Scaling Fixed-Field Alternating-Gradient Accelerators with Reverse Bend and Spiral Edge Angle

Abstract

A novel scaling type of Fixed-Field Alternating-Gradient (FFAG) accelerator is proposed that solves the major problems of conventional scaling FFAGs. This scaling FFAG accelerator combines reverse bending magnets of the radial sector type and a spiral edge angle of the spiral sector type to ensure sufficient vertical focusing without relying on extreme values of either parameter. This new concept makes it possible to design a scaling FFAG for high energy (above GeV range) applications such as a proton driver for a spallation neutron source and an accelerator driven subcritical reactor.Particle accelerators were developed initially as a tool to explore particle physics at the energy frontier. Recently, however, many accelerators have been constructed for other fields of physics mostly with the aim of producing secondary or tertiary particles such as neutrons, muons and neutrinos. A figure of merit in this area is a measure of the number of energetic particles, usually protons, that are used to create secondary or tertiary particles through impact with a production target. The energy of each particle does not have to be as high as in accelerators for research at the energy frontier; instead emphasis is put on the beam intensity, which is always demanding. The research field that this type of accelerator explores is called the intensity frontier, and the accelerator is usually referred to as a proton driver.Considering the cross-section of the secondary and tertiary particle production, the energy range of a proton driver covers a range from a few 100 MeV to some 10's of GeV. Cyclotrons cover the lower end: the machines at PSI and TRIUMF, for example, have just enough energy for neutron and muon production. Linear accelerators (linacs for short) with and without an accumulator ring and rapid cycling synchrotrons (RCS) usually produce beams of a few GeV to produce neutrons most efficiently. ISIS, SNS, the J-Parc RCS and ESS (under construction in Sweden) belong to this category. When protons with energies higher than a few GeV are required for the production of kaons and neutrinos through pions, slow cycling synchrotrons are the only option. BNL-AGS, CERN-PS and J-Parc MR are examples.Fixed-Field Alternating-Gradient (FFAG) accelerators were invented in 1950s and developed over the following years, initially as accelerators for energy frontier physics [1,2]. At the same time, an alternating-gradient synchrotron had been developed and its more compact magnets relative to the FFAGs became a big advantage when looking to increase beam energy, so the objectives of the FFAG accelerator development faded out. Although there were remained pockets of interests on FFAG accelerators, for instance [3][4][5][6][7], little development beyond paper studies took place until the late 1990's when the * shinji.machida@stfc.ac.uk idea of a neutrino factory called for an accelerator that could rapidly accelerate muons before they had time to decay [8][9][10].When FFAGs were invented, it was realized that an important advantage over oth...

On the feasibility of a pulsed 14 TeV c.m.e. muon collider in the LHC tunnel

“…With fixed-frequency rf, a continuous train of bunches could be acceleraterated to full energy for accumulation in the collider ring. Non-scaling or recently proposed scaling FFAG arcs [24] could also be considered in multi-pass synchrotron scenarios (100-1000 turns) which would use ramped frequency RF acceleration systems.…”