Shinji Machida

The EMMA lattice design

EMMA is a 10 to 20 MeV electron ring designed to test our understanding of beam dynamics in a relativistic linear non-scaling fixed field alternating gradient accelerator (FFAG). This paper describes the design of the EMMA lattice. We begin with a summary of the experimental goals that impact the lattice design, and then outline what motivated the choice for the basic lattice parameters, such as the type of cells, the number of cells, and the RF frequency. We next list the different configurations that we wish to operate the machine in so as to accomplish our experimental goals. Finally, we enumerate the detailed lattice parameters, showing how these parameters result from the various lattice configurations.

FFAGS for muon acceleration

Due to their finite lifetime, muons must be accelerated very rapidly. It is challenging to make the magnets ramp fast enough to accelerate in a synchrotron, and accelerating in a linac is very expensive. One can use a recirculating accelerator (like CEBAF), but one needs a different arc for each turn, and this limits the number of turns one can use to accelerate, and therefore requires significant amounts of RF to achieve the desired energy gain. An alternative method for muon acceleration is using a fixed field alternating gradient (FFAG) accelerator. Such an accelerator has a very large energy acceptance (a factor of two or three), allowing one to use the same arc with a magnetic field that is constant over time. Thus, one can in principle make as many turns as one can tolerate due to muon decay, therefore reducing the RF cost without increasing the arc cost. This paper reviews the current status of research into the design of FFAGs for muon acceleration. Several current designs are described and compared. General design considerations are also discussed

Particle beam resonances driven by dispersion and space charge

We study parametric resonances in circular accelerators, incorporating the effect of space-charge self-fields. A general Hamiltonian formalism is constructed for this purpose. The particle-in-cell simulation technique is employed to systematically explore the role of space-charge forces on resonant instabilities in two-dimensional beams. It is shown that momentum dispersion peculiar to rings can be an additional source of resonances.

Beam injection into emma non-Scaling FFAG

Non-Scaling FFAG has unique characteristics of large transverse acceptance and rapid beam acceleration with a relatively small beam excursion for a fixed field accelerator, and broad range of application is expected. To demonstrate the feasibility as a practical accelerator, construction of a test machine called EMMA is proposed. The project is planned to build a Non-Scaling FFAG which accelerate an electron beam from 10MeV to 20 MeV. As the nature of a test machine, the injection and extraction scheme must accommodate large varieties of conditions. Due to the nature of the accelerator, that is the betatron tune changes drastically changes during beam acceleration, the requirements enforces a different approach in the design of injection system compared to the conventional circular accelerators, and make it challenging. In the paper, the injection scheme of EMMA non-scaling FFAG is described.

Development of FFAG Accelerator at KEK

The 150MeV proton FFAG accelerator is constructed and a beam is extracted at the final energy. This is the prototype FFAG for various applications such as proton beam therapy. We are now in preparation for using an extracted beam in the practical applications.

Fixed field alternating gradient

The concept of a fixed field alternating gradient (FFAG) accelerator was invented in the 1950s. Although many studies were carried out up to the late 1960s, there has been relatively little progress until recently, when it received widespread attention as a type of accelerator suitable for very fast acceleration and for generating high-power beams. In this paper, we describe the principles and design procedure of a FFAG accelerator.

Injection/Extraction Studies for the Muon FFAG

The non‐scaling fixed field alternating gradient (NS‐FFAG) ring is a candidate muon accelerator in the Neutrino Factory complex according to the present baseline, which is currently being addressed by the International Design Study (IDS‐NF). In order to achieve small orbit excursion, motivated by magnet cost reduction, and small time of flight variation, dictated by the need to use high RF frequency, lattices with a very compact cell structure and short straight sections are required. The resulting geometry dictates very difficult constraints on the injection/extraction systems. Beam dynamics in the non‐scaling FFAG is studied using codes capable of correctly tracking with large transverse amplitude and momentum spread. The feasibility of injection/extraction is studied and various implementations focusing on minimization of kicker/septum strength are presented. Finally the parameters of the resulting kicker magnets are estimated.

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

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.

Commissioning and first results of the Intense Beam EXperiment (IBEX) linear Paul trap

The Intense Beam Experiment (IBEX) is a linear Paul trap designed to replicate the dynamics of intense particle beams in accelerators. Similar to the S-POD apparatus at Hiroshima University, IBEX is a small scale experiment which has been constructed and recently commissioned at the STFC Rutherford Appleton Laboratory in the UK. The aim of the experiment is to support theoretical studies of next-generation high intensity proton and ion accelerators, complementing existing computer simulation approaches. Here we report on the status of commissioning and first results obtained.

Amplitude-dependent orbital period in alternating gradient accelerators

Orbital period in a ring accelerator and time of flight in a linear accelerator depend on the amplitude of betatron oscillations. The variation is negligible in ordinary particle accelerators with relatively small beam emittance. In an accelerator for large emittance beams like muons and unstable nuclei, however, this effect cannot be ignored. In this study, we measured orbital period in a linear non-scaling fixed-field alternating-gradient accelerator, which is a candidate for muon acceleration, and compared it with the theoretical prediction. The good agreement between them gives important ground for the design of particle accelerators for a new generation of particle and nuclear physics experiments.