Accelerated Proton Beams Research Articles

Transport and energy selection of laser generated protons for postacceleration with a compact linac

Laser accelerated proton beams have a considerable potential for various applications including oncological therapy. However, the most consolidated target normal sheath acceleration regime based on irradiation of solid targets provides an exponential energy spectrum with a significant divergence. The low count number at the cutoff energy seriously limits at present its possible use. One realistic scenario for the near future is offered by hybrid schemes. The use of transport lines for collimation and energy selection has been considered. We present here a scheme based on a high field pulsed solenoid and collimators which allows one to select a beam suitable for injection at 30 MeV into a compact linac in order to double its energy while preserving a significant intensity. The results are based on a fully 3D simulation starting from laser acceleration.

Effect of inside diameter of tip on proton beam produced by intense laser pulse on double-layer cone targets

AbstractThe laser-driven acceleration of proton beams from a double-layer cone target, comprised of a cone shaped high-Z material target with a low density proton layer, is investigated via two-dimensional fully relativistic electro-magnetic particle-in-cell simulations. The dependence of the inside diameter (ID) of the tip size of a double-layer cone target on proton beam characteristics is demonstrated. Our results show that the peak energy of proton beams significantly increases and the divergence angle decreases with decreasing ID size. This can be explained by the combined effects of a stronger laser field that is focused inside the cone target and a larger laser interaction area by reducing the ID size.

Dynamics of high-energy proton beam acceleration and focusing from hemisphere-cone targets by high-intensity lasers

Acceleration and focusing of high-energy proton beams from fast-ignition (FI) -related hemisphere-cone assembled targets have been numerically studied by hybrid particle-in-cell simulations and compared with those from planar-foil and open-hemisphere targets. The whole physical process including the laser-plasma interaction has been self-consistently modeled for 15 ps, at which time the protons reach asymptotic motion. It is found that the achievable focus of proton beams is limited by the thermal pressure gradients in the co-moving hot electrons, which induce a transverse defocusing electric field that bends proton trajectories near the axis. For the advanced hemisphere-cone target, the flow of hot electrons along the cone wall induces a local transverse focusing sheath field, resulting in a clear enhancement in proton focusing; however, it leads to a significant loss of longitudinal sheath potential, reducing the total conversion efficiency from laser to protons.

High-energy proton beam accelerators for subcritical nuclear reactors

Schemes for high-power accelerators to be used in electronuclear facilities are reviewed. The possibilities of the electronuclear method of obtaining energy and using accelerators for the transmutation of radioactive wastes as well as in reactor materials engineering are reviewed briefly. The parameters of accelerators which are currently operating, under construction or being designed in the world for subcritical reactor schemes, complexes for salvaging wastes and power neutron generators are presented.

Parametric study of a variable-magnetic-field-based energy-selection system for generating a spread-out Bragg peak with a laser-accelerated proton beam

Laser-based proton beam acceleration, which produces broad energy spectra, is unsuitable for direct clinical use. Thus, employing an energy selection system is necessary. The purpose of the present study was to investigate a method whereby a variable magnetic field could be employed with an energy selection system to generate a spread-out Bragg peak (SOBP). For energy selection, particle transport and dosimetric property measurements, the Geant4 toolkit was implemented. The energy spectrum of the laser-accelerated proton beam was acquired using a particle-in-cell simulation. The hole size and the position of the energy selection collimator were varied in order to determine the effects of those parameters on the dosimetric properties. To generate an SOBP, we changed the magnetic field in the energy selection system for each beam weighting factor during beam irradiation. The overall results of this study suggest that the use of an energy selection system with a variable magnetic field can effectively generate an SOBP suitable for proton radiation therapy applications.

Laser-Driven Proton Acceleration Enhancement by Nanostructured Foils

Nanostructured thin plastic foils have been used to enhance the mechanism of laser-driven proton beam acceleration. In particular, the presence of a monolayer of polystyrene nanospheres on the target front side has drastically enhanced the absorption of the incident 100 TW laser beam, leading to a consequent increase in the maximum proton energy and beam charge. The cutoff energy increased by about 60% for the optimal spheres' diameter of 535 nm in comparison to the planar foil. The total number of protons with energies higher than 1 MeV was increased approximately 5 times. To our knowledge this is the first experimental demonstration of such advanced target geometry. Experimental results are interpreted and discussed by means of 2(1/2)-dimensional particle-in-cell simulations.

Study on the RF Set Point for the PEFP DTL by using a phase scan method

The drift tube linac (DTL) is used to accelerate proton beams from 20 MeV to 100 MeV in the linear accelerator of the Proton Engineering Frontier Project (PEFP). The phase scan signature method is a common technique to determine the radio-frequency (rf) set point, including the rf amplitude and phase, in DTL tanks. In this work, we applied the phase scan method to the first tank of the PEFP’s DTL in order to study the procedure for determining the rf set point by using artificial experimental data generated by using the PARMILA code.

Malignant melanoma of the uvea: radiotherapy techniques

AbstractPurpose Malignant melanoma of the uvea is a relatively radioresistant tumor which can be treated with radiotherapy only with high dose. For this reason only radiotherapy techniques with precise location of the radiation doses are usedMethods Proton beam therapy has been used since 1975 by Gragoudas in Boston and the in Europe since 1983.Because of the Bragg pick, the use of an accelerated proton beam allows delivering homogenous high dose to the tumor while sparing the normal tissue around. Brachytherapy is also widely used. It consists to suture to the sclera against the tumor a radioactive plaque that can contain iodine 125 seeds or ruthenium. Iodine 125 is a low energy gamma emmeting isotope; the radiation is totally stopped by heavy metals like gold .The seeds need to be changed every two months because of its half life. Ruthenium 106 is a beta emmiting isotope. Its low penetration prevents its use for the bigger tumors. With brachytherapy the dose of 90 grays is usually delivered to the top of the tumor while the base receives more than 300grays.Results Tumor control is excellent with proton beam (less than 5% recurrence at 5 years) and good with brachytherapy (less than 10% recurrence at 5 years) Globe preservation is possible in more than 90% of treated patients. The visual acuity depends of the size and location of the tumor. Mortality by metastasis is equal after conservative management by radiotherapy or enucleation.Conclusion Various techniques of radiotherapy can achieve good local control and globe preservation in patients with uveal melanoma

Calibration and application of medical particle accelerators to space radiation experiments

In this paper, we introduce radioisotope facilities and medical particle accelerators that can be applied to space radiation experiments and the experimental conditions required by the space radiation experiments. Space radiation experiments on the ground are critical in determining the lifetimes of satellites and in choosing or preparing the appropriate electrical parts to assure the designated mission lifetime. Before the completion of building the 100-MeV proton linear accelerator in Gyeongju, or even after the completion, the currently existing proton accelerators for medical purposes could suggest an alternative plan. We have performed experiments to calibrate medical proton beam accelerators to investigate whether the beam conditions are suitable for applications to space radiation experiments. Based on the calibration results, we propose reference beam operation conditions for space radiation experiments.

SU-E-T-296: Optimization of the Energy Selection System with Varying Magnetic Field for Laser-Accelerated Proton Beams.

Laser-based accelerated proton beams are unsuitable for clinical use because of their broad energy spectra. For this reason, it is essential to employ an energy selection system (ESS). The purpose of this study is to determine optimum parameters of the ESS which uses a varying magnetic field to generate Bragg-peak. We simulated an accelerated proton beams using radiation pressure acceleration mechanism with carbon-proton mixture target. The density ratio (n = 6) between the protons and the carbon ions is one of optimization parameters in determining the accelerating mechanisms. The ESS was implemented by the Geant4 Monte Carlo toolkit. In order to optimize the hole size and position of the energy selection collimator, and magnetic field at ESS, these parameters were simulated for acquiring energy and dose distributions by changing each values. The proton energy distributions had a poly-energetic distribution after passing through the ESS. As the magnetic field was increased, the mean energy of the proton beams also was increased. Also as the hole size was increased, the energy bandwidth of proton passed through the ESS was increased. The hole size and position of the energy selection collimator were effectively optimized to 2 cm and 5 cm from the z-axis, respectively. We simulated laser-accelerated proton beams using ESS for generation of Bragg-peak. Our results suggest that the ESS with magnetic field variation can effectively generate a Bragg-peak suitable for use in proton radiation therapy. Our ESS can be applied to pencil beam scanning proton therapy.

Rayleigh-Taylor Instability of an Ultrathin Foil Accelerated by the Radiation Pressure of an Intense Laser

We report experimental evidence for a Rayleigh-Taylor-like instability driven by radiation pressure of an ultraintense (10(21) W/cm(2)) laser pulse. The instability is witnessed by the highly modulated profile of the accelerated proton beam produced when the laser irradiates a 5 nm diamondlike carbon (90% C, 10% H) target. Clear anticorrelation between bubblelike modulations of the proton beam and transmitted laser profile further demonstrate the role of the radiation pressure in modulating the foil. Measurements of the modulation wavelength, and of the acceleration from Doppler-broadening of back-reflected light, agree quantitatively with particle-in-cell simulations performed for our experimental parameters and which confirm the existence of this instability.

Laser-driven proton acceleration using a conical nanobrush target

A conical nanobrush target is proposed to improve the total proton energy-conversion efficiency in proton beam acceleration and investigated by two-dimensional particle-in-cell (2D-PIC) simulations. Results indicate a significant enhancement of the number and energies of hot electrons through the target rear side of the conical nanobrush target. Compared with the plain target, the field increases several times. We observe enhancements of the average proton energy and total laser-proton energy conversion efficiency of 105%. This enhancement is attributed to both nanobrush and conical configurations. The proton beam is well collimated with a divergence angle less than 28°. The proposed target may serve as a new method for increasing laser to proton energy-conversion efficiency.

The effect of beam interruptions on the integrity of ADSR fuel pin cladding: A thermo-mechanical analysis

During its lifetime in the core, the cladding of an Accelerator Driven Subcritical Reactor (ADSR) fuel pin is expected to experience variable stresses due to frequent interruptions in the accelerator proton beam. This paper investigates the thermal fatigue damage in the cladding due to repetitive and unplanned beam interruptions under certain operational conditions. Beam trip data was obtained for four operating high power proton accelerators, among which the Spallation Neutron Source (SNS) superconducting accelerator was selected for further analysis. 9Cr–1Mo–Nb–V (T91) steel was selected as the cladding material because of its proven compatibility with proposed ADSR design concepts. The neutronic, thermal and stress analyses were performed using the PTS-ADS, a code that has been specifically developed for studying the dynamic response to beam-induced transients in accelerator driven subcritical systems. The lifetime of the fuel cladding in the core was estimated for three levels of allowed pin power and specific operating conditions.

Laser accelerated protons captured and transported by a pulse power solenoid

Using a pulse power solenoid, we demonstrate efficient capture of laser accelerated proton beams and the ability to control their large divergence angles and broad energy range. Simulations using measured data for the input parameters give inference into the phase-space and transport efficiencies of the captured proton beams. We conclude with results from a feasibility study of a pulse power compact achromatic gantry concept. Using a scaled target normal sheath acceleration spectrum, we present simulation results of the available spectrum after transport through the gantry.

The compensation of quadrupole errors and space charge effects by using trim quadrupoles

The China Spallation Neutron Source (CSNS) accelerators consist of an H-linac and a proton Rapid Cycling Synchrotron (RCS). RCS is designed to accumulate and accelerate proton beam from 80 MeV to 1.6 GeV with a repetition rate of 25 Hz. The main dipole and quadruple magnet will operate in AC mode. Due to the adoption of the resonant power supplies, saturation errors of magnetic field cannot be compensated by power supplies. These saturation errors will disturb the linear optics parameters, such as tunes, beta function and dispersion function. The strong space charge effects will cause emittance growth. The compensation of these effects by using trim quadruples is studied, and the corresponding results are presented.

Publisher’s Note: “Simulations of stable compact proton beam acceleration from a two-ion-species ultrathin foil” [Phys. Plasmas 18, 043110 (2011)

Publisher’s Note: “Simulations of stable compact proton beam acceleration from a two-ion-species ultrathin foil” [Phys. Plasmas 18, 043110 (2011)

Prospects of the Hadron Physics at J-PARC

An overview of the leading subjects of hadron physics with an emphasis on those relevant to J-PARC is presented. J-PARC is a new high intensity proton beam accelerator facility built at Tokai, Japan. The subjects include (1) strangeness nuclear physics, (2) generalized nuclear force, and (3) exotic hadron spectroscopy.

Focusing of laser-accelerated proton beams using curved targets, and improved energy deposition

We use numerical simulations for laser-plasma interaction and particle transport, to study proton acceleration from curved targets and their potential for isochoric heating. Combining a proton dot geometry, to produce a low-energy cut-off in the accelerated proton beam spectrum, and a cylindral shape of the substrate, to bend proton trajectories, we compute increased energy deposition in an auxiliary target placed in the proton beam path, compared to protons that would be accelerated from a flat substrate. The highest temperatures are obtained when placing the auxiliary target slightly after the theoretical focus position, confirming the trend observed in the PIC simulations that cylinders focus slightly after their radius. Moving the target out of the proton beam focus, the peak temperature decreases and a larger transverse region can be heated.

A compact post-acceleration scheme for laser-generated protons

Protons generated by irradiating a thin metal foil with a high-intensitylaser have shown to posses interesting characteristics in terms of energy, emittance, current, and pulse duration. Therefore, in the near future, they might become a competitive source with respect to conventional proton sources. Previous theoretical, numerical, and experimental studies have already demonstrated efficient coupling between laser-accelerated proton beams with traditional radio frequency (RF)-based particle accelerators. These hybrid proton accelerators benefit from both the excellent properties of the laser-based source and the flexibility, reliability, and know-how of beam handling as provided by RF-based accelerator structures. In this paper, state of the art experimental results of laser-accelerated proton beams are used as input for a numerical study using compact and innovative conventional accelerator structures designed for medical applications. Results show that this compact hybrid accelerator allows even more efficient capture and acceleration of the laser-generated proton beam.

The treatment of uveal melanoma by accelerated proton beam

The treatment of uveal melanoma by accelerated proton beam