collimators in front of the magnets, the maximum power deposition in the SC coils is reduced dramatically, which is proven to be valid for protecting the SC magnets from quenching.

Short bunch beams of high intensity are required by many applications, and they are usually obtained by using bunch compression before the extraction in relatively slow cycling synchrotrons or accumulator rings. In this article, short bunch extraction by the bunch compression method is proposed to apply to a rapid cycling synchrotron (RCS) where the time duration is very limited to exploit the bunch compression process. The method is practically applied in the RCS of the China Spallation Neutron Source (CSNS) to obtain short-bunch beams for white neutron applications. Different short-bunch extraction scenarios have been studied, from keeping full beam power to reduced beam powers. A special desynchronization method is designed to solve the problem of slow acceleration during the bunch rotation process when the magnetic field is still ramping up. The space charge effect and beam loading effect during the bunch compression have also been taken into account in this high-intensity RCS. Multiparticle simulations have been carried out to show the effectiveness of the method with the input of the CSNS RCS. With a sacrifice of about twothirds of the beam power, the rms bunch length of the extracted beam can be reduced to about one-ninth of the one in the nominal operation mode.