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Thomas Planche

Publications and source records attributed to Thomas Planche.

8 recordsLinked to original sources
arXiv2026

A particle-in-cell model of beam dynamics in a dielectric wall accelerator

Dielectric wall accelerator (DWA) technology has been proposed as a compact, cost-effective alternative to rf accelerators for proton therapy, but its beam dynamics and practical feasibility remain relatively unexplored. In this work, we derive a three-dimensional, time-dependent axisymmetric electromagnetic field model from a prescribed on-wall excitation and implement it as stacked external field elements in the particle-in-cell code Warp. In the absence of experimental DWA beam-transport data, the implementation is cross-checked against a previously developed linear optics model in TRANSOPTR using deliberately idealized beam conditions. Strong agreement is observed between the two models in this regime. The models are then compared for larger transverse and longitudinal emittances, bunch charges up to 1x10^8e, and beam parameters representative of a low-energy proton source. The PIC simulations remain consistent with the linear predictions over much of the investigated range, while also identifying wall interactions, longitudinal phase-space distortions, and space-charge induced aberrations. The PIC model represents an intermediate step between linear optics and combined, geometry-specific electromagnetic and particle-transport simulations. It resolves particle-level transport and beam self-fields while retaining an analytical field description that can be varied without committing to a particular DWA structure. More detailed effects may be introduced through externally generated field data or empirical corrections, including models of cell-to-cell coupling, providing a practical basis for increasingly realistic DWA field and beamline studies.

physics.acc-ph↗
arXiv2026

Analytic descriptions of soft-edge quadrupoles for beamline design in multi-particle simulations

All physical quadrupoles have a fringe field falloff, giving rise to intrinsic higher order aberrations. It is especially important to consider these aberrations when designing beamlines with strong, longitudinally cramped optics used to capture and transport large emittance beams. This paper presents relatively simple analytical formulae which describe the fields of quadrupoles including their higher order aberrations for implementation in beamline design. We review the analytic model for quadrupoles described by a $\mathrm{sech}^2$ strength function and subsequently expand it to quadrupoles whose strength function instead follows a tanh function, adding the effective length of the quadrupole as a free parameter. The implementation of these analytic field descriptions in envelope code TRANSOPTR and multi-particle codes GEANT4 and FLUKA is presented using the optics design of the DarkLight experiment at TRIUMF as example.

physics.acc-ph↗
arXiv2025

Tuning methods for multigap drift tube linacs

Multigap cavities are used extensively in linear accelerators to achieve velocities up to a few percent of the speed of light, driving nuclear physics research around the world. Unlike for single-gap structures, there is no closed-form expression to calculate the output beam parameters from the cavity voltage and phase. To overcome this, we propose to use a method based on the integration of the first and second moments of the beam distribution through the axially symmetric time-dependent fields of the cavity. A beam-based calibration between the model's electric field scaling and the machine's rf amplitudes is presented, yielding a fast online energy change method, returning cavity amplitude and phase necessary for a desired output beam energy and energy spread. The method is validated with 23Na6+ beam energy measurements.

physics.acc-ph↗
arXiv2022

Intensity Limit in Compact H$^-$ and H$_2^+$ Cyclotrons

Compact H$^-$ cyclotrons are used all across the globe to produce medical isotopes. Machines with external ion sources have demonstrated average extracted currents on the order of a few mA, although reported operational numbers are typically around 1\,mA or below. To explore the possibility of extracting even more current from such cyclotrons, it is important to understand the mechanisms that drive intensity limits and how they scale. In this paper we review some of the key aspects of the beam dynamics in the central region of compact cyclotrons, including rf electric focusing and space charge effects. We derive the scaling of the phase acceptance with the rf gap voltage, harmonic number, etc. We also explore the scaling with different types of ions such as H$^-$, H$_2^+$ and H$_3^+$. We discuss the impact of mechanical erosion of the central region electrodes. Thoughout the paper, we use examples and experimental data from two compact H$^-$ cyclotrons for reference: the TR-30 series and the TRIUMF 500\,MeV machine.

physics.acc-ph↗
arXiv2022

Constant-Tune Cyclotrons

In this paper we demonstrate that cyclotrons can be made to have precisely constant betatron tunes over wide energy ranges. In particular, we show that the horizontal tune can be made constant and does not have to follow the Lorentz factor gamma, while still perfectly satisfying the isochronous condition. To make this demonstration we developed a technique based on the calculation of the betatron tunes entirely from the geometry of realistic non-hard-edge closed orbits. We present two particular cyclotron designs, one compact cyclotron and one ring cyclotron. The compact cyclotron design is backed up by a 3-dimensional finite element magnet calculation, that we also present here.

physics.acc-ph↗
arXiv2022

Report of the Snowmass'21 Workshop on High-Power Cyclotrons and FFAs

This whitepaper summarizes and the state of the field of high-power cyclotrons and FFAs as discussed by international experts during a three-day workshop of the same name. The workshop was held online from Sep 7 to Sep 9, 2021 as part of the US Snowmass'21 Community Exercise, specifically the Accelerator Frontier (AF) and the subpanel Accelerators for Neutrinos (AF02). Thus, we put emphasis on the application of high-power cyclotrons in particle physics, specifically neutrino physics, and as drivers for muon production. In the introduction, we discuss the role of cyclotrons for particle physics, and later we highlight existing and planned experiments in the corresponding sections. However, as these same accelerators have important applications in the fields of isotope production - both for research and medicine - and possibly even in energy research, by providing beam to demonstrator experiments in the areas of Accelerator Driven Systems (ADS), we include these far-reaching topics to provide a full picture of the status and applications of high-power cyclotrons. Furthermore, Fixed Field Alternating Gradient accelerators (FFAs) have recently seen renewed interest. They are in many respects (basic operating principles) similar to cyclotrons and have thus been included in this workshop and whitepaper as well. We are discussing current projects and whether FFAs have the prospect of becoming high-intensity machines.

physics.acc-ph↗
arXiv2018

Conformal Mapping Approach to Dipole Shim Design

Passive shims are often used to reduce the size and cost of room-temperature magnetic dipoles. In this paper we revisit an analytic approach to the problem of optimum shim design, and we extend it by taking into consideration the effect of magnetic saturation. We derive an abacus curve to determine optimum shim dimensions as a function of the desired dipole nominal field. We show that, for nominal fields below 1.2 T, a pole with such shims can be made at least one half gap height narrower than a pole without. We discuss the range of validity of this approach and verify its predictions using 2 and 3-dimensional finite-element calculations.

physics.acc-ph↗