Intense Proton Research Articles

Design of a compact beam transport system for laser-driven proton therapy

Abstract We put forward a new design of a compact beam transport system for intense laser-driven proton therapy, where instead of using conventional pulsed solenoids, our design relies on a helical coil irradiated by a nanosecond laser pulse to generate strong magnetic fields for focusing protons. A pair of dipole magnets and apertures are employed to further filter protons with large divergences and low energies. Our numerical studies combine particle-in-cell simulations for laser-plasma interaction to generate high-energy monoenergetic proton beams, finite element analysis for evaluating the magnetic field distribution inside the coil, and Monte-Carlo simulations for beam transport and energy deposition. Our results show that with this design, a spread-out Bragg peak in a range of several centimeters to a deep-seated tumor with a dose of approximately 16.5 cGy and fluctuation around 2% can be achieved. The instantaneous dose rate reaches up to 109 Gy/s, holding the potential for future FLASH radiotherapy research.

The Mean Free Path of 13–64 MeV Protons Derived from Statistical Results of Solar Energetic Particle Events

A recent study by Wang et al. investigated gradual solar proton events with energies >10 MeV, as observed by STEREO-A, STEREO-B, and the Solar and Heliospheric Observatory spacecraft. For each event, the spacecraft with the best magnetic connection to the source region among the three spacecraft was identified, and energetic proton intensities observed by the spacecraft were analyzed through fitting. The fitting process produced two parameters, b and c, for four energy channels (13–16 MeV, 20–25 MeV, 32–40 MeV, and 40–64 MeV) in each event. Parameters b and c govern the rise and decay of particle intensities, respectively. Statistical analysis revealed a power-law correlation between b and c, expressed as c ∼ b −γ . In this study, in order to explain the relation between the two parameters, we investigate the model of particle diffusion coefficients in the interplanetary space. In our simulations, the radial mean free path is modeled as a power function of radial distance, successfully reproducing the b–c relation. Consequently, the observations demonstrate that the radial mean free path varies with radial distance in a power law. In future research, the model of diffusion coefficients holds promise in determining the mean free path of energetic protons.

Silicate-lunar regolith composite: A vacuum self-hardened and comprehensively durable extraterrestrial construction material

Extraterrestrial exploration, represented by Lunar base construction, has been promoted worldwide as a multi-disciplinary, cutting-edge and strategic issue. Herein we proposed a novel extraterrestrial construction material composed of Lunar/Martian regolith simulants and only 4 wt% of silicate adhesive. This silicate-regolith composite can be directly self-hardened in vacuum within 4.5 h without any curing to achieve 29 MPa of hardening strength. Meanwhile, it shows comprehensive durability with stable microstructures and >70 % of residual strength against long-term vacuum exposure, huge temperature difference and intense γ-ray and proton radiations. Its in-situ solidification and durability originate from vacuum dehydration, where silica clusters in solution spontaneously cohere into a solid network with strong connections of silica tetrahedra and bound water. A moderate silicate modulus around 2.5 and appropriate modifications can disperse finer silica clusters to increase oligomer silica units in solution and enhance hardening strength. Compared with lunar geopolymer and other existing extraterrestrial construction materials, this vacuum self-hardening composite allows a cryogenic preparation even below −40 ℃ using diverse regolith with a wide range of compositions and sizes, proposing a facile, durable and versatile solution towards in-situ extraterrestrial constructions.

How Does Cancer Occur? How Should It Be Treated? Treatment from the Perspective of Alkalization Therapy Based on Science-Based Medicine.

This review article investigates the relationship between mitochondrial dysfunction and cancer progression, emphasizing the metabolic shifts that promote tumor growth. Mitochondria are crucial for cellular energy production, but they also play a significant role in cancer progression by promoting glycolysis even under oxygen-rich conditions, a phenomenon known as the Warburg effect. This metabolic reprogramming enables cancer cells to maintain an alkaline internal pH and an acidic external environment, which are critical for their proliferation and survival in hypoxic conditions. The article also explores the acidic tumor microenvironment (TME), a consequence of intensive glycolytic activity and proton production by cancer cells. This acidic milieu enhances the invasiveness and metastatic potential of cancer cells and contributes to increased resistance to chemotherapy. Alkalization therapy, which involves neutralizing this acidity through dietary modifications and the administration of alkalizing agents such as sodium bicarbonate, is highlighted as an effective strategy to counteract these adverse conditions and impede cancer progression. Integrating insights from science-based medicine, the review evaluates the effectiveness of alkalization therapy across various cancer types through clinical assessments. Science-based medicine, which utilizes inductive reasoning from observed clinical outcomes, lends support to the hypothesis of metabolic reprogramming in cancer treatment. By addressing both metabolic and environmental disruptions, this review suggests that considering cancer as primarily a metabolic disorder could lead to more targeted and effective treatment strategies, potentially improving outcomes for patients with advanced-stage cancers.

The “SEP Clock”: A Discussion of First Proton Arrival Times in Wide-Spread Solar Energetic Particle Events

This work analyzes the appearance of wide-spread deka-MeV solar energetic proton (SEP) events, in particular the arrival of the first protons within ≈ 4.5 – 45 MeV measured at Earth–Sun L1, and their relationship with their relative solar source longitude. The definition of “wide-spread SEP event” for this study refers to events that are observed as a 25 MeV proton intensity increase at near 1 AU locations that are separated by at least 130∘ in solar longitude. Many of these events are seen at all three of the spacecraft, STEREO (Solar-Terrestrial Relations Observatory) A, STEREO B, and SOHO (Solar and Heliospheric Observatory), and may therefore extend far beyond 130∘ in longitude around the Sun. A large subset of these events have already been part of a study by Richardson et al. (Solar Phys., 289, 3059, 2014). The event source region identifications draw from this study; more recent events have also been added. Our focus is on answering two specific questions: (1) What is the maximum longitude over which SEP protons show energy dispersion, i.e., a clear sign of arrival of higher-energy protons before those of lower energy? (2) What implications can be drawn from the ensemble of events observed regarding either direct magnetic connectivity to shocks and/or cross-field transport from the site of the eruption in the onset phase of the event?

Search by the SENSEI Experiment for Millicharged Particles Produced in the NuMI Beam.

Millicharged particles appear in several extensions of the standard model, but have not yet been detected. These hypothetical particles could be produced by an intense proton beam striking a fixed target. We use data collected in 2020 by the SENSEI experiment in the MINOS cavern at the Fermi National Accelerator Laboratory to search for ultrarelativistic millicharged particles produced in collisions of protons in the NuMI beam with a fixed graphite target. The absence of any ionization events with 3 to 6 electrons in the SENSEI data allow us to place world-leading constraints on millicharged particles for masses between 30 to 380MeV. This work also demonstrates the potential of utilizing low-threshold detectors to investigate new particles in beam-dump experiments, and motivates a future experiment designed specifically for this purpose.

Phase space reconstruction technique for beam optimization in the Low Energy High Intensity Proton Accelerator (LEHIPA)

The Low Energy High Intensity Proton Accelerator (LEHIPA) has been commissioned to the design energy of 20 MeV at BARC, India. The low energy beam transport (LEBT) channel of LEHIPA consists of two solenoids and drift spaces for matching the 50 keV proton beam from the ECR ion source (ECR-IS) to the RFQ. The ion beam extracted from the ECR-IS also contains molecular species like H2 + and H3 +. Proton fraction in the beam is found to degrade slowly with time due to surface contamination of the plasma chamber and this reduction in proton beam current has implications for longitudinal and transverse beam dynamics. Hence, it becomes important to characterise the beam at different proton fraction levels to understand the end-to-end beam dynamics of LEHIPA. Computed Tomography (CT) technique has been used for the beam phase-space reconstruction in LEHIPA, using a Python program, incorporating the feature of filtering secondary species from the beam profiles measured using slit scanners in the LEBT. Simultaneous Algebraic Reconstruction Technique (SART) is used in the reconstruction since it is identified to be a better technique for a limited number of projections. The reconstruction program is benchmarked with the TraceWin beam dynamics code and implemented on the measured beam profiles to recreate the phase space distribution at the beginning of LEBT. Further, the tomographic reconstruction method is compared with the solenoid scan method and the rms emittance values are found to be in good agreement. The measured tomographic phase space distribution has then been used as TraceWin input for LEHIPA end-end beam dynamics simulations and the LEHIPA beam line parameters are re-optimized for minimum beam emittance growth. This paper presents the simulations of CT technique, benchmarking simulations with TraceWin, phase space reconstruction with measured beam profiles and beam dynamics studies of LEHIPA using the reconstructed beam distributions.

A new approach to combined proton-photon therapy for metastatic cancer patients

Objective. Proton therapy is a limited resource and is typically not available to metastatic cancer patients. Combined proton-photon therapy (CPPT), where most fractions are delivered with photons and only few with protons, represents an approach to distribute proton resources over a larger patient population. In this study, we consider stereotactic radiotherapy of multiple brain or liver metastases, and develop an approach to optimally take advantage of a single proton fraction by optimizing the proton and photon dose contributions to each individual metastasis. Approach. CPPT treatments must balance two competing goals: (1) deliver a larger dose in the proton fractions to reduce integral dose, and (2) fractionate the dose in the normal tissue between metastases, which requires using the photon fractions. Such CPPT treatments are generated by simultaneously optimizing intensity modulated proton therapy (IMPT) and intensity modulated radiotherapy (IMRT) plans based on their cumulative biologically effective dose (BED α /β ). The dose contributions of the proton and photon fractions to each individual metastasis are handled as additional optimization variables in the optimization problem. The method is demonstrated for two patients with 29 and 30 brain metastases, and two patients with 4 and 3 liver metastases. Main results. Optimized CPPT plans increase the proton dose contribution to most of the metastases, while using photons to fractionate the dose around metastases which are large or located close to critical structures. On average, the optimized CPPT plans reduce the mean brain BED2 by 29% and the mean liver BED4 by 42% compared to IMRT-only plans. Thereby, the CPPT plans approach the dosimetric quality of IMPT-only plans, for which the mean brain BED2 and mean liver BED4 are reduced by 28% and 58%, respectively, compared to IMRT-only plans. Significance. CPPT with optimized proton and photon dose contributions to individual metastases may benefit selected metastatic cancer patients without tying up major proton resources.

High intensity proton source based on a hollow-cathode reflex discharge.

We describe here the electrode system, design, and parameters of an ion source based on a Penning-type hollow-cathode reflex discharge developed for generation of proton beams. Especially for proton beam generation, a modified geometry of both hollow and reflex cathodes was fabricated. The working gas is molecular hydrogen. Ion extraction and beam formation are performed using a three-electrode single-aperture optical system with a 3-mm diameter emission aperture. At an accelerating voltage of 33-35kV and a discharge current of 0.55A in continuous mode, the ion beam current was 15-17 mA, and in pulsed mode, at a discharge current of about 2A, the beam current was 55 mA. The beam consists mainly of H+, H2+, and H3+ ions, with the proton (H+) fraction up to 27% in continuous mode and 40% in pulsed mode.

Towards ion stopping power experiments with the laser-driven LIGHT beamline

The main emphasis of the Laser Ion Generation, Handling and Transport (LIGHT) beamline at GSI Helmholtzzentrum für Schwerionenforschung GmbH are phase-space manipulations of laser-generated ion beams. In recent years, the LIGHT collaboration has successfully generated and focused intense proton bunches with an energy of 8 MeV and a temporal duration shorter than 1 ns (FWHM). An interesting area of application that exploits the short ion bunch properties of LIGHT is the study of ion-stopping power in plasmas, a key process in inertial confinement fusion for understanding energy deposition in dense plasmas. The most challenging regime is found when the projectile velocity closely approaches the thermal plasma electron velocity ( $v_{i}\approx v_{e,\text {th}}$ ), for which existing theories show high discrepancies. Since conclusive experimental data are scarce in this regime, we plan to conduct experiments on laser-generated plasma probed with ions generated with LIGHT at a higher temporal resolution than previously achievable. The high temporal resolution is important because the parameters of laser-generated plasmas are changing on the nanosecond time scale. To meet this goal, our recent studies have dealt with ions of lower kinetic energies. In 2021, laser accelerated carbon ions were transported with two solenoids and focused temporally with LIGHT's radio frequency cavity. A bunch length of 1.2 ns (FWHM) at an energy of 0.6 MeV u $^{-1}$ was achieved. In 2022, protons with an energy of 0.6 MeV were transported and temporally compressed to a bunch length of 0.8 ns. The proton beam was used to measure the energy loss in a cold foil. Both the ion and proton beams will also be employed for energy loss measurements in a plasma target.

Evolution of ALISES 3 Light Ion Source at CEA Saclay

Since 1995, the Laboratory for Accelerator Studies and Development at CEA Saclay specializes in producing ECR intense Light Ion Sources, for high intensity proton or deuteron. The initial source SILHI (Source d’Ions Légers Haute Intensité) designed for IPHI accelerator in 1995 was the root of sources provided to laboratories worldwide, such as IFMIF, FAIR or SPIRAL2. In parallel, the Ion Source team started a new R&D program on high intensity ECR compact ion sources with the ALISES source family (Advanced Light Ion Source Extraction System). The years spent testing and improving ALISES v1&2 led us to design a new source, named ALISES v3. The development of this source gathers the advantages of each improvement tested on ALISES v1&2, to achieve an even smaller and pragmatic configuration. The manufacturing of ALISES v3 took place during the improvement of the BETSI test bench in 2018, from 50 kV to 100 kV. The goal of this source is to obtain the same characteristics as the original SILHI, with fewer parts and easier maintenance. This article describes the evolution of ALISES v3 and the beam characteristics at every stage. BETSI test bench is equipped with an Allison Scanner and a Faraday cup to analyse the emittance and the beam current.

Effects of boron doping on the surface modification and defect evolution of silicon induced by proton implantation and annealing

Ultra-thin silicons can be obtained using SMART CUT technology, but there is a lack of systematic research on the effect of boron doping. This paper reports the effects of boron doping on surface modification and defect evolution. Monocrystalline silicon samples with different concentrations of boron doping were implanted to 3.5 × 1017H+/cm2 using a 1.52 MeV High Intensity Proton Implanter (HIPI) and annealed at 300, 400, and 550 ℃. The annealed samples were analyzed by non-contact optical profilometry, Raman spectroscopy, SEM, and TEM. The results show that appropriate boron doping can reduce the surface roughness of the exfoliated samples; excessive boron doping leads to a significant increase in surface roughness (∼525 nm) and produces a step-like morphology. Boron doping leads to changes in the type, concentration and dissociation temperature of hydrogenated defects during implantation. These changes result in the width of damage band changes vary with doping concentration. The density and diameter of the hydrogenated extended defects also changed, which results in the surface modification of samples, such as the change of the surface morphology and substrate roughness. In the end of the paper, the paper discusses the correlation between surface morphology and internal damage for different concentrations of boron doping.

For intense proton beam production with compact ion sources: the ALISES ion source family developed at CEA Saclay

The production of intense proton beams in CEA Saclay started in the 90’s with the development of the SILHI source to inject the IPHI accelerator. This ECR ion source is still in operation nowadays. ECR plasma is a well-known heating process and plasma chamber internal dimensions were investigated in order to reduce size and maintenance time. In 2012 R&D investigations on those simple plasma chamber parameters were started with the design of the first ALISES ion source that will give birth to a new source family still in progress today. This paper will summarize the different steps of this development.

Laser-to-proton conversion efficiency studies for proton fast ignition

We assess the conversion efficiency from intense picosecond laser pulses to multi-MeV ion beams for a wide range of laser and target parameters, using 2D kinetic particle-in-cell simulations. Scalings are addressed in a quasi-one-dimensional geometry, leaving out beam divergence. Then, we study the conversion efficiency into a narrow spatial band along the laser axis for flat and hemispherical targets in large-scale 2D simulations. Combining these findings allows us to calculate the energy requirements for ignition of a compressed ICF target with an intense proton beam in a fast-ignition scenario.

Correlation of Coronal Mass Ejection Shock Temperature with Solar Energetic Particle Intensity

Solar energetic particle (SEP) events have been observed by the Parker Solar Probe (PSP) spacecraft since its launch in 2018. These events include sources from solar flares and coronal mass ejections (CMEs). The IS⊙IS instrument suite on board PSP is measuring ions over energies from ∼ 20 keV nucleon−1 to 200 MeV nucleon−1 and electrons from ∼ 20 keV to 6 MeV. Previous studies sought to group CME characteristics based on their plasma conditions and arrived at general descriptions with large statistical errors, leaving open questions on how to properly group CMEs based solely on their plasma conditions. To help resolve these open questions, the plasma properties of CMEs have been examined in relation to SEPs. Here, we reexamine one plasma property, the solar wind proton temperature, and compare it to the proton SEP intensity in a region immediately downstream of a CME-driven shock for seven CMEs observed at radial distances within 1 au. We find a statistically strong correlation between proton SEP intensity and bulk proton temperature, indicating a clear relationship between SEPs and the conditions in the solar wind. Furthermore, we propose that an indirect coupling of SEP intensity to the level of turbulence and the amount of energy dissipation that results is mainly responsible for the observed correlation between SEP intensity and proton temperature. These results are key to understanding the interaction of SEPs with the bulk solar wind in CME-driven shocks and will improve our ability to model the interplay of shock evolution and particle acceleration.

Analysis of single particle and collective beam effects in high intensity beams in a periodic quadrupole channel

In high intensity proton accelerators, there are two main mechanisms that can cause beam degradation: incoherent and coherent effects due to nonlinear space charge forces. The incoherent effects represent the single particle dynamics while the coherent effects represent the collective response of the beam. Of particular interest is the region above a zero current phase advance (σ0) of 90° where the (coherent) second-order envelope instability and the (incoherent) fourth-order particle resonance are seen to lead to emittance growth. Large emittance growth is also seen below the envelope instability region as the full current beam phase advance (σ) decreases. In the present study, we have studied the nonlinear effects in a high intensity beam propagating through a focusing-defocusing (FD) quadrupole channel for σ0 greater than 90°, both analytically, by studying the solutions of Kapchinsky-Vladimirsky (KV) equation and the particle core model, and through detailed particle-in-cell (PIC) simulations using the code. The KV envelope equation gives the collective response of the beam while the particle core model gives the contribution of the single particle effects. With pic simulations, which resemble the behavior of the real beams more closely as compared to envelope calculations or the particle core model, it is possible to study the evolution of the beam in a self-consistent manner. Our studies show, that it is possible to identify the specific process responsible for beam degradation in high intensity beams. It is also possible to identify which process dominates under different conditions. We further show that the width of the emittance increase stop band calculated from PIC simulations is wider than that calculated by the envelope equations and that the width depends on the length of the channel being studied. Published by the American Physical Society 2024

High power electrostatic beam splitter for a proton beamline

The High Intensity Proton Accelerator facility (HIPA) delivers a 590 MeV cw (50.6 MHz) proton beam with up to 1.4 MW beam power (2.4 mA) to spallation and meson production targets serving particle physics experiments and material research. The main accelerator is the ring cyclotron, an isochronous proton machine accelerating an injected 72 MeV beam to a final 590 MeV. A few meters downstream of the ring cyclotron, an electrostatic beam splitter was installed in the 1980s and originally designed to peel off from a 200 μA beam up to 20 μA (12 kW beam power). Future initiatives will also make use of the splitter. Specifically, as part of the Isotope and Muon Production using Advanced Cyclotron and Target technologies (IMPACT) upgrade project, Targeted Alpha Tumour Therapy and Other Oncological Solutions (TATTOOS), an online isotope separation facility will allow to produce promising radionuclides for diagnosis and therapy of cancer in quantities sufficient for clinical studies. The TATTOOS facility includes a dedicated beamline intended to operate at a beam intensity of 100 μA (60 kW beam power), requiring continuous splitting of the high-power main beam via the splitter. As a step forward toward reaching the desired beam intensity, a beam study was carried out to test the viability of the existing splitter for TATTOOS. The results of this study show that a record of 90 μA (53 kW beam power) was peeled off a horizontally and vertically enlarged beam by the splitter. The successful beam strategy employed during the study as well as the results of several key measurements are presented in this paper, with particular emphasis on diagnostic measurements. Additionally, to support the measurements, a computational model of the splitter has been implemented using Monte Carlo simulation tools, including realistic geometry, electrostatic fields, beam optics, and power deposition calculations. Overall, the results of this paper show that through the combination of beam measurements and simulations, the existing splitter can be used to reach the 100−μA beam intensity requirement for TATTOOS. Published by the American Physical Society 2024

MiniSCIDOM: a scintillator-based tomograph for volumetric dose reconstruction of single laser-driven proton bunches

Abstract Laser plasma accelerators (LPAs) enable the generation of intense and short proton bunches on a micrometre scale, thus offering new experimental capabilities to research fields such as ultra-high dose rate radiobiology or material analysis. Being spectrally broadband, laser-accelerated proton bunches allow for tailored volumetric dose deposition in a sample via single bunches to excite or probe specific sample properties. The rising number of such experiments indicates a need for diagnostics providing spatially resolved characterization of dose distributions with volumes of approximately 1 cm ${}^3$ for single proton bunches to allow for fast online feedback. Here we present the scintillator-based miniSCIDOM detector for online single-bunch tomographic reconstruction of dose distributions in volumes of up to approximately 1 cm ${}^3$ . The detector achieves a spatial resolution below 500 $\unicode{x3bc}$ m and a sensitivity of 100 mGy. The detector performance is tested at a proton therapy cyclotron and an LPA proton source. The experiments’ primary focus is the characterization of the scintillator’s ionization quenching behaviour.

Study of the 20Ne(p,γ)21Na reaction at LUNA

The NeNa-MgAl cycles are involved in the synthesis of Ne, Na, Mg, and Al isotopes. The 20Ne(p,γ)21Na (Q = 2431.68 keV) reaction is the first and slowest reaction of the NeNa cycle and it controls the speed at which the entire cycle proceeds. At the state of the art, the uncertainty on the 20Ne(p,γ)21Na reaction rate affects the production of the elements in the NeNa cycle. In particular, in the temperature range from 0.1 GK to 1 GK, the rate is dominated by the 366 keV resonance corresponding to the excited state of EX = 2797.5 keV and by the direct capture component. The present study focus on the study of the 366 keV resonance and the direct capture below 400 keV. At LUNA (Laboratory for Underground Nuclear Astrophysics) the 20Ne(p,γ)21Na reaction has been measured using the intense proton beam delivered by the LUNA 400 kV accelerator and a windowless differential-pumping gas target. The products of the reaction are detected with two high-purity germanium detectors. The experimental details and preliminary results on the 366 keV resonance and on the direct capture component at very low energies will be shown, together with their possible impact on the 20Ne(p,γ)21Na reaction rate.

Calibration of the 2-Phase Bubble Tracking Model for Liquid Mercury Target Simulation with Machine Learning Surrogate Models

The Spallation Neutron Source (SNS) at Oak Ridge National Laboratory is one of the most powerful accelerator-driven neutron sources in the world. The intense protons strike on SNS’s mercury target to provide bright neutron beams, which also leads to severe fluid-structure interactions inside the target. Prediction of resultant loading on the target is difficult particularly when helium gas is injected into mercury to reduce the loading and mitigate the pitting damage on vessel walls. A 2-phase material model that incorporates the Rayleigh-Plesset (R-P) model is expected to address this multi-physics problem. However, several uncertain parameters in the R-P model require intensive simulations to determine their optimal values. With the help of machine learning and the measured target strain, we have studied the major uncertain parameters in this R-P model and developed a framework to identify optimal parameters that significantly reduce the discrepancy between simulations and experimental strains. The preliminary results show the possibility of using this mercury/helium mixture and surrogate models to predict a better match of target strain response when the helium gas is injected.