Helium Beam Research Articles

Robust single modified divacancy color centers in 4H-SiC under resonant excitation

Color centers in silicon carbide (SiC) offer exciting possibilities for quantum information processing. However, the challenge of ionization during optical manipulation leads to charge variations, hampering the efficacy of spin-photon interfaces. Recent research predicted that modified divacancy color centers can stabilize their charge states, resisting photoionization. This study presents a method for precisely creating single divacancy arrays in 4H-SiC using a focused helium ion beam. Photoluminescence tests reveal consistent emission with minimal linewidth fluctuations (∼50 MHz over 3 h). By measuring the ionization rate for different polytypes of divacancies, we found that the modified divacancies are more robust against resonant excitation. Furthermore, angle-resolved photoluminescence excitation spectra unveil two resonant-transition lines with orthogonal polarizations. Enhanced optical and spin characteristics were notably observed in these color centers compared to those generated through carbon-ion and shallow implantation methods, positioning modified divacancies as promising contenders for advancing quantum networking.

Minimal lateral damage fabrication of high-temperature superconducting nanowires via focused helium ion beam irradiation

Abstract Low-temperature superconducting nanowire single-photon detectors have become a key infrared photon counting technology in communication and astronomy applications. However, the constrained physical space of devices demands high-performance superconducting detectors capable of operation at higher temperatures. To date, high-temperature superconductor nanowires still face seriously uneven lateral damage in the ion etching process during fabrication. In this work, we report a promising fabrication method for high-temperature superconducting YBa2Cu3O7−x (YBCO) nanowires, using a focused helium ion beam to minimize the lateral damage of the cut. Based on simulations, we designed tangent circles and adjacent isosceles triangles to replace lines in cutting nanowires to reduce the superimposed damage by He+ ions. The lateral damage of a single helium ion cut has been reduced with a decrease in superimposed damage width from 58.8 nm to 29.7 nm. This work provides a platform for boosting YBCO nanowires to achieve single photon detection.

Thermal helium beam diagnostic for 2D profile measurements in the divertor of ASDEX Upgrade.

A new thermal helium beam diagnostic has been implemented in the outer lower divertor of the ASDEX Upgrade tokamak. The purpose of this diagnostic is to measure two-dimensional profiles of electron density (ne) and temperature (Te) with high temporal and spatial resolution. The geometry of the lines of sight is chosen to avoid the influence of prompt recycling and to optimize the resolution without significantly impacting the divertor structure. Moreover, the effect of long-term helium recycling has been analyzed, and its amplitude compared to the active signal is negligible. Finally, the reconstruction of ne and Te is done via a collisional radiative model, while a static and a dynamic model were implemented and compared with SOLPS simulations as well as divertor Thomson scattering data. Furthermore, a new 2D parameterization of the outer divertor volume, which is required for the dynamic model, was developed. Due to its fast and local ne and Te profile measurements, the diagnostic is suitable for investigating fast processes such as divertor transitions and filaments.

Nanofabrication of high transition temperature superconductive electronics with focused helium ion irradiation

Superconductive electronics from Josephson junctions are governed by quantum mechanical tunneling through sub-10 nm scale insulating tunnel barriers. The electrical properties are exponentially sensitive to this dimension, which necessitates fabrication with nanoscale precision and uniformity. For circuits in high-transition temperature YBa2Cu3O7−δ (YBCO) thin films, direct writing of the material with a focused helium ion beam has shown promise in the creation of uniform nanoscale insulators for YBCO Josephson junctions and other circuit regions. In this paper, we report on the procedures and variables associated with this process and discuss the potential for scaling up the number of junctions for quantum sensing and complex energy efficient digital circuits.

TEM-EELS analysis reveals the W-atom mediated radiation-induced amorphization in M23C6

To gain a mechanistic understanding of the phase stability of M23C6 upon irradiation, the bulk W-doped M23C6 (Cr-W-C system) in the range of 0–12 at.% W concentration was prepared and subjected to helium beam irradiation, following with a thorough electron energy loss spectroscopy (EELS) analysis. Radiation-induced amorphization (RIA) was observed only at the 4 W sample with a W concentration of ∼12 at.%. Analysis of the low-loss spectrum showed that the inelastic mean free path (λ) could be applied an effective indicator of the presence of an amorphous phase. The white line ratio of the carbon K-edge spectrum showed that the chemical bonding state in the crystalline state is mainly 2p3/2 bonding, and it changes to dominantly 2p1/2 bonding accompanying with the crystal-to-amorphous (c-a) transition. Discussion on the relationship between the change in λ (Δλ) and the lattice parameter (Δa) due to irradiation reveals that Δa is not dependent on Δλ, indicating that Δλ is mainly caused by the volume expansion due to the c-a transition. In addition, a crystalline state is remained even after a lattice parameter change of ∼1.5 % in 0 W and 1W-samples, whereas, a lattice expansion of ∼0.2 % would trigger the occurrence of crystal-to-amorphous transition in the 4W-sample. The detailed EELS analysis demonstrated that the constitutional W atoms play an important role in facilitating the occurrence of RIA in M23C6, that is, the phase instability accompanying the lattice expansion due to irradiation was emphasized by the addition of W in M23C6. The insights obtained here suggest that a higher W concentration in M23C6 is more susceptible to RIA, and therefore the resistance to amorphization is achievable by decreasing the W concentration in the steels.

A strategy to fabricate nanostructures with sub-nanometer line edge roughness

Line edge roughness (LER) has been an important issue in the nanofabrication research, especially in integrated circuits. Despite numerous research studies has made efforts on achieving smaller LER value, a strategy to achieve sub-nanometer level LER still remains challenging due to inability to deposit energy with a profile of sub-nanometer LER. In this work, we introduce a strategy to fabricate structures with sub-nanometer LER, specifically, we use scanning helium ion beam to expose hydrogen silsesquioxane (HSQ) resist on thin SiNx membrane (∼20 nm) and present the 0.16 nm spatial imaging resolution based on this suspended membrane geometric construction, which is characterized by scanning transmission electron microscope (STEM). The suspended membrane serves as an energy filter of helium ion beam and due to the elimination of backscattering induced secondary electrons, we can systematically study the factors that influences the LER of the fabricated nanostructures. Furthermore, we explore the parameters including step size, designed exposure linewidth (DEL), delivered dosage and resist thickness and choosing the high contrast developer, the process window allows to fabricate lines with 0.2 nm LER is determined. AFM measurement and simulation work further reveal that at specific beam step size and DEL, the nanostructures with minimum LER can only be fabricated at specific resist thickness and dosage.

A combined transport-defect evolution model of microstructure damage in silicon carbide induced by precise irradiation of focused helium ion beams

In this paper, a combined transport-defect evolution multiscale model describing the generation and the evolution of microstructure damage in silicon carbide (SiC) induced by focused helium ion beams is developed. In the proposed model, the transport of helium ions and displaced atoms in the SiC substrate and the generation of point defects are described by the Boltzmann transport equations, while the subsequent defect evolution is characterized by a set of rate equations with the contributions of the modeling of the bubble coalescence as well as the substrate swelling. The validity and superiority of the transport equations are verified by comparing the simulation results with the data from experimental measurements and available simulation methods. The subsurface amorphous profile, onsurface swelling profile, and the spatial and size distribution of helium bubbles in a SiC substrate irradiated by focused helium ion beams are simulated using the proposed multiscale model. The damage morphology simulated by the proposed model is in good agreement with the transmission electron microscopy images at different beam energies and doses. This work provides an effective tool for full-stage modeling of complex evolutionary mechanisms of microstructure damage induced by precise and high-throughput helium irradiation.

Bayesian modelling of multiple plasma diagnostics at Wendelstein 7-X

Abstract Inference of electron density and temperature has been performed using multiple, diverse sets of plasma diagnostic data at Wendelstein 7-X. Predictive models for the interferometer, Thomson scattering and helium beam emission spectroscopy (He-BES) systems have been developed within the Minerva framework and integrated into a unified model. Electron density and temperature profiles are modelled using Gaussian processes. Calibration factors for the Thomson scattering system and predictive uncertainties are considered as additional unknown parameters. The joint posterior probability distribution for the electron density and temperature profiles as well as Gaussian process hyperparameters and model parameters is explored through a Markov chain Monte Carlo algorithm. Samples from this distribution are numerically marginalised over the hyperparameters and model parameters to yield marginal posterior distributions for the electron density and temperature profiles. The profile inferences incorporate various data combinations from the interferometer and Thomson scattering as well as constraints at the limiter/divertor positions through virtual observations or edge data from He-BES. Additionally, the integration of x-ray imaging crystal spectrometer data into the model for ion temperature profiles is presented. All profiles presented in this study are inferred with optimally selected hyperparameters and model parameters by exploring the joint posterior distribution, inherently applying Bayesian Occam’s razor.

Light-Driven Ionic and Molecular Transport through Atomically Thin Single Nanopores in MoS2/WS2 Heterobilayers.

Nanofluidic ionic and molecular transport through atomically thin nanopore membranes attracts broad research interest from both scientific and industrial communities for environmental, healthcare, and energy-related technologies. To mimic the biological ion pumping functions, recently, light-induced and quantum effect-facilitated charge separation in heterogeneous 2D-material assemblies is proposed as the fourth type of driving force to achieve active and noninvasive transport of ionic species through synthetic membrane materials. However, to date, engineering versatile van der Waals heterostructures into 2D nanopore membranes remains largely unexplored. Herein, we fabricate single nanopores in heterobilayer transition metal dichalcogenide membranes with helium ion beam irradiation and demonstrate the light-driven ionic transport and molecular translocation phenomena through the atomically thin nanopores. Experimental and simulation results further elucidate the driving mechanism as the photoinduced near-pore electric potential difference due to type II band alignment of the semiconducting WS2 and MoS2 monolayers. The strength of the photoinduced localized electric field near the pore region can be approximately 1.5 times stronger than that of its counterpart under the conventional voltage-driven mode. Consequently, the light-driven mode offers better spatial resolution for single-molecule detection. Light-driven ionic and molecular transport through nanopores in van der Waals heterojunction membranes anticipates transformative working principles for next-generation biomolecular sequencing and gives rise to fascinating opportunities for light-to-chemical energy harvesting nanosystems.

Monte Carlo simulation of initial and volume ion recombination correction factor in plane parallel ionization chambers exposed to ion beams

Objective. Accurate reference dosimetry with ionization chambers (ICs) relies on correcting for various influencing factors, including ion recombination. Theoretical frameworks, such as the Boag and Jaffe theories, are conventionally used to describe the ion recombination correction factors. Experimental methods are time consuming, the applicability may be limited and, in some cases, impractical to be used in clinical routine. The development of simulation tools becomes necessary to enhance the understanding of recombination under circumstances that may differ from conventional use. Before progressing, it is crucial to benchmark novel approaches to calculate ion recombination losses under known conditions. In this study, we introduce and validate a versatile simulation tool based on a Monte Carlo scheme for calculating initial and volume ion recombination correction factors in air-filled ICs exposed to ion beams with clinical dose rates. Approach. The simulation includes gaussian distribution of ion positions to model the distribution of charge carriers along the chamber volume. It accounts for various physical transport effects, including drift, diffusion, space charge screening and free electron fraction. To compute ion recombination, a Monte Carlo scheme is used due to its versatility in multiple geometries, without exhibiting convergence problems associated with numerically solved procedures. Main results. The code is validated in conventional dose rates against Jaffe’s theory for initial recombination and Boag’s theory for volume recombination based on parameters derived from experimental data including proton, helium and carbon ion beams measured with a plane parallel IC. Significance. The simulation demonstrates excellent agreement, typically 0.05% or less relative difference with the theoretical and experimental data. The current code successfully predicts ion recombination correction factors, in a large variety of ion beams, including different temporal beam structures.

Role of radiation re-absorption in the thermal helium beam diagnostic.

The Thermal Helium Beam (THB) is a diagnostic for simultaneously measuring the electron temperature and density profiles of the plasma edge and scrape off layer (SOL). It exploits the line ratio technique of selected He line intensities, emitted by He gas puffed inside the plasma, to locally estimate the plasma properties through a dedicated collisional radiative model (CRM). Standard THB diagnostics used in nuclear fusion devices measure three HeI emission lines: 667.8, 706.5, and 728.1nm. For the RFP experiment RFX-mod2, a new THB is designed and tested for the first time at the TCV tokamak. It acquires an additional emission line at 501.6nm, which is exploited to estimate the radiation re-absorption, which is not negligible in regions of large neutral He densities (leading to high re-absorption) and simultaneously low electron density and temperature (lack of other excitation channels). It affects the measurements most strongly at the far SOL, while the significance of re-absorption decreases as it approaches the separatrix. In this paper, plasma density and temperature profiles of the plasma edge at the outboard midplane of TCV, measured with this newly designed THB, are presented. For the first time, the effect of radiation re-absorption on the estimation of electron temperature and density profiles is experimentally measured in a tokamak using the 501nm line emission intensity. Different CRMs are compared with and without radiation re-absorption, showing good agreement when re-absorption is included and demonstrating how it plays an important role in the far SOL, as expected.

In vitro validation of helium ion irradiations as a function of linear energy transfer in radioresistant human malignant cells

Purpose Based on considerable interest to enlarge the experimental database of radioresistant cells after their irradiation with helium ions, HTB140, MCF-7 and HTB177 human malignant cells are exposed to helium ion beams having different linear energy transfer (LET). Materials and methods The cells are irradiated along the widened 62 MeV/u helium ion Bragg peak, providing LET of 4.9, 9.8, 23.4 and 36.8 keV/µm. Numerical simulations with the Geant4 toolkit are used for the experimental design. Cell survival is evaluated and compared with reference γ-rays. DNA double strand breaks are assessed via γ-H2AX foci. Results With the increase of LET, surviving fractions at 2 Gy decrease, while RBE (2 Gy, γ) gradually increase. For HTB140 cells, above the dose of 4 Gy, a slight saturation of survival is observed while the increase of RBE (2 Gy, γ) remains unaffected. With the increase of LET the increase of γ-H2AX foci is revealed at 0.5 h after irradiation. There is no significant difference in the number of foci between the cell lines for the same LET. From 0.5 to 24 h, the number of foci drops reaching its residual level. For each time point, there are small differences in DNA DSB among the three cell lines. Conclusion Analyses of data acquired for the three cell lines irradiated by helium ions, having different LET, reveal high elimination capacity and creation of a large number of DNA DSB with respect to γ-rays, and are between those reported for protons and carbon ions.

Design of a Facility for Simultaneous Irradiation with Two Ion Beams based on the HIPR Accelerator for Simulations Neutron Influence

Ion accelerator facility is a powerful tool to simulate neutron irradiation effects in reactor materials. Defects in the crystal lattice arise and the accumulation of transmutation products (helium and hydrogen) occurs in the structure of the material under the action of neutrons in the structural materials of nuclear installations. At Kurchatov Complex for Theoretical and Experimental Physics the heavy ion accelerator HIPr (heavy ion prototype) is used to simulate radiation damage in steels and alloys using a 5.6 MeV Fe2+ ion beam. The second beam line is designed at the HIPr facility to simultaneously implant helium (or hydrogen) into the region of defects. The second beam line provides a beam of helium ions with energy up to 300 keV. The report presents a description of second beam line design and a status of construction the second beam line.

Status of edge electron density and temperature measurements with Helium Beam Emission Spectroscopy (He-BES) on EAST

Helium Beam Emission Spectroscopy (He-BES) diagnostic has been developed on EAST, which is able to measure the edge electron density and temperature profiles simultaneously using a helium line intensity ratio method. The diagnostic includes the beam injector and the detection system. There are 20 observation channels within an observation range of 80 mm in the detection system at the low filed side, which can cover the whole scrape-off layer (SOL) and part of the pedestal region of EAST. The beam injector system has been upgraded to Supersonic Molecular Beam Injector (SMBI) system to realize deeper helium injection since the 2021 campaign. Four spectral lines at wavelengths of 728.1 nm, 706.5 nm, 667.8 nm and 656.3 nm are detected by the He-BES. The first three spectral lines, including 728.1 nm, 706.5 nm, 667.8 nm, are measured for calculating edge n e and T e profiles based on the collisional-radiative model (CRM) model, and the last spectral line (656.3 nm) is used for the measurement of D α emission. The edge electrostatic fluctuations can be obtained from the power spectrum of D α emission. The electron density and temperature profiles calculated from the 667.8/728.1 and 728.1/706.5 nm line ratios are in good agreement with those from other diagnostics in the edge region of plasma. The self-consistency of He-BES diagnostic is also verified, such as the density pump out caused by LHW and the lower edge temperature caused by the lower heating power.

Towards precise LET measurements based on energy deposition of therapeutic ions in Timepix3 detectors

Objective. There is an increasing interest in calculating and measuring linear energy transfer (LET) spectra in particle therapy in order to assess their impact in biological terms. As such, the accuracy of the particle fluence energy spectra becomes paramount. This study focuses on quantifying energy depositions of distinct proton, helium, carbon, and oxygen ion beams using a silicon pixel detector developed at CERN to determine LET spectra in silicon. Approach. While detection systems have been investigated in this pursuit, the scarcity of detectors capable of providing per-ion data with high spatial and temporal resolution remains an issue. This gap is where silicon pixel detector technology steps in, enabling online tracking of single-ion energy deposition. The used detector consisted of a 300 µm thick silicon sensor operated in partial depletion. Main results. During post-processing, artifacts in the acquired signals were identified and methods for their corrections were developed. Subsequently, a correlation between measured and Monte Carlo-based simulated energy deposition distributions was performed, relying on a two-step recalibration approach based on linear and saturating exponential models. Despite the observed saturation effects, deviations were confined below 7% across the entire investigated range of track-averaged LET values in silicon from 0.77 keV µm−1 to 93.16 keV µm−1. Significance. Simulated and measured mean energy depositions were found to be aligned within 7%, after applying artifact corrections. This extends the range of accessible LET spectra in silicon to clinically relevant values and validates the accuracy and reliability of the measurements. These findings pave the way towards LET-based dosimetry through an approach to translate these measurements to LET spectra in water. This will be addressed in a future study, extending functionality of treatment planning systems into clinical routine, with the potential of providing ion-beam therapy of utmost precision to cancer patients.

The potential of mixed carbon–helium beams for online treatment verification: a simulation and treatment planning study

Objective. Recently, a new and promising approach for range verification was proposed. This method requires the use of two different ion species. Due to their equal magnetic rigidity, fully ionized carbon and helium ions can be simultaneously accelerated in accelerators like synchrotrons. At sufficiently high treatment energies, helium ions can exit the patient distally, reaching approximately three times the range of carbon ions at an equal energy per nucleon. Therefore, the proposal involves adding a small helium fluence to the carbon ion beam and utilizing helium as an online range probe during radiation therapy. This work aims to develop a software framework for treatment planning and motion verification in range-guided radiation therapy using mixed carbon–helium beams. Approach. The developed framework is based on the open-source treatment planning toolkit matRad. Dose distributions and helium radiographs were simulated using the open-source Monte Carlo package TOPAS. Beam delivery system parameters were obtained from the Heidelberg Ion Therapy Center, and imaging detectors along with reconstruction were facilitated by ProtonVDA. Methods for reconstructing the most likely patient positioning error scenarios and the motion phase of 4DCT are presented for prostate and lung cancer sites. Main results. The developed framework provides the capability to calculate and optimize treatment plans for mixed carbon–helium ion therapy. It can simulate the treatment process and generate helium radiographs for simulated patient geometry, including small beam views. Furthermore, motion reconstruction based on these radiographs seems possible with preliminary validation. Significance. The developed framework can be applied for further experimental work with the promising mixed carbon–helium ion implementation of range-guided radiotherapy. It offers opportunities for adaptation in particle therapy, improving dose accumulation, and enabling patient anatomy reconstruction during radiotherapy.

Ultra-High Dose Rate Helium Ion Beams: First In Vivo Evidence for Neuroprotective FLASH Effect.

To investigate ultra-high-dose rate helium ion irradiation and its potential FLASH sparing effect with the endpoint acute brain injury in preclinical in vivo settings. Raster-scanned helium ion beams were administered to explore and compare the impact of dose rate variations between standard dose rate (SDR at 0.2 Gy/s) and FLASH (at 141 Gy/s) radiotherapy (RT). Irradiation-induced brain injury was investigated in healthy C57BL/6 mice via DNA damage response kinetic studies using nuclear γH2AX as a surrogate for double-strand breaks (DSB). The integrity of the neurovascular and immune compartments was assessed via CD31+ microvascular density and microglia/macrophages activation. Iba1+ ramified and CD68+ phagocytic microglia/macrophages were quantified, together with the expression of inducible nitric oxide synthetase (iNOS). Helium FLASH RT significantly prevented acute brain tissue injury compared with SDR. This was demonstrated by reduced levels of DSB and structural preservation of the neurovascular endothelium after FLASH RT. Moreover, FLASH RT exhibited reduced activation of neuroinflammatory signals compared with SDR, as detected by quantification of CD68+ iNOS+ microglia/macrophages. To our knowledge, this is the first report on the FLASH-sparing neuroprotective effect of raster scanning helium ion radiotherapy in vivo.

Experimental evidence for the drift wave nature of the weakly coherent mode in ASDEX Upgrade I-mode plasmas

The improved energy confinement mode (I-mode) is a potential candidate for future fusion power plants, as it combines ELM-free operation with good confinement. The unusual edge transport and turbulence in this regime is still not fully understood. This study analyzes the turbulent structure of the weakly coherent mode (WCM) in ASDEX Upgrade. Measurements from Doppler back-scattering and a thermal helium beam diagnostic are used to determine velocities of the background plasma and the WCM over multiple discharges. A phase velocity of the WCM of the order of 2–5 km s−1 in the electron diamagnetic drift direction is found, quantitatively close to a drift wave assuming negligible temperature fluctuations. A good agreement with a previously proposed mechanism behind the I-mode regime is observed. This marks the first experimental verification of a specific understanding of the WCM and the I-mode regime.

Development and verification of an electron Monte Carlo engine for applications in intraoperative radiation therapy.

In preparation of future clinical trials employing the Mobetron electron linear accelerator to deliver FLASH Intraoperative Radiation Therapy (IORT), the development of a Monte Carlo (MC)-based framework for dose calculation was required. To extend and validate the in-house developed fast MC dose engine MonteRay (MR) for future clinical applications in IORT. MR is a CPU MC dose calculation engine written in C++ that is capable of simulating therapeutic proton, helium, and carbon ion beams. In this work, development steps are taken to include electrons and photons in MR are presented. To assess MRs accuracy, MR generated simulation results were compared against FLUKA predictions in water, in presence of heterogeneities as well as in an anthropomorphic phantom. Additionally, dosimetric data has been acquired to evaluate MRs accuracy in predicting dose-distributions generated by the Mobetron accelerator. Runtimes of MR were evaluated against those of the general-purpose MC code FLUKA on standard benchmark problems. MR generated dose distributions for electron beams incident on a water phantom match corresponding FLUKA calculated distributions within 2.3% with range values matching within 0.01mm. In terms of dosimetric validation, differences between MR calculated and measured dose values were below 3% for almost all investigated positions within the water phantom. Gamma passing rate (1%/1mm) for the scenarios with inhomogeneities and gamma passing rate (3%/2mm) with the anthropomorphic phantom, were>99.8% and 99.4%, respectively. The average dose differences between MR (FLUKA) and the measurements was 1.26% (1.09%). Deviations between MR and FLUKA were well within 1.5% for all investigated depths and 0.6% on average. In terms of runtime, MR achieved a speedup against reference FLUKA simulations of about 13 for 10 MeV electrons. Validations against general purpose MC code FLUKA predictions and experimental dosimetric data have proven the validity of the physical models implemented in MR for IORT applications. Extending the work presented here, MR will be interfaced with external biophysical models to allow accurate FLASH biological dose predictions in IORT.

New accelerator designs: NIMMS

PurposeThis article summarises the presentation given at the “Hadrontherapy: status and perspectives” event.MethodsStructure, methodology, and objectives of the Next Ion Medical Machine Study collaboration are introduced. Its four Work Packages are: small synchrotrons for particle therapy, curved superconducting magnets for synchrotrons and gantries, superconducting gantry design, and high-frequency ion linacs. Synchrotrons under study include a superconducting design for carbon ion therapy, and a normal-conducting design for ions up to helium. Superconducting magnet R&D is carried out in two European projects. Within the scope of these projects, five magnet demonstrators with different technologies are in different phases of design and production. Beam optics and mechanical design of a superconducting gantry for carbon ions is being developed. A high-frequency linac design has been completed, and tests are starting on a prototype high-frequency injector.ResultsThe designs of two facilities based on NIMMS technological developments are presented. A carbon ion research and therapy facility was designed for the SEEIIST project, based on a conventional synchrotron with high beam intensity. A smaller facility aimed at cancer therapy and research with light ions, in particular helium beams has also been designed. Both facilities can produce FLASH-type beams.ConclusionsThe traditional design of carbon ion therapy facilities can be improved by adding new features as higher beam intensity and new beam extraction schemes. A cost-effective alternative to the traditional design is a compact facility for light ions, exploiting the potential for treatment with helium ions and allowing an experimental programme with different ion species.