Carol Johnstone

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

HIGH-ORDER DESCRIPTION OF THE DYNAMICS IN FFAGs AND RELATED ACCELERATORS

In this paper, we describe newly developed tools for the study and analysis of the dynamics in FFAG accelerators based on transfer map methods unique to the code COSY INFINITY. With these new tools, closed orbits, transverse amplitude dependencies and dynamic aperture are determined inclusive of full nonlinear fields and kinematics to arbitrary order. The dynamics are studied at discrete energies, via a high-order energy-dependent transfer map. The order-dependent convergence in the calculated maps allows precise determination of dynamic aperture and detailed particle dynamics. Using normal form methods, and minimal impact symplectic tracking, amplitude- and energy-dependent tune shifts and resonance strengths are extracted. Optimization by constrained global optimization methods further refine and promote robust machine attributes. Various methods of describing the fields will be presented, including representation of fields in radius-dependent Fourier modes, which include complex magnet edge contours and superimposed fringe fields, as well as the capability to interject calculated or measured field data from a magnet design code or actual components, respectively.

Calibration and performance of the E706 lead and liquid-argon electromagnetic calorimeter

Abstract We report on the calibration and performance of a large lead liquid-argon electromagnetic calorimeter used by experiment E706 at Fermilab. The reconstructed π 0 mass was used to calibrate the energy response of the calorimeter. The systematic uncertainty in the linearity and uniformity of the mean-energy response of the calorimeter after calibration was found to be less than ±0.5% for the sample of data analyzed. Detector characteristics, including sampling fluctuations and position resolution, are discussed.

Simulation and Optimization of the Tevatron Accelerator

The Tevatron accelerator, currently the particle accelerator with the highest energy in the world, consists of a ring with circumference of four miles in which protons are brought into collision with antiprotons at speeds very close to the speed of light. The accelerator currently under development at Fermilab represents a significant upgrade, but experienced significant limitations during initial operation. The correction of some of the problems that appeared using techniques of automatic differentiation are described. The skew quadrupole correction problems are addressed in more detail, and different schemes of correction are proposed.

Progress in absorber R & D for muon cooling

A stored-muon-beam neutrino factory may require transverse ionization cooling of the muon beam. We describe recent progress in research and development on energy absorbers for muon-beam cooling carried out by a collaboration of university and laboratory groups.

Design of the muon collider isochronous storage ring lattice

The muon collider would ex-tend limitations of the e{sup +} e- colliders and provide new physics potentials with a possible discovery of the heavy Higgs bosons. At the maximum energy of 2 TeV the projected luminosity is of the order of 10{sup 35} cm{sup {minus}2}s{sup {minus}1}. The colliding {mu}{sup +} {mu}{sup {minus}} bunches have to be focused to a very small transverse size of few tenths of {mu}m which is accomplished by the betatron functions at the crossing point of {beta}* = 3mm. This requires the longitudinal space of the same length 3 mm. These very short bunches at 2 TeV could circulate only in a quasi-isochronous storage ring where the momentum compaction is very dose to zero. We report on a design of the muon collider isochronous lattice. The momentum compaction is brought to zero by having the average value of the dispersion function through dipoles equal to zero. This has been accomplished by a combination of the FODO cells together with a low beta insertion. The dispersion function oscillates between negative and positive values.

New nonscaling FFAG for medical applications

A hybrid design for a fixed-field alternating-gradient (FFAG) accelerator has been invented which uses edge and alternating-gradient focusing principles applied in a specific configuration to a combined-function (CF) magnet to stabilize tunes through an acceleration cycle which extends over a factor of 6 in momentum. Using normal conducting magnets, the final, extracted energy from this machine can attain slightly more than 400 MeV/nucleon without the use of superconducting elements. By using fixed-fields, the machine proposed here has the high current advantage of the cyclotron yet retains important features of the synchrotron: smaller radial aperture, variable energy, and both kicker-based and resonant extraction. This machine, without modification, supports a proton and a carbon ion beam in the energy range of interest for cancer therapy. Competing machines for this application include superconducting cyclotrons[1], synchrotrons [2], and, more recently, scaling FFAGs. As such this machine represents a broad innovation in therapy machines.

Convection-type LH2 absorber R&D for muon ionization cooling

Abstract A feasibility study on liquid hydrogen (LH 2 ) absorbers for muon ionization cooling is reported. In muon ionization cooling, an LH 2 absorber is required to have a high cooling power greater than 100 W to cool heat deposited by muons passing through. That heat in LH 2 can be removed at either external or internal heat exchangers, which are cooled by cold helium gas. As one of the internal heat exchanger types, a convection-type absorber is proposed. In the convection-type absorber, heat is taken away by the convection of LH 2 in the absorber. The heat exchanger efficiency for the convection-type absorber is calculated. A possible design is presented.

THE INFLUENCE OF FRINGE FIELDS ON PARTICLE DYNAMICS IN THE LARGE HADRON COLLIDER

Abstract The need of maximizing luminosity in the Large Hadron Collider requires the use of High-Gradient Quadrupoles in the interaction region. These quadrupoles combine relatively short length, large aperture, and short focal length with a rather peculiar configuration of the return coils, all of which enhances the relevance of their fringe field effects. The influence of resulting nonlinearities on the dynamics is analyzed via high-order maps determined with Differential Algebraic (DA) techniques and the code COSY INFINITY. Normal form methods are utilized to determine amplitude-dependent tune shifts as well as resonance strengths. An analysis based on a detailed description of the fringe field of the superconducting quadrupoles reveals that the strength of resonances increases by more than one order of magnitude, and that amplitude-dependent tune shifts are enhanced substantially.

Interaction regions with increased low‐betas for a 2‐TeV Muon Collider

The difficulty encountered in designing an interaction region (IR) for a 2‐TeV Muon Collider lies in the extreme constraints placed on beam parameters at the point of collision. This paper examines a relaxation of the interaction‐point criterion insofar as it impacts luminosity, the design, and stability of the interaction region.