While laser wakefield acceleration (LWFA) in the bubble regime demands ultra-short, high-peak-power laser pulses, operation in the self-modulated regime (SM-LWFA) works with more relaxed pulse conditions, albeit at the cost of lower beam quality. Modern laser systems can deliver pulses with durations of a few tens of femtoseconds and peak powers on the order of a few terawatts, at kHz repetition rates. These systems are well-suited for developing SM-LWFA applications where high average energy and charge are prioritized over beam quality. Such beams could be used to generate high-energy bremsstrahlung photons, capable of triggering photonuclear reactions to produce radioisotopes like molybdenum-99. This isotope decays into technetium-99m, the most widely used medical radioisotope, with over 30 million applications worldwide per year. This work explores the use of Bayesian optimization to maximize the energy and charge of electron beams accelerated via SM-LWFA. Particle-in-cell (PIC) simulations model a 5 TW, 15 fs-long Gaussian laser pulse, propagating through tailored hydrogen gas-density profiles. In these simulations, over multiple iterations, the algorithm optimizes a set of input parameters characterizing the gas-density profile and the laser focal position. Three distinct profiles, with total lengths ranging from 200 to 400 micrometers and combining ramps and plateaus, were investigated. Optimal configurations were found to produce electron beams with median energies ranging from 14 to 17 MeV and charges of 600 to 1300 pC, considering electrons with energies above 8 MeV. Preliminary estimates of the molybdenum-99 yields for the optimal beams were obtained by employing their phase spaces, retrieved from PIC simulations, as radiation source inputs in Monte Carlo simulations irradiating a combined tantalum and molybdenum target.

The charged particles moving through a carbon nanotube (CNT) may be used to excite electromagnetic modes in the electron gas produced in the cylindrical graphene shell that makes up a nanotube wall. This effect has recently been proposed as a potential novel method of short-wavelength-high-gradient particle acceleration. In this contribution, the existing theory based on a linearized hydrodynamic model for a localized point-charge propagating in a single wall nanotube (SWNT) is reviewed. In this model, the electron gas is treated as a plasma with additional contributions to the fluid momentum equation from specific solid-state properties of the gas. The governing set of differential equations is formed by the continuity and momentum equations for the involved species. These equations are then coupled by Maxwell's equations. The differential equation system is solved applying a modified Fourier-Bessel transform. An analysis has been realized to determine the plasma modes able to excite a longitudinal electrical wakefield component in the SWNT to accelerate test charges. Numerical results are obtained showing the influence of the damping factor, the velocity of the driver, the nanotube radius, and the particle position on the excited wakefields. A discussion is presented on the suitability and possible limitations of using this method for modelling CNT-based particle acceleration.

The interactions of charged particles with carbon nanotubes (CNTs) may excite electromagnetic modes in the electron gas produced in the cylindrical graphene shell constituting the nanotube wall. This wake effect has recently been proposed as a potential novel method of short-wavelength high-gradient particle acceleration. In this work, the excitation of these wakefields is studied by means of the linearized hydrodynamic model. In this model, the electronic excitations on the nanotube surface are described treating the electron gas as a 2D plasma with additional contributions to the fluid momentum equation from specific solid-state properties of the gas. General expressions are derived for the excited longitudinal and transverse wakefields. Numerical results are obtained for a charged particle moving within a CNT, paraxially to its axis, showing how the wakefield is affected by parameters such as the particle velocity and its radial position, the nanotube radius, and a friction factor, which can be used as a phenomenological parameter to describe effects from the ionic lattice. Assuming a particle driver propagating on axis at a given velocity, optimal parameters were obtained to maximize the longitudinal wakefield amplitude.

The ISOLDE Scientific Infrastructure at CERN offers a unique range of post-accelerated radioactive beams. The scientific program can be improved with the "Isolde Superconducting Recoil Separator" (ISRS), an innovative spectrometer able to deliver unprecedented (A, Z) resolution. In this paper we present an overview of the physics and ongoing technical developments.

Charged particle acceleration using solid-state nanostructures has attracted attention in recent years as a method of achieving ultra-high-gradient acceleration in the TV/m domain. More concretely, metallic hollow nanostructures could be suitable for particle acceleration through the excitation of wakefields by a laser or a high-intensity charged particle beam in a high-density solid-state plasma. For instance, due to their special channeling properties as well as optoelectronic and thermo-mechanical properties, carbon nanotubes could be an excellent medium for this purpose. This article investigates the feasibility of generating ultra-high-gradient acceleration using carbon nanotube arrays, modeled as solid-state plasmas in conventional particle-in-cell simulations performed in a two-dimensional axisymmetric (quasi-3D) geometry. The generation of beam-driven plasma wakefields depending on different parameters of the solid structure is discussed in detail. Furthermore, by adopting an effective plasma-density approach, existing analytical expressions, originally derived for homogeneous plasmas, can be used to describe wakefields driven in periodic non-uniform plasmas.

With the advancement of high-power UV laser technology, the use of nanostructures for particle acceleration attracts renewed interest due to its possibility of achieving TV/m accelerating gradients in solid state plasmas. Electron acceleration in ionized materials such as carbon nanotubes and graphene is currently considered as a potential alternative to the usual laser wakefield acceleration (LWFA) schemes. An evaluation of the suitability of a graphene target for LWFA can be carried out using an effective density model, thus replacing the need to model each layer. We present a 2D evaluation of the longitudinal electric field driven by a short UV laser pulse in a multi-layer graphene structure, showing that longitudinal fields of ∼ 5 TV/m are achievable.

Charged particle acceleration using solid-state nanostructures is attracting new attention in recent years as a method of achieving ultra-high acceleration gradients in the order of TV/m. The use of carbon nanotubes (CNTs) has the potential to overcome limitations of using natural crystals, e.g. channelling aperture and thermo-mechanical robustness. In this work, we present preliminary particle-in-cell simulation results of laser and beam interaction with a single CNT, modelled as 20 parallel plates of Carbon ions and electrons. This is the equivalent to a 10-layers tube in 3D. We further discuss simulation of anisotropic particles to model 2D quasi-free electrons in CNT walls. Further research ideas are outlined along with the presentation of a possible proof-of-principle experiment.

Received 21 June 2016DOI:https://doi.org/10.1103/PhysRevAccelBeams.19.079901This article is available under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.© 2016 American Physical Society

The ECOS is considering the construction of a new facility for accelerating high intensity stable beams with energies at and above the Coulomb barrier, the LINCE light and heavy ion accelerator. This facility could be based on a normal conducting CW-RFQ and a superconducting linac, working at 72.75 MHz. This paper presents a design study for the RFQ system which is able to achieve 500 keV/u output for A/Q = 7 ions in only 5 m length.

ECOS-LINCE (Martel I et al., Proceedings IPAC’14, 2014) is a proposal for a new European First Class high intensity heavy-ions accelerator for stable ions, with energies at and above the coulomb barrier. The low energy section will be achieved using a 72.75 MHz normal conducting four vanes RFQ designed to give a 460 keV/u boost for A/Q = 7 ions in about 5 m (Orduz AK et al., IPAC’14, 2014). The geometry vanes are modeled to accommodate windows in order to obtain a clear separation of the RFQ modes (Ostroumov P et al., Rev ST Accel Beams 15:110101, 2012). This article presents the experimental results of the RF test carried out on a aluminum prototype.

During the last years, the ECOS working group has been considering the construction of a new high-intensity accelerator of stable ion beams for the next Long-Range Plan of the nuclear physics community in Europe. The new facility (LINCE) will be a multi-user facility dedicated to ECOS science: fundamental physics, astrophysics, nuclear structure and reaction dynamics. In this paper, we summarize preliminary design studies of the low-energy part of this facility based on the use of a multi-ion superconducting linac.

The 72.75 MHz LINCE RFQ [1] is designed to function at room temperature. Effective operation of the RFQ cavity requires efficient water cooling in order to dissipate significant resistive power non-uniformly distributed on the copper walls and vanes. This amounts to about 10 kW for one 0.5 m long RFQ section. Cylindrical cooling channels have been designed and optimized by varying their diameter and position in order to minimize the frequency shift generated by thermal displacements. The article reports results of power loss simulations coupled with electromagnetic modelling studies and their consequences on the RFQ performance in terms of resonant frequency and thermal deformations. INTRODUCTION The four-vanes RFQ is designed for LINCE high intensity accelerator complex [2]. The structure provides a 72.75 MHz resonating mode with a 1.3 MHz margin controlled by the tuners [1]. The initial beam is made of 2 ns long bunches of 40 keV/u and the aim of the design is to achieve 500 keV/u. The modulation was simulated using the DESRFQ code [3] with 82 kV inter-vane potential on a vane tip tested in ANL [4]. A complete loop of coupled numerical studies is achieved as shown in Fig. 1. The RF Analysis has been carried with COMSOL [5] resulting in an estimate for the resistive power losses. These are scaled and coupled with Heat Transfer model in order to obtain a temperature map at the vanes surface. The next step is the optimization of the cooling system according to the heat map. Two optimization for channel position, channel diameter, fluid and velocity temperature are carried out. The final heat flux is coupled to a Solid Mechanics study to estimates the stress and displacements due to thermal expansion. The frequency shift is obtained through a new RF study of the deformed structure. RF ANALYSIS The first study has been done with DESRFQ and Track [6] codes. Eigenfrequency studies have been done using COMSOL software, as shown before [1]. For the last version of the study the whole structure with modulated vanes was simulated and a 73.25 MHz for the quadrupole mode T E211 resonance is obtained. Heat Map Resistive power losses are calculated and that show the maximum loses are in the window corners as it is show in ∗ Work supported partially supported by the Spanish Government (MINECO-CDTI)under program FEDER INTERCONNECTA Figure 1: Study steps. Fig. 2. This study is coupled with a non-isothermal pipe flow simulation in a quarter symmetry model (section) of the RFQ. The total resistive power dissipated by the RFQ working mode at 67.35 MHz is 10.67 kW. A cooling system must be design to control the heat dissipation in the RFQ. Figure 2: Resistive power losses [kW/m].

The last decade brought much interest in proton therapy within the medical and accelerator communities. Using normal conducting technology, the high-energy beams required can be handled only with large and heavy magnets which causes prohibitive costs. While lattice design work on a superconducting gantry has been carried out for a decade [1] there is yet no practical implementation. The University of Huelva in collaboration with the Andalusian Foundation for Health Research (FABIS) is currently involved in developing and assembling a prototype for a compact superconducting proton gantry [2]. Magnet design and performance is described along with beam dynamics results for the main gantry arcs and for the final spot scanning system using realistic magnetic field maps thoroughly.

The properties of the neutrino provide a unique window on physics beyond that described by the standard model. The study of subleading effects in neutrino oscillations, and the race to discover CP-invariance violation in the lepton sector, has begun with the recent discovery that θ 13 > 0 . The measured value of θ 13 is large, emphasizing the need for a facility at which the systematic uncertainties can be reduced to the percent level. The neutrino factory, in which intense neutrino beams are produced from the decay of muons, has been shown to outperform all realistic alternatives and to be capable of making measurements of the requisite precision. Its unique discovery potential arises from the fact that only at the neutrino factory is it practical to produce high-energy electron (anti)neutrino beams of the required intensity. This paper presents the conceptual design of the neutrino factory accelerator facility developed by the European Commission Framework Programme 7 EURO ν Design Study consortium. EURO ν coordinated the European contributions to the International Design Study for the Neutrino Factory (the IDS-NF) collaboration. The EURO ν baseline accelerator facility will provide 10 21 muon decays per year from 12.6 GeV stored muon beams serving a single neutrino detector situated at a source-detector distance of between 1 500 km and 2 500 km. A suite of near detectors will allow definitive neutrino-scattering experiments to be performed.

The University of Huelva is presently involved in R&D projects for developing RF accelerator cavities. Two types of cavities are presently under design, a prototype of room temperature RFQ injector and a quarter-wave resonator for high intensity heavy-ion linear accelerators. The laboratory is equipped with dedicated test-bench for RF measurements, which includes high-power RF generators, network analyzer, amplifiers and power meters. A clean room is also available having a dedicated space for high-precision mechanical metrology and cavity mounting, together with a vertical cryostat for superconducting cavity test.

The low-energy part of the LINCE facility [1] can be based on a 72.75 MHz normal-conducting RFQ designed to give a 450 keV/u boost for A/Q=7 ions in about 5 m length. The vanes have been electromagnetically designed to accommodate dedicated RF windows producing effective separation of the RFQ modes in an octagonal-shaped resonance chamber [2]. This article outlines the optimization of the quality factor of the cavity by using numerical methods for electromagnetic calculations. Experimental results of RF test carried out on a prototype are also discussed.

Beam transport optics of the LINCE Linac experimental areas has been optimized for a few ion species using transfer matrix calculations performed in MAD-X. An alpha spectrometer based on a double bending achromat lattice has been used as dispersion suppressor. This optics design correspond to the first three planned beam lines. Further studies for the beam tracking and magnets design are being developed in order to conclude the whole design of this first LINCE phase.

Continuous beams delivered by the LINCE [1] ECR ions source will be bunched by a multi-harmonic buncher in order to be injected into an RFQ. Its numerical design is reported along with electric field maps and beam dynamics studies carried out with the codes TRACK [2] and GPT [3]. First experiments with multi-harmonic bunchers were carried out in 1970s at Argonne National Lab. (ANL) [4] and it is used in the design of modern accelerator facilities e.g FRIB and Spiral 2.