A. Alekou

Bucked Coils lattice: a novel ionisation cooling lattice for the Neutrino Factory

A successful muon ionisation cooling channel for the Neutrino Factory and Muon Collider, requires simultaneously a strong focusing and a large mean RF gradient. To date, all candidate design lattices achieved these requirements with a large magnetic field in the RF cavities, which can potentially limit the achievable gradient leading to RF breakdown. This paper presents the Bucked Coils lattice, designed to reduce the magnetic field at the RF cavities while achieving a satisfactory cooling effect and muon transmission. The Bucked Coils managed to achieve significantly reduced magnetic field components at the RF position, while also achieving a comparable transmission to the FSIIA lattice, the current reference ionisation cooling lattice of the Neutrino Factory. A detailed comparison with respect to the magnetic field reduction, cooling dynamics and transmission is given. A preliminary feasibility study taking into account the hoop stress of the coils and their superconducting operation is also presented.

Performance study of the Bucked Coils cooling lattice for the Neutrino Factory

In a Neutrino Factory (NF), neutrinos are produced from the decays of muons. The muon beam itself is produced with large emittance at the NF front-end and in order to be efficiently transported to downstream accelerator systems, the beam emittance needs to be cooled using ionisation cooling. The reference ionisation cooling channel of the NF reduces the transverse emittance by a factor of ~3. However, this lattice has a large magnetic field at the position of the RF cavities and therefore its feasibility has come under question when recent studies indicated high external magnetic field may lower the maximum achievable gradient of the RF cavities. The present work summarizes the performance of a new lattice named Bucked Coils, designed to mitigate the magnetic field issue of the reference lattice of the NF while aiming to achieve similar cooling performance and transmission. This new lattice offers solution by reducing the longitudinal component of the magnetic field to almost 0 T while at the same time achieving a transmission comparable to the reference lattice within the transverse acceptance of 30 mm. Detailed comparison between the Bucked Coils lattice and the reference lattice of the NF follows with respect to the magnetic field reduction, cooling performance and transmission.

Numerical study of a bucked-coil system for muon transport and cooling

A Neutrino Factory, which can deliver an intense flux of ∼1021 neutrinos per year from a multi-GeV stored muon-beam is seemingly the ideal tool for studying neutrino oscillations and CP-violations for leptons. The front-end of this facility plays a critical role in determining the number of muons that can be accepted by the downstream accelerators. Delivering peak performance requires transporting the muon beams through long sections of a beam channel containing high-gradient rf cavities and strong focusing solenoids. Here, we propose a novel scheme to improve the performance of the cavities, thereby increasing the number of muons within the acceptance of the accelerator chain. The key element of our new scheme is to apply a set of bucked coils along the lattice, thus forcing the external magnetic field to drop substantially within the cavity. We incorporate this idea into a new lattice design for a Neutrino Factory, and detail its performance numerically.