Challenges and Status of the ESSnuSB Accumulator Design

Abstract

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.

The European Spallation Source neutrino super-beam conceptual design report

“…Each beam pulse must instead be split into several sub-pulses or batches. The batch length is limited by the storage time in the accumulator ring-about 1000 turns, corresponding to 1.3 ms-before instabilities are likely to develop [2]. A pulsing scheme with an overall 28 Hz macro-pulse structure has been selected as the baseline design, corresponding to Option A+ in Fig.…”

“…Each batch is stacked in the accumulator ring, compressing the pulses to 1.2 µs, which are subsequently extracted to the target. By splitting the macropulse into four batches, the power on each target is limited to 1.25 MW, and the space charge tune shift [3] in the accumulator ring is limited to an acceptable level [2,4].…”

“…The Penning source was first developed by Dudnikov [13] and has also been used at Los Alamos National Laboratory (LANL) [27]. The Penning ion source can produce high currents, up to 100 mA, provide high-emission current densities ¿ 1 A/cm 2 and have a fairly low energy spread of < 1 eV. In routine operation, the Penning 1X source at ISIS produces 55 mA in 0.25 ms pulses at 50 Hz (1.5% duty cycle).…”

“…The emerging picture from the last decades of neutrino oscillation measurements [250,251] is that of two distinct mass splittings, the "solar" mass splitting Δm 2 21 = 7.4 × 10 −5 eV 2 and the larger "atmospheric" one, |Δm 2 31 |= 2.5 × 10 −3 eV 2 , with Δm 2 ij = m 2 j − m 2 i . On the other hand, after the discovery of a non-zero θ 13 [252][253][254][255], the structure of the PMNS matrix describing lepton flavour mixing is surprisingly different from its CKM counterpart in the quark sector, making the Standard Model flavour puzzle even more intriguing.…”

The Integrable Optics Test Accelerator

“…The next generation of accelerator-based neutrino experiments rely on proton drivers exceeding the 1 MW benchmark [1,2,3]. At Fermilab, the Proton Improvement Plan II (PIP-II) will provide 1.2 MW beam power at 120 GeV, which is the initial requirement for the Deep Underground Neutrino Experiment (DUNE) physics program [4].…”